Process for treating kaolin clays for pitch control and the treated clays

A process for beneficiating crude kaolin clay under defined conditions with a sufficient amount and concentration of aluminum chlorhydrate (0.5 to about 5.0 active wt. %) to improve the clay's ability to adsorb pitch during the process of making paper. The invention also relates to the treated clay and to the use of the clay in a papermaking process to absorb pitch and/or anionic trash.

FIELD OF THE INVENTION 
This invention relates to an improved method of treating or beneficiating 
kaolin clay to improve its ability to adsorb pitch and thus control the 
deposition of pitch during the process of making paper. The invention also 
involves the chemically treated clay, as well as the utilization of said 
treated clay to control pitch deposition or to remove anionic trash during 
the process of making paper, and a process for preparation of the treated 
clay. 
BACKGROUND OF THE INVENTION 
As explained in commonly assigned U.S. Pat. No. 4,927,465 to Hyder et al., 
in the operation of a pulp mill in the production of paper, one of the 
recurring problems is control of the pitch which is deposited during 
operation. Pitch is the sticky, resinous substance of varying composition 
which originates from the extractive fraction of wood in the papermaking 
process. Pitch is reported to be composed of fatty acids and rosin acids 
and their corresponding calcium, magnesium, and sodium salts. The pitch 
exists in its dispersed state until chemical changes in the paper furnish 
cause it to agglomerate and deposit on screens, belts or other paper 
machine surfaces. This results in holes or breaks in the sheet and 
expensive down time for clean-ups. It is reported that the paper industry 
loses thirty million dollars annually because of lost production caused by 
pitch problems. Though various measures have been taken to combat these 
problems, by far the most effective measure taken to the present date is 
the use of talc to adsorb the pitch, thereby preventing agglomeration and 
subsequent deposition. The talc pitch complex is retained as part of the 
final product so that no difficulty arises from its presence. There is 
discussion of this problem by Gill in "Pulp Processing", Volume 48, No. 9 
(August, 1974) page 104. In addition, there is disclosed in Tappi 
Conference Paper: Alkaline Pulping Test, 1976, a publication by Albert R. 
Kaiser of St. Regis Paper Company on "The Use of Talc to Control Pitch 
Deposition", pages 133-134. 
Use of talc as a pitch deposition control agent, however, is expensive 
because of the price of talc, so there is a need to increase efficiency of 
such pitch deposition controls, while at the same time increasing cost 
savings in operation of the process. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an agent to control 
pitch in the papermaking process by treating crude kaolin clay with 
aluminum chlorhydrate in the absence of any other processing chemical, and 
by using specified process parameters to obtain results equivalent to 
those in conventional papermaking processes, with cost performance 
benefits greater than what has been possible previously. 
The aluminum chlorhydrate treated clays of the invention act to control 
pitch by adsorbing the fatty and rosin acids comprising pitch residues via 
electrostatic attraction. The fatty and rosin acids contain negatively 
charged carboxylate groups while the aluminum chlorhydrate treated-clays 
exhibit cationic charge properties. This ionic reaction produces a 
clay-pitch complex that ultimately becomes a filler pigment in the sheet. 
The cationic charge properties of these treated clays is therefore of 
paramount importance to their ability to adsorb pitch in wet-end paper 
systems. The magnitude of their positive surface potential and the point 
of zero charge are both important charge characteristics for the products 
of this invention. 
The treatment chemical, aluminum chlorhydrate, has the active oxide formula 
Al.sub.2 (OH).sub.5 Cl.cndot.2H.sub.2 O, is sold commercially under the 
name Chlorhydrol.RTM. by Reheis Chemical, as Sumachlor.RTM. 50 by Summit 
Research Labs, and by other suppliers. As available commercially, 
Chlorhydrol.RTM. is a clear, colorless 50% active solution and is 
preferably used in that form in this invention, although other physical 
forms of the chemical agent may also be used to treat the kaolin. By 
referring to lower process costs, it is meant that the pitch control clay 
is equivalent in terms of control at the same chemical dosage. This 
process provides a more uniform surface coverage of the clay by the 
treating chemical, aluminum chlorhydrate. In other words, better mixing 
between the clay and the treating chemical is achieved. 
