NZ202702A - Reducing slurry viscosity of kaolinitic clays - Google Patents

Description

New Zealand Paient Spedficaiion for Paient Number £02702 202702 r.sR- priority Da^ ' Complete Epecifi<»^f'-(*«:3r,/?1*' Class* .. • ^ ^ ^ "" ^c:,^o:.Jt.?.W.«... j^p-iX Jpu/vwai McS »■'•»""• " HO B i£< WE, NORD KAOLIN COMPANY, a Partnership of General and Limited Partners, organized under the Laws of the State of Georgia, United States of America, of 8111 Timber lodge Trail, Dayton, Ohio 45459, United States of America, hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement - 1 - (followed by page 1A) 2 027 0 2 * • * i REDUCING SLURRY VISCOSITY OF KAOLINITIC CLAYS This invention relates to a process for reducing the low shear, slurry viscosity of a kaolinitic clay that is contaminated with one or more forms of expanding clay, such as degraded illite. More particularly, it relates to a chemical treatment of certain high viscosity kaolin clays that are presently valued only as marginal reserves, to reduce their inherent viscosities in an economic manner and enable them to be used efficiently as paper coatings.

Kaolinitic clays, i.e., clays that are composed primarily of the mineral kaolinite, have various uses. One important use is as a coating material for paper, e.g., for preparing the glossy paper preferred for printing magazines.

When a kaolinitic clay is processed or handled, it is often preferred that it be in the form of an aqueous slurry. As compared to the dry bulk form, slurries are easier to handle and cause fewer environmental problems. The shipping of kaolin in slurry form has been gaining greater acceptance in recent years, despite the fact that the water adds significantly to the weight of such shipments. Kaolin users often need to have the clay in slurry form before they can use it; therefore, by receiving it already suspended in water, they receive the added benefit of not having to subject it to the slurrying step that is required when the clay is shipped to them in balk form. Such slurries will typically contain about 70 to 71 weight percent solids.

A clay slurry is only easy to handle, however, if its low shear viscosity is sufficiently lew to permit it to be pumped without great difficulty. High grade kaolin deposits provide clays that have good rheological properties and require no treatment to lower their slurry viscosities to an acceptable level. Many kaolin deposits are inferior in that respect, how- - 1A - 202702 ever, and must be treated chemically or mechanically to reduce their low shear slurry viscosities before they can be used. Many of these inferior kaolins are presently considered uneconomical to treat or to blend with lower viscosity kaolin and are presently held as marginal reserves. If there were seme method of economically improving their rheological properties, these deposits would have greatly increased value.

Much of the kaolinitic clay in marginal reserves today is contaminated with one or more forms of expanding clay. Probably a majority of the gray clays in the central and eastern Georgia kaolin districts have expanding clay impurities. By "expanding clay" is here meant a clay having a dynamic lattice structure in the c dimension. Examples of such clays are well known and include montmorillonite, sauconite, vermiculite, nontronite, saponite, hectorite, and various forms of degraded illite.

I have concluded that expanding clays present as impurities in high viscosity kaolinitic clays often include forms of degraded illite. Examples of these impurities are the vermiculite-like minerals derived from the weathering of muscovite and illite (Kunze and Jeffries, Soil Sci. Soc. Amer. Proc., vol. 17, 242-244; Van der Marel, Soil Sci. vol. 78, 163-179) and the montmoril-lonite-like minerals resulting from the more severe weathering of the same materials (White, Soil Sci. Soc. Amer. Proc., vol. 15, 129-133). The process of the present invention is especially directed to the treatment of kaolin that is contaminated with one or more forms of degraded illite.

For purposes of the present description, the term "degraded illite" is not intended to embrace the smectite family of expanding clays. I intend to differentiate between those two types of clay on the basis of the ability of degraded illite to absorb potassium at room temperature from a 10 weight percent solution of potassium chloride and, after room temperature drying, exhibit a resultant contraction of its lattice structure in the c dimension. 2 027 0 2 »? '' i (t Seme degraded illites will absorb sufficient potassium in that manner to raise their K^O content to as much as 3 percent or more (dry weight basis) fran an initial K2O content of less than 2 percent. After being dried at room temperature, the KC1-treated material might exhibit a c-dimension value of as low as 11 angstroms (A.) or less, as compared to a pre-treatment value of about 16 A. or more for the expanded mineral.

The snectite family of clays, on the other hand, which include typical montmorillonite, will not contract as a result of such treatment. That is how the two types of clay can be differentiated.

I have found that the lew shear, slurry viscosity of a kaolinitic clay that is contaminated with one or more forms of expanding clay can be reduced by a process comprising the steps of (a) intimately admixing the clay with a source of cationic potassium and (b) heating the potassium-treated clay to a temperature of at least about 100°C. It is believed that the potassium cation is absorbed into the lattice structure of the expanding clay and that the heat treatment stabilizes the potassium there. Where the expanding clay impurity is degraded illite, it is believed that the effect of the process is to cause that mineral to revert in form to normal illite. Very often, the high shear viscosity of the clay is also reduced by the treatment of the present invention. The principal objective of the treatment, however, is to reduce the clay's low shear viscosity.

The kaolinitic clay that is treated according" to the process of the present invention preferably has an expanding clay content of about 2 or 3 to 15 weight percent, on a dry solids basis. The process is perhaps most useful in treating those kaolimitic clays in which at least 50 weight percent of the expanding clay content is made up of degraded illite.

The treatment of the present invention is more likely to be cost effective if the clay, prior to treatment, has a low shear minimum viscosity 202702 at 20 rpm of at least about 1000 centipoises, e.g., about 2000 to 5000 centi-poises, as determined at 70 to 71% solids content by TAPPI Procedure No. T 648 su-72. These viscosity values would be as measured with the pH of the clay adjusted to that point within the range of about 6 to 8 at which the clay exhibits the lowest low shear viscosity.

The treatment of the present invention is especially useful in the processing of marginal reserve kaolin clays to be used in paper coatings. Preferably such clays will be fractionated prior to the treatment, so that at least 50 percent, preferably about 75 or 80 percent or more, of the particles (based on the dry weight of the clay) will have equivalent spherical diameters of less than 2 microns.

Any potassium ocmpound that demonstrates a lattice contraction of degraded illite may be used in the process of the present invention. Preferred sources of potassium cation for the treatment of the pres ent invention are water-soluble potassium compounds, e.g., potassiun hydroxide, potassium bicarbonate, potassium carbonate, potassiun sulfate, potassium chloride, and potassium citrate. Based upon the data gathered thus far, potassium bicarbonate appears to be the best choice. Potassiun chloride performs about as well, or better, than potassiun bicarbonate, but its use may create safety problems in the work place. Chlorine gas and noxious chlorine compounds are released when potassiun chloride is the potassiun source used in the process. The optimum amount of potassiun bicarbonate to use will vary according to the amount of expanding clay impurities in the kaolin. On average, however, it appears to be in the range of about 0.05 to 0.2 percent, based on the weight of solids in the clay.

Preferably, the potassiun compound will be dissolved in water prior to being mixed with the clay, e.g., at a solution strength of about 1 to 20 weight percent, preferably about 3 to 10 percent, calculated as cationic potassium. ^ 202702 The extent to which the slurry viscosity of the kaolinitic clay is lowered by the present treatment is proportional to the amount of potassium cations that sure admixed with the clay, until the point of minimum achievable viscosity is reached. Usually it will be preferred to mix the clay with about 1 to 10 pounds (e.g., about 2 to 5 pounds) of the potassiun source (calculated as cationic potassiun) per ton of the clay (dry weight basis).

Preferably, the clay will be in aqueous slurry form when the potassium compound is mixed with it, e.g., as a slurry containing about 25 to 35 weight percent solids. The mixing can be carried out in various pieces of equipment, such as, for example, an agitated storage tank.

As stated above, the potassium-treated clay is heated in the present process to a temperature of at least about 100° C., e.g., a temperature within or 30(P the range of about 100 to 250°C/. If a temperature of 120° C. or above is used, the treatment will provide an added benefit. It will kill the most ccmnon forms of bacteria that are likely to oontaminate the clay and possible discolor it. At the high end of the temperature range, however, the brightness of the and the clay can become unacceptably abrasive; clay can suffer/ also, the added cost may outweigh any enhancement of the viscosity reduction. Ordinarily, therefore, it will be preferred to operate no higher than about 200° C., e.g., in the range of about 120 to 200° C.

It is not known that the length of time that the treated clay is held at the elevated temperature is critical. It is contemplated, therefore, that the clay be held at about 100°C. or above for only an instant or for prolonged periods, for example, 1/2 hour or more, say up to about 5 hours, e.g., in the range of about 1 to 2 hours.

The heating step may be used, if desired, to evaporate the treated clay slurry to dryness, for example by spray drying or rotary drying. Alternatively, the traafeedt£lay, in the form of a wet filter cake, or slurry, may be heated in/a^>ressure <&}&sel, and just enough water be permitted to evapo- • 2 027 0 2 rate from the clay to produce a slurry having the desired solids content for shipment, e.g., approximately 60 to 70 weight percent.

Hie preferred embodiment of the process of the present invention is as follows: High viscosity, raw, kaolinitic clay that has a significant content of degraded illite is degritted and fractionated by conventional kaolin processing methods to yield the desired particle size fraction. The solids content of the fraction is adjusted to about 25 to 35 weight percent. The resultant slurry is mixed with an aqueous solution of the potassium compound and the mixture is gently agitated for about 6 to 24 hours. Then the potassium-treated slurry is flocced with sulfuric acid and bleached. If an oxidizing bleach, e.g., sodium hypochlorite, is used, the bleach is mixed with the clay at a neutral 01 (about 6 to 8) and the floccing with sulfuric acid is performed afterwards. Reducing bleaches, such as sodium hydrosulfite, operate at acidic pHs, however, and are preferably added to the clay after it has been flocced. For certain clays, such as the gray clays, ozone oxidation prior to floccing is recommended in order to improve brightness.

The resultant slurry is then filtered on a rotary drun filter to yield a pastelike filter cake having a solids content of about 58-65 weight percent. The filter cake is treated with a conventional dispersing agent for kaolin and its pH is adjusted to about 6 to 8. Then the clay is heated for about 1 to 2 hours in a stirred autoclave at a temperature of about 120° C. and a pressure of about 15 psig. The conditions in the autoclave are controlled so that at the end of the heat treatment the clay has a solids content of about 71 weight percent. The resultant product is a kaolinitic clay ready for shipment that has a substantially lower low shear slurry viscosity than it had prior to the treatment. 202702 The following examples describe various experiments using the process of the present invention. Unless otherwise indicated, viscosities were measured at 71% solids cont;*rit, following TAPPI Method No. T 548 su-72. (For low shear viscosities, that entailed the use of a Brookfield Syncro-lectric Viscometer Model KVF 100 operating at 20 rpm with a No. 2 spindle). Unless otherwise indicated, percentages are by weight. Brightness was measured after ozonation and bleaching, following TAPPI Method No. T 646 os-75, ar*3 it is reported as percentage of the brightness of magnesium oxide. Particle size is reported as the percent, by weight, of the clay particles that had the indicated equivalent spherical diameters. The clay mineral contents of the samples were determined by X-ray diffraction and scanning electron microscopy techniques; they are reported as percentages, based on the total weight of clay minerals in the sample. The chenical compositions of the samples were determined by atomic absorption spectrophotometry and are reported as weight percentages. Because of the difficulty in doing so, the precise amount of degraded illite present before treatment in each of the clays used was not determined. Evidence was, however, that degraded illite probably accounted for at least 50 percent, by weight, of the expanding clay content in each of the samples. Where screen sizes are reported, they are in U.S. Seive Series.

EXAMPLE I A gray, central Georgia kaolin contaminated with degraded illite and having a low shear viscosity of 1600 cps at 71% solids and pH 7 was treated with a KOH solution in the following manner.

The kaolin was a degritted fraction of which about 80 percent, by weight, of the particles had equivalent spherical diameters of less than 2 microns. A slurry was prepared using 1400 ml of H2O and 600 grams of the kaolin.

Sodium silicate was used as the dispersant in the slurry at a concentration p 2 027 0 2 equivalent to about 4-1/2 lbs. per ton of clay (dry basis). Thirty milliliters of a 10% KOH solution was introduced into the slurry and the mixture was slowly agitated for 24 hours. A pH of 9.5 was obtained during this process. After 24 hours of saturation, the slurry was flocced with 25 ml. of 10% H2SO4 at a pH of 2.7. The flocced slurry was placed into filtering bowls and filtered to remove water, water-soluble salts, and excess KOH. Filter cake obtained from the filtering process was placed in a dryer set at 200°C. for two hours. The dried clay was remixed with water and sodium hexametaphosphate to form a 71% solids slurry. The pH of the slurry was adjusted to about 7 by addition of sodium hydroxide. low shear viscosity measurements that were remeasured indicated 490 cps, a 70% decrease in low shear viscosity.

EXAMPLE II A gray, central Georgia kaolin contaminated with degraded illite and having a lew shear viscosity of 4,000 cps at 71% solids and pH 7 was treated with a KHOO3 solution in the following manner.

The kaolin was a degritted fraction of which about 80 percent, by weight, of the particles had equivalent spherical diameters of less than 2 microns. A slurry was prepared using 1400 ml of H2O and 600 grams of the kaolin. Sodium silicate was used as the dispersant in the slurry — again at a concentration equivalent to about 4-1/2 lbs. per ton of clay. Thirty milliliters of a 10% KHCD3 solution was introduced into the slurry, which was then slowly agitated for 24 hours. A pH of 9.8 was obtained during this process. After 24 hours of saturation the slurry was flocced with 5 ml. of 50% alum at a pH of 5.1. The flocced slurry was placed into filtering bowls to remove water, water-soluble salts, and excess KHCO3. Filter cake obtained frcm the filtering process was placed in a dryer set at 200°C. for two hours. Hie dried clay was remixed with water and sodium hexametaphosphate to form a 71% solids slurry. Hie 20270 pH of the slurry was adjusted with sodium hydroxide to about 7. Low shear viscosity measurements that were remeasured indicated 800 cps, an 80% decrease in lew shear viscosity.

EXAMPLE III A crude, white kaolin clay from a central Georgia deposit, containing seme degraded illite, was washed, degritted, filtered, and dried in accordance with conventional clay processing techniques. Fractionation of the clay to 80%-less-than-2 micron-size produced a clay-water slurry having 30% solids. This crude clay generated a low shear viscosity of 2650 cps at 70.4% solids. Three portions of the fractionated clay (30% solids) were treated with three different K+ salts. Each portion of slurry was treated with a 10% solution of one of the following compounds: KOH, KHCO3, or K2SO4, for 24 hours under slow agitation. Following the saturation period the slurry was flocced with H2SO4. After the filtration process removed free H2O, water-soluble salts, and excess K+ salts, the filter cakes were placed in an air convection dryer set at about 105° C. The filtered, dried kaolin was then heated for two hours in an oven set at 200°C., after which it was remixed with H2O and sodium silicate dispersant to form a 71% solids slurry. Lew shear slurry viscosity, pH, and time fraction data were accumulated from the treated clays from each test run, as set forth in Table 1.

TABLE 1 Wt. % TEST LOW SHEAR VISCOSITY, cps SAMPLE Added pH Initial 24 hours 48 hours 72 hours 240 hours Control -no heat 0.6 9.1 2650 2750 2850 3360 2660 KOH 0.5 8.4 1495 1680 1700 1760 1610 KHCO3 0.4 8.9 1740 1760 1760 1760 1610 K2SO4 0.5 8.7 1800 1850 1940 1930 1800 202702 EXAMPLE IV A second specimen of degritted, crude, white kaolin clay (original pH:4.6), in the form of an aqueous slurry having a 30% solids content, was processed in substantially the same manner as described in Exanple III. This particular clay, also obtained from central Georgia, had the following properties after degritting, floccing, filtering, and drying: Particle Size: 80% less than 2 microns Brightness: 89.1% Low Shear Viscosity: 17,000 cps. pH at Time of Viscosity Measurement: 8.1 Clay Mineral Content — Expanding Clays: 4% Mica (fine grain, like illite): 1% Halloysite: 5% Kaolinite: 90% Utilizing the same K+ salts used in Exanple III, and in the same amounts, and employing the same heat parameters, the following table illustrates the low shear viscosity reduction results obtained.

TABLE 2 Wt. % TEST Dispersant LOW SHEAR VISCOSITY, cps SAMPLE Added PH INITIAL 24Hrs. 48Hrs 196Hrs 264Hrs 720Hrs Control-no heat 0.35 7.7 17,000 52,000 52,000 50,000 36,800 ,000 KOH 0.25 7.8 6,400 ,860 ,700 6,270 6,140 4,350 KHCO3 0.25 8.4 4,020 4,550 4,600 4,700 4,740 4,100 K2S04 0.25 7.3 6,650 8,820 9,500 9,850 9,800 9,800 202702 EXAMPLE V Another gray, central Georgia kaolin that was contaminated with degraded illite was subjected to the treatment of the present invention. First a control sample of the crude clay, which had a pH of 5.1, was degritted by screening through a 200 mesh screen, followed by sedimentation. The degritted clay was flocced with sulfuric acid to a pH of about 3.0 to 3.5 and then filtered. The filter cake was placed in a 105° C. oven until it was dry. Thus prepared, the control sample had the following properties: Particle Size: 31% less than 2 microns Brightness: 87.7% Low Shear Viscosity: 880 cps.

High Shear Viscosity: 900 RPM pH At Time of Viscosity Measurement: 8.4 Clay Mineral Content — Expanding Clays: 4% Mica (fine grain, like illite): 2% Kaolinite: 94% Chemical Composition — SiC>2: 43.74% A1203: 38.95% Fe203: 0.46% MgO: 0.36% K20: 0.25% Ti02: 1.01% Structural H2O: 13.54% A second (treatment) sample of the same crude clay was degritted in the manner just described. After degritting, this sample was adjusted to a 202702 solids content of 35%; then a 10% aqueous solution of potassium carbonate was added to the clay in an amount sufficient to provide 0.2% of K2CO3, based on the solids content of the slurry. The clay slurry was slowly mixed for six hours and then flocced with sulfuric acid to a pH of about 3.0 to 3.5. Then the slurry was filtered. The filter cake was dried in a 105° C. oven, then heated in a 200° C. oven for two hours. After being reconstituted to 71% solids content, the resulting clay exhibited a low shear viscosity of 448 cps.

EXAMPLE VI A third portion of the crude kaolin clay used in Exanple V was treated in the same manner as in the treatment sample in that exanple, except that 0.2% potassium citrate was used instead of potassium carbonate. The low shear viscosity of the clay was reduced to 520 cps.

EXAMPLE VII A fourth portion of the crude kaolin clay used in Exanple V was treated in the same manner as the treatment sample in that exanple, except that 0.05% potassium bicarbonate was used instead of potassium carbonate. The low shear viscosity of the clay was reduced to 500 cps.

EXAMPLE VIII A fifth portion of the crude kaolin clay used in Exanple V was treated in the same manner as the treatment sample in that exanple, except that 0.1% potassium bicarbonate was used instead of potassium carbonate. The low shear viscosity of the clay was reduced to 432 cps.

EXAMPLE IX A sixth portion of the crude kaolin clay used in Exanple V was treated in the same manner as the treatment sample in that example, except that 0.075% 2 027 potassium bicarbonate was used instead of potassium carbonate. The low shear viscosity of the clay was reduced to 688 cps.

EXAMPLE X Another gray, central Georgia kaolin that was contaminated with degraded illite was subjected to the treatment of the present invention. Again a control sample of the crude clay, which had a pH of 4.8, was degritted by screening through a 200 mesh screen, followed by sedimentation. The degritted clay was flocced with sulfuric acid, to a pH of about 3.0 to 3.5, and then filtered. The filter cake was dried in a 105° C. oven. Thus prepared, the control sample had the following properties: Particle Size: 80% less than 2 microns Brightness: 85.6% Low Shear Viscosity: 1528 cps.

High Shear Viscosity: 2.3 dynes pH At Time of Viscosity Measurement: 7.4 Clay Mineral Content — Expanding Clays: 6% Mica (fine grain like illite): 1% Kaolinite: 93% Chemical Composition — SiC>2: AI2O3: Fe203: MgO: 42.6% 39.3% 0.49% 0.5% K2O: TiC>2: Structural H20: 0.41% 0.92% 14.1% • 202702 A second (treatment) sample of the same crude clay was degritted in the manner just described. After degritting, this sample was adjusted to a solids content of 36%; then a 10% aqueous solution of KOH was added to the clay in an amount sufficient to provide 0.2% of KOH, based on the solids content of the slurry. The resulting mixture was slowly blended for 18 hours and then flocced with sulfuric acid to a pH of about 3.0 to 3.5. Then the slurry was filtered. The filter cake, which contained about 60% solids, was placed for two hours in an autoclave maintained at 120°C. and 15 psig pressure. A portion of the water evaporated under those conditions, adjusting the solids content to about 70.5%. At that solids content the resulting clay exhibited a lew shear viscosity of 870 cps.

EXAMPLE XI A third portion of the crude kaolin clay used in Exanple X was degritted in the same manner as the control sample in that example. After de-gritting, the solids content of this sample was adjusted to 36%; then a 10% aqueous solution of potassium hydroxide was added to the clay in an amount to provide 0.2% KOH, based on the solids content of the slurry. Hie mixture was slowly blended for 24 hours and then flocced with sulfuric acid to a pH of about 3.0 to 3.5. Then the slurry was filtered. Hie filter cake was dried in a 105° C. oven, following which it was heated in a 190° C. oven for two hours. The low shear viscosity of the clay was reduced to 610 cps.

EXAMPLE XII A blend of two, white, central Georgia kaolin clays that contained degraded illite was subjected to the treatment of the present invention. First a control sample of the crude clay was degritted by screening through a 200 mesh screen, followed by sedimentation. After degritting, the clay was flocced with 202702 i 1/ »' sulfuric acid to a" pff'of about 3.0 to 3.5, filtered, and dried in a 105° C. oven.

Thus prepared, the control sample had the following properties: Particle Size: 80.5% less than 2 microns Brightness: 89.6% Lew Shear Viscosity: 395 cps.

High Shear Viscosity: 1.1 dynes 0! At Time of Viscosity Measurement: 7.8 Clay Mineral Content — Expanding Clays: 3% Mica (fine grain, like illite): 0.5% Kaolinite: 96.5% A second (treatment) sample of the same crude clay was degritted in the manner just described. After degritting, this sample was adjusted to a solids content of 35%; then a 10% aqueous solution of potassium bicarbonate was added to the clay in an amount sufficient to provide 0.1% of KHCO3, based on the solids content of the slurry* The resulting mixture was slowly blended for six hours, then flocced with sulfuric acid to a pH of about 3.0 to 3.5.

Then the slurry was filtered. The filter cake was dried in a 105° C. oven.

The resulting clay exhibited a low shear viscosity of 345 cps.

EXAMPLE XIII A third portion of the crude kaolin clay used in Exanple XII was treated in the same manner as the treatment sample in that exanple, except that once the filter cake was dry, it was held in a 200°C. oven for two more hours. The lew shear viscosity of the clay was reduced to 310 cps.

EXAMPLE XIV A composite sample of a gray, central Georgia kaolin that was contaminated with degrated illite was subjected to the treatment of the present 20270 invention. The sample was a mixture of random segments of a core sample that had been cut out of the deposit. A control sairple of the crude clay, which had a pH of 5.1, was first degritted by screening through a 200 mesh screen, followed by sedimentation. After degritting, the clay was flocced with sulfuric acid to a pH of about 3.0 to 3.5, and then filtered. The filter cake was dried in a 105° C. oven. Thus prepared, the control sample had the following properties: Particle Size: 81% less than 2 microns Brightness: 87.1% Low Shear Viscosity: 2120 cps.

High Shear Viscosity: 8 dynes 01 At Time of Viscosity Measurement: 8.3 Clay Mineral Content — Expanding Clays: 6% Mica (fine grain, like illite): 2% Kaolinite: 92% Chemical Composition— SiC>2: 43.6% AI2O3: 38.7% Fe203: 0.51% MgO: 0.48% K20: 0.38% Ti02* 1.1* S tructural H20: 13.6 % A second (treatment) sample of the same crude clay was degritted in the manner just described. After degritting, this sample was adjusted to a solids content of 40%; then a 10% aqueous solution of potassium carbonate was added to the clay; in, an ^ampunt sufficient to provide 0.1% of K2OO3, the solids content of the slurry. The resulting mixture was slowly blended for 24 hours, then flocced with sulfuric acid to a pH of about 3.0 to 3.5. The slurry was filtered and the filter cake was dried in a 105° C. oven. The resulting clay exhibited a lew shear viscosity of 1280 cps.

EXAMPLE XV A third portion of the crude clay used in Exanple XIV was treated in the same manner as the treatment sanple in that exanple, except that instead of drying the IT1" treated filter cake it was heated for two hours in a pressure reactor maintained at 120° C. and 15 psig pressure. In the course of the heating, the solids content of the clay increased, due to partial evaporation of the water, from about 60% to about 71%. The low shear viscosity of the clay was reduced by the treatment to 920 cps.

EXAMPLE XVI Yet another gray, central Georgia kaolin that contained degraded illite was subjected to the treatment of the present invention. First a control sanple of the crude clay was degritted by screening through a 200 mesh screen, followed by sedimentation. Then the clay was flocced with sulfuric acid to a pH of about 3.0 to 3.5, then filtered. The filter cake was dried in a 105° C. oven. Thus prepared, the control sanple had the following properties: Particle Size: 81% less than 2 microns Brightness: 86.5% Lw Shear Viscosