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UNITED STATES DEPARTMENT OF THE INTERIOR

THE ACTION OF SOME AQUEOUS

SOLUTIONS ON CLAYS OF THE

MONTMORILLONITE GROUP

GEOLOGICAL SURVEY PROFESSIONAL PAPER 197-F

UNITED STATES DEPARTMENT OF THE INTERIOR 

Harold L. Ickes, Secretary

GEOLOGICAL SURVEY 

W. C. Mendenhall, Director

Professional Paper 197—F

THE ACTION OF SOME AQUEOUS

SOLUTIONS ON CLAYS OF THE

MONTMORILLONITE GROUP

BY

P. G. NUTTING

Shorter contributions to general geology, 1941-42

(Pages 219-235)

UNITED STATES 

GOVERNMENT PRINTING OFFICE

WASHINGTON t 1943

-4-

For sale by the Superintendent of Documents, 'Washington, D. C. ...... . Price 10 cents
CONTENTS

	Page 

Abstract__________________________________ 219

Introduction _______________________________________ 219

Solubility of silica_________________________________ 220

Solubility of montmorillonite clays in acid solutions,____ 222

Discussion of data______________________________ 223

Interpretation of data.___-______________________ 229

Solubility of montmorillonite clays in alkaline solutions. 

Electrodialysis of hydrosols.________________________

Summary and conclusions——______________________

Index.__-___-__-__--__-_-_-___------_-_----_-----

230

230

232

235

ILLUSTRATIONS

FIGURE 23. Solubility of opaline silica in water at different 

temperatures. __________.>______________

24.' Solubility of silica in hydrochloric acid solutions. _. _ ___ ______________________

25. Wyoming bentonite in hydrochloric acid 

solutions. _____________________________

26. Wyoming bentonite in oxalic acid solutions.-

27. Japanese acid clay in hydrochloric acid solutions. _ ___ ---__ _ _________-----___._

Page 

221 

221

225

225

226

Page

FIGURE 28. Polkville bentonite in hydrochloric acid solutions. ___________________-__---------- 226

29. Quincy clay (Florida fuller's earth) in hydrochloric acid solutions.______________---- 228

30. Soil in hydrochloric acid solutions.-________ 228

31. Filtrol (activated bentonite) in hydrochloric

acid solutions________-_______-_-----_- 229

32. Wyoming bentonite in sodium carbonate

solutions._____________________________ 231

II
THE ACTION OF SOME AQUEOUS SOLUTIONS ON CLAYS OF THE

MONTMORILLONITE GROUP

By P. G. NUTTING

ABSTRACT

This experimental investigation of the solubility of several 

types of montmorillonite clay covers the range of acid and alkali 

concentration from 0 to 4 percent, using two liters of solvent and 

excess clay. Each solubility-concentration curve changes slope 

in its central portion (0.2 to 0.6 percent), the variation being 

characteristic of the type of montmorillonite. Silica dissolved 

exceeds the saturation limit (about 0.4 gram per liter) over a 

range of concentration probably due to partial recombination as 

silicate micellae. Dissolved sesquiosides are partly water insoluble silicates and partly soluble salts. The results are discussed and their interpretation suggested.

INTRODUCTION

Silicates of the montmorillonite-beidellite group are 

much more easily attacked by dilute acids than those 

of the kaolin, mica, talc, or pyrophyllite groups. They 

have been chosen for study for this reason and because 

they are the more active constituents of many soils and 

are readily available in nearly pure form in the bentonites. The study of their chemical behavior promises 

to throw light on the different processes of weathering 

and the formation of plant food in soils as well as on 

mineral replacement and alteration.

The bases of the montmorillonite clays are removable 

by digestion in hot 20 percent (6 normal) hydrochloric 

acid for a few hours, leaving behind isotropic silica. 

In pure water these clays dissolve to the extent of at 

least 36 parts per million even after repeated digestion 

of the same sample, the portion in solution being richer 

in silica than the original clay.1 In dilute acids 2 of the 

proper concentration (0.1 to 0.4 percent), bases and 

silica go into solution in the same proportion as in the 

original clay. In dilute alkalies 3 maximum silica is 

removed at about one-tenth (0.02 percent) that concentration of alkali. Clays such as the well-known 

swelling bentonite of Wyoming, which are sodiumsaturated to nearly base-exchange capacity, dissolve 

rather freely in water.

In the present investigation the solubilities of a 

variety of montmorillonites were determined in dilute 

acid solutions of a wide range of concentration in order

1 Nutting, P. G., Solution and dispersion of minerals in water: Washington AcadSci. Jour., vol.. 22, p. 261-267, 1932.

2 Nutting, P. G., a study of bleach clay solubility: Franklin Inst. Jour., vol. 224, 

pp. 339-362, 1937. 

»Idem, pp. 359.

to determine possible equilibrium relations between the 

four components—silica, bases, water, and acid—with 

clay in excess. Silica and bases were determined in the 

solids recovered from the filtrate by evaporation. T\e 

state of bases and silica in solution was further investigated by electrodialysis. The next step in this research 

is the synthesis of clays by combining bases and silica 

(both in solution) with water a.nd free acid in varying 

proportions.

The experimental procedure was to put 30 grams of 

ground clay in a 2-liter flask, fill with distilled water, 

add acid or alkali to the desired concentration, tten 

digest for 48 hours at 90° C. on an electric stove. TTie 

usual series of concentrations was 0.02, 0.04, 0.1, 0.2 

to 4 percent with interpolations in the critical regie ns 

between 0.2 and 1 percent and others between 0.0 and 

0.02. Repeated runs showed satisfactory duplication. 

Higher precision would require thermostatic control of 

digestion aad filtration temperatures.

Each filtrate was evaporated down to 150 mifliliters, 

placed in a weighed pyrex beaker, then brought to dryness 

at 160° C. and weighed. The water-soluble salts were 

next removed with hot distilled water, the residue 

brought to 160° and again weighed. A final digestion in 

hot strong acid separated silica and bases. Watersoluble and water-insoluble bases were separately determined. Special tests indicated that little or no 

R2O3 was insolubilized by drying, probably because free 

acid is always present.

A set of preliminary tests on 22 related clays, each in 

2 liters of Q.2 preceut hydrochloric acid, gave without 

exception a light-brown water-insoluble residuum. A 

typical residue analyzed by R. E. Stevens, of the 

Geological Survey, had the composition of montmo^illonite. A thermal analysis gave a weight-temperature 

curve similar to that of montmorillonite but lacking the 

shoulder at 500° C. indicative of lattice water. These 

residues were, of course, isotropic and remained so for 

months. Such substances as bentonites, fuller's earths, 

glauconites, decomposed granites, and garden soil all 

gave 1 to 2 grams of residue. Pyrophyllite, bauxites, and 

tuffs gave only about half a gram. Other experiments 

showed the effect of added chlorides (aluminum, iron, 

magnesium, calcium) to be slight, but added silica solution 

gave an enhanced yield of bases.

219
220 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1941-42

The gist of the problem is then to find relations between (1) the ions in solution, (2) the hydrosols carrying 

ionic atmospheres, and (3) the bases contained in the 

alumino-silicate clay structure. In the present series of 

experiments the clay was always in excess, but with clay 

limited to one or two grams per liter the picture is quite 

different.4 With clay limited and an excess of solvent 

solution, a fraction of the clay is always left undissolved. 

This is a further indication that the equilibrium 

established is a reversible one.

