:1-0( 

::;..~~(, 

~3'. 

~ UNITED STATES 

liEPARTMENT OF THE INTERIOR 

HAROLD L. ICKES, Secretary 

GEOLOGICAL SURVEY 

W. C. MENDENHALL, Director 

---0-

CIRCULAR 3 

---oTHE BLEACHING CLAYS 

BY 

P. G. NUTTING 

WASHINGTON 

1933 
LIBRARY 

'CJ OF T HE 

UfJ1ED STATES 

DEPARTM~ OF AGRICULTURE 

~ . 

Class €?{ 1 ___ ______ _ Book _ ~j C __ -3 

1 • 8. (}O\'ERl'OI£;\"T rft/STI!'/11 o FFICI:: 1':1:!7 8-1577 
~ -.... UNITED STATES 

DEPARTMENT OF THE INTERIOR 

HAROLD L. ICKES, Secretary 

GEOLOGICAL SURVEY 

W. C. MENDENHALL, Director 

--0--

CIRCULAR 3 

-0--

THE BLEACHING CLAYS 

P. G. NUTTING 

WASHINGTON 

1933 
Page 

Abstract •..... ~.,........................................ 3 

Introduction ................................ :............... 4 

Occurrence and production ..•.•.•..... .'. • . . . . . . . . . . . . . . . . 5 

~he clays; preparation and use.......................... 7 

Source and origin of bleaching clays.................... 8 

Seat and origin of bleaching action. . . . • • . • • . • . . . . . . • • • • 11 

The forma~ion and stability of the active sillcates..... 18 

Association with wate~hygroscopicity....... .......... •• 22 

Association with water--hydrothermal relations.......... 32 

The bleaching action ..................... · .....• ; • . . . • • . • 43 

Maximum bleaching powers and efficiencies............... 50 

Figure 1. 

2·. 

3. 

4. 

5. 

6. 

7. 

8. 

9. 

10. 

11. 

ILLUSTRATIONS 

Worked clay bed near Macon, Ga •...•••.•• • .• • • • 6 

Face of worked clay at Quincy, Fla........... 6 

Weight-humidity curves.. . • . . • • • . • • . . • • • • • • • . . 24 

Weight-humidity curves of clays........... . . • • 24 

Energy-log concentration, permutite •.•....••• · 26 

Weight-humidity, treated serpentine.......... 27 

Thermal dehydration curves of hydrous oxides. 34 

Thermal dehydration curves of related clay 

minerals.................................... 35 

Thermal dehydration curves of active clays... 37 

Thermal dehydration curves of active clays... 38 

Energy of dehydration of permu.tite ••...•••... ·42 

T.ABLES 

1. Energy ·of association with water •...•••••••...• •. •.. 25 

2. Moisture content at various hu.nidities ...•...... ··· · 30 

3. Thermal dehydration da.t0- of the hydrous oxides of 

figures 7 and 8 •.••••••••.••••••••...• •. . • • • • • • 36 

4. Thermal dehydration dnta of the active clays of 

figll.I'es 9 and 10 •.... o ..... ~ . . . . . . . . . . . . . . • . . . • 39 

5.. Energies of dehydration of permuti te. o.............. 41 

6. Bleaching and solubility tests......... . . . . • • . . . . . • • 44 

7. Miscellaneous clay tests •....•.. ····•o••····o••······ 46 

2 
75000 

The Bleaching Clays 

By P. G. Nutting 

Abstract · 

Bleaching clays of both the naturally active and the activable types 

are abundant and widely distributed in this cmu1try south of latitude 38. 

Neither type occurs in glaciated areas. 

Three chief source materials are recognized ~ volcanic ash and 

certain igneous rocks that are low in silica and high in bases and partly 

decomposed and the marine secondary mineral glauconite. Partial leaching with dilute aqids renders these highly active bleaching agents. The 

naturally ~ctive clays may be derived from the same source materials by 

long leaching in fresh water, assisted in some cases by plant acids. 

Active bleaching clays result when bases iri the surfaces of the clay 

particles are replaced by the hydrog·en:_ and hydroxyl of acid. These are 

driven off as water by heat, leaving the open bonds essential for bleaching. Bleaching power is at a maxirrn:un when only part of the bases are 

removed. If the leaching of bases is carried too far, the material degenerates into an ordlnary clay or into a less active complex of hydrous 

oxid.es. 

There appears to be a fixed upper limit to bleaching power closely 

approached by many treated bentonites available in great quantities. 

The best naturally active clays, treated slag, and various synthe~.ic 

bleaching media are considerably lower in bleaching power. A few clays 

may be prepared in granular form from the percolation process of bleaching. A few bentonites sl~~e in water without leaving hard granules and 

are adapted to the mud process, requiring no grinding. Although there 

is an insistent demand for more powerful bleaching agents for treating 

valuable products such as lubric~nts and cotton oil, no clay capable of 

higher activity than many of the bentonites is likely to be found, nor 

is any process of activation yet discovered more effective than mild acid 

leaching. Synthetic bleaching media, treated slag, and activated alumina 

will serve other purposes but are not good bleaching agents. 

The study of bleaching power here recorded included a study of the 

vapor p1·ess1u-e of hydrous clays and of their thermal dehydration. These 

properties bear directly on their adsorbing and bleaching properties. 

Each clay has its ovvn characteristic weight-h1llllidity and weight-temperature 

curves, which ma~ be interpreted in terms of energy of adsorption. 

The testing of bleaching clays covers ~t only the bleaching power 

and hydration but acid solubility and identification of the acid-soluble 

constituents. A table of test data is gi ve!.n covering a few of. the 200 

clays studied. Much further work remains t:o be done relating to standard 

methods of testing and to the application of active clays to other purposes 

than decolorizing, such as solvent recovery, catalysis, and desiccation. 

3 
75000 

Introduction 

A1 though bleaching clay or fuller• s earth is produced in considerable 

quantity by many independent operators, it has received very little intensive study. Not much is knovm of the seat of the decolorizing action 

nor of its nature except that it is a selective adsorption or some kind. 

An active clay can be distinguished from one that is inactive by actual 

test of its bleaching or adsorbing power. Some clays are inactive until 

leached with acid; others have their activity much diminished by the same 

treatment. Many of the naturally active clays are improved by acid treatment. Producers of bleaching clays operate entirely by cut and try methods. 

The study here .reported was undertaken to find the' fundamental properties 

of such clays as a part of a comprehensive study of the relations between 

oil, silica, and water. Many than.1cs are due to the various producers mentioned for their whole-hearted cooperation in supplying clay samples and 

data and for permission to visit their plants and deposits. Members of the 

Geological Survey staff, C. s. Ross in particular, have made many helpful 

comments. 

The clay materials that are the characteristic materials of clays, 

. soils_, and shales have been studied at the Survey for several years past. 

These include such classes as kaolinite, halloysite, beidellite, no tronite, 

and montmorillonite. The dominant mineral in many regions of prof d 

weathering and especially in china and paper clays is kaolinite, th 

characteristic mineral of k.1.olin. The kaolins have been subdivided into 

nacrite, dickite, and kaolinite-an~.LL~ite by Ross and Kerr.1/ All t ese 

have essentially tl1e same chemical composition (2H20.Al203.2Si02), t 

they differ from one another slightly in internal structure as reve led 

by X-ray spectra •. Kaolinite is commonly but not invariably derive from 

the feldspars (K2,1:Jet.2,Ca)A1203•6Si02• The kaolin minerals are dehy ated 

abruptly at temperatures betgeen 500° a~d 600° c. Before dehydrati n they 

do not absorb water or bleach oil, nor can either the l(aolins or fe dspars 

be activated by acid treatment. Dehydration disrupts the structure (shown 

by X-ray) and imparts [-l. slight adsorbing power. The crystalline in ctive 

kaolin minerals appear to be the product of extreme weathering of 

kinds of i_gneous rocks and are highly stable. 

The bleaching clays appear to be composed chiefly of the less 

and less completely weathered clay minerals. They are characterize by 

high contents of loosely held water and by :partial solubility in di ute 

ordinary acids, such as hydrochloric or sulphuric acid. The water ·s 

largely adsorbed water and is removable by l1eating to 200° C., but ter 

of constit~tion and probably water of crystallization are also pres 

On the other hand, inactive clays, such as kaolin, retain almost al 

their water up to a red heat (500° c.) and then lose it abruptly ~d 

a short temperature range. Moderate dehydration to 200° C. is suff cient 

to develop the full bleaching power of the active clays, but heati · to 

600°-800° C. destroys that power; hence we infer that it 

1/ Ross, C. R., and Kerr,. P •. F., The kaolin minerals: u.s. Geol. S ey 

Prof. Paper 165, PP• 151-176, 1930. 
73000 

off between 50° and 200° C. that rrro.st be present in bleaching clays and 

must be driven off to induce bleaching po~er. Acid-leached clays require 

similar heat treatment follordng aciJ. treatment and washing to .bring out 

their fuli bleaching power. 

Most bleaching clays are improved by acid leaching; a few are rendered 

less active by such leaching, find a fe.111 of the best are inactive until 

leached. ~.ae solubility of bleaching clays in acid runs from 10 to 30 percent, and the material removed is chiefly iron and alu.rnina. The alkalies 

and alkaline earths are readily soluble if present but rarely appear in 

large amounts in active clays. In contrast we may cite the insolubility 

in acids of the: alkalies in feldspars and of the alumina in kr..olin, The 

replacement of a base in the su.rface of a mineral by the hydrogen of water 

or of an acid, followed by the removal of that hydrogen (by heating) to 

leave an open bond, appears to be the essential in producing an actively 

absorbing (bleaching) surface. 

The thermal dehydration curves of the bleaching clays (see below) are 

all of the zeolite-silica gel type. T4ey show definitely that neither 

the kaolins nor halloysite is present in any appreciable amount. Clay 

minerals characterized by acid-soluble (or ~eplaceable) bases, low refractive index, open lattice str~cture, and high silica:alu.mina ratio may 

be present, but the evidence ei t.her way is not decisive, as tbese minerals 

give flat dehydration c1.::~ves that are easily supp::-essed by excess hydrous 

silica or alumina. .Many or possibly all of the bleacD.ing clays would go 

over to kaolins if suffjeiently leached and given sufficient time to take 

on water of constitution. A few clays have been thus transformed (from 

bleaching clay to china clay) in the laboratory by water treatment alone. 

The structure and probable origin of the bleaching clays are discussed 

farther on in this paper. 

Occurrence and production 

The great quantities of bleaching clay used in the :East for refining 

cotton oil and petroleum lubricants come chiefly from the Georgia-Florida ' 

district extending from Macon, Ga., to Ocala, Fla., and centering in a 

50-mile tract astride the Georgia-Florida line northwest of Tallahassee. 

Plants at Attapulgus, Ga., and Quincy, Fla., each produce more than 10,00~ 

tons a month of finished clay, 1ll.Sed chiefly on petroleu..'!l. At Macon and 

Ocala are plants producing clay that is used chiefly in refining cotton 

oil. 

North of central Georgia and east of the Missouri River the only commercial production to my l<nowledge is at Olmstead, Ill. (near Cairo) where 

quantities of clay rather high in iron ore are mined by one of the large 

oil companies for its own use. Glaciated areas appear to contain no commercial deposits of bleaching clays. 

5 
Figure 1.--Twiggs cl~y member of the Barnwell formation (upper Eocene) . 

Clay deposit of the General Reduction Co., near Macon, Ga., being 

worked in 1931. · Phot ogrn.ph by P. G. Nutting. 

Figure 2.--Hawthorn formation (lower Miocene) . Fresh worked clay bank 

I'loridin Co. 1 s deposit at ~incy, Fla. Photograph ·oy P. G. 

Nutting at 15 feet . Note pressure bedding but absence of sedimentary bedding. 
75000 

The larger worked deposits of the West are near Creede, Colo .• ; near 

San Antonio, Tex.; in centre.1 Utah (Aurora); in ·.7estern Nevada near Death 

Valley; near Chambers, Ariz.; and near Tehl.cha.pi, Calif~ Clay from 

De·ath Valley is sold to refiners in P-ennsylvania, and Arizona clay pre~ 

pared in Los .Angeles has been ~ihil)ped to England, the original home of 

fuller's earth. English clay is imported chiefly for refining lard. A 

Bavarian treated clay is imported for refining cotton oi. There are 

several good -deposits in Japan, used locally .• 

There is no dearth of good clay, and each producer has several deposits i.n reser"ie mapped ready for rmrk. A 50-acre tract does not last 

long where worked with steam shovels at the rate o;f 500 tons a day, and 

when the overbUrden becomes too thick (15 feet) or the clay too thin 

(5 feet) another tract is opened and perhaps a new mill is built in 

another location. The clay beds already located are sufficient to supply 

even a largely increased demand for many years, and there is every reason 

to believe that the enormous deposits of the Southeast and the far West 

are practically ineXhaustible. 

The worked deposits are mostly 10 ·to 20 feet thick and (in the East) 

c~vered with soil and vegetation. Beneath is usuallY. a bed of san~, and 

below this test drills sometimes show a second bed of active clay, too 

deep to be profitably worked. Sandy clay is not worked in this country, 

for the jills used are of the flour-mill type and sand rerr.oval would add 

materially to the expense of production. The Bavarian treated clay is 

screened as a thin rrrud before treating with acid, washing, drying, and 

milling. ___:E) Although the bulk of the present domestic output consists 

of low-priced clay for decolorizing petroleum and cotton oil and is merely 

dried and milled, the domes tic marJ:et calls for considerable clay of high 

strength and efficiency and low retention which will yield a stable product. Doubtless the chief advances of the near future will be the d~ 

velopment of high-grade special clays to meet these domestic demands. 