A further object of the invention is to employ a solids/liquids mixer in 
which the degree of mixing is controllable in a manner independent of the 
clay throughput rate. The mixing technique involves use of a piece of 
mixing equipment which will produce a clay with equivalent pitch control 
without using added moisture to effect good mixing. Thus, starting with 
crude clay, which contains 18 to 22 wt. % moisture when mined, no 
additional water needs to be added during processing. 
A still further object of the instant invention relates to mixing the 
treatment chemical with a clay in a manner compatible with other 
processing steps necessary to achieve other product properties. In this 
connection, the ultimate product has a grit specification which must be 
satisfied by a step or technique to remove a predetermined amount of grit 
present in the crude clay as mined. Grit is defined here as plus 325 mesh 
residue which is largely quartz. For removing the grit, it is an object 
herein to use a process in which the crude clay need not be degritted 
prior to treatment with aluminum chlorhydrate. Rather, the method is 
inherently capable of degritting the aluminum chlorhydrate-treated clay. 
An important object of the invention is the provision of a process which 
will avoid the use of any processing chemicals having, or suspected of 
having, a negative or neutralizing effect on the aluminum chlorhydrate's 
ability to aid kaolin clay in its role as a pitch control agent. For 
example, anionic dispersants are commonly used in processing water washed 
clays, but ionically react with aluminum chlorhydrate and render it 
ineffective by neutralizing its cationic charge. The instant process 
however allows the aluminum chlorhydrate to independently modify surface 
charge without interference and thereby yield a high positive zeta 
potential or surface charge on the clay particles. 
A further object of the invention is to provide a method to produce 
cationic clay products, via aluminum chlorhydrate treatment of crude 
kaolin clay, which have a more positive zeta potential at pH 4-5 as well 
as exhibiting a higher pH value at its point of zero charge than the 
treated clays of the prior art. 
An even further object is to provide a method to produce a treated, 
cationic clay product having the ability to control pitch under acidic as 
well as under neutral or slightly alkaline wet-end paper conditions. Pitch 
control under neutral or slightly alkaline papermaking conditions was not 
provided by the treated clays of the prior art because of their negative 
surface charge properties at these pH's. 
A still further object of the invention is to provide treated clay products 
of high cationic charge that are capable of removing anionic trash from 
the white water systems present in paper mills. Such anionic trash 
commonly consists of latex and other binders, that originate from coated 
broke in the papermaking process. The removal of this anionic trash is 
provided in much the same way by which the treated clays of this invention 
adsorb pitch. 
As will become evident from an inspection of the prior art, the instant 
invention involves an improvement upon the combination of several U.S. 
patents. In U.S. Pat. No. 3,807,702 to Grillo et al., the subject matter 
involves apparatus denominated "a pin mixer". Conversely, the present 
invention concerns itself with a process, rather than just said piece of 
equipment. Though the pin mixer is employed in the preferred embodiment of 
the current invention, there are other aspects of the process which 
comprise the novelty of the invention. It is the combination of the pin 
mixer with these other aspects, such as the use of essentially undried 
lump crude clay, which represents the novel features of the invention. 
Also, there are other mixers besides the pin mixer which may be used. For 
example, a person skilled in the art of solids mixing would consider a 
paddle mixer, a Bepex Turbulizer or a ribbon blender as a suitable 
substitute for the pin mixer. 
In U.S. Pat. No. 4,186,224 to Grillo, the inventor is concerned with a 
process for making certain chemically treated clays, including the 
utilization of a pin mixer to blend the clay with the necessary agents. 
However, the chemicals are hydrophobic organic materials and, therefore, 
require a solvent as a critical part of the process. Also, the clay must 
be dry to accept and mix well with the organic solvent and chemical. On 
the other hand, the present invention is operable with crude clay and its 
naturally occurring moisture, as previously indicated in the objects of 
the invention. Although the Grillo '224 patent relates to the use of a pin 
mixer in carrying out the steps of its operation, the present invention is 
not directed to the use of a pin mixer, per se, as the invention. 