SOLUBILITY OF SILICA

At each temperature, opaline silica has a perfectly 

definite solubility or dispersibility in water. The state 

of the hydrosol in solution or dispersion is not definitely 

known, but the micellae must be very small, because 

even a saturated solution or dispersion is readily filterable and dialyzible. The silica itself is not ionized, but 

the particles appear to carry adsorbed hydrogen and 

hydroxyl charges in equal proportion, as shown by electrodialysis. The hydrosol particles appear to vary 

little in size or character in any one solution up to ten 

times supersaturation.

A silica solution may be made highly supersaturated 

by evaporation in pyrex or metal vessels if all solid 

particles are removed from it by filtration. At 10- to 

20-fold saturation the solution becomes cloudy, and at 

40- to 60-fold saturation the hydrosol turns to a gel. 

Silica hydrosol, like a gelatin solution or a clay suspension, will lose water in a saturated atmosphere until its 

water content is about 44 percent (Si20,2.5H2O). In an 

atmosphere free from water vapor it will dry at room 

temperature until its water content is about 12 percent. 

At 100° C. its weight is about 1.10 times base weight 

at 950° C., at 500° about 1.05 times, and at 800° about 

1.02 times, the slope of the weight-temperature curve 

being fairly uniform from 120° to 940° C. Silica gel 

holds more water at 700° C. than even such wellformed silicate structures as those of talc and pyrophyllite. At lower temperatures, therefore, silica gel is an 

indefinite mixture of hydrates or silicic acids.

The solubility of opaline silica in water has been carefully determined by Lenher and Merrill 5 at 25° and 

90° C. and by Hitchen 6 at 13 higher temperatures up 

to 336° C., using a specially designed autoclave. Their 

values agree well with each other and with many less 

precise determinations of my own and form a smooth 

curve from which are taken the values given in table 

1 and plotted in figure 23. The uncertainty in these 

values of solubility is probably less than 2 percent. If 

greater precision is required, attention should p.erhaps

* Idem, p. 359.

6 Lenher, V., and Merrill, H. B., The solubility of silica: Am. Chem. Soe. Jour., 

vol. 39, p. 2630, 1917.

6 Hitehen, C. S., A method for the experimental determination of hydrothermal 

solutions, with notes on its application to the solubility of silica: lust. Min, Met, 

Bull., vol. 364, pp. 1-26, 1935.

first be given to the temperature range 50° to 150° C. 

and to avoiding supersaturation.

TABLE I—Solubility of opaline silica in water

Temperature

Q

25

50

100

150__ _ __

Silica 

(parts per 

million)

106

185

270

445

650

Variation 

per, degree 

centigrade

3. 10

3.20

3.34

3.80

4.5

Temperature

/OCi \

200 _ ____

300

350 _ ____

Silica 

(parts per 

million)

915

-1250

1700

2400

Variation 

p?r degree 

centigrade

5.8

7.5

10. 5

19.0

Of chief interest here are the factors which 

solubility. Dilute acids (0 to 0.5 percent) dissolve 

precisely the same amount of silica as pure water, strong 

acids (6 to 20 percent) dissolve less. The removal of 

hydrogen and hydroxyl ions from the silica, irdeell&e 

causes them to flocculate and precipitate Strong solutions of acids and of many salts, as well as e^ectrodialysis, have this effect on hydrosols, an effect similar 

to plasmolysis in biology. A silica solution supersaturated as much as ten tunes (2 grams per liter) may be 

kept at room -temperature for years in good bottles or 

pyrex glass without any precipitation of silica if no 

particles of solid silica are present. With solid silica 

present, the concentration will drop to saturation in a 

few days; with certain clays present,, it will drcD in a 

few hours.

The solubility of silica gel in acids of different concentrations at 90° C. was determined by Lenher and 

Merrill. 7 Their values for hydrochloric acid arc given 

in table 2 and figure 24.

TABLE 2.—Solubility of silica in hydrochloric acid solutions

Strength of acid 

(percent)

0.0_.____________

1.2... ___________

3.0-__._________

3.8________._____

5.3_______-______

6.3______________

Silica dissolved 

(grams per 

liter)

0 418

408

374

354

302

268

Strength of acid 

(percent)

7.6._._ __________

&3________-__-_-

10.0_____. ______

13.6_____-____-._

15.8—, __--_.___

18.6... __________

Silica dissolved, 

(grams per 

lit^r)

0 230

19O

182

112

08S

05$

Solubility zero is indicated for about 24 percer t acid. 

The plotted curve is slightly S-shaped rathe:" than 

linear. Plotting log solubility against log acid concentration gives a curve of steadily increasing slope, 

hence the effect of the acid increases continuously as 

regards energy of solution. Evidently the silicr, being 

dissolved is less and less hydrated as the acid concentration is increased, the hydrochloric acid anc1 silica 

micellae competing for the water. The effect here 

noted doubtless has a bearing on the commercial activation of bentonites where 20 percent acid is used.

i Lenher, V., and Merrill, H. B., op. eit., p. 2636.
ACTION OP SOME AQUEOUS SOLUTIONS ON CLAYS OF THE MONTMOBILLONITE GROUP 221

fie 

u h

-I g

fc 

U 

Q.

<

O

J

in

5' 

$O

/

100 200 3OO

TEMPERATURE °C. 

FIGURE 23.—Solubility of opaline silica in water at different temperatures (after Hitchen),

4OO

.4

.3

\

X

X

6 9 12 15 18 

PERCENT HYDROCHLORIC ACID 

,—Solubility of silica in hydrochloric acid solutions,

21 24
222 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1941-42

Very different in their effect on the solubility of silica 

are the hydrates and salts of such bases (sodium, 

potassium, magnesium) as combine with silicic acid 

to form silicates. Each base has its own specific 

behavior and its effect varies also with concentration, 

with acidity, with temperature, and with age. Even 

electro dialysis fails to disclose all the details of the 

effect of an added salt. Sodium chloride promotes the 

transport of silica as cations, aluminum chloride as 

anions, yet a solution of sodium silicate gives equal 

transport of silica as anions and cations. A silica gel 

containing a little sodium silicate cannot be freed from 

sodium by washing in water; the sodium must first be 

converted to another salt.

Factors affecting the solution or dispersion of silica 

in water may then be thus roughly classified:

1. Adsorbable ions, nonsilicate forming. Effect nil 

in low concentrations, solubility depressing at high.

2. Cations capable of forming soluble silicates. 

These assist more silica into solution.

3. Cations forming insoluble silicates. These do 

not affect the limiting saturation.

Substances loosely called "mineralizers" by geologists may fall in any of these three classes but perhaps

more commonly in the third. Hitchen 8 defines them 

as substances which inhibit the formation of structureless aggregates and thus promote crystallization.

SOLUBILITY OF MONTMORILLONITE CLAYS PT ACID 

SOLUTIONS

The six clays selected for study represent different 

types commonly met with, ranging from the alkaline 

swelling variety to the Japanese acid clay. The 

Polkville clay is the purest montmorillonite bentonite 

now known. The Quincy clay is a selected fuller's 

earth of high purity, but it differs slightly from ordinary 

montmorillonite in its optical properties and in its 

weight-temperature curve. Soil was included in order 

to compare the behavior of its soluble constituents, 

thought to be chiefly montmorillonite, with those of 

pure bentonites. Filtrol, an acid-activated Arizona 

bentonite, showed the effect of the preliminary removal 

of about half its bases. All filtrates became hydrogel 

when their concentration reached about 1 gram per 

20 milliliters. Total and water-insoluble residues 

were weighed after heating to 160°, R2O3 and silica 

after ignition. The data, given in grams per liter of 

solution, are summarized in tables 3 to 8.

8 Hitchen, C. S., A method for the experimental investigation of hyirothermal 

solutions, with notes on its application to the solubility of silica, author's reply to 

discussion: Inst. Min. Met. Bull. 375, p. 27,1935.

TABLE 3.—Total residue

Wyoming clay: 

Hydrochloric acid _ __ _ ___ __ _ __

Sulphuric acid _ _ ______._-_--_-__-_.

Oxalic acid _ _ ______ _____ _ ______

Polkville clay, hydrochloric acid. __________

Quincv clay, hydrochloric acid ____________

Filtrol , hydrochloric acid __ ___________ __

0.0

0.405

405

405

073

/ 042

I 021 

080

117

717

0.02

0.433

. 521

. 522

. 294

} .344

. 568

. 342

'

0.04

1.031

. 545

1. 120

.478

.520

. 960

. 453

.842

0. 10

1.675

.680

1.448

.684

,.777

1. 483

.829

1. 237

0.2

1.900

.872

1. 987

. 771

1. 264

1. 903

1. 263

1.408

0.4

3. 21

1. 25

4. 63

1.30

2. 15

1.98

2. 25

2. 25

1.0

3.58

2. 35

6.53

2. 54

4.28

3.16

2. 90

7.67

2.0

5.61

6. 95

2. 82

8.83

5. 25

5.36

10. 53

4.0

8.30

11. 20

TABLE 4.— Water-soluble part of residue

Percent acid_____ ______ ________________

Wyoming clay, hydrochloric acid_ _________

Japanese clay, hydrochloric acid_ _________

Polkville clay, hydrochloric acid __ ________

Quincy clay, hydrochloric acid ___ _-__

Soil, hydrochloric acid _ ___ _____ __ ___

Filtrol, hydrochloric acid_ _______ _______

0.0

0. 312

None

f 017

I 015 

023

074

313

0.02

0.347

. 198

} . 240

.287

.212

0.04

0.716

.293

.369

. 574

. 298

.304

0. 10

1.063

. 231

. 552

.886

.498

.411

0.20

1.055

.303

.740

,966

.782

.464

0.4

1.58

. 491

1.176

.934

1.720

.725

1.0

2.02

.651

a 42

2.11

1.83

6. 12

2.0

a 90

.692

8.05

4.27

4. 22

8. 90

4.0

6. 19

10.64
ACTION OF SOME AQUEOUS SOLUTIONS ON CLAYS OF THE MONTMOEILLONITE GEOUP

TABLE 5.—Water-insoluble residue (silicates, etc.)

223

Percent acid ______________ _ _______

Wyoming clay: 

Hydrochloric acid__________ _

Sulphuric acid _ _____ ____ __

Oxalic acid. _ ______________ _

Japanese clay, hydrochloric acid______

Polkville, clay, hydrochloric acid _____

Quincy clay, hydrochloric caid _ __ __

Soil, hydrochloric acid _______________

Filtrol, hydrochloric acid_.___,____ __

0.0

0.093

.093

.093

.073

f .025

\ . 006 

.057

.043

.404

0.02

0.086

.080

. 264

. 096

} .104

.281

. 130

.486

O ft4

0. 315

. 158

.620

. 185

. 152

.386

. 156

.538

0.1

0. 612

. 226

. 621

. 454

.325

.597

.331

.826

0 9

0.845

.251

.933

. 468

.524

. 937

. 481

. 944

0

9

1.289

.573

1. 120

7QQ

.810

1. 035

.545

1.430

0.4

1.64

.869

1. 156

.806

.971

1.050

.532

1.524

0.-6

1.71

. 950

1. 149

.797

1. 025

1.062

.689

1.545

1.0

1.57

. 971

1. 11

1.89

.860

1.049

1. 062

1.55

2.0

1. 70

.917

2. 13

.775

.987

1.141

1.63

4 0

2. 11

1.30

. 566

TABLE 6.—Silica dissolved

Percent acid __ ___________________

Wyoming clay: 

Hydrochloric acid__ _ ____________

Sulphuric acid____ _____ __ _ _

Japanese clay, hydrochloric acid______

Polkville clay, hydrochloric acid_____

Quincy clay, hydrochloric acid _ _____

Soil, hydrochloric acid_____ ___ _____

Filtrol, hydrochloric acid _____ __ __

0.0

0.064

•.064

.064

. 053

/ .024

I .010 

.050

.018

. 353

0.02

0 04Q

.070

. 188

.082

| .084

. 169

.038

.358

0.04

0.198

. 138

.446

. 136

. 140

.300

.066

.328

0. 1

0.378

.204

. 551

.239

.244

.434

140

.430

0.2

0.461

. 232

QOO

. 275

. 361

.557

. 232

.464

0.3

0. 808.

.406

1.100

.332

.558

.573

. 268

.556

0.4

0.885

.747

1. 156

.459

.664

.580

. 290

.594

0.6

0. 744

.958

1. 110

. 522

.695

.579

.421

.574

1.0

0.662

.971

.896

.558

. 668

.559

.563

.549

2.0

0.877

.917

. 634

.618

.354

.504

. 491

4.0

0.957

.206

TABLE 7. —R^Os from water-soluble salts (chlorides, etc.)

Percent acid __ _ __________________

Wyoming clay: 

Hydrochloric acid ______________

Oxalic acid______ --_-________ _

Japanese clay, hydrochloric acid_ ______

Polkville clay, hydrochloric acid____ _

Quincy clay, hydrochloric acid. ____ _

Soil, hydrochloric acid _ _______ ____

Filtrol, hydrochloric acid_ _____________

0.0

None

0.010

0.02

None

0.031

.027

.051

.041

0.04

0. 010

.064

. 012

.042

.071

"NT.~M"ip

0. 1

0.022

.205

.039

. 015

. 158

. 146

"\ff\-np

0.2

0 082

695

034

034

183

269

021

0.3

0 126

658

075

144

179

480

024

0.4

0.150

. 598

. 106

. 161

. 172

.637

.026

0.6

0.219

.652

. 115

. 148

.173

. 995

. 120

1.0

0.333

.781

.117

. 109

.546

1.123

1.598

2. 0

0.730

.300

2. 292

1.300

1. 158

2.650

40

1.891

3.540

TABLE 8. —R^Os from water-insoluble salts (silicates, etc.)

Wyoming clay:

Oxalic acid. _ __ _ ____________

Japanese clay, hydrochloric acid _____

Polkville clay, hydrochloric acid___ _

Quincy clay, hydrochloric acid _ __

Soil, hydrochloric acid. ______ _____

Filtrol, hydrochloric acid ____________

0.0

ATnnp

0.002

None

None

0.02

NOHG

0. 031

.015

NOR©

.068

.025

ATnnp

0.04

NOHG

0. 142

.019

.034

.034

.032

0. 1

0.042

. 071

. 116

.027

.084

. 101

.099

0.2

, 0. 146

094

092

239

149

192

0.3

0.290

. 135

.174

.302

. 125

.350

0.4

0.362

None

.185

209

313

113

442

0.0

0.432

051

370

216

298

145

481

1.0

0.391

.212

.730

.174

.339

.287

.517

2. 0

0 469

.622

.065

.406

.333

. 649

40

0.779

. 266

DISCUSSION OF DATA

In these clays the silica ranges from 70 to 76 percent 

on a water-free basis. For comparison there have 

been computed (1) the silica fraction in the waterinsoluble residue, (2) the ratio of silica to 

in the residue (clay formed?), and (3) the ratio of silica 

to total R2O3 in the original solution (clay dissolved?). 