The clays; preparation and use 

The active clays are all light gray when dry; some ha~e a faint bl~ 

ish or greenish or yellowish tint. Tney ~re, of course, much darker when 

fresh and moist. Most of them dry 2..t room tempernturc to h['..rd blocks 

without cracking, but a few-for example, the clay at Macon, Ga. - become rather frinble. To the eye or touch thoy cannot be distinguished. 

from Y~olin or bentonite, but a'lump of active clay placed in water does 

not swell not slake nor become plastic, lika many clays and soils. As 

mined they are very moist but not plastic. At one bed near Attapulgus, 

.Ga., the good clay shades to a puttylike consistency (recognized by the 

test drillers) at the thin odge. 

gj Burghardt, o., Activated bleaching clays: Ind. and Eng. Chemistry, vol. 23, No. 7, pp. 800-802, July 1931. 

7 
75000 

The ultimate grains of these clays are very small. fi1ey are microscopic or submicroscoric in size, but X-ray diffraction patterns show 

that practically all clays Hre compo:.:.ecl largely of par1~icles having some 

crystalline structure. What one ~;ees l.lllde:i. .. the moderate magnification 

of a binocular miscroscope is a. 'nass of roundeCl. opaque lumps whose size 

depends only upon the crusing and siftint; the clay has undergone. 

Certain bleaching clays are valued only because they can be prepared in granular form (1&-30 mesh, 30-60, 60-100, 100-200, and 200 up 

are the commercial sizes) not broken down by handline or by burning for 

reuse. Clays in granular form are used in percolation filtering, the 

topped and dewaxed oil passing slowly down thro11r:-r:h 4 to 10 feet of 

granular clay. ~1e first oil to come thro1ygh is water-vn1ite; then come 

green, yellow, orange, and red oils, which are afterward blended to 

obtain the color desired. In the 11 contac.t'!'1method of bleaching, very 

finely ground earth (usually 200 mesh) is mixed with the oil in sufficient quantity to give the desired color, the mixture is well agitated 

for a half hour, and then the clay is separated in a filter press. The 

contact method is in general use except in a few of the older refineries. 

Most bleaching is done at high tem-peratures (150°- 2009c.) to insure 

maximum efficienty, particularly in working 1.7i th viscous oils .f1nd fats:· 

This temperature is sufficient to expel the residual H. and OH ions in 

the clay, and hence clay so used ncud not te entirely dehydra.ted. The 

clay may even be injected as mud into the hot still. But when blec:vching 

~lay is to be used cold on mineral oils such as gasoline or lubriaants 

~t must be thoroughly dried by heating for some tirne to about 175 c. 

Many highly active clay~~ when used clry, however, will crack wl1i te neutral 

oils, gasoline, or fused paraffin. The cracl:ed. portions are at once 

absorbed by the clay, leaving the filtrate still water-white but unstable 

toward light. It is claimed that the hot wet method of bleaching produces oils more stable toward light. Storage in the dark improves the 

stability of light-sensitive filtered oils. 

Source and origin of bleaching clays 

The weathering of most igneous rocks, such as dunite, granite, basalt, 

and rhyolite, is a very complex process, partly physical and partly chemical. Water penetrates between individual mineral crystals and into 

cleavage planes and surfaces of structural discontinuity within the crystals. 

The water carries H and OH ions, dissolved oxygen, carbon dioxide, organic 

at::!ids, and miscellaneous dissolved Gal ts, but simple sol·ation appears to 

be the dominant factor in decomposition by weathering. The surfaces that 

are Yl8t may be ~drated or dissolved· away or may exch.:=mgc bases and other 

ions for the H and OH of the water. Drying p2.rtly removes mct.teria.l in 

solutiGn and suspension and m~ikes easier the subsequent entry of water. 

Periodic wetting and drying or drainage is therefore nmch more effective 

in decomposing the rocks than a permanently arid or permanently submerged 

condition., 

8 
75000 

Mechanical decomposition (softening) is only· the first step in 

weatherin. Checical dccomposi tion ancl l;;;ac:ling continue, removing 

alkali and alkaline-earth bases ;:'ncl siiica and leaving behind the sesquioxides .Al20~ and Fe;iO , their sllic.:'.tef;, c::.nd cr;:,rste.lline qUt."'.rtz, 

vrhich are the chief cons~i tuents of fully weathered_ rocks. Climate, 

vegetation, and bacterial action influence the end product, which is 

usually either a soil or an inactive cla~r containing WG:.ter of crystallization. 

The residual soils in the imnediate vicinity of Washington are the 

result of weathering of granites, gneisses, and locally of gabbro. Of 

these products the most activable are the yellow a~d green soils containing excess quartz, usually unaltered, but little mica or alkali-rich 

feldspars; these yield the most active bleaches. The ash-gray variety 

composed largely of kaolin is far less acti V8.ble, and a darJ.:-green 

material high in mica and a white nearly pure feldspar rock cou~d not be 

activated even by leaching with acid. 

The solid residues of rock weathering have most open bonds and are 

most higl1ly absorbent when the decomposition and leaching are far advanced but before the highl;>l stable end products are approached.. Decomposed (in place) and ~pc::1.rtly leached granite from Washington, D. C., 

diabase from Virginia, anc~ duni te from Webster, N. C., were fol1nri to be 

active filtering ~nedia. Ey carrying the leaching a little further by 

boiling in several changes of distilled vvater or by treating with dilute 

acid, each of these mate::.~ials was co:1verted into an excellent bleaching 

earth. Many soils possess considerable bleaching power. 

The composition of the mother rock naturally affects the number and 

strength of the open bonds on the surfaces of the residual grains. Out 

of the almost infinite variety of such rocks, it is difficult and probably 

useless to select those which weather to the most active residuals in the 

average climate, but laboratory studies have shown which types of residual 

material are the most active when conditioned tc maximum strength. 1nese 

are derived from the magnesian and ferromagnesian silicates. If fully 

activated silica (silica gel) is taken as standard, other dehydrated 

amorphous oxides (Fe. Mg. Al, etc.) are about on a par with it in activity 

as a bleaching agent and so is hydrous aluminum silicate that has been dehydrated by ignition. Some magnesium-bearing alura}nosillicate clays are 

twice as active, and many iron and magnesium beai"'ing si1ica.tes exce.-.:d it by 

50 percent. 

The beds of commercial bleaching clays are probably the accumulated 

wash of decomposed igneous rocks. The associated sand and mica may well 

have been separated and deposited elsewhere by gently flowing water. The 

active clay might have become soil had it been exposed to the organic 

acids of vegetation. Although probably dep~sited in water and always 

kept saturated, it has not become reduced to pure aluminosilicate (Kaold.n) 

with or without inert iron oxide, because chemical conditions (sec below) 

were unfavorable. 

9 
75000 

Most of the clay deposits that are be in&; worked comL;ercially cont~in in themselves little evidence as to the mode of their deposition. 

One at Quincy, Fla. (Hawthorn ::ormation), '?2) shown distinctly an old 

stream beet with two laterals fillocl with sandy peat extending from top 

to bottom (about 20 feet) of tht:; .::.ctivc clay. Whether theso streom 

L:..eposi ts were laid dovm at the time the active clay wc:~s deposited. or 

subsequently is not entirely clear, bu.t they were probably filled in 

later. They are evidently not offshore marine de~osits. In a nRighboring bed the well-preserved skeleton of a manatee was found near one edge. 

Tho clay bed being worked east of Macon, Ga., (T·,vigss cl['.y member of the 

Eocene Barnwell formation; i/ see fig. 1), is thick and horizontal and 

sug;ests a deposit in the bl;d of a lo.lco. The extreme clarity of any 

watur in contact with e:ny of those active clays is notev:rorthy. Evidently no suspension is stable under conditions now existing in tho clay bed, 

nor does running water take up active clay. A stream will trickle dovm 

over a stoep bank of active clay (AttapulGUS, Ga., May 1931) vd thout 

becoming a~ all muddy. 

. Finally must be mentioned the synthetic bleaching media, tho amorphous oxides and silicates. Such hydroxides as Al (OH) 3 or (OH) 4 , if 

precipitated in 11ator, washo<i free from sc,l t, and thoroughly dried, possess 

good adsorptive powsrse Comincrcial 11 dializecl iron" mcroly d.riccl and ground 

is in this class, as are activated alumina ond silica gel. Silicates 

are easily prepared in a simiL:tr manner by mixing clilute solutions of a 

metallic chloride, for ex2-mple, with e. dilu"'::e solution oi water glass. 

These "silicates" ac'lsorb like the amorp:1ous oxides, cracking some oils 

and fil terinr?; v;ater-vrhi te until e:x:lmusted. .Ad~:;orbents of this nature are 

useful chiefly for the recovery of solvent vapors, as they do not yield 

an intermediate series of green, yellow, and re!l oils. Many are effective 

bleaching agents f~.1r vegetable oils and for fats, but they are too ex.-

pensive to compete v-:ith the naturally activo clays in petrole-um filtre.tion. 

Y For G. desr:ription of the Hawthorn formation see Cool:e, C. W., and 

Hossorn, Stuart, Geology of Florida: Florida Geol. Survey Twentieth A.."1n. 

Rept., 00. ll5-137, 1929Q 

.. j) The TvJigGs clay memoer is described in Cooke, C. W., ancl Shearer, 

H. K., Deposj.ts of Claibo:cne and Jackson e.r;e in Georgia; U. S. Geol. Survey 

Prof. Paper ::..20, pp. 41-JJ., and. Shearer, .. 11. K., A report on the bauxite and 

fuller 1 s earth of the Coastal Plain of Geor:·sia: Georgia Geol. Survey Bull. 

31, 1917. 

10 
75000 

Seat and origin o~ bleaching action 

The property of selective a.osorption is by no mee.ns lini ted to 

the bleaching clays. .Active S1J.:~f;3.Ces may be produced on many minerals 

by suitable means. Even ptu1e ~1~rtz beach ssnd may be activated by 

etching the grain surfaces with caustic soda or hydrofluoric .g,cid or 

with wate-r at high temperatures. The Tensleep oil sand, o::- Wyoming, is 

almost pure quartz with grain surface0 naturally active. These surfaces 

have adsorbed tarry substances from the oil such that a brown layer 0.75 

micron thick cannot be washed off by even the most powerful solvents. 

If it is removed by chromic acid ( 11wet combustion"), a ·white roughened 

surface is left which is active and will readsorb a similar lRyer if 

left a few hours in Tensleep crude oil. Tho oil sand of BI·adford, Pa., 

also has active surfaces but vii th more or less alumina and ferrous 

oxide associated with the surfaces of the quartz grains, which are vory 

rough and irregular. 

The basic constituents of many natural minerals for example, 

serpentine, greensand, glauconite, and the zeolites -- are easily removable by ordinary acids, leaving hyfu1 ated, more or less impure silica behind. 

This residue, after thorough washing to remove all free irons except H and 

OH, followed by thorough drying at 190° - 200° C. to e:~el these, is found 

to be an active adsorbent or bleaching·mediwn. 

Clays of apparently similar chemical composition may be either highly 

active bleaching agents or entirely inactive. On the other lk~nd, clays 

differing widely in composi 'iion rnay be s irnilar in bleaching power • Hor 

i~ the molecular structuu~e as revealed by X-rays a safe guide, for an inactive clay after activation by chemical treatnent generally shows little 

0r no change in structure by activation. However, a knowledge of structural 

type, as discussed later in this section,' is a va1ua1Jle guide in the study 

of activation. 

As the bleaching action is essentially a selective adsorption of 

coloring matter on exposed solid. surfaces in contgct with the liquid ~o 

be decolorized, such surfaces rrmst be the seat of the bleaching action. 

Study of active and inactive surfaces and particularly of the activation 

of inactive surfaces leads to the conclusion that it is the presence on a 

surface of open bonds or free valencies th8~t mru~e them selectively 

adsorbing. Any solid ad~; orbs every fluid that wets it in the sense that 

near the boundary surf~ce internal pressL1re, density, and viscosity arc 

increased. In certe.in combinations these effects are hoighte11ed by 

chemical affinity. A greased surface holds cliamonds ra tl1er tlw.n quartz 

pebbles. A clean quartz grain prefers water to oil, but a tar-coated 

grain or grain of coke prefers oil to water. 

11 
For fulling cloth (removing grease) a highly active earth is not 

necessary.. The fuller t s earth mined neal" Clinton, l\lc'lss., used for 

fulling cloth for many years, aprears to be nothinc but a very fine 

glacial silt... It has no filtering or 1;lea.ching pow·er fo:::- petroleum, 

as the grain surfaces are not activated. 

In the cases just mentioned the adsorbed coating may be removed 

75000 

by solvents without chemical change of the adsorbed II1':1terial. Eut the 

coloring matter on·a used filter cannot be removed (except the loosely 

held outer layers) by even the most powerful solvents.. It can be removed only by combustion -- that is, by converting it to carbon dioxide 

and water by igniting or by treating with chromic acid. It is this J:..ind 

of adsorption which is thought ... to occur when open bonds are present. 

These open bonds may be limited to the visible surface (activated quartz 

grains) or may occur on the walls of submicroscopic pores (silica gel) 

or of lamellar cleavage surfaces. In a few r.:.inerals bases may be leached 

out even from the interior of grain structures, yielding bleaching earths 

of the most valued type. 

The production of active sur!"aces on solid minerals is very simple 

in theory. It is apparently sufficient that the surface be attacked by 

a reagent which leaves the acid and ·basic constituents out of bal2Jlce on 

that surface. In quartz the mere etching avray of a part of e.. surface 

layer appears to leave open bonds -- bonds that were previously attached 

.: to atoms which have been removed. The minerals of basaltic rocks (calcic 

plagioclase, augite, olvine, etc.), serpentine, and. blast-furnace slag 

readily part with their basic constituents whan treated with an ordine.ry 

acid, and only :;?ure or nearly pure silic.s. remains. Pure kaolinite, 

Al2o3.2Si02.2H2o, roasted at 600°C., and goethite, Fe2o

3.H2o, roasted 

at 300°C., give up their Hand OH as water and become active like silica 

gel but not water-absorbent. Co~~ercial active clays, either raw or acidleached, are considerably lowered in bleaching power (to about ,two thirds} 

after ignition to 800°C. 

Some untreated natural clays are nearly as ctctive bleaching agents 

as any treated clays or as any that can be produced in the laboratory. 

(See test data, below.) Natural weathering must have been accomplished 

mainly by nearly pure water. In rare instances the activated mineral may 

have been exposed to solutions from v1hich it could adsorb material, enhancing its bleaching power •. The fundamental problem is therefore to 

determine what pure or nearly pure water may do to decomposed roCk. 

12 
75000 

The snlubili ty (')f a decompe"sec1_ granite from Washington, D. c., was 

founa to be about 50 part~ per million, and saturation is appr~ach6d in 

about 20 hours at 80°C. (steam bath.) At ~rdinary temperature (25 C.) 

sa~ation is about 35 p~rts per million and is approached only in a 

week or two. The initial solubility of fresh material is ·about twicG 

as great as the ultimate solubility reached after long-continued washing. 

Two weeks' treatment at 80°C. gave no higher concentration than two days. 

A solution boiled down in the clay gave no increase in concentration, 

but a clear, filtered solution at (50 parts per million) may be cC~ncentrated in pyrex or platinum tn several thousand parts per million 

bef&re precipitation begins. Decomposed diabase ~d dunite and commercial bleaching clays from Florida and Death Vallay gave solubilities 

and supersaturations of the same order ~f magnitude. Bentbnite shows a 

much higher initial solubility (350 parts per million) but also approacl1es 

50 parts per million after repeated washes. Amorphous silica (gel) has a 

constant solubility ijf about 180 parts per million. Solutions of· this 

concentration may be concentrated (with care) to 16,000 parts pe~.million 

before precipitatiqn begins. . 

During weathering rock surfaces are exposed to thin films of moisture, 

which are dilute but neariy--saturated solutions. .Alumina cind ferric 

oxide appear tl1 be the most resi3tant to weathering in the absence cf 

vegetation, but where vegetation and th& crganic acids derived from deca~ 

ing vegetation are present even these may be removed, releasing more ~ilica 

in soluble form. Slightly less resistant are quartz and the potash feldspars, and calcium, magnesium, and sodium complexes in general yield readily. 

Leaching with acid removes bases from many decomposed igneous rocks 

but tends to leave grain structures with the original edges and corners 

intact, as the residual silica is insoluble, whereas in pure water, on 

the contrary, it appears to yield indefinitely until exhausted or equi-

*ibrium is reached. Diluting the acids assists the dissociation and 

removal of the soluble components. In treating commercial clays with 

acid about 20 percent hydrochl~ric acid or sulphuric acid is preferred, 

and the mass is kept hot and stirred for some hours or over night. Under 

such c0nditions silica is one of the least s~luble constituents, and 

there is a tendency in many clays t~ leave too pure a silica for the best 

activation. The gentler action of weru~er acids or tf a salt soluti~n 

leaves more active ions and allli~ina as silicates. Aluminmn chloride, 

chromic acid, and oxalic acid solutions have given excellent results with 

minerals that yield to~ readily tn the stronger acids. 

13 
75000 

Conditions daring weathering are also favorable to the colloidal 

dispersion of the constituents, whereas conditions during the artificial 

acid treatment are not. In a. colloidal suspension near its isoelectric 

point, the particles do not settle nearly as readily as they <io if any 

excess of either positive or negative ions is present. It follows, 

therefore, that near the isoelectric point physical decomposition is 

favored. In natural weathering the adsorbed fihn of water, except in 

rare instDnces, remains near its isoelectric point-~a condition favoring the escape and removal of ions and small particles from the mineral 

surfaces. In the decomposed and claylike weathered products of granite, 

duni te, and diabase the free pa.rticles constituting most of the suspension 

after extended treatment with pure water consist largely of iron oxide, 

which has been set free by the water treatment. By water treatment alone 

the clay materials of the rocks just mentioned have been converted into 

good bleaching earths, and commercial bleaching clays and bentonites have 

been converted into plastic clays resembling ball clays. 

The interchange of ions between a solid mineral surface and the 

solution in contact with it also takes place much more freely near the 

isoelectric point. On the surface of a silicate crystal ions of the 

silicates are freely displaced by OH and other anions. The net result 

is that the free colloidal complexes (grains of silicates) represent a 

wide variety in compos:ttion and in properties. This interchange has been 

intensively studied by Mattson §} in connection with ionic equilibria in 

soils. 

Vegetation affects the course of decomposition and the composition 

of the end products by sup·qlying free weak acids and substances for a 

rich bacterial growth. 'p1~t acids dissolve sesquio:x:ides, silicates, 

bases, and even metals more freely than they are attacked in simple 

weathering, but such products are usually stored and partly returned 

to the soil instead of being carried away. Most eoils possess some 

bleaching power, if~reened to remove coarse material and treated with 

chromic acid to remove organic matter--in fact, some diabase soils 

approach the best commercial clays in activity. 

Soil, active clay, and inactive (kaolin) clay beds lie in contact in 

some places with little or no intermediate gradation. In many deposits 

of this type even tree roots in shallow soil do not penetrate the active 

clay beneath. Soil supporting luxuriant vegetation, resting on partly 

kaolinized feldspar without half an inch of gradation, is not unusual_in 

the South. On the other hand, roots of plants :penetratG decomposed 

granite, even the highly active varieties, freely. 

§} Mattson, Sante, The laws of soil colloidal behavior, V: Soil 

Science, vol. 31, p. 319, 1931 •. 

14 
75000 

The decomposed granite still contains much of its slightly soluble 

bases and hence may serve as plant food. The beds of bleaching clay, 

on the other hand, consist of only the finest material which has been 

superficially leached of all water-soluble constituents by long contact 

with excess water, deposited in watsr, and kept saturated with water 

nearly free from ions other than H :md OE •. Soil represents an unstable 

chemical (ionic) composition which is continually v;rying within a 

considerable range. The active clay beds of the East and South also 

represent an unstable equilibrium b11t one which has become stabilized 

for that particular environment through the removal and absence of 

practically all exchangeable ions from the surfaces of the clay particles 

and the presence of considerable bound, interstitial we.ter. Many of the 

active clays of the far West are only incompletely leached. The cer&nic 

clays of the ball-clay type represent an. approach to the true chemical 

equilibrium (irdth water), having all their bonds satisfied. Deposits of 

active clay may sh~de off into inactive clay and '§Oil at their thin edges 

when ionic interchange with acid and base ions is~provided. Wny active 

and inactive clays are ~laid down in separate beds .:Q.n the same basin remains to be explained but may provisionally be attributed to long-period 

climatic changes, the bleaching clays being le~~s completely leached than 

the ordinary clays. 

Susceptibility to molecular breakdown by wee.tharing or chemical 

treatment, which is the basis of activation, is of course lctrgely a matter 

of the molecular structure of the original rninaral. The structure of many 

silicates has been tentatively established, but the stability of such 

structures toward removal of individual n.toms and a.tomic groups has received little attention. The little that is known may be briefly sketched. 

Acid and basic atoms alternate in all these structures. The ease 

with which bases may be removed or replaced of course varies widely with 

the nature of the structure as well as with the particular base affected. 

In some open lattices, such as the zeolites and some clays, replacement of 

certain ions may be effected without destroying the lattice. Lamellar 

and fibrous structures are cowmen a~d are readily broken do~n. Breakdown 

and replacement of bases are often superficial only. 

Bragg §} and his co·yorkers have considered the following five classes 

of structures for the silicc:.te minerals, which form a convenient basis 

for considering ste.bili ty. The corrunents relating to ease of breakdown 

are my own. 

§j Bragg, W. L., The structure of silicates: Zeitschr. Kryst., 

vol. 74, pp. 237-305. 1930; cf. p. 300. 

15 
75000 

I. The orthosilicates, composed of independent Si04 groups. In 

this class minerals such as olivine yield very.readily to weathering 

and to chemicals. 

II. Diorthosilicates, rir:.g structures (beryl), and·other complex 

orthosilicates. ~nese are fairly stable toward weathering and do not 

readily'exchange bases. 

III. Silicon-oxygen chains, as in the pyroxenes and amphiboles. 

These minerals yield rather readily to weuthering, and t4~der suitable 

conditions the bases of their alteration products are largely replaceable 

by the hydrogen of acids and of water. 

IV. Silicon-oxygen sheets of the micalike minerals. Many of these 

minere~s of micaceous h2.bit are extremely resistant to activation methods 

on their faces. Heither muscovite, biotite, vermiculite, nor kaolinite 

can be made into good filtering media by leaching. :similarly needles 

(actinolite) and fibers (asbestos) do not yield to the simpler activation methods, on their larger faces at least. 

V. Three-dimensional silicon-oxygen networks. This class includes 

extreme types of stability. ~aartz is very resistant and stable, but the 

zeolites readily exChange bases with no alteration in structure. This 

group should be subdivided. 

Bragg 1 s rough .classification appears to be more sui table than any 

other yet offered to· serve as the basis of the intensive study of 

structural stability and atomic or ionic intercr~geability necessary to 

clear up the study of active minerals. Structural stability chiefly 

concerns weathering; chemical stability relates to leaching and base 

exchange. 

Igneous rocks are the ultimate source of probably all the bleaching clays. In such rocks the minerals most readily converted to active 

clays are the complex augites, hornblendes (class III), biotites, and 

olivines. Feldspars tend to alter to kaolinitic (nonactive) materials, 

but u.~der favorable conditions they too may alter to the type of clay 

material that is capable of becoming active under the proper conditions. 

The large commercial beds are all sedimentary deposits derived from 

weathered rock material. Mines in Arkansas, worked until e,bout 20 years 

ago, are igneous ferromagnesian (basic) dikes about 4 feet thick and nearly 

vertical where the minerals have been weathered in place and the original 

composition is evident from the retained structure. 1/ Igneous rocks of 

1/ Miser. H. D., Developed deposits of fuller's earth in Arkansas: 

U. S. Geol. Survey Bull. 530, pp. 207-220, 1913. 

16 
'75000 

the same general type in which the feldspars are dominant weather in 

~his region to plastic clays; and those in which nephelite is in excess 

weather to bauxite. The Arkansas de~osits are no longer worked, nor 

is any other bet of rock decomposed in place, as the expense ·of sorting and sifting is too great to compete with vast, deposits of sedimentary clay of equally good quality already sorted and sifted by the 

processes of nature. Here in Washington different varieties of 

decomposed rock may be noted, not far apart. 

The bleaching cl~s of the Georgia-Flori~~ region were probably 

formed. in embaynents along the coast 1 and the material must h[>..Ve been 

derived from the weathering rocks of the Piedmo::1t and P,l~~e Rtr~ge region 

to the north. Rocks composed wholly or even dominantly of amphiboles, 

pyroxenes, or olivine are of only local occurrence in ·chis region, and 

feldspathic rocks are domin&~t. For this reason it is 1tnlikely that the 

active clays of the Georgia-Florida region have been derived wholly or 

even dominantly from ferromagnesian (basic) minerals, like the active 

clays of Arkansas. Therefore the development of the active clays of 

the Georgia-Florida region has probably been cont~olled by conditions 

of weathering ~~d deposition, rather than by derivation from the type o~ 

minerals (ferromagnesian) that most readily yield active clays. 

The relation between Bragg's classification of silicate structures 

and activation is illustrated by the action of acids· on se::pe!..1tines and 

varmicu.li tes. Orcli.nary P-reen seroentine treated ... ~ th :r_yclroc:lloric acid 

yields its m%onesiw'Tl end. ~'iron, le~vi::1g active, nearly p·J.:;:oe ~d.lica. When 

the rock is treated. 1N:i. th hydrofluoric acid, the silica and j.ron yield 

to solution, leaving a white active magnesian residue. Both the silica 

and the magnesia residues are fairly good filters for oil. ~~t fibrous 

serpentine (asbeston) low in iron and alumina does not yield to hydro- -

chloric acid and is not activated by it. It yields readily to hydrofluoric acid, leaving a finely divided active magnesian residue. Raw 

vermiculite yields readily to either hydrochloric acid or hydrofluoric 

acid, without destruction of its 1nicaceous structure, but neither residue 

is active toward oil. 

This evidence sup:Jorts the view that activation consists in removing 

one or more constituents from an associated sol~~-~J. comrlex. It is usually 

associated v:ater that is removed to leave or.en ·bc.ndst ~ut it may be 

almost any element or group, or simply an ir ... terc:nJ.nge. Fi1J"!.·ous structures 

that yield in but a. single dimension a...Yld mice.ceous str-u.ctures that are unyielding in one dimension (Bragg's class IV) aJ.•e probably not exceptions 

to the general rule. 

17 
75000 

The formE~tion and stability of the active silicates 

The bleaching action of certain cl~~s is only a special case of 

-union between oppositely charged ions or molecular aggregates. In 

general, a positively charged group 11nites with a negatively charged 

group. If either group consists of solid particles or a porous solid, 

the other may be ultramicroscopic, ionic, or even molecular, and attachment to the solid (adsorp~ion) removes it from solution or suspension. 

We are here dealing with systems of which one component (the clay) consists of relatively large aggregates, while the other (the e.dsorbed 

material) usually consists of single molecules or small groups of colored 

molecules in solution or suspension. In this section are considered more 

in detail the action of water on silicates and the conditions necessary 

for the stanility of the wet active clays. 

In general any solid particle in susnension in a liquid will migrate 

either with or against an 'electric current when a potential gradient is 

applied. If the particles are large enough to be seen with a microscope 

the movement may be seen (cataphoresis}, the velocities being commonly a 

few microns per second per volt per centimeter. In ordinary electrolysis 

there is a similar but invisible movement of ions (charged atoms or groups 

of atoms). When a visi.ble particle is r:1oving in an electrolyte, acid or 

base may be added till the movemeut is reversed. When no motion occurs, 

the particle is at its isoelectric point, and its total charge is zero •. 

Charged particles tend to uu1ite, positive with negative, if both are 

present, just as do ions in solution in ora.inary chemistry. This union 

of acidoid particles with be.sic colored ions in suspension, for example, 

is the basis of the filtering or bleaching action of active clays. But 

while the small chemical ions Dre single, the large charged particles 

tend to collect neighboring ions and so neutralize their charges and become less active. ~urther, the exter~~l ions tend to react with individual 

component ions at the s1rrface of tho large particles ~~d neutralize their 

charges and tend to break down their structure if t!k~t is weak. I. 

Starting with the simplest case we may quote Mattson: §} 11 In general 

all inert substances charge themselves negatively in water. This may be 

accounted for by assuming the electrical forces within the oriented, 

interfacial layers of molecules to be such as to attract and fix the OH 

ions of the water while the H iorts (or any other cation which may have 

displaced the H ion) remains free and diffused into the surrounding water, 

which then assumes a corresponding positive charge. 11 Or it may be simply 

as~ed that the bond attaching the OH ion is more powerful or more readily 

attached than that attaching the H atom (it is part of a potential double 

bond). 

~ Mattson, Sante, Isoelectric precipitates: Soil Science, December 

1930, p. 463. 

18 
75000 

Thus clay particles in water tend to surround themselves with an 

atmosphere of ch8.rged ions--some frmn their own material if any are 

free but supplemented by H, OH, and other ions from the water. As 

the H is small and mobile while the OE tends to remain with the silica, 

there is a marked tendency for H to diffuse away from the silicate 

particle and be replaced by other less mobile bases if these are available. The very high dielectric co;nstant of w-ater assists this action. 

Alumina and ferric oxide ere most like the silica and even less soluble 

in water, so they tend to remain with it to the last • 

.At the isoelectric point a. parttcle does not migra.te either with or 

against an electric current. Hence the total charge, consisting of that 

within the solid particle plus the ions on its surface and in its atmosphere must be zero. Ions (for example, W) may be escaping with the 

current. but others must be joining the aggregate at the same rate. In 

a large excess of pure we.ter mineral particles Iml.st in time closely 

approach their isoelectric points, bases at or near the surface have 

mostly escaped, and the ion atmosphere must (owing to mass action) consist chiefly of H+ and oH-. When bases are locked in the interiors of 

the grains and-either time or water has been insufficient for the complete removal of bases or of silica in excess of the 1:2 ratio, then clays 

of .beidellite-montmorillonite type may result. When both time and water 

supply have been ample for such removal, many silicates may go to hydrous 

aluminum silicates of the kaolin type. These in :pure wa.ter have a hydrogen-hydroxyl ion concentration near the isoelectric point and in sufficient 

time may crystallize to kaolinite. 

The eastern active clays have been rather thoroughly leached at the 

grain surfaces but have apparently been weathered under such conditions 

and laid down so rapidly that the bases have been leached awa:y only a.t the 

surface and after deposition, the supply of water (locked in) has been 

very small, and the isoelectric point could not therefore be attained. 

In the western active clays there has been even less leaching, a more 

rapid deposition, and a more limited supply of water. 

It is worth noting that when the OH ions are forcibly removed from 

kaolinite by heating above 500° c., the residue having open bonds is a 

very good filter and is partly soluble in ordinary acids. The solubility 

in acid after ignition may be used to estimate the fraction of kaolinite 

in a mixed cl~. The filtering.power of ignited kaolinite, as would be 

expected, is similar to that of amorphous silica and alumina and about 

half that of the best neutral earths; and ~ch material yields but little 

of the intermediate yellow and red grades of oil in filtering. 

19 
75000 

The bleaching clays, then, consist of particles of mixed aluminosilicates of somewhat variable composition but belonging to the less 

stable group of clay minerals whose surfaces are only partly balanced 

with removable ions. Water and weathering have prepared these surfaces, 

and lack of time or of a sufficient supply of suitable ions has prevented 

their complete leaching and recrystallization into permanent stable units 

(secondary silicates). Activation consists simply in the removal of the 

ions loosely held at the surface, so that in filtration other chosen ions 

or charged.aggregates may be adsorbed and thus removed. from solution or 

suspension. 

The clays under consideration here are then accumulations of the 

miscellae of suspensions. Of the many types possible, considering the 

nature of the original source rock and of subsequent weathering and water 

treatment, at least three may be distinguished: 

· 1. Clays consisting of basoid particles whose surfaces have been 

leached to unsqturation, the open bonds temporarily holding ions, chi,efly 

hydrogen and hydroxyl. 

2. Clays consisti~g of basoid particies with surfaces either unleached or covered with adsorbed bases. Groups 1 and 2 commonly have an 

alumina-silica ratio greater than 1:2--that is, 1:3 to 1:5. 

3. Kaolinitic clays composed of particles leached free from bases 

and hydrated to A1293.2Si02.2H20. 

Ordinary clays consist largely of,Al203 and smaller but variable 

quantities of Fe2o3 , combined with SiOz and HzO in variable proportions. 

If the proportion of silica is· low ru1d hydrous oxides are abundant, they 

may lean either toward laterite or toward bauxite, according to which 

oxide is in excess. 

Most active clays do not slake in water, although bentonites and 

ball clays slake readily. This property is significant. Colloidal 

suspensions precipitated by electrolytes {acid, basic, or salt solutions) 

readily break down physically in water, even after drying to a hard lump. 

Hence precipitation by sea water is not a probably method of deposition 

of the active clays. 

20 
75000 

Nonslaking dried sediments may be obtained by precipitating 

one colloid by another--for example, an acid clay or diatomite by 

dialyzed iron, all electrolytes being excluded. This is evidence, though 

not conclusive, that the active clays consint of positive and negative 

particles nicely balanced in sufficient proportion to give a nonslaking 

character to the whole mass. Material from decomposed ferromagnesian 

igneous rocks, thoroughly leached in a large excess of rather pure water, 

would give rise to such a combination. Particles that were smaller and 

more easily leached woul~ be adsorbed by particles less leached, thus 

neutralizing and precipitating them. The base-exchange properties of the 

active clays are not pronounced, as this theory would require. They are 

highly stable toward water ru1d give up a few ions to it. 

The sedimentary active clays are also highly impermeable to water 

and probably for much the same reason that thev do not slake in water--

namely, that·_.the grain surfaces are interlocked by chemical bonds. Other 

factors are the fineness of grain and fineness of pores between and 

through the grains. \Vater cannot pass through a channel less than 0.01 

millimeter in diai·neter, for such a duct is· choked by adsorbed water. 

Bentonite slakes readily but is impervious to water when confined so that 

it is unable to ·expand, because its pores are too s~~ll to permit water 

to pass through them. 

The complex silicates constituting the active clays range from 

slightly acid aluminosilicates to those that are only partly leached and 

decidedly basoid. In the latter class acid treatment is indicated to 

remove the excess of the stronger bases K, Na, and Ce.. by replacing them 

by H. Good natural filters may be composed largely of silicates rich in 

magnesia but are more commonly com:;?olmds of alumina, iron, and silica. 

After an acid treatmeht, thorough washing is required to remove all salts 

formed, because otherwise these may be adsorbed in preference to the 

colored ions ,to be removed in the bleaching process. A wash with even 

dilute alkali (KOH) will ruin a filter; but a final dilute acid wash is 

not seriously detrimental. 

An active bleaching clay placed in a hydrocarbon containing no 

oxygen atoms (such as netroleun1) will adsorb colored ions of the nature of 

-CnH2n+l• detached parts of multiply-bonded carbon chains of rings. If 

these are not present, a good filter will breruc out (crack) and adsorb . 

parts of even saturated chains or rings. If the filter is not completely 

dry, H a~d Oh.ions remain on its surface and its activity is nmch reduced, 

so that is adsorbs only the blackest hydrocarbon groups and passes the 

yellow and red fractions. 

21 
75000 

Filtering a hydrocarbon containing oxygen atoms to a water-white 

color•is much more difficult. In this class are the animal and vegetable 

fats and oils, fatty acids, and esters. The colored groups are probably 

as readily adserbed, but the efficiency of the filter is unavoidably 

reduced by H and OH ions already adsorbed, so that the less active greens 

and yellows are not removed. If an alcohol (high in OH) is added to 

petrole~~ even a good petroleum-bleachine clay has almost no power to 

filter it. There appears to be some advantage in using the more siliceous 

type of filters, which have a higher capacity for OH adsorp~ion and combination. Also there appears to be a selective advantage in high temperatures_, which appear to d.ri ve off OH more readily than hydrocarbons from 

an active surface. It might be thought that the ~arboxyl radical -COOH 

of the fatty acids would be more readily adsorbed on siliceous surfaces, 

but this is weakly negative and probably seldom colored or adsorbed. 

Association with water - Hygroscopicity 

Water is associated with minerals in many different ways, often 

difficult to determine. It may be adsorbed on surfaces, absorbed in 

minute pores or ~les, or be simply in solution in the mineral. It 

may be water of crystallization in molecular association, or water of 

constitution in chemicul combination as II and OH ions. In any of these 

forms it may be driven off by heat. It is to be regarded as an additional oxide, but one more readily dissociated and more easily·vaporized or replaced then most others. In chemical analyses it is customary 

to regard water not removed by heating to 110° c. for some time as combined water, that driven off below 1100 c. being either .free moisture 

or adsorbed water, but in many analyses such a division cannot be made. 

Some adsorbed water is not driven off even at 200° C., and some hydrates 

break up and release water below 100° c. 

The signific~~ce of the association of water in bleaching clays is 

that.· where bonded hydrogen and hydroxyl ions are d.ri ven off from so lids 

they leave open bonds, whether or not such removal results in structural 

breakdown or is reversible. The vapor pressure of bonded water is always 

less than that of free water; hence a study of vapor pressures and 

various percentages of water present gives a measure of the degree of 

association~ Heats of wetting also give a measure of bond number and 

strength, but those heats are only a few calories, experimental difficulties are great, and corrections and uncertainties are large, so that 

this method is little used. 

22 
75000 

Clay exposed to a given relative humidity reaches a fixed weight. 

That weight is always the same whether equilibrium is reached from a 

dryer or moister condition and nearly the same whether the cl~ is in 

lump form or po·v~dered. T~e cul"ve of weight plotted against lro.midity 

is not a straight line, as for simple solutions (Henry's law). but is 

somewhat S-shaped, indicating some chemical association of water with 

clay. Typical curves are reproduced in figures 3, 4, ru1d 5. 

These curves suffice to show the wide difference in response to 

water vapor. Pure silica gel represents one extreme type of response;· 

a powdered chemical salt, like potassium chloride, the other extreme. 

The salts take up no water--that is, their vapor pressure remains 

practically nil--up to a limiting high humi~ity, above which they take 

it up freely and go into solution. The clay curves are all intermediate 

and S-shaped. Of two high-graue clays, that from#Chambers, Ariz., 

is one extreme in trueing up the most water, while the other, from Death 

Valley, takes up the least. The curve for acid~-treated serpentine has 

the silica gel type of shoulder at its upper end but has the toe (0-20% 

humidity) of a clay type of curve, convex upward. 

To have a vapor pressure approaching ·saturation most clays must 

have a high water content, the affinity of clay for water being high. 

On the other hand, a clay mud will lose water even in a saturated atmosphere in a closeD. glass vessel. There may be clear water above the . settled mud, but the loss of water goes on just the same in a perfectly 

smooth curve at a steadily decreasing rate. A hare: block of d.ried clay 

of course gains \"Tater in a saturated atmosphere. The block and the mud 

eventually (in a year or two) approach the same water content, which is 

not far from that found in conmercial clay ·beds when mined. A mud of 

powdered glas~. on the other hand, neither gains nor loses water in a 

saturated atmosphere, but a salt or a sulphuric acid solution continually 

gains water under like concti. tions. 

The energy and pressure connected with the adsorption of water vapor 

are of interest. If saturated water vapor is in contact only with 

liquid water and an inactive solid such- as glass, the work RT in calories 

per mole (18 grams), or.RT/18 calories per gram, will condense the vapor 

to liquid. T is the absolute temperature and R the constant 1.985. At 

26° C.= 26 + 273 = 299° absolute, this work is 32.9 calfgm. As soon as 

the vapor is condensed, internal forces pulling the molecules together 

do the additional work RT.d log C/d log T, amoUllting (at 26° C.) to 

548.9 cal/gm, called the internal work. The sum 548.9 + 32.9 = 581.8 is 

the total heat of vanoration. The concentration C refers to the water 

vapor in grams p't c~bic centimeter. 

23 
~25~----~----+-----+-----~+---~-----r----~~+--+~hr~~---; 

1-

~ 

~20 

uJ 

(). 

o! 

~ 15~----+-----~----~~--~~--~~--~~~~~--~7r-----+-----; 

20 30 40 50 60 70 80 

RELATIVE HUMIDITY 

Figure 3 .-:-Weig:.Lt-1n:uni0.i ty curves. Notation of tfible 2. 

90 100 

40.-----~----.------r----~----~------~----TT----.------r~~~ 

~25r-----~----~----~-----+----~--~~~--~~----~~~~----~ 

~ ~ 

~2or-----+-----,_-----r-----+----~~~--~----+,~~~~---+----~ z 

u.J 

() 

~ 

/ / 

~ ISr-----+-----,_--~~-----+~--~~----~----~~~~~~/--~----4 

10 20 30 40 50 60 70 80 90 100 

RELATIVE HUMIDITY 

Figure 4.-Weight-huniidi ty curves of clays. Notation of table 2. 
75000 

With an adsorbed film of water in equilibrium with unsaturat~d 

water vapor in a glass enclosure, the extra work of condensation is 

RT log (p/P) or RT log H, where F is the rele.tive humidity and p is 

the vapor pressure, less than thE saturation pressure P. This extra 

work or energy is due to adsorption, tl1e total external work being 

RT log H to bring the vapor to st;turatiori, plus RT to condense it to 

liquid, or RT (l + log H) altogether. The expression RT leg H for 

ext erna1 work d:ue to adsorption nay be shown by stat'i stical methods 

to hold whenever the C·Jntact is between water vapor and liquid water 

(at least one layer of Inolecules of water adsorbed) and whenever capilL.ry or other forces are negligible--that is, except at high water 

contents. .At 26° C. the extra energy is as follows: 

Table 1.--Energy o~ association with water 

. h~ -log H cal/grn H~b -log H cal/grn 

l 4. 6052 151.85 50 0.6932 22.86 

2 3.9120 128.99 60 .5108 16 .. 84 

5 2.9957 98.78 70 .3572 11.78 

10 2 .. 3026 75.92 80 .2231 7.36 

15 1.8971 62.55 90 .1053 3.47 

20 1.6094 53.07 95 .0513 1.69 

30 1.2040 39.70 100 .00 .00 

40 .91G3 30.21 

The third colu.rn.'1 of this table gj.ves the external energy in calorie-s 

per gram of water adsorbed when the water content is such as to be in 

equilibrium with the relative hurriuity of the first column. Curves such 

as those of figure 3 then, with this table, supply data for finding a 

relation between adsorption energv and water content or thickness of film 

if the surface is known. .As would be expected, the energy is very high 

for the first moisture adsorbed b~t falls off rapidly as the thickness 

increases. The form of these ene~gy-concentration (percent water) curves 

suggests an exponential, and in figure 5 is plotted log H against log C 

for permutite. 

25 
4 

laJ 

" 

(.!) 

0 

.J 

3 

2 

I 

0 

-4 

.... 

~ 

~ 

""' ~ 

-3 

~ -z 

~ 

LOG C 

Ficwe 5.--Znercy-lcy~ co:t1centrfltlo::.1, perrrru.ti te. 

75000 

The first eie,ht points lie on a perfectly straicht line E = log H = 

-2.788 - 1.515 log C or dE/dC = -1.515/C. The rate of falling off of 

energy (or press~ e) is therefore inversely proportional to the thickness of the adsorbed layer. This law holds u:p to a concentration of 13 

percent moisture in permuti te. At hit;hc~r percentages of water either 

the law breaks dowr.L or other effects (such as capillarity) enter. All 

the observed curves for the clays and simple amorphous oxides show this 

simple linear rel~tion E = log R =A+ B log C for the lower hurr.ddities 

and water concentrations. 

In differential form, this relation is dB./H (= dpjp = BdC/C, wb.ich 

states that the percentage increase in vr-tpor pressure is directly proportional to the percentage i~crease in concontra~ion of watE?r in clay. 

Rewri tt~n as dE/dC = B/C the law· states th8.t the 1~ate of falling off of 

energy with thickl1ess (or the attraction between contiguous layers of 

adsorbed water) varies inversely as the thickness of the adsorbed layer 

of water (which is proportional to C for C small). The constant B is a 

measure of that rate of :falling off of energy with thickness and hence 

must be closely related to the orienting power, for \'lat.or molecules, of 

the adsorbing active surface of the solid. The constant A/B is likewise 

a measure of the extreme thickness at which the adsorptive force is 

appreciable (E = o, log C = A/B)--that is, it is a measure of maximum 

concentra.tion adsorbed from a water-saturated atmosphere (p = P, H = 1, 

E = log H = o) •· 

26" 
75000 

The well-known empirical law of Freundlich, q = apn, for the 

quantity of liquid q adsorbed from a gas or vapor at a pressure p, 

may be tre,nslated into the law discussed above and similarly interpreted, as quantity adsorbed, thickness of adsorbed layer (at low 

concentrations), and concentration are all proportional to one another, 

and the logarithmic derivative is the same whichever variable is used. 

If vapor pressure p is measured in terms of saturation pressure P, its 

logD.rithmic derivative is also not affected •. Our constant :B is thereciprocal of Freundlich's 1!-• His fornm.la states that the vapor pressure 

of an adsorbed layer is simply proportional to some power of its thiCkness. 

Heat treatment, leaching with acid, and hydration modify the weighthumidity curves. In figure 6 are shown curves for serpentine raw, ignited 

to 800° C., and leached to white, nearly pure silica with hydrochloric acid. 

The original grains were 150 nesh, a clear dark ~een. 

a! 

IIJ 

r 

~ 

20~--~---4----+---~--~~--~---+----+---~~~ 

~ 15r---~---4----+----r--~~--~---+~~+-r--r--~ 

LLJ 

u 

Q! 

ILl 

~ 10~---~---4----+-~~--~b-~~--~~--+----r--~ 

10 20 30 40 50 60 70 80 90 100 

RELATIVE HUMIDITY 

Fi€,"tlre 6.--Weight-humidi ty, treated serpentine. Raw, untreated grains. 

Ig, ignited to BOOO C. in air. Ttd, HCl leached until white, then 

washed free from chloride. lJotc different vertical scales for percent moisture. (See table 2.) 

27 
75000 

Ignition nearly doubles the water adsorption and affects that 

at high humidities most. Acicl. treatment increases water adsorption 

more than ten times e:.nd gives a curve similar to tha.t for silica gel• 

A possible variation of hydration with size of grain was sought 

by using the Quincy earth in the 30-60 mesh commercial grade in comparison with the same material ground to pass 300 mesh (0.05 millimeter). The amount of water taken up was very nearly the same for the 

powdered and granular clays for all rntmidities from 0 up to 50 percent. Either the increased surface due to powdering is negligibly small 

in comparison with the active pore surfaces, or else the new surfaces 

are inactive. Between humidities of 60 and 95 1)ercent the coarse material 

took up about l percent more moisture than the .fine. Similar but less 

precise results had previously been obtained with bentonite. The fines 

in that experiment were obtained by evaporating a suspension that had not 

settled in months and pulverizing the dried residue. The close agreement 

in the results of the two experiments indicates that the extremely fine 

material remaining in suspension has essentially th.e s&~e composition and 

character as the mass from which it was derived. (Compare 0 and P of 

table 2.) 

Freshly treated raw clays and most synthetic active silicates are 

known to become somewhat less active in time. The effect of ageing on 

the amount of water taken up was studied with a silicate precipitated by 

chromic acid, freshly made and after 30 months. There was no change in 

moisture adsorption at a humidity of 30 percent. At humidities from 0 to 

30 percent the aged mat·erial took up a little more water than the fresh; 

above 30 percent it took up less, with a steadily increasing divergence. 

At 90 percent humidity the fresh material took on 62.3 percent of water, 

the aged but 37.5 percent. Probably few other materials exhibit so 

large an ageing effect. The results indicate that the change with time 

is not merely a closing of some open bonds but is explained by more active 

but fewer b?nds in aged material. (Compare K and L, table 2.) 

A test was made of the reversibility of the water left in an active 

clay at zero humidity, usually between 3 and 10 percent. A powdered clay 

was put in the usual P205 desiccator until constant weight was reached, 

~hen heated to about 2000 c. to drive off part of the .remaining moisture, 

then put back in the desiccator. In a week it had regained over half the 

water driven off by heat, proving that i~ was able to take water even 

from fresh P205, which has a vapor pressure below a billionth of ru1 atmosphere. The residual moisture in clays therefore represents a definite 

equilibrium, which is at le~st partly reversible. Ignition (800° C.) 

destroys the avidity of most silicates for water for a time, and after a 

moderate heating most active clays are much more powerful desiccants than 

even P205. 

28 
75000 

In table 2 are presented data on hydration for several synthetic 

amorphous o~ides, simple natural minerals, and bleaching clays. They 

are perfectly definite and repeatable va.lues, ap:proa.ched from either 

higher or lowe:&."' humidities for the same sample of material, but the 

method of preparation of a material may profoundly influence its dehydration curve. Part of the data on serpentine and analcite were 

published in an earlier paper, ~ in which various details of the method 

used may be found. 

~ lrutting, P. G., The associ~tion of water with serpentine: 

Washington Acad. Sci. Jour., vol. 18, pp. 81-89, 1928. 

29 
Relative 

humidity 

Jnercent) 

5 

10 

20 

30 I 

40 I 

I 

50 

60 

70 

80 

90 

95 

Ig.8000 

: 

Relative 

lmmidity 

(percent) 

5 

10 

20 

30 

40 

50 

60 

70 

80 

90 

95 

Ig.aooo 

Table 2.- Moisture content at various l1umidities 

(Percent by vreight) 

--r-

.A :s c D 

:.6 j F G 

1.5 1.7 3.0 1.1 0.24 0.39 

2.5 3.4: 4.8 2.0 4.0 I .39 .62 

4.0 7.5 6.9 "3.3 6.0 I .60 .90 

5.4 12.8 8.3 4.6 8.2 

I 

.73 1.03 

7.5 22.1 10.5 I 5.8 10.7 .82 1.13 

9.8 30.5 14.3 8.1 13.1 I .951 1.28 

14.5 35.1 19.3 11.3 14.9 1.11 1.51 

28.4 37.3 24.8 13.7 16.2 I 1.32 1.89 

57.3 38.5 29.6 14.5 16.9 I 1.59 2.52 

61.9 . 39.4 32.5 15.9 17.2 1.94 4.22 

62.8 39.8 33.4 18.5 17.3 2.16 5.90 

-9.3 -10.6 -17.6 .00 

M N 0 p -Q,-+ R s 

··-

2.19 2.25 3.01 3.10 2.21 2.2 I 1.6 

3.52 4.15 4.7--1 4.86 3.7 3.71 2.6 

5.48 6.90 6.69 6.80 5.8 I 5.8 :.3.8 

7.12 8.45 7.91 7.99 7.3 I 7.3 4.6 

8.70 9.35 I 8. 78 8.79 8.4 I 8.4 5.6 

10.2 10.2 110.4 9.83 s. 6 1 9.6 6.8 

11.7 11.5 13.2 11.5 11.8 ! 11.8 8.7 

13.3" 13.7 116.1 14.5 I 15.C I 14.6 13.7 

16.3 17.9 . 20.6 19.2 20.7 ! 18.7 21.6 

22.4 28.6 33.2 31.3 31.3 I 26.6 30.9 I 31.4 38.5 46.4 

I 

43.9 40.8 ! 33.1 37.2 

-19.9 -10.9 -9.4 -8.7 '"' 7 I -o. i -.6 -5.7 

i 

30 

75000 

H r .-

2.0 3.7 

3.5 6.0 

6.0 9.1 

8.2 12.2 

10.9 15.5 

14.6 18.8 

18.9 21.9 

24.3 25.1 

27.8 28.3 

29 .. 5 33.6 

30.1 38.5 

-8.3 

--I--

T u 

' 

4.0 2.8 

7.5 5.0 

12.8 8.2 

15.8 11.1 

17.4 13.8 

19.3 19.2 

21.8 28.6 

25.0 38.3 

29.1 46.4 

34.6 53.1 

41.1 56.2 

-9.5 -10.2 

K 

1.2 0 

0 

1 

9 

4 

2 

0 

2.1 

3.4 

4.3 

5.1 

6.0 

7.2 

9.4 

17.8 

62.3 

v 

--

1 .. 

2. 

3. 

4 • 

5. 

7. 

a. 

11. 

13. 

17. 

19. 

-11. 

2 

1 

3 

.2 

4 

0 

9 

3 

9 

0 

3 

5 
.A. 

B. 

c. 

D. 

E. 

F. 

G. 

H. 

I. 

. K. 

L. 

M. 

N. 

o. 

P. 

Q. 

R. 

s. 

T. 

u. 

v. 

75000 

Silica gel, ion-free, prepared by Nutting, 1928, 100 mesh. 

Silica gel, commercial (Patrick), crushed to 100 mesh. 

.Al203 from pure .Al(OH)3 , prepared by Nutting, 1928, 100 mesh. 

Activated alumina, from Aluw,inum Co. of America, 1931, 150 mesh. 

Fe203 from FeCl3 dialized ion-free b~y Nutting, 1931, 150 mesh. 

Raw serpentine, 150-300 mesh, clear-yellowish green. Si02 35.6%, 

MgO 39.9, Al203 2.5, F0203 4.6, FeO 2.0 (F • .A. Gonyer). 

Ignited se~)entine from same stock as F. 

Serpentine from smne stock digested in IICl and. washed. White. 

Bentonite (otaylite), California, white, crude. Si02 50.3%, Al203 

16.0, CaO Rnd MgO 7.8, H20 23.6. 

fiQhromium silice.te. II .A greenish-yelloW synthetic ~preparation Of 

silica gel m3.de from water glass ~:)recipi tcted wi tl1 Cr03 solution, 

100 mesh. Fresh. 

The ·same stock 2 1/2 years old, shovving age effect. 

Permutite, Folin preparation, old stock, white, 100 rr.esh. 

Fuller's earth, Qnincy, Fla., raw clay dried and powdered to .150 mesh. 

Fuller's earth, · Clu.incy, Fla., com..rnercial 30-60 mesh. 

Fuller's earth, same as 0 but finely powdered. · 

Clay from Macon, Ga. , General Reduction Co. , raw clay fresh ground 

to 150 mesh. 

Clay from Macon, Ga., baked at 2000 F., then ground to 150 mesh. 

Clay from Macon, Ga., ground fresh clay, HCl leached, then washed. 

Clay from Cha~bers, Ariz., Filtrol Co., raw clay ground to 150 mesh. 

Clay from Chambers, Ariz., same clay acid-treated, then washed. 

Clay from Nevada near Death Valley, Calif., high in Mg, raw clay ground 

to 150 mesh. 

The synthetic amorph~1s oxides Si02 , A1203, and Fe203 are characterized by humidity curves having pronounced shoulders at high humidities 

(70-95 percent). Si02 hydrated to Si(OH)4 would contain 3?.5 percent H20. 

Both the silica gels studied take up more than that at 95 percent humidity, 

indicating that the water is adsorbed an well as combined, and the reversibility at room temperature indicates that little if any is combined 

with the silica. Similarly for the pure Alz03 , Al(OH)3 is 30.? percent 

H20, and the amorphous form takes up 33.4 percent at 95 percent humidity. 

And instead of 25.2 ~ercent H20 in Fe(OH)3 , the prepared oxide takes up 

18.5 percent H20 at 95 percent humidity. 

On the other hand, the curves for the naturally active cleys and 

the complex synthetic silicates point steeply upward at humidities 

approachir.g saturation. Ignited serpentine has a curve of the clay type, 

but acid-leached serpentine has the characteristics of silica gel, as it 

should after removal of the stronger bases. 

31 
75000 

Conversely, moist clays have a definite vapor pressure corresponding to each percentage of water retained. That vapor pressure is 

approximately 25 millimeters times the relative h1unidity with which 

the clay is in equilibrium, as observations were made near 26° C. 

Curves of the simple oxide type, such as that for silica gel, indicate 

that a definite equilibrium concentration is attained at saturation 

pressure. A thin mud of water sus;)ension of materials of this class, 

placed in a sat1.1rated o.tmos2Jhere, ;:ill neither gain nor lose water. 

On the other hand, humidity curves of the active clay type seem to overshoot the saturation line, and muds of such clays will lose water in a 

saturated atmosphere until equilibriu...'!l with saturated water vapor is 

reached, generally when the clay ha.s consolidated into fairly hard lmnps. 

Soils, which always contain some active colloidal material, according to 

these observations would never ta.ke up wate:' vu.por from the atmosphere. 

On the other hand, if 1.7et with liquid. water (rain) to a mud they tend 

to rid themselves of the excess and will nrovide a saturated atmosphere 

for plant roots under surroundings far le~s humid and u.l'ltil they are 

themselves fairly dry. 

Association with water - Hydrothermal relations 

As hydrous minerals arc heB.ted they gradually lose water - first 

free water, then adsorbed and combined we.ter, H and Oh ions. At 800° C. 

all but a very few minerals are anhydrous. The curves of dehydration 

with increase in temperature vary widely in form, from a smooth continuous slope to curves hc~ving steep shoulders c:1.aracteristic of definite minerals containi:ag water in molecular proportions. ~he dehydration-temperature curves are useful in studying the composition and 

structure of clays. In :partiC\l.lar they give valuable clues to the 

nat1~e of water associ~tion and hence to the activity of the clay as a 

filtering agent. 

Hydrothermal curves are perfectly definite a...'>ld repeatable but are 

reversible within a reasonable time only at the lower temperatures (below 

about 200° C.). Kaolinite, which lJB,rts with 2H..,O abruptly at about -· G 

500° C. (a low red heat), with loss of crystal structure, was thought 

to have irreversible lJroperties, but heating with water in an autoclave 

to 300° C. in time restores the combined water and crystal structure.1QJ 

It is probable, therefore, that tho reversion would occur even at ordinary 

temperatures, given sufficient time (probably hundreds of years). 

1Qf Schachtschabel, Paul, Ueber Dehydratisierur1g und Rebydratisierung des Kaolins: Chemie der Erde, Band 4, pp. 395-419, 1928. 

32 
75000 

These thermal dehydration curves supply additional evidence 

that it is not chemical composition but struc~ure which determines 

the behavior of a mineral toward water or other adsorbed substances. 

Diaspore (Al203.H20) shows the sharp sholllders (469°-483° c.) characteristic of pure hydrated salts. Allophane (Al2o3.Si02.3-5H20), however, 

dehydrates (fig. 7) in a very smooth curve with no shoulders. The 

high-temperature kaolin mineral ("dickite" of the new classification 

of Ross and Kerr ll./) .Al2o3.2Si02.2H20 also :r~as a sharp shoulder at 

500°-545°C. Impurities affect the s:':lapes· of these curves at temperatures below that of the sharp break (if there is one) and round off the 

shoulders but do not a£fect the temperature of the break. As little 

as 10 percent of the pure mineral diaspore or of a kaolinite in a 

mixed clay should show in a thermal analysis. 

11} Ross, C. S., and Kerr, P. F., The kaolin minerals: U.S. Geol. 

Survey Prof. Paper 165, pp. 151-176, 1931. 

33 
75000 

~6~~~~~--+-~--+-----4-----~~~4-~--~----~ 

~ ~ 

~5~~~++~~~~--~----~--~~----~+---~----~ 

loU 

(.) 

Q! 

I.LJ 

~~----~~--~~~r+r---~----~+----;~~~----~ 

Figure ?.--Thermal dehydration curves of hydrous oxides. D, Diaspore 

(Al203.H20), from Rolla, r~ro., selected by c. s. Ross; evidently very 

pure. G, Geothi te (Fe203.H20), alteration product from marcasite going over to hematite at 2500-310° c. K, Kaolin mineral ( 11 dickite11 ), 

fairly pure, from Chihuahua, Mexico; the rounded shoulder (dotted) is 

for a similar kaolin (slightly impuxe) from a hot spring near Bishop, 

Calif. A, Allophane (Al203• Si022.3-5H20); note absence of shoulders. 

S, Serpentine contq,ining some iron e.nd alumina. Si02, Al203, Fe203, 

amorphous oxides pl~epared from :precipi tatod hydrates and carefully 

freed from salts. Al203 is ]Jlotted x 1/2. P, Perrnutite (Folin), so.-

called a.rtificial zcoli te, prepared by fusion for water softBning by 

base exchange. SA, A3bestos ser~pentine containing but 0.3 percent 

of iron. ( Seo table 3.) ~ 

34 
75000 

lOr-----~----~----~----~------~----,-----~---

~ 6~--~~~~~----~----~------~----~-----r-----1 

~ 

~ 5~--~~r---~----~~~~~----~----~----~-----; LaJ 

u 

IX 

~4r-----~~~~~=-_.~--~~-~~~ 

oL-----I~0-0----2~0~0-----3~00-----40~0-----5~00--~~6~0~0--~7~0~0~~8~00. 

TEMPERATURE (°C.) 

Figure e.--Thermal dehydration curves of related clay mineTals. 0, 

11 0taylite, 11 a pure-white montmorillonite bcntonit,~:. A, .lmalcite 

(Na20.Al203.4Si02.2Hz0). B, :Savari<:nl 8,cid-:-treated com.mercial bleaching clay. G, Greensr;..nd., 0.10-0.15 millimeter, raw. Gt, Same greensand acid-leached, white. The curve for acid-leached serpentine 

is nearly identical with Gt. S, Gray· silicic docomposGd granite, 

fron D. C. , acid-leached; bloaching action low. F, Yollow-greon 

iron-rich decomposed granite, D. c., acid-tr~:.~ated; high in bleaching power. (Seo table 3.) 

35 
75000 

Table 3.- Thermal dehydration data of t~1.e hydrous oxides of Figures 7 and 8 

(Percent by ~eight) 

·-----...,..--.___,.--.....,-.----------.,-----··-!--·-·- ···--- - ... Temperature j j 

__ (~o-.:!c~ ....... )_---+-_D _____ -~-~~-~-· --r-~i04:A-12_o~ Fea03 P ~~1abaz~~· 

so 1~.7 12.2 1~.3 1 2s.o 11.sl ~7.7 17.4 20.1 ;··· 

100 1o.6 12.0 lo.2 I 20.0 9.6 I ~3.6 11.7 14.1 G2.6 

150 16.6 11.5 10.2 I 16.3 s.s

1

· 21.7 7.5 10.4 16.3 

200 16.5 11.2 16.2 13.8 8.3 19.9 4.5 7.8 11.4 

250 16.4 10.1 16.2 I 12.0 7.8 I 18.3 2.9 6.0 8.3 

300 I 16.3 5.0 16.2 10.4 7.3

1 

16.3 2.1 4.3 6.2 

350 16.3 1.6 16.2 8.9 6.3 I 13.7 1.6 2.0 4.6 

400 16.2 I 1.0 15.2 I 7.5 5.4 ,, 9.5 1.2. 2.2 3.4 

I I 450 15.9 • 8 16.2 l 6.1 5. ~3 l 4. 3 ! • 8 1. 5 2. 5 

500 1.6 .8 14.0 3.8 5.0 I 2.8j .5 .9 1.7 

550 • 9 • 7 2.1 I 2. 7 4. 3 I 2.1 • 2 • 6 1.1 

~gg :f :~ l:;J I ~:~ ~:i 1:~ :~ :~ :! 

7 5o • o • o • 2 • 5 2. Q i • 2 1 • o • o • o 

800 • 0 • 0 • 0 • 0 l. ?I . 1 I . 0 • 0 • 0 

-------1---+------~--· -t ~------·---+--__..__ ____ _ 

Temperature t- 1 

_.....l(...._o-=c_:_..)"--1--Q-+-1 _A ___ +- __ :s_ ~---~-~:.!·-+·-~-- __ F __ -+-_SA---~-----

50 . . . . 8 • 9 I 3 ·;, 5 6 • 8 7 • 6 ! E1 • 5 7 • 2 

100 10.5 8.61 6.8 I 6.3 5.7 i 4.6 I 4.5 

150 7.3 8.3 6.3 6.0 4.2 j 4.3 4.0 

200 6.7 7.7 5.9 5.9 3.8 1 

4

4 •• 2

1

· j 3.8 

250 6. 4 6. 9 5. 4 5. 6 3. 6 ' 3. 6 

300 5.7 5.5 5.0 5.4 3.5 4.01 

350 5.2 3.1 4.6 5.1 3.1 3.9 

400 5.0 I 1.4 4.2 4.8 2.5 3.8 

!~g I i:~ I :~ ~:i I t~ t~ ~~!I ~~ ij :g 1:~ I t~ :i I 

75o • 7 • o • 3 1 • 6 .1 

800 • 4 I . 0 • 1 I • 3 • 0 I 

: I I 

36 

.3 

.1 

.o 

.o 

3.5 

3.4 

3.3 

3.1 

2.5 

.9 

.5 

.z 

.1 

.0 

.o 

19.6 

18.8 

18.5 

18.3 

18.0 

17.8 

17.6 

17.4 

17.3 

17.2 

17.1 

16.0 

6.1 

1.5 

.a 

.3 
75000 

10~----~----~----~----~-----r-----T----~----~ 

7 

«s l.tJ 

~ ~ 

~5 

L\J 

(.) 

0:: 

L\J 

0..4 14 

O IO----l__jL2J0~0----3j00 _____ 4~0~0--~5JO~O--~~~~~~~ O IOO TEMPERATURE (°C.) 

Figure 9.--thermal dehydration curves of active clays. :rp, Commercial 

clay ftom ~uincy, Fla. A, Clay from Attapulgus, Ga. M, Clay near 

Macon, i Ga., submitted by the General Reduction Co. E, English fuller's 

earth tecontly imported for refining lard, XL brand. C, Commercial 

earth rom Creed.e, Colo. 0, Comr.1urcinl earth from pit near Ocala, 

Fla., ubmitted by the Superior Earth Co. (See table 4.) 

3? 
75000 

10~--~~----------~-----------T----~----~----~ 

~6~---4~~~~----~----~-----+-----4----~~--~ 

r-

~ 

~5~----+-~--~~--~~~~-----+-----+----~----~ 

L&J 

(.) 

IX 

~4~----+-----~----~~~~~~~~---+----~----~ 

O'L---~L---~----~-----L----~----~--~~~~ 

0 100 zoo 300 400 500 600 700 800 

TEMPERATURE(°C.) 

Figure 10.--Thermal dehydration curves of active clays. T, Untreated 

raw clay from tehachapi, Calif., from the Filtrol Co., Los Angeles. 

J, Japanese 11 acid clay11 obtained through Prof. Yoshio Tanaka. 

U, Raw clay near Aurora, Utah, as used for refining petroleum, from 

Wes.tern Clay & Metaln Co. The other clay supplied by this company 

for refining vegetable oils has a curve identical throughout except 

for a slight dip centered at 460°. 0, Clay from Olmstead, Ill., 

mined and used by Sinclair Oil Co. DV, Magnesian clay from Nevada 

npar Death Valley. Or, Raw clay from Chambers, .P...riz.; low in filtering power. Ct, S~..me clay acid-treated; highly active. (See table 4.) 

38 
CN. 

tO 

Table 4.- Thennal (Percent by weight) Dehydration Data of the Active Clays of Figures 9 and 10 

I 

T 1

anperature F A M E c 0 T J u 0 DV Cr (0 c.) 

50 15.8 12e6 11.8 12.8 g.B 7-0 11.5 11.6 g.s 6.9 . 8.0 ••• 

100 12.2 11o0 7e4 7 .. 9 6 .. 9 4g7 8.6 7-2 6.2 5-8 6.9 8.8 

150 11.2 10.5 5-8 5-9 5e5 4.0 1·0 5-8 5·0 5·1 6.1 6.5 

200 10.7 7·8 5·6 5·2 . 4 .. 8 3·7 6.1 5•2 4.6 4.7 5.6 5·7 

250 9.1 7.,1 5·6 4.9 44)4 3·4 5·5 4.8 4.3 4.4 5-4 5-4 

300 8~8 6~8 5·3 4.8 4.0 3·1 5-0 4 .. 6 4.1 4.1 5·2 5·2 

350 1·9 5·9 4.9 4.4 3e7 2.8 4.6 4o2 3·9 J.S 4.9 5-0 

4oo 6 .. 4 3·3 4.8 4.0 3-4 2.4 4.3 3·9 3·6 3-4 4.6 4.7 

450 s.o 1.9 4.6 3·6 3e2 1.9 4.0 3-6 3·3 2.9 2.9 4~4 

500 4.3 1.2 4.0 3-4 2.8 1.6 3-4 3·2 J.O 1.9 1.9 4.2 

550 3-7 ·1 3·1 3cl 2.3 1.1 2.4 2.6 2.7 1.1 1.1 3·8 

600 3.4 .4 2.2 2.6 1.6 ·5 2.0 1.7 2.1 ·1 ·1 2.7 

650 < 3-2 ~2 1.7 1.2 ·7 ·3 1e8 ·9 1.1 .4 .4 1.4 

700 2.9 .1 ·1 .4 .2 .1 1.2 ·3 .2 .2 .2 ·1 

750 ·7 .o .2 .1 .1 .1 r .o .1 .o .1 .1 .4 

800 .o .o .o .o .o .o .2 1.0 .o .o .o .2 

; 

Ct 

s.o 

7-2 

6.1 

5•2 

4.7 

4.2 

3·8 

3·5 

3-1 

2e.7 

2.1 

1.4 

•7 

·3 

.1 

.a 
75000 

These thermal dehydration curves arc perhaps most striking in 

their individuality: each is unlike all the rest. A dozen of the commercial clays (figs. 9 and 10) r~ve curves lying within a characteristic 

band between those of the clays from Macon an.d Death Valley above and 

that from Ocala below, but two of tho most important clays; those from 

Attapulgus and Quincy, have curves well outside that band. These. two 

curves resemble each other in. their shoulders at 200° and 300° C. • but 

the third shoulder at 700° on the Quincy clay is entirely absent on the 

.Attapulgus clay (fig. 9). These two clays are mined less than 30 miles 

apart. The gr~v and green decomposed D. c. granites (S and F, fig. 8) 

are similar in forn, but the gray holds more water in. the range 1000 -

500° c. 

The curves for the artificia.l hydrous oxides Fe3o2 a~d Al20

3 (fig. 7) 

bear no apparent relation to the .correspon~ding hyclrated ml.nerals goethite and diaspore, nor does the curve for the hydrated aluminosilicato 

(K, fig. 7) bear any resemblanc·e to those for hydrous alumina or silicate. 

Some of the shoulders on various clay curves might be identified with 

those on the primary oxides, b11t not with any certainty. The acid leaching of a clay displaces its curve to".V"ard that for silica gel. This 

effect is most marked in clays (DV) and other miuerals (greensand and 

serpentine) high in the easily removable magnesia. 

Water driven off by heating to 50° c. is probably so loosely held 

that its removal opens no active bonds useful in bleaching.. On the 

other hand, heating to 200° C. is sufficientto develop maximum bleaching power. In general this results in removing nearly all except the 

water of constitution, but· without destruction of crystal structure. 

A higher temperature of dehydration may open additional valence bonds, 

but it m~st close others, as it does not further enhance bleaching power. 

Hence the quantity of water d.rive;1 off in the temperature range from 

50° to 200° c. should roughly correspond to bleaching power. The correlation is fairly good, a.s sho~~ by the bleaching tests given below. 

~though water of crystallization and water of constitution (H20, 

H, and OH) are driven off at the higher temperatures (300°-1,000° C.), 

by no ·-means all the water driven off in that range is molecular water. 

Amorphous gel still contains considerable w~ter, even at 800°, and 

several- clays do also. A sharp shoulder in the dehydration curve is 

apparently the sole criterion for molecular water. A distinction cannot always be drawn, on the basis of dehydration curves, between adsorbe¢water, water of constitution, and water of crystallization. 

And o~:course absorbed water shades off imperceptibly into adsorbed 

water in these curves, as the corresponding energies overlap. 

40 
The theory of the energy involved in dehydration is simple. 

In calories per gram molecule (q) it is 

.9. _ d log C 

R - d(l/T) 

75000 

where R = 1.985, C is concentration of water in mineral {or any quantity 

. proportional to it), and T is absolute temperature. Djviding q by 18, 

the molecular weight of water, gives the energy in calories per gram of 

water driven off. The'curves give for kaolinite 3,442, for diaspore 

3.857, and for goethite 601 calories per gram at tlic steepest part of 

the shoulder when combined water is being drive~ from the interiors of 

crystalline hydrates. Molecular proportio::.1s (cc..lc~ulrtted) correS})Ond 

w~ll with the observed :percentB.t~es at these shoulcters. 

With t~;.e clays and other com11lex silicates there are no sharp 

ohoulders (like tilose on the simpler hydrates) on the therma.l d.ehldration curves. The general method of finding the energy of association 

as a function of water concentration in the samRle is illustrated by 

figure 11 and table 5. As a typical example I have a.gain chosen the 

artificial silicate permutite, data for which are given in figure 7 and 

column P in table 3. 

Table 5.- Energies of dehydration of ~ermutite 

I Concen- I 

Tc I tration 1/Ta log C qjR cal/gm 

·i of H?O 

50 0.201 0.003096 -1.6045 751.9 82.9 

100 .141 .002681 -1.9590 877.2 96.7 

150 .104 .002364 -2.2634 1,101.9 121.5 

200 • 078 .002114 -2.5511 1,315.8 . 145.1 

300 .043 .00174·5 -3.1466 2,076.1 229.0 

400 .022 .001486 -3.8167 3,409.0 375.9 

500 .009 .001293 -4.7105 5,555.5 612.7 

600 .003 .001145 -5.8092 12,307.7 1,357.3 

41 
75000 

-2. 

- thickne115 

500 400 100 50 

.0010 Yra. .0015 .0020 .0025 .0030 

Figure 11.--Energy of dehydratton of permuti te. 

In figure 11 are plotted log C, the :n:J.tural log of the water concentration, B{'A-inst reciprocal nbsolute tem_-pern.tures 1/Ta ( Ta = Tc + 273) • 

From this curve the slo-pe d log C/d(1/Ta) is found at en.ch point. This 

is qjR, which is converted to calories ncr :::;rm:1 by the factor 0.11028 

(= 1.985 -:- 18). The energy-concentrn:t,i-;n curve is also plotted in figure 

11 (left). It :ts a. smooth eurve, hiGh for low :porcenta{~cs of moisture 

in the mineral and low and stoD .. clily f-'1-lJ.in£; ±~ol .. hish percentages • 

.All the data on hydration and dehydration lend addi ti.onal su.pport 

to the hypothesis that each 'bleaching mcdiurn offers a wide range of contim.lously varying adsorbing properties. In the clays cornposi tion may 

vary widely from point to point 0V(5r the surface. In the simpler synthetic amorphouc oxidos probably only the structure varies and the range 

of adsorbing powers is narrower. In pernruti te &ery basic ion, internal 

as well as on the surface, is considered exchangeable, but this material 

is not exceptional among bleaching agents nor in its relation to water. 
75000 

The bleaching action 

The rating of active minerals according to their bleaching 

efficiency is obviously a quite arbitrar~r matter, because the relative 

bleaching power of any series of cla.ys will be different for every test 

liquid used. To avoid this arbitrariness, dyes dissolved in benzine 

have been used, but this standard test is too artificial. Even with 

a specific clay and test oil there is the question of which cut to 

choose as standard--whet~J.er water-white (complete filtration), complete ex.~stion of filterin~ power, or intermediate filtration to 

green, yellow,_orange, or some particular shade of red. 

The tests here reported refer to complete filtration (to waterwhite), and the numerals under "Bleach re.,ting11 in table 6 are the ratios 

of volumes of oil so filtered to the vol,_,_:r:>es of clay so filtering it. 

Thus if 1 inch of clay filters 1.5 inches of oil water-v;hite before 

going to green or yellow its rating is 1. 5. The test oil was a highgravity black natural petrole11:.11 1 free from sulphur. Obviously this 

rating has little practical significru1ce and was chosen partly for tl1at 

reason. 

43 
75000 

Table 6.- Bleaching and solubility tests 

Acid- Soluble~)~ seale 

!!/ Bleach.:r:a.ting soluble Clf lC. 

Type Raw Tx:eated (percent) Fe Al ·Ql_ Mg 

A.ttapulgu.s, Ga. . . . . . M o.a 0.5 la.·6 4 4 

~ 1 

Macon, Ga ••• . . . . • . . v .5 .9 ao.a 6 2 Tr. 

Quincy, Fla. . . . . . . . M .7 .6 25.6 4 3 ·a Tr. 

Ocala, Fla. • . . • • . . . M,V .6 .9 26.1 3 4 $ Tr. 

Creede, Colo. • . • • . . . Iv1, V .a 1.2 11.1 6 3 •t 0 

San .Antonio, Tex. • . . . . M .a 1.1 11.1 6 3 l Tr. 

Olmstead, Ill. . . . . • . M .6 .3 23.3 7 3 Cl> Tr. 

Aurora, Utah • . . • • • • M 1.4 1.2 10.9 4 3 ~ 1 

Aurora, Utah • . . • • • . v 1.1 1.2 9.8 4 4 2 Tr. 

Death Valley, Nev •• . . . . M 1.a 1.2 24.9 Tr. 1 l a 

Tehachapi, Calif. . . . • • v 1.1 1.1 13.1 4 4 ~. 2 

Chambers, .Ariz. . . . • • • M .6 2.0 I 22.6 5 4 l Tr. I 

English, XL • • • . • • . • v 1.2 2.0 19.9 5 4 J+ Tr. 

·Japanese acid • . . • . . . M,V 1.0 1.1 14.2 3 6 ] 0 

D.C. granite, green • . . . M .o 1.5 32.6 8 2 ~. 0 

D.C. granite, gray. • . . . M .4 1.0 13.7 5 5 t· Tr. 

N.C. dunite, treated. .. . . M 1.2 1.2 4b.O 5 0 0 5 

Va. decomposed diabase. . • M .2 1.0 16.1 7 1 2 Tr. Be~tonite (otaylite), Calif. M .3 1.8 31.3 2 a ~ 0 

Oklahoma, white • . . . . • M 1.1 .a 9.1 0 6 4f Tr. 

Riverside, Tex. . . . . . • M .6 1.1 11.2 4 2 ~ 2 

l i 

~ M, Mineral; V, vegetable. 

The e.'3.stern clays would of course rate mu.ch higher on the practiqal 

basis of red oil. None of them are much improvsd by acid leaching, aQd the 

clay from Attapulgus is actually harmed. .A number of our cleys rate ais high 

as the best English, Japanese, and German clays. Bavarian acid-leach~d cley· 

tests 1.3 on this scale. 

Silica gel and amorphous t...l2o3 and Fe2o3 rate about 1.0 on this ~cale 

but are useless for filtering lubricants, because they cease fi1terin@ 

abruptly at the end of the water-white. For vegetable oils they are better, 

but their chief field of usefulness is in solvent recovery. .A number !of the 

western active clays ~d decomposed rocks are rednced almost to pure ~ctive 

silica by acid. leaching~ 

44 
75000 

The acid-soluble fraction of .these clays ranges from 10 to 40 

percent and bears no apparent relation to bleaching power. Rough 

analyses of the dissolved material (last four columns) shows that 

this is largely iron and alumina. Soluble calcium is always low, 

magnesium also except in two examples-both excellent bleaching 

materials. 

Many of the most powerful bleaching clays will crack water-white 

gasoline, melted paraffin, and even highly refined. and stabilized 

laxative mineral oil, immediately adsorbing the ·brown portion cracked 

aut and leaving the liquid colorless. 

Numerous specimens of a.ctivc clays have been studied with a view 

to obtaining a basis for classification ancl developing possible relations between bleaching power and other ~roperties and possible origin. 

Test data on the more interesting of these clays are given in table 7. 

The rating of activity is on the srume scale as in table 6 •. Activity 

of the ignited raw clay is given for some of the specimens. Relative 

weights at room tem~erature and. after heating to 160° and 800° C. show 

the percente~e of moisture in these two ranges and indicate clay types. 

Kaolinitic clays lose their mositure in the higher ~&~ge, bentonitic 

chiefly in the lower range (25°-160°). The complete dehydration curves 

show many significant details but require so much time to make that only 

a selected few have been run. 

45 
75000 

Table 7.- Miscellaneous clay tests 

-- ·-[_-!ie_-~-~~h~=r~~!~--~--~-----:~~-d --- ~- s~1i;1~~~~;1~we~- htc!~~) (p e~= Clay ~- Treat- Ig- solubl e --- -- ---- ~ --

_________ __J__Raw ed n:i.te c1. (:pe rcent!. Fe All Ca Mg 25°-160° 160°-Bcx:P 

,,. 

l. Otay, Calif. 

2. Oklahoma 

0 .. 5 

l.l 

. 6 

.5 

.7 

1.8 31.3 

9.1 

11.3 

2 8 Tr..O 11.3 · 5.2 

.a 0 6 \1 4 Tr. 8.1 5.2 

3. Texas 1.1 

. 8 

. 8 

4 2 2 2 5.2 6.0 

4. Ga. ba:u..xi te 

I 

5. Micl.way, Fla. 

0 

2

9 I l Tr. .2 23.4 

33.0 2 6 Tr. 6.6 13.3 

6. Tenn. bentonite 1 

7. Ala. bentonite I 

8. Miss ., Smith Co. I 

9. Miss., TimJah Co. 

10 . Miss., ba~ite I 

11. Okla. bentonite I 

12. Woodward, Okla . I 

13. Silver Cliff,ColoJ 

14. San~a Rit a , N.Mcx.l 

15. Sal2ne Co., Ark. 

16. 

17. 

18. 

19. 

20. 

21. 

22. 

23. 

24 .. 

25. 

Gordon, Ga. 

N.C. nontronite 

Ga. halloysite 

Permutite 

Cordele, Ga. 

Durant, Ga. 

I 

I 

I 

I 

.4 

.4 

. 8 

.8 

. 0 

.5 

.6 

.8 

.8 

.8 

l.O 

. 0 

l.O 

l.l 

1.3 

. 6 

.3 

. 9 

1.4 

.; 8 

1.3 

1.3 

1.2 

1. 0 

.4 

1.7 

1.7 

2 . 0 

1.5 

1.6 

1.2 

1.6 

1.4 

1.7 

1.3 

.3 

.4 

1. 8 

1.5 

1.3 

0 .9 

1. 0 

1.8 

.8 

1.2 

. 3 

.7 

.8 

4.7 

8 .5 

7.9 

27.5 

26 . 0 

37.9 

41. 0 

30.7 

21.7 

2S.5 

3 . 6 

55 . 0 

53 . 0 

15.1 

11.5 

6. 5 

30.6 

38.3 

18.9 

4 

5 

5 

4 ~ I 

5 5 1 

I 

3 0 

1 0 

2 Tr. 

0 Tr. 

Tr. 0 

5 ! 4 

5 4 

l 7 

3 5 

l 8 l

I 

l 

2 0 

~ I 

o 5 I 5 o 

8 2 I 0 0 

o 10 I Tr. o 

o 

1

, 10, o o 

4 5 I l Tr. 

I I 

I 0 ~ 0 ' 1 i 

0 ::.o i 

5 5 1 

10 o I 

5 4 I 

0 0 

0 0 

l Tr • 

T:r. Tr. 

l 0 

Fort Valley, Ga. 

Musselwhite, Ga. 

Md . glauconite 

Clarendon, Tex. 

26. Fort Gaines, Ga. 

27. St. Paul , Minn . i t:~ t:! 1

:! 2~:~ ~ ; I i ~ I, 1:6 i:~ :! ~;:! ; ; I ~ ~r. 28. Laurel, Miss . 

29. Ga. bentonite 

3(:;. Wrens , Ga. l. 2 l. 2 l. 2 20 . 4 5 3 I 2 Tr • 

I I 31. 

32. 

33. 

34. 

35. 

Ogl ethorpe , Ga. I 1.0 1.4 1.2 6 .9 7 Tr.l 3 0 

Tennille, Ga. I 1.2 1.3 1.2 ;7

1 

•. 1

5 

7 .~:r.,. 

2

3 0

1 

.. 

Westcliffe 1 Colo .,l. 3 l. 9 • 7 ._, 0 

u. J. glauconite 1.2 1. 3 .3 40.4 9 1 I o o 

Co~~:c_l_· a_l_b_e_n_t_or_1i __ • 7---'---l-.3 ~-· 7_ .L ___ l_9_. 7 __ _,___3_L I 2 ~f.lr. 

46 

3.7 

13.1 

3.5 

5.4 

12.0 

13.1 

14.4 

12.2 

14.6 

0 • J 

18.5 

9.4 

2.0 

.4 

.3 

5.4 

3.5 

5.6 

4.3 

1. 6 

16.8 

2.7 

15.0 

1.3 

9.1 

16.1 

1.9 

6.3 

6.4 

8.5 

5. 0 

5.3 

12.0 

11.2 

5.6 

6.5 

6.9 

15.4 

9.0 

14.2 

8.8 

13.8 

13.1 

8.6 

5.9 

6.0 

6.0 

6.2 

6.2 

7.2 

5.4 

3.6 

5.3 

4.8 

5.1 

5.9 
75000 

1. Bentonite from Otay, near San Diego, Calif. Supplied by 

the Standard Oil Co. of California. Treated and used by that company. 

2. A white Okla.."loma clay sent in by Max B. Miller. 

~3. Riverside, Tex., from Continental Oil Co. 

4. A Georgia Ba'tL~i t e hn.ving some· blea.ching power. 

5. Midway, Fla. Clay mined by the J?ullers Earth Co. of Cleveland. 

One of the first l:no~TI deposits of active clay. 

6. A greenish-gray Ordovician bentonite near Evansville, Tenn. 

7. .A similE'.r red bentonite near Birminghar.a, .Ala. 

8. White active clo.y from Smith County, Miss. 

9. .A greenish-grny clay from Tippah County, Miss. 

10. Bauxitic; clc:.y from same locali tJ as 9. 

11. Vfhi te OklEthoma bentonite. 

12. Pink bentonite from Woodward, Okla. Note similarity to No. 11 

.shown by the test. 

13. Pink bentonite (volcanic ash) from Silver Cliff, Colo. Similar 

in appearance to No. 33. 

14. Volcanic ash from Santa Rita, N. Mex., very possibly from the 

same horizon as Nos. 13 and 33. 

15. Bentonite from Saline County, .Ark., submitted by John C. Branner. 

16. vVhito kaolinitic clay near Gordon, Ga. 

17. Olive-green nontronit.e from Sandy Ridge, N. C. 

18. Halloysi te nce.r Rome, Ga. 

19. Synthetic zeolite (perrnutite), Folin preparation. 

20- 23. Hard gray clays near Cordele, Durant, Fort Valley, and 

Mussolwhi te, Ga. 

24. Dark-green glauconite from Lyons vv:harf, Md. 

25. .An active clay near Clarendon, Tex. 

26. A light-yellowish clay near Fort Gaines, Ga. 

27. .A dark-green silt from an excavation in St. Paul, Minn. 

28. Bentonite from the vicinity of Laurel, Miss. Byram marl. 

29. .An Ordovician bentonite from Chickamauga, Ga. 

30- 32. Active clays ncar Wrens, Oglethorpe, and Tennille, Ga. 

33. A pink volc~nic ash from Westcliffe! Colo. 

34. Glauconite (greensand) near Sewell, N. J. 

35. Gray co~~ercial (Wyoming?) bentonite having pronounced swelling 

and gel-forming properties. 

Only a few of these clays are highly activo without acid treatment, 

rated by the water-white bleach of cold crude netroleum. Conspicuous in 

this class are the glauconiten (24,34). ~he clays from Cordele, Fort 

Gaines, St. Paul, Wrens, and Tennille (20, 26, 27, 30, 32) also show this 

character and may all be J.erived in part from glauconite or its counterpart, the waxy green clay not uncomr1on in decomposed igneous rocks. 

47 
?5000 

All true glauconites have been shown by Ros~ to lie between the two 

end members 

2H2o.K20.2(Mg,Fe)0.2(Fe,Al) 2o

3

.10Si02 

2H2

0.K9 0.(Mg,Fe)0.3(Fe,Al) 0 .lOSiO~ 10..1 2 3 ~ .. 

The thermal hydration curve of the clay from Fort Gaines is almost identical 

with that of marine glauconite. 

Another interesting and perhaps commercially important class or subclass is the group of clays whose activity is but slightly affected by 

eiti1er acid leaching or ignition. The list is the same as before, with 

the omission of St. Paul. .A glauconitic origin subsequently mod.ified by 

lime or kaolin (from c~ecomposed felds];-~ar) is ind.icated. Kaolinite is 

inactive until ignited. Cl~s of this type would best withstand burping 

for reuse. 

The bentonitic (volcanic ash) tYl;e of clays res,ond best to acid 

leaching. Pro?erly prepared, they are not excelled in activity by any 

clay or synthetic bleach. Otaylite and the clay from Chambers, Ariz., 

the only clays acid.-treated a...'1d ;r•L.rketed on a large scale in this country, 

are far western. The eastern market is largely supplied by imported 

acid-leached GelTJ1al1 clay. This also, accorc.ing to .KArr, !.E) is largely an · 

im:;;ure bentonite from decomposed volcanic ash. Bentonites were therefore 

given particular attention in this stuey. Clays 6, 7, 11, 12, 13, 14, 

15, 23, 29, 33, and. 35 are kno·.·m to be bentordtes; 3, 8, 23, and 25 behave 

like bentonites diluted with other clays. Halloysite (18) activates 

like a bentonite but has a dell~yd.ration curve entirely dJfferent in 

character, with a large loss (12 percent) in moisture at 470° c., whereas the bentonite curves h2.ve a sn~ll ·but pronounced shoulder at 570° C. 

~ Ross, C. S., The optical properties and chemical composition of 

glauconite: U. s. Nat. Mus. Proc., vol. 69, art. 2, 1926. 

1§:} Kerr, P. F., Montmorillonite or smectite as constituents of 

fuller's earth and bentonite: .Am. Mineralogist, vol. 17, p. 192, 1932. 

48 
75000 

Bentonitic clays of high grade are widely distributed, and each 

deposit usually extends over a large ~rea but is not very thiCk• 

Thickness, overburden, and location with reference to markets will be 

dominant factors in future production. Clays ofthis class respond 

nm.ch more readily to attack by acid than the glauconites. 

The active clays of northern Florida and southwestern Georgia are 

in a distinct class by themselves, charactP-rized b.y fair bleaching power 

without other treatment than drying and grind.ing and being unaffected 

by acid bleaching. Electrodialysis to remove soluble salts nearly 

doubled (0.7 to 1.3) the bleaching power of the clay mined at Qpincy 

and Attapulgus, Ga., and Ocala, Fla. Leaching in ·a large quantity of 

hot distilled water was found to give a similar enhancement of bleach-

. ing power. A third method was to mix sawdust with clay, wet to a mud, 

and allow bacterial action t6 take its course. Clay thus treated also 

rates 1.3. Other clays are either unaffected or harmed by this excessive water leaching. 

Washing an active cley in hard wat.er of course destroys its bleaching power, for it provides the cation-hungry open bonds with cations, 

thereby destroying their affinity for the black particles in oil. 

An acid-leached clay must be washed in water kept below pH 7.0. So 

long as the wash water is kept acid, cations cam1ot be adsorbed by the 

clay surfaces but must remain in solution. If the wash water is allowed 

to become alkaline, anion acceptors are provided, an~ cations are 

adsorbed by the clny. If only hard water is available for washing 

acid-leached clays, it should be kept well on the acid side of neutrality. 

Many important problems connected with the bleaching action of 

clays remain to be investigated. Why do some clays crack even saturated 

pure paraffines, whereas othemdo notr Why do some clays cease bleaching abruptly, and others give a long serie~ of intermediate green, yellow, 

orange, and red oils? What is the optimum a,cid leach? Why is the bleaching power of some clays unaffected by ignition, which destroys that of 

many others? One clay is inactive on hot crude oil when raw but highly 

active when acid-leached; on cotton oil, however, its behavior is just 

the reverse, ru1d on cold crude oil it is high~ active either raw of 

.acid-treated. Some clays leave the bleached oil stable toward light and 

air; others leave it unstable. M1at is the value of active clay as a 

catalyst, for the recovery of solvent vapors, or for water softening? 

49 
75000 

Maximum bleaChing powers and efficiencies 

Some questions of considerable :practical interest are frequently 

asked, such as (1) What naturally_ active clays are the best, and are 

much better ones likely to be discovered? (2) _4ffiong the treated clays. 

which respond best to treatment, what is their maximum activity, and 

what treatment gives best B.ctivat~on at :least expense? (3) :By what 

process ma,y other types of clays be converted into blec-"ching clays, and · 

which of such processes are commercially feasible? (4). Tihat are the 

possibilities of producing synthetic bleaching media? Although these 

questions may be tentatively answered with some assurance as a result 

Of the laboratory studies here recorded, COffil)lete ~1swers must await the 

results of much further study. The results thus far indicate that the 

market structure is not likely to be upset or even seriously disturbed 

by new developPlents in any line. 

Natural bleaching clays.- Tests of scores of samples from all 

parts of this country arJ.d from several foreign countries indicate tbat 

the ma.."'{i:qrum bleaching ))ower to be expected of a11y natural bleaching ela.y 

is about 1.6 to 1.8 on the scale used in tuble 7. This rating is approa;ched by a number of selected western clays. This· statement applies to clays 

treated only by milling anct dehydrating to 180° c. (= 350° F.) just before 

using. The bleaching power of clay thus dried is two to three t Lrnes that 

of the same clay merely roo::n-dried at say 30 percent relative l1.umidity. 

The lower-grade eastern clays retain their large market through lower 

transportation and production costs. Selected natural minerals, pulverized and subjected to treatment sirmJ.lating weathering, may be m&de to 

approach but not to exceed this e"pparently fixed limit to ~leaching power. 

Tests of samples through vertical and lateral sections of cl~ deposits indicate wide vari<::'..tion in filtering }:>ower, in some deposits within a few feet. Check tests in the field are readily made with simple 

apparatus and must be made in most deposits to e.void including poor 

material, with consequent loss in quality of the product. 

1~ otherwise excellent bleaching clays contain grit and other 

inactive material (such as quartz .:md feldspar grains and kaolin). 

At the present time in this cou..."ltry such <.tlays cannot be .considered commercial sources, on account of the expense of screening. There appears 

to be an almost unlimited quantity of excellent olay nvailable which 

requires no screening and can be mined, dried, Etnd milled at li.:3SS than 

the cost of screening. 

50 

·, 
75000 

Treated clays .. - ClP.ys tree.ted with acid to remove their excess 

bases and thus (after dehydration) provide their surfaces with open 

bonds appear also to approach a :fixecl rJinimum of filtering power, which 

is about. 2. 0 on the scale of t2:t:l8 ? o I he.ve studied the activation of 

many different clays with various acids but have never been able to 

exce-ed this lirni t. The rna.."'tirrrurn is a little higher for a natural complex 

oxide (mixed with silicate) than for any of the similar component oxides, 

fully activated. Starting witb. a complex alteration product composed of 

ferromagnesian silicate, screened and thoroughly water-leached free from 

water-soluble bases, it seems to make little difference whether the iron 

oxide, the silica, or the magnesia is partly removed to leave open bonds. 

Activation depends very little on whet acid is used or what oxides are 

left, so long as the clay is att~cked. 

A wide variation of decomposed rocks, base-containing clays, bentonites, and some partly altered volcanic ashes are available for conversion to high-grade bleaching clays by acid treatment. Some yield too 

readily, going over to nearly pure silica, which is not a good oil'bleach. 

Diatomite with simple washing or no treatment at all is in this class. 

At the other extreme are rock powders, very resistant to acid, and ordinary 

(brick)clays which have gone too far and wollld require roasting before 

yielding to acid treatment. There is no lack Jf material available. 

Probably the best sources of raw material are decomposed rocks ra~ging 

from ferromagnesian diabases to dunites. In this field preliminary work 

and check tests are indisT)ensable to rational uroduction. The cost of 

screening is not prohibit~ve when acid treatme~t is to follow and a highgrade product made. 

Synthetic bleaching media.- A great many hydrous oxides may be 

readily prepared by chemical methods. Dehydration by simple heating 

leaves these in active form, but their bleaching power is no higher·than 

that of many natural clays. Nor is there apparently any advantage in 

precipitating any two or three oxides together. The chief field of such 

synthetic preparations appears to be the recovery of valuable solvent 

vapors, for which they ~re well suited, as they are efficient and can be 

reused indefinitely. 

The chief advancements to be looked for in the bleaching-eart~ 

industry lie not in the discovery of new beds or more powerful earths, 

nor in the development of new methods of treating clays, nor yet in the 

creation of synthetic products, but rather in the preparation at low 

cost for s~ecial purposes of special clays having u minimum cracking 

power and minimum retention, with a maximum of decolorizing or deodorizing power, together with the property of leaving a stable filtrate. 

51