A relatively recent invention is described in U.S. Pat. No. 4,927,465 to 
Hyder et al. This patent concerns the use of dry clay or a clay slurry as 
the starting material for a chemical treatment. During the critical step 
of mixing the chemical with the clay, the clay is still in one of two 
forms, dry or slurry. On the other hand, in the invention herein, the 
starting clay is lump crude clay in its original undried form which is 
mixed with a chemical. The improvements in the product of this process 
reside in the control of the combined parameters of moisture, degree of 
mixing, chemical dosage, chemical concentration, crude clay selection and 
clay lump size. These process improvements result in a treated clay 
product having better performance properties than that to which the claims 
in the noted Hyder et al. patent are directed. In particular, treated clay 
products having increased positive surface charge are produced by the 
process of the instant invention. This surface charge is measured in 
millivolts as a zeta potential, which is the electrical potential that 
exists across the interface or surface of all solids and liquids. 
A divisional patent of the above, U.S. Pat. No. 5,037,508, Hyder et al. 
claims a method for adsorbing pitch in a papermaking process using an 
aluminum chlorhydrate-treated kaolin clay or a hydrotalcite-treated kaolin 
clay. The present invention, as previously explained, applies to using 
undried lump crude clay as the starting material, whereas the referenced 
patent covers using dry or slurried clay. 
In the preferred embodiments of the two Hyder et al. patents, a minimum 
amount of anionic dispersant (0.1-0.15% Calgon.TM.) is added to the clay 
prior to the addition of the aluminum chlorhydrate. The present invention, 
to the contrary, requires no dispersant. In addition, the claims in the 
two Hyder et al. patents limit the amount of aluminum chlorhydrate to the 
range of between 0.5 to 1.5 active wt. %. In the invention at hand, the 
method of processing the clay allows a broader useful range of aluminum 
chlorhydrate treatment. The examples support the indicated broader range, 
which is reflected in the claims.

DESCRIPTION OF PREFERRED EMBODIMENTS 
The present invention concerns 1) a method of improving the chemical 
modification of kaolin clay; 2) the beneficiated clay; 3) the employment 
of said modified clay as an agent for controlling pitch or removing 
anionic trash in the papermaking industry; and 4) a process for 
preparation of the modified clay. Although kaolin clay has previously been 
improved by reaction with a double bond hydroxide of magnesium and 
aluminum (Hyder et al. '465), and has been modified with either aluminum 
chlorhydrate (Chlorhydrol) or hydrotalcite, the invention herein provides 
an improved modified kaolin as compared with those previously disclosed. 
Throughout the southeastern part of the United States, kaolin clays are 
mined and processed for use in various industries. The particular clay is 
identified by the region from which it is obtained, such as Middle Georgia 
cretaceous clays and East Georgia tertiary clays. The present invention 
relates to improving the pitch control properties of all such clays. 
More specifically, the process for preparing an improved kaolin clay for 
pitch control in the present invention involves treating crude fine 
particle kaolin clay in lump form, with a moisture level such that the 
mineral can be transported by belt and/or screw conveyors. The lump clay 
is broken into small particles by means of a mechanical comminute or 
pulverization mill. The so pulverized mineral is conveyed into a mixer in 
a controlled manner simultaneously with the addition of the treatment 
chemical, aluminum chlorhydrate, to said mixer. It is then thoroughly 
mixed to blend the clay with the treatment chemical so as to obtain 
uniform surface modification. 
The treated mineral is further dried, if necessary, to a moisture level 
suitable for shipping and/or to achieve product specifications. The dried 
treated mineral is further pulverized to a controlled degree of fineness, 
undesirable coarse particles being removed from the dried and pulverized 
mineral using an air classification type of separation. A controlled level 
of coarse particles are permitted to remain in the product. 
The process is preferably conducted on a continuous basis, starting with 
lump crude mineral. Thus, the rate at which the mineral and chemicals 
enter the mixing equipment is essentially the same as that at which the 
treated mineral exits from the mixer. When the lump mineral requires 
partial drying, this may be accomplished by using drying equipment, such 
as a rotary dryer. For mechanically pulverizing or comminuting the lump 
mineral, a hammermill or a chain mill is the apparatus of choice. On the 
other hand, for mixing the kaolin with the treatment chemical, a pin mixer 
is preferred, although, as previously mentioned, a paddle mixer, a Bepex 
Turbulizer, or a ribbon blender may also be used. To convey the pulverized 
mineral to the mixer in a controlled manner, a loss-in-weight feeder or a 
weigh belt feeder is generally employed. 
The concentration of moisture in the lump crude material is controlled by 
using an in-line moisture instrument, installed at a point between the 
pulverizer and the mixer, as described above. The treated material may be 
further dried by utilizing a rotary dryer and/or a flash dryer. In a 
particularly preferred embodiment, the drying equipment, the pulverization 
equipment and the air classification equipment are all combined into a 
single piece of apparatus, such as a Raymond Roller Mill or a Raymond IMP 
Mill. 
The selected starting mineral for the process is kaolin clay in an 
as-mined, crude form. It is desirable that this clay feed have a TAPPI 
brightness of at least 70% and more preferably above 80%, since the 
resulting clay-pitch complex will ultimately become part of the filled 
sheet and can affect paper brightness. Said clay is preferably partially 
dried to a moisture level between about 12 and 18 wt. %. In addition, this 
crude clay preferably exhibits a zeta potential equal to or more positive 
than -10 mv at pH 5. 
As noted above, the treating chemical is a waterbased solution of aluminum 
chlorhydrate. The solution employed contains above about 25 wt. % and 
preferably is about 50 wt. % of aluminum chlorhydrate, the concentration 
in the commercial product, Chlorhydrol.RTM.. The treating chemical is 
added to the kaolin by means of a metering pump in an amount equal to 
between about 0.5 and 5 active wt. % of said clay on a dry basis, 
preferably between about 2.0 and 5.0 active wt. %. 
EXAMPLE 1 
In FIG. 1, there is shown the zeta potential in millivolts against pH for a 
very dilute slurry of an airfloat, fine particle, hard clay, having 
selected treatment levels of 0 to 5 active wt. % aluminum chlorhydrate. 
The zeta potential measurements of an extremely dilute aqueous clay slurry 
were made as a function of pH on a Malvern Zetasizer 4 instrument that 
determines particle surface charge by electrophoretic mobility. 
The varying levels of aluminum chlorhydrate treatment on the airfloat, hard 
clay of FIG. 1, lead to the following conclusions: 
A. It is preferred that the treated clay product have a +30 mv or greater 
potential at pH 4 for purposes of pitch control. Cationic potential 
equates to pitch control capability as described in the Hyder and Kunkle 
patent (U.S. Pat. No. 5,037,508). 
B. It is also preferred that the treated product have a point of zero 
charge that occurs at pH 7.5 or above. The higher the pH value for zero 
charge, the greater the clay's potential for pitch control in neutral or 
alkaline papermaking systems. 
C. The typical desirable aluminum chlorhydrate treatment level is about 2.5 
active wt. % for resulting pitch control in acid wet end paper systems. 
The useful level is 0.5-5.0 active wt. %; the most preferred level is 
2.0-3.0 active wt. %. 
D. It is obvious from the point of zero charge observed in FIG. 1 that a 
higher aluminum chlorhydrate treatment is required for alkaline 
papermaking pitch control. The treatment level should be 3.0-5.0 active 
wt. % for neutral or alkaline papermaking wet end systems. 
Clays that can be used as starting materials to produce a pitch control 
product, as shown in FIG. 2A, are identified as follows: 
AF hard--airfloat, hard (fine particle) from South Carolina; 
Crude EGa--crude, fine particle clay from East Georgia; 
AF soft--airfloat medium particle clay from South Carolina; 
WW EGa--waterwashed (processed), fine particle clay from East Georgia; and 
AF MGa--airfloat, medium particle clay from Middle Georgia. 
Defining the preferred clay feedstocks on the basis of their surface charge 
properties for producing the pitch control product leads to the following 
conclusions for FIG. 2A. 
A. In general, airfloat and unprocessed crude clays are better feedstocks 
than chemically processed clays (i.e., no anionic dispersants). 
B. For the airfloat clays and unprocessed crude clays, the most preferred 
ones at a pH of 5 have a zeta potential equal to or more positive than -10 
mv. 
C. The waterwashed clay had the most negative zeta potential because of the 
use of an anionic dispersant during its processing. This extra anionic 
charge will partially negate the effectiveness of subsequent aluminum 
chlorhydrate treatment. 
The clays presented in FIG. 2A were then surface treated with 2.0% active 
aluminum chlorhydrate for zeta potential measurements. All the clays 
except for the treated in crude form using a bench scale Hobart.RTM. mixer 
waterwashed East Georgia clay WW EGa were chemically treated in crude form 
using a bench scale Hobart.RTM. mixer by a procedure where the aluminum 
chlorhydrate solution was added to the crude lump clay (having 15 to 20% 
moisture content) while the clay was being well mixed. After mixing, the 
wet clay was dried and pulverized. In contrast, the aluminum chlorhydrate 
solution was added to the waterwashed East Georgia clay in slurry form 
(which contained Calgon dispersant) and the slurry subsequently spray 
dried in accordance with the teachings of Hyder et al. 
The zeta potential of these clays after surface treatment with 2.0 active 
wt. % aluminum chlorhydrate are shown in FIG. 2B. The zeta potentials of 
the treated clays show the same relative charge profiles as the untreated 
clays of FIG. 2A. Those untreated clays with the higher potentials also 
have the higher zeta potentials when treated with aluminum chlorhydrate. 
The treated airfloat and crude clays are cationic over a considerably 
wider pH range than the treated waterwashed clay. 
With respect to the fine particle East Georgia clay shown in FIG. 2C, this 
involves both crude and waterwashed examples with zero and 2.0 active wt. 
% aluminum chlorhydrate treatment. Both the crude samples, untreated and 
treated, have much higher zeta potentials over most of the pH range than 
do their waterwashed clay counterparts. These charge differences can be 
attributed to the addition of process chemicals, most notably anionic 
dispersants in the waterwashed process. A comparison of the zeta 
potentials of the airfloat, South Carolina, hard clay and the waterwashed 
fine particle East Georgia clay for both untreated and 2.0 active wt. % 
aluminum chlorhydrate-treated versions are compared in FIG. 3. The 
airfloat clay shows a considerable cationic potential advantage over the 
waterwashed clay in both the untreated and treated versions. As the 
treated waterwashed clay represents the preferred product of the 
Hyder/Kunkle patent, it is obvious to one skilled in the art that the 
feedstock clay and the processing described herein lend themselves to a 
more desirable pitch control product than that previously obtained. 
EXAMPLE 2 
Reference is made to FIG. 4 and a method for preparation of the treated 
clay of the invention. 
In the method of FIG. 4, crude kaolin lump clay from source 10, containing 
20 TPH clay, wet, 21 wt. % water, and 2.5 wt. % grit, is passed by line 11 
to be comminuted into small particles by a mechanical comminuter or 
pulverization mill such as hammer mill 12. Prior to introduction into 
hammer mill 12, the clay feed is dried in rotary dryer 14 via lines 13 and 
13' so that the clay feed to hammermill 12 contains about 15 wt. % water. 
The pulverized mineral, now containing clay lumps of 3/8 inch or smaller 
diameter, is passed by line 15 for weighing in weigh belt feeder 16 and 
then conveyed into pin mixer 18 in a controlled manner simultaneously with 
the addition of the treatment chemical, aluminum chlorhydrate. Aluminum 
chlorhydrate from source 21 is passed by line 22 to pump 23 and then 
pumped by line 24 into mixer 18 at the rate of 21 pounds per minute of 50 
wt. % active solution, specific gravity=1.34. The aluminum chlorhydrate is 
then thoroughly mixed and blended with the clay in pin mixer 18. 
The aluminum chlorhydrate-treated clay is then partially dried to a 
moisture level of about 12 wt. % water, via line 19 to rotary dryer 20. 
The partially dried treated clay is then conveyed via line 25 to roller 
mill 26. There the clay is pulverized to a controlled degree of fineness, 
undesirable coarse particles being removed from the dried and pulverized 
mineral using an air classification type of separation. Grit and the like 
is removed at 27. A controlled level of coarse particles is permitted to 
remain in the product which is recovered at 28. Also within the roller 
mill, the treated clay is further dried to a moisture level suitable for 
shipping. The product recovered at 28 is a kaolin clay containing a 2.0 
wt. % treatment level of aluminum chlorhydrate, and also contains about 
0.5 wt. % grit and about 2.0 wt. % water. 
The invention has been described with reference to certain preferred 
embodiments. However, the embodiments are by way of exemplification, 
rather than limitation. The invention is as defined in the following 
claims.