These are given in tables 9 to 11,
224 SHORTEB CONTRIBUTIONS TO GENERAL GEOLOGY, 1941-42 

TABLE 9.—Silica fraction of the water-insoluble material

Wyoming clay:

0

0.688

.688

.727

.933

.872

.429

.874

0.02

0.563

.764

S4.8

.808

.603

.292

.736

0.04

0.629 710

.735

.921

.777

.423

.610

0.1

0 618

887

526

751

727

450

521

0.2

0.546

1.000

.588

. 679

.594

.482

.492

0.3

0.627

1.000

.416

.689

. 554

.492

.389

0.4

0. 540

1. 000

.569

.684

. 442

.545

.390

0.6

0.435

.966

.655

.678

. 546

.611

.372

1.0

0.422

.807

.295

.777

. 533

.530

.354

2.0

0. 522

.2f

.797 ,

. 3f9

.442

.301

4.0

0. 454

.417

TABLE 10.—Ratio of silica to SiO^-}-water-insoluble

Wyoming clay: 

Hydrochloric acid_ _____________

Japanese clay, hydrochloric acid __ __

Polkville clay, hydrochloric aeid___ __

Soil, hydrochloric acid_ __ ___ _ ___

Filtrol, hydrochloric acid_ _____ _

0

1.000

1.000

.996

1.000

1.000

1.000

1.000

0.02

1.000

.858

.845

1.000

.713

.603

1. 000

0.04

1 000

759

877

1 000

898

660

911

0.1

0. 900

.886

.673

.900

.838

. 596

.813

0.2

0 759

1 000

745

797

700

609

707

0.3

0.736

1.000

.711

.762

.655

.682

.614

0.4

0.710

1.000

.486

.761

.649

.720

.573

0.6

0.633

..956

.763

.660

.744

. 544

,u/

0.629

.809

.433

.793

.622

.662

.515

2.0

0. 652

4S9

915 4*>6

6^2

431

4.0

0.551

.470

TABLE 11.—Ratio of silica to Si02 -\-total R20a

Percent acid __ _________ ___ __

Wyoming clay: 

Hydrochloric acid__ _ __ _________

Oxalic acid _ __________________

Japanese clay, hydrochloric acid_____

Polkville clay, hydrochloric acid _ _

Quincy clay, hydrochloric acid __ ____

Soil, hydrochloric aeid__ ________

Filtrol, hydrochloric acid__ _____ ___

0

1.000

1.000

.964

1.000

1.000

1.000

.972

0.02

1.000

.858

.639

1. 000

.641

.333

.897

0.04

1.000

74.fi

.621

. 921

. 798

.386

. 911

0.1

0 855

666

607

853 642-

376

813

0.2

0.669

.573

.682

.741

. 569

.357

.685

0.3

0.660

.626

.613

.637

.544 OHQ

.598

0.4

0.634

.659

.612

. 642

.545

.279

. 559

0.6

0 533

612

518

656

551

270

489

1.0

0.478

. 474

.397

.702

. 387

OCK

.206

2.0

0.422

407

208

172

CPLQ130

4.0

0.264

o^s

Water and very dilute acids tend to dissolve excess 

silica, but the residues from the stronger acid solutions 

(1 to 4 percent) are deficient in silica. Soil departs 

from this rule, organic matter apparently lowering the 

solubility of silica at the lower acid concentrations. 

Each series of residues bears .no simple relation to the 

acid present (nor is this the case with alkaline solutions) 

and they must be represented graphically to show significant details.

The solubility of silica (shown in fig. 25) is slightly 

lower for 0.02 percent acid (0.0486 gram per liter) than 

for pure water (0.0641), the silica of sodium silicate 

being insolubilized by the acid. This bentonite contains about 2.5 percent Na2O. From 0.02 to about 0.2 

percent acid the solubility increases steadily, jumps to 

a maximum (0.8859 gram per liter) at 0.4 percent, drops 

to a minimum (0.662) at 1 percent, then rises again to 

0.957 at 4 percent. The release of sesquioxides begins 

at about 0.05 percent acid. Water-soluble R2O3 (as 

RClj) increases regularly. The -graph of water-insoluble R?O, is similar to that for sjliea? but with points of

inflexion displaced toward higher concentration.

The silica released by oxalic acid (see f^. 26) is 

considerably greater in quantity than that re1 eased by 

hydrochloric acid; but the graphs show simitar trends. 

The sesquioxides however behave very d:fferently. 

The water-soluble salts (oxalates) show a pronounced 

maximum (at 0.2 percent) and minimum (at 0.4 percent 

acid). The recombined R2O3 , after rising to 0.142 

gram per liter at 0.04 percent, drops to zero at 0.2 to 

0.4 percent, then rises steeply. This loss of power to 

recombine through a range of acid concentrations was 

not found with any other acid or clay.

The silica removed from the Japanese acid clay 

(see fig. 27) increases from the start (in pure water 

0.0529 gram per liter, in 0.02 percent acid 0.0816 gram 

per liter) but at a varying rate. A critical acid concentration between 0.2 and 0.3 percent is indicated for 

even this clay. The curves for both soluble £,nd insoluble R2O3 are irregular. The excess of insoluble (silicate) 

RaOs over silica (0.730 to 0.558 gram) at about 1 percent 

acid is noteworthy.
ACTION OP SOME AQUEOUS SOLUTIONS ON CLAYS OF THE MOHEttOBILLONITE GROUP 

1.00

225

I.OO

.01 .02 .04 O.1 .2 .4- 1.0 

PERCENT HYDROCHLORIC ACID

.—Wyoming bentonite in hydrochloric add solutions.

.or ,az o.r

462559—43

.z , ,4- i.o

OKAUC ACID 

I'jflUEa 26.— Wyoming bentonite in oxalic add solutions.
SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1941-42

.01 .02 .04- O.I .2 .4- 1.O 

PERCENT HYDROCHLORIC ACID

FIGTJBE 27.—Japanese acid clay In hydrochloric acid solutions.

.01 .OZ .04 0.1 .2 ,4- I.O 

PERCENT HYDROCHLORIC ACID

FIGURE 28.—Polkville bentonite In hydrochloric acid solutions.

10
ACTION OF SOME* AQUEOUS SOLUTIONS ON CLAYS OP THE MOHTMORILLONITE GROUP 227

The solubility curves (fig. 28) for the Polkville 

bentonite, a very pure montmorillonite, are simple and 

may be regarded as standard for this type of material. 

No secondary effects due to minor impurities are 

apparent. The silica dissolved in pure water is very 

low, 0.0236 gram per liter for first run and only 0.0102 

for a second run on the same material. With 0.02 

percent acid it is 0.0816 gram per liter, and it rises 

steadily to normal (0.42 gram per liter at 90°) at about 

0.23 percent, then rises steeply to a high broad maximum of about 0.7 gram per liter. Recombined R2O3 

rises to a similar broad maximum at about the same concentration of acid, but is zero at concentrations below 

about 0.04 percent acid, and is small or zero above 

about 3 percent acid. Silica hi the recombined material 

is in the same proportion as in montmorillonite over the 

range 0.25 to 0.7 percent acid, and is higher than normal 

above and below this range. Above 2 percent acid the 

silica hydrosol is unable to withhold much R2O3 against 

solution in acid, although at 0.5 percent its retarding 

effect is a maximum. Of the dissolved material, a 

part (chiefly RCls) is water-soluble after drying at 

160° C. Taking the ratio of this to the maximum possible aluminum chloride computed from the acid present 

gives a curve dropping from 0.983 at 0.02 percent acid 

to a minimum 0.241 at 0.4 percent acid, then rising 

again at higher concentrations, thus checking closely 

with the silica and silicate R2O3 curves. Of 1.5 grams 

of this clay digested hi 2 liters of 0.3 percent hydrochloric acid, 22.5 percent remained undissolved after 

48 hours, the residue closely resembling the original 

clay.

The shift of equilibrium produced by a large reduction 

hi concentration was investigated on this Polkville 

bentonite. About 4 grams was digested hi 100 milliliters of 20 percent hydrochloric acid until all bases were 

in solution, leaving pure white silica. Then solution 

and silica were dumped into two liters of water at 90° 

and left for 5 days to come to a new equilibrium. The 

question was whether the silica would take up bases or 

the bases hi solution take up silica to form montmorillonite in equilibrium with such a solution. On filtering 

and analyzing, no bases were found with the solid silica 

(less than 0.1 percent left by hydrofluoric acid). In 

the evaporated filtrate were found the normal amounts 

of water-soluble and insoluble residue, that is, waterinsoluble R2O3, 0.1789 gram per liter, and SiO2 0.1481 

gram per liter, equivalent to 45.3 percent. An electrodialysis of 600 milliliters of the final solution gave for 

silica as cations 55.7 percent, as anions 44.3 percent, 

while the R2O3 as cations was 75.0 percent, as anions 

25.0 percent. In another test, dissolved bases (slightly 

acid), dissolved silica, and water were combined in 

proportion to synthesize a clay, then a few grams of 

pure dry silica was adde.d. In this case the bases nearly 

all went to the solid silica, some were left in solution 

after sufficient acid had been set free to .keep them in

solution. With neither pure acid norsolid silica present 

some of the trivalent bases hydrolyze and precipitate, 

releasing acid.

The Quincy clay used in the tests was selected natural 

rock from the Hawthorn formation of Miocene age, in 

northwest Florida, the purest and highest grade of 

fuller's earth known. A thin section shows it to be all 

or nearly all crystalline material, of which large aggregates have little orientation. Its thermal dehydration curve differs widely from those of known p^ire 

montmorillonite, such as the Polkville clay, and there is 

some doubt as to the nature of the dominant mineral. 

Chemical analyses and the solubility curves (fig. 29) 

tell little on this point. Of 1.5 grams of this clay 

digested 48 hours in 2,000 milliliters of 0.3 percent 

hydrochloric acid 16.2 percent remained undissolved.

The silica dissolved from this clay varies like that 

dissolved from the pure bentonite (Polkville cKy), 

but the maximum is broader and the solubility is tvice 

as high in 0.02, 0.04, and 0.1 percent acid. On acccunt 

of the high solubility in 0.02 percent acid, extra points 

were determined at 0.004 and 0.01 percent acid to s^w 

the nature of the approach to solubility in pure WE ter. 

Recombincd R2O3 shows three maxima at 0.02, 0.4, and 

1.8 percent acid. Water soluble R2O3 starts at al out 

0.01 percent and shoots up at 1 percent acid.

In testing soil the material used was that part of a 

good garden soil that could be put through a 150-mesh 

sieve by rubbing without grinding. It was essentially 

well decomposed rock with abundant humus and some 

exchangeable lime. The solubility in pure water is 

low (see fig. 30) and rises but little in very dilute acids. 

The solubility of silica rises above that in pure water 

between 0.6 and 3 percent acid, witH a maximum at 1 

percent. Recombined R2O3 has two maxima at 0.2 

and 1.6 percent acid. Water soluble R2O3 (as R^13) 

rises steeply above 0.2 percent acid. Organic matter 

interfered, but the three curves indicate that soil 

fines behave toward dilute acids essentially like 

montmorillonite.

Commercial "filtrol," a bentonite from Chambers, 

Ariz., previously activated by removal of about half 

its bases in 20 percent acid, was used in this test. It 

is of interest in showing the effect of this pretreatment 

on the solubility. In pure water and in acid solutions 

up to 0.1 percent acid the silica solubility (see fig. 31) 

is just'below that of silica gel (0.420 gram per lite1" at 

90°), but from 0.1 percent to 4 percent acid it is higher. 

Recombined R2O3 indicates the usual critical region at 

about 0.3 percent acid. All the dissolved R2O<- is 

recombined in the range 0.04 to 0.1 percent, and the 

uncombined R2O3 is very low over the whole range 

from 0 to 0.4 percent acid.. At higher acid concentrations, however, it shoots1 up. This clay exhibits 

the usual critical range, 0.2 to 0.4 percent acid, and is 

unusual only in its high silica solubility and in the 

nearly complete recombination of R2O3 in solution.
228 SHOKfER CONTBlBtJTIONS TO GBNEEAL GEOLOaT, 1941-42

.004 .01 .02 .04- O.I .2 .4 

PERCENT HYDROCHLORIC ACID

1.0

29.—Quincy day (Florida fuller's earth) in hydrochloric acid solutions.

PERCENT HYDROCHLORIC ACID 

FWUBS 80.—Soil in bydrooillorie add solutions.
ACTION OF SOME AQTJHOtJ8 ON CLAtS OF TfiE

filtrot

a

I>•) soluble 

03

Soluble 

f?2 03

-Ol .02 .04- O.I .2 .4 l.O 

PERCENT HYDROCHLORIC ACID

FIGTTBE 31.—Filtrol (activated bentonite) in hydrochloric acid solutions.

10

INTERPRETATION OF DATA

The system to be considered is one of at least five 

components—montmorillonite (in excess), water, free 

acid, chlorides hi solution, and hydrosols in suspension 

—brought to equilibrium by a 48-hour digestion at 

90° C. The montmorillonite is finely crystalline with 

a definite structure and narrow range of composition. 

Its bases are readily removed by acids, leaving amorphous silica readily soluble in water at 90° up to 0,420 

gram per liter. Silica in solution is not ionized to any 

appreciable extent, if at all,'but is hydrated. It probably exists as micellae of 1,000 or more molecules in 

each aggregate, but these are submicroscopic and 

filterable. Although not itself ionized, a silica micella 

has the unusual property of attracting other ions to 

itself and holding them either fixed on its surface or 

under restraint in its osmotic atmosphere. If the 

micella is forcibly stripped of these ions, the silica 

floculates and precipitates as gel. In addition to the 

just-mentioned three forms of water associated with 

silica—free water, ionized H and OH and osmotic, and 

adsorbed water—there is doubtless a fourth, familiar 

to biologists, namely intermicellar H and OH, which 

differs from the osmotic water in that the ions are free 

to wander within the confines of the micellar group.

Basic ions are drawn into solution by the free acid 

and out of solution by the clay and by the silica hydrosol. With removal of free acid, bases revert to the 

silica. Chloride and silicate ions compete for the 

bases, whereas hydrogen ions compete with otter 

cations for anions. In either effect the law of mess 

action applies, each being reversible.,

The curves of figures 25 to 31 check well with such 

an interpretation. It is only after silica has approached 

saturation (0.42 gram per liter) that combined RjO8 

rises sharply. At the lowest concentrations of acid it te 

chiefly the ions of water that are active in dissolving 

clay and reforming silicate in solution. With increasing 

acid, the ratio of H (or H3O) to Al adsorbed on the 

hydrosol decreases steadily from nearly unity to nearly 

zero. Within the critical range of acid concentrations 

(silica in solution exceeding saturation) RjOg combines 

with the silica in solution in such a manner as to withdraw it from competition with the unconibiaed silica, 

for the water, probably as montmorillonite in composition though not in structure. This is shown clearly by 

the upper curve in figure 28, SiOsj:(SiO2 +JlgO,). 

With high acid concentrations (2 to 20 percent), excens 

hydrogen is again available, the solubility of silica 

drops, and acid anions are again able to hold bases 

from union with silica. The ratio of soluble salts to 

total acid shown in figure 28 also checks with this conclusion. That ratio is a minimum over the critical 

range.
230 SHOKTEK CONTRIBUTIONS TO GENERAL GEOLOGY, 1941-42

With low and increasing concentrations of acid the 

silicate hydrosol ranges from the pure hydrate silicic 

acid as end member up to the composition of montmorillonite, the ratio of hydrogen to aluminum dropping 

steadily. It should be possible to compute an equilibrium constant but that the amount of free acid is 

unknown and the various bases present are not adiabatically interchangeable. The curves of figures 25 to 31 

are plotted as mass against log concentration of acid. 

Horizontal portions of these curves (maxima and minima) indicate no net work done by acid of that concentration. At a silica maximum, silica goes from clay to 

hydrosol without assistance from acid. With the 

Japanese clay (figure 27) assistance, possibly hi breaking down structure, is required at all concentrations. 

With the alkaline Wyoming clay (fig. 25), the slope is 

reversed between 0.4 and 1 percent acid, the interpretation being perhaps that silica is unable to compete with 

free acid for the bases in this range. When the curve 

for recombined R2O3 is horizontal, evidently acid and 

hydrosol are stalemated for possession of the bases. 

With the Quincy clay (fig. 29) there are three such 

maximuma but two of these may perhaps be attributed 

to hydrates in the clay.

Calcium is a minor constituent in all these clays but 

was determined in each solution. It has not been mentioned because it evidently plays a minor role. From 

the four pure montmorillonite clays it is not removed, 

more than a trace, by pure water. It appears in the 

most dilute acid solutions, accounting for about onefourth of the acid. It increases in proportion to the 

acid up to about 0.1 percent of acid, reaching a value 

that is constant for higher acid concentrations. Soil 

and acid-treated filtrol give up calcium even to pure 

water (5 and 75 milligrams, respectively, per liter), 

and with 0.02 percent or more of acid the calcium in 

solution remains constant (28 and 130 milligrams). 

Magnesium was not regularly determined, as it was 

found hi but few solutions in barely measurable amounts.

SOLUBILITY OF MONTMORILLONITE CLAYS IN ALKALINE SOLUTIONS

As with acid solutions, 30 grams of montmorillonite 

clay was digested 48 hours at 90° in 2-liter solutions of 

sodium carbonate of different concentrations. The filtered solution was acidified during evaporation, the 

residue was washed hi hot distilled water and silica determined. There was no RO or R2O3 beyond mere 

traces. Results for Wyoming bentonite hi sodium carbonate solutions are shown hi table 12 and figure 32.

The silica curve (fig. 32) is of the same general character as for acid (figs. 25 and 26). It rises to a low 

maximum at about 0.025 percent sodium carbonate, 

descends to a minimum at 0.05 percent, tl en rises 

steadily to a final maximum of 0.70 gram per liter at 

1 percent sodium carbonate. At 0.005 percent the 

silica is a little higher than for pure water, irstead of 

lower as with an acid. The first maximum ir at onetenth the concentration of the maximum for acid solutions. Up to 0.05 percent alkali there is no free carbonate hi the filtered solution—the carbon dioxide is 

either released by the clay or retained upon it. - At and 

above 0.1 percent sodium carbonate there is free carbonate hi solution. At the second maximum (about 

1.5 percent) as at the first (0.025 percent) there is apparently no net energy change in passing from clay to 

hydrosol. At intermediate concentrations, the're appears to be a net energy difference. Although equilibrium is attained, the capacity for transfer is limited.

The ratio of dissolved silica to sodium carbonate is 

significant. If all the soda were used in producing 

Na2Si4O9 that ratio would be 2.30. However, the ratio 

found is a maximum (1.34) at low concentrations, is 

dropping rapidly at 0.02 percent, reaches a nearly 

constant value (0.26) through the critical range, then 

descends gradually to about 0.07 at one percent sodium 

carbonate.

ELECTRODIALYSIS OF HYDROSOLS

The experiments on the solubility of clay described 

above indicated the existence of a reversible equilibrium 

between clay, reagent (water plus acid or alkali), and 

product, as some clay and some reagent alway^ remain 

free. The product is therefore not simply silica plus 

salt but some combination of silica with bases in equilibrium with clay and acid. Further evidence is the 

fact that silica is found in some solutions far in excess 

of the saturation limit.

In search for more direct information as to tt^ nature 

of the product formed by' clay and reagent solutions, 

some 35 of these solutions were electrodialyzed. A 

Mattson dializer with 1X10X15 centimeter coll, sheet 

platinum electrodes, and cellophane membranes was 

used. These membranes pass salts and silica tydrosols 

freely but not dialized iron. Current was limited to 0.8 

ampere by a lamp in series. Electrode liquors were 

changed every hour for 3 or 4 hours then finished with 

an overnight run. Anode and cathode liquors were 

evaporated and analyzed separately. Silica, if any, 

remaining in the cell was determined.

TABLE 12.—Silica dissolved from Wyoming bentonite by solutions containing sodium carbonate

Percent NasCO3 -- _________ -- _ _ _

SiO2 in solution _____ ___________ — _____

SiC^NazCOs ___________________

0.0

0.064

0.005

0.067

1.34

a 01

0. 132

1.32

0.02

0.178

CO

0.05

0. 133

.266

0.1

0.260

.260

0.2

a 397

.200

0.5

0.59?

.12C

1.0

a 700

.070
ACTION OF SOME AQUEOtJS SOLUTIONS ON CLAYS OF THE MONTMORILLONITE GEOUP 

.8

231

.005 .02 .05 0.1 .2 .5

PERCENT SODIUM CARBONATE 

FiotTEE 32.—Wyoming bentonite in sodium carbonate solutions.

1.0

A saturated solution of silica, evaporated to onefourth volume was dialized. Of 0.1974 gram of total 

silica, 0.0610 was found with the positive ions, 0.0607 

with the negative, 0.0180 still in the filtered cell solution, and 0.0577 as precipitated silica in the cell and 

on the membranes. As the transports of silica with 

and against the current are equal and the silica micella 

itself cannot be both positive and negative, it is evident that different micellae must carry equal and opposite charges as adsorbed H (or H3O) and OH ions. The 

precipitated silica remaining untransported indicates 

that possibly some micellae were stripped of their 

charges before they could be transported or else that 

there were insufficient H and OH ions present to supply 

them.

The same supersaturated silica solution with ammonium chloride or hydrochloric acid added to supply 

more free ions than water alone still gave equally divided 

silica but with more instead of less precipitated silica. 

A sodium silicate solution, diluted to about 30 grams per 

liter, also gave equal transport in the two directions 

with about half the total remaining in the cell. Equal 

transport was also found with most of the equilibrium 

clay .solutions disussed below and many of these gave 

little or no cell residue. When sodium aluminate was

added to a saturated solution of pure silica and dializei, 

more than 96 percent of the silica was precipitated 

without transport. Despite the high affinity of -bo^h 

ions for silica, they rob it of its H and OH and leave it 

to coagulate.

When sodium chloride is added to a pure silica 

solution and dialized, twice as much silica goes wi*h 

the positive ions as with the negative. A similar test 

with added aluminum chloride shows the opposite 

effect—5.5 percent positive, 13.1 percent negative, 

and 81.4 percent precipitated. A well-aged clear liquor 

from Wyoming bentonite (alkaline) plus water, showed 

twice as much positive (64.6 percent) as negative (33.5) 

silica, with almost none (1.9 percent) precipitated. 

The same liquor with hydrochloric acid added before 

dialysis gave nearly equal transport (48 against 44), 

while with sodium chloride added the transport was 95.5 

positive against 4.5 negative.

Electrodialysis of equilibrium clay-acid solutions 

always gave silica nearly equally divided between .positive and negative ions. The results of a few typical 

runs are given in table 13. The volume of filtrate 

stated was evaporated to 150 cubic centimeters for 

electrodialysis.
SHORTER CONTRIBUTIONS TO'GENERAL GEOLOGY, 1941-42

TABLE 13. — Electrodialysis of clay&

PolkTille clay in 0.2 perc«nt hydrochloric acid, 1,575 milliliters filtrate

Cations _ ___

CelL________-__

Anions__ _ _.__

Total 

solids

1. 2886 

.3537 

.5190

Water 

isnsoluble

0. 2754 

.3340 

.2155

Si02

0. 1170 

.2810 

. 1166

Insoluble 

Rj-Os

0. 0927 

Trace 

.0272

CaO

0. 05580 

Trace 

. 1380

Quincy clay in 2 percent hydrochloric acid. 400 mittiliters filtrate

Cations __ ___,

Cell___-___----_

Anions_____-___

1. 4787 

.0300 

.5956

0. 1822 

.0250 

.3559

0. 0378 

.0100 

.0368

0. 0724 

,0052 

.1745

None 

None 

.0402

Soil in 1 percent hydrochloric acid, 400 milliliters filtrate

Cations. ____-„_ 1, 0656 

.4547

0. 1475 

.2532

0. 0752 

.0834

0. 0482 

. 1010

0. 0735 

Trace

Acid-treated Filtrol in 1 percent hydrochloric acid. 400 milliliters filtrate

Cations. _ _. _

Anions_ ______ v _

1. 7601 

.5889

0. 1605

.2827

0. 0535 

.0425

0. 0455 

. 1115

0. 1219 

.0617

Quincy clay in 0.02 percent hydrochloric acid. 2,000 milliliters filtrate

Cations __ __ ,_

CelL____-_----_

0. 6093 

.2077 

. 1976

0. 1236 

. 1329 

,1040

0. 0795 

. 1885 

.0900

Trace 

None 

Trace

0. 3640

None 

None

Qnincy clay in 0.5 percent potassium hydroxide. 500 milliliters filtrate

CelL__---_---__

An ions _ _,_.--,

4. 9082 

. 1128 

1. 3084

0. 2256 

.0603 

.4575

0. 2305 

.0375 

.4185

Trace 

None 

None

None 

None 

None

Silica is transported nearly equally in both directions 

in every acid solution. With potassium hydroxide as 

solvent, nearly twice as much is transported as negative 

k>ns._ No free ions are left in the cell, and in two cases, 

no silica even. Calcium is transported as anions in 

some eases. The R2O3 is decidedly unbalanced, usually favoring the anions. That silica is balanced from 

the start was shown by separate analyses of the first 

cation and anion liquors removed.

Clay solutions are a complex mixture of salts and 

hydroxides of the amphoteric elements aluminum, iron, 

and silicon, together with magnesium and calcium, 

which function only as bases. Pure solutions and suspensions of the amphoterie hydroxides show equal 

transport as anions and cations when electrodialyzed. 

Aluminum hydroxide in water below about 509 C. is 

ionized as A1OOH'=»A1O2 .H+A1O.OH, and iron hi like 

manner. Above about 50Q C. each goes to a monohydrate, such as A12O3 .H2Q diaspora. Hydrated silica 

HSiOaH apparently ionizes as HSiQ3.H and HSiO2 .QH, 

as, it shows equal transport with and against the current. 

Ca(OH) 2 or Mg(OH)2 alone in water shows only cation

transport. In those experiments listed in table 13 

where anion transport of calcium is shown, it was probably attached to one or several aniqns. To fully interpret the varied results shown in this tabh, much 

more experimental work on simpler systems will be 

required.

SUMMARY AND CONCLUSIONS

The solubility of a number of clays in acids and 

alkali of a wide range of concentrations indicates that 

the solution process is of at least three kinds for every 

clay, dependent on the concentration of solvent.

At equilibrium, a fraction of the acid or alkali remains free, and a fraction of each clay remair <? undissolved regardless of the proportions present. Hence, 

the reactions appear to be reversible, as indicated by 

varying equilibrium conditions.

Over a range of low acid concentrations, 0.05 to 0.2 

normal, the "solution" is essentially a silicate hydrosol 

similar in composition to the clay dissolved. 1 1 higher 

concentrations it contains also salts in solution; at 

lower concentrations excess silica. At acid concentrations of 20 percent and over, bases but no silica go into 

solution and no hydrosols are formed.

Over a range of low alkali concentrations, 0.002 to 

0.005 normal (0.02 to 0.05 percent) sodium carbonate, 

the solution is essentially an alkali silicate 1 ydrosol, 

only silica being removed from the clay. At concentrations of alkali below the critical range, no carbonate 

is left in solution.

With montmorillonite clays the critical anion concentration is around 0.1 mole per liter while the critical 

cation (Na+) concentration is around 0.001 mole per 

liter. Within the critical acid range, the anions may 

be considered as competing on substantially equal terms 

with silicic acid for the bases of the clay. Witnin the 

critical alkali range, the alkali in solution is competing 

on equal terms with the bases of the clay for the silica.

A saturated solution (hydrosol) of pure silica is practically un-ionized and, nearly nonconducting for electricity. When electrodialized, however, the silica is 

transported equally with cations and anion§. Silica 

hydrosol, when stripped of adsorbed ions flocculates and 

precipitates in large aggregates^ When concentrated* 

it goes over to a hydrogel at a concentration of about 

5 percent.

A silicate nydrosol, stabilized with, respect to clay 

and jree acid, if electrodialized shows equal transport 

of silica in the two directions. It appears tfe»t a variety 

of ions are adsorbed in inverse proportion to their 

valence so that the total positive and negative charges 

are equal.

When alien ions are added to an equilibrium siliqate 

hydrosol, electrodialysis no longer gives equal transport
ACTION OF SOME AQUEOUS SOLUTIONS ON CLAYS OF THE MONTMOEILLONITE GROUP 233

of silica in the two directions if either cation or anion 

has an affinity for silica greater than that of H and OH, 

otherwise they have little effect on that balance.

In base-exchange work, it is well known that the 

nature of the anions as well as the bases must be taken 

into account. This investigation indicates that the con-, 

centrations of the anions present may also be of critical 

importance.

Defining "mineratbsers" as added constituents which 

promote the deposition of crystalline solids from scJution, it is evident that within the scope of this inve^tigation no such agent exists. Even strong salt solutions 

diminish the concentration of silica solutions only to 

half saturation. Silica and silicate hydrosols go over 

to hydrogels on concentration, not to crystalline solids. 

Given sufficient time/however, they might form crystals.

INDEX

Page 

Calcium, determination of_____.______.______._________ 230

Experimental procedure._— .. —..____....____.________ 219 

Filtrol, electrodialysis of_...___...____..________..___.... 232

solubility of, in acid solutions.________...___._____ 222-224,227,229 

Hydrosols, electrodialysis of..________.--..-.__...______..... 230-233 

Japanese clay, solubility of, in acid solutions....—__._.__ 222-224,226,230 

Mineralizer, definition of..__.____________...______.__ 222,233 

Montmorillonite clays, solubility of, in acid solutions,._.____ 219,222-230,232

solubility of, in alkaline solutions.__.___ — _._._______.___ 230,232 

Polkvflle clay, electrodialysis of_____.______.____________ 232

solubility of, in acid solutions.___._____ ______ ___ 222-224,227 

Purpose of the report________.______. _______. ______ 219

Quincy clay, character of ^— — —— .——..————————....—————_——— 227

electrodialysis of._______.._.-...-——_'.————.......——_ 232

solubilityof, in absolutions—— — ——————.—— 222-224,227,22P, 230

Silica, dialysis of..—-—--———-—————-——————-— 231

solubility of, factors affecting...———..._-——————.......... 220,222

in hydrochloric acid solutions..._ —.——.—————.———.—— 220.221 

in water——————————————.............—...... 220, 221

Soil, electrodialysis of-- ——.———————-----——.——————... 232

solubility of, in acid solutions————————— ———... 222-224,227,228

Wyoming bentonite, solubility of, in acid solutions..________ 222-224,22" 230 

solubility of, in alkaline solutions.—— ——-_-__-...—.——— 231,231

235

O

UNITED STATES DEPARTMENT OF THE INTERIOR 

Harold L. Ickes, Secretary

GEOLOGICAL SURVEY 

W. C. Mendenhall, Director

Professional Paper 197

SHORTER CONTRIBUTIONS TO 

GENERAL GEOLOGY

1941-42

PAPERS BY

ESPER S. LARSEN, THOMAS B. NOLAN, P. G. NUTTING

AND OTHERS

UNITED STATES

GOVERNMENT PRINTING OFFICE 

WASHINGTON : 1943

CONTENTS

[The letters In parentheses preceding the titles are those used to designate the individual papers]

(A) Alkalic rocks of Iron Hill, Gunnison County, Colorado, by Esper S. Larsen (published in March 1942)________________ 1

(B) Oligocene Foraminifera near Millry, Alabama, by Joseph A. Cushman and Winnie McGlamery (published in March

1942)___________--__________.___________________________________________________________________________ 65

(C) Lower Pennsylvanian species of Mariopteris, Eremopteris, Diplothmema, and Aneimites from the Appalachian region, by

David White (published in———1943)___________________ ___________________________________________*_ 85

(D) The Basin and Range province in Utah, Nevada, and California, by Thomas B. Nolan (published in ———1943)_______ 141

(E) Some standard thermal dehydration curves of minerals, by P. G. Nutting (published in———1943)-________________ 197

(F) The action of some aqueous solutions on clays of the montmorillonite group, by P. G. Nutting (published in———1943)-- 216

ILLUSTRATIONS

PLAIE 1. Geologic map of Iron Hill area, Gunnison County, Colo-----------_---__--_---_--_---------_-_-_------- In pocVet

2. Panorama of the Iron Hill area____.._____----__ _________________________________________________________ 2

3. A, B, Pyroxenite on south side of Stone Gulch; C, Banded syenite________________________________________ 18

4. Miliolidae, Ophthalmidiidae, Lagenidae, and Polymorphinidae___._____-______-__________,-_--__-_-____-__ 78

5. Polymorphinidae, Nonionidae, Heterohelicidae, and Buliminidae_________________________________________ 79

6. Buliminidae, Ellipsoidinidae, and Rotaliidae________-_____-_-____-____-______-_-________-_____._________ . 80

7. Rotaliidae, Amphisteginidae, Cassidulinidae, Anomalinidae, and Planorbulinidae___________________________ 81

8-39. Species of Mariopteris, Eremopteris, Diplothmema, and Aneimites,- — .- _____________________________________ 105

40. Stratigraphic sections of Paleozoic sedimentary rocks in belts parallel to the axis of the Cordilleran geosyncline__ 152

41. Stratigraphic sections of Paleozoic sedimentary rocks in belts normal to the axis of the Cordilleran geosyncline__ 152

FIGURE 1. Marble-pyroxenite contact____---__-____--____-________- -.-_________-___________-___„-________-_______ 5

2. Section south of Stone Gulch, showing variation in pyroxenite___,___________________ ______________________ 17

3. Section on north side of Stone Gulch, showing variation in pyroxenite_______________________________________ 18

4. Section south of Deldorado Creek, showing variation in pyroxenite_______________________________________ 18

5. Section northeast of gully B, showing complex relations of uncompahgrite and varieties of pyroxenite-_________ 19

6. Pseudo-binary diagram of equilibrium in mixtures of nepheline and diopside._______________________________ 24

7. Optical properties of the pyroxenes carrying acmite plotted against content of Fe2O_ and acmite_______________ 48

8. Soda tremolite and glaucophane amphiboles, atomic ratios plotted against Mg+Fe" — Al— Fe'"_______________ 51

9. Soda tremolite and glaucopbane amphiboles, j8, YAc, and specific gravity plotted against Mg+Fe" — Al—Fe'"__ 51

10. Map showing outlines of the portion of the Basin and Range province described in this paper and the localities to

which reference is made._________________________________________________________________________ 143

11. Map of the Pleistocene lakes in the Great Basin region__.________ .__--_-______________-__-_____--__-_____ 170

12. Distribution of known thrust faults in the Great Basin region____________________-___-______„_________-___ 175

13. Block faulting in three areas in Utah: A, Stockton and Fairfield quadrangles; B, A portion of the southern Wasatch

Range; C, Gold Hill quadrangle.. .___-________-_-__.._-_-_____________-___-__----_-__-__--_-___-_-_ 181

14. Curves of slight curvature variation_._______-______________________ ____________________________________ 200

15. Curves for hydrous oxides and zeolites______________j______________________________________-_--________ 202

16. Curves for hydrous oxides and related silicates. ____-____-_____-_-_____-.-_-__.-_-_____----____---_-___--- 204

17. Curves for the kaolin group._______________________________ _________________________________________ 206

18. Curves for montmorillonites___________________________________________________________________________ 208

19. Curves for the montmorillonite group._____________________________________ ____________________________ 210

20. Curves for chlorites and related silicates________________________________________________________________ 212

21. Curves for micas.___________________________________________________________________________________ 214

22. Curves for carbonates_-_,_-------_---__---___-___--____-_-_-______________________________________— __ 216

23. Solubility of opaline silica in water at different temperatures__--__--__---__-_---_-___-_----_--_-------__-- 221

24. Solubility of silica in hydrochloric acid solutions____-________---______- _________________________________ 221

25. Wyoming bentonite in hydrochloric acid solutions_____-_________'____----____-_--____--_---__------_--_-_ 225

26. Wyoming bentonite in oxalic acid solutions___________________________-______-__________-___-___________ 225

27. Japanese acid clay in hydrochloric acid solutions.________________________________ ______________________ 226

28. Polkville bentonite in hydrochloric acid solutions____-__-_-_---_----_---_------_-----_-___---_----------- 226

29. Quincy clay (Florida fuller's earth) in hydrochloric acid solutions._________________________-____-__---,'_.-_-- 228

30. Soil in hydrochloric acid solutions___--__________-____-_____________-__,______-__.-___-_-____---__-_..-- 228

31. Filtrol (activated bentonite) in hydrochloric acid solutions-.-----------------.----------------------.----- 229

32. Wyoming bentonite in sodium carbonate solutions_---_____----_-_-__-------_-_--___--------_-_---_------ 231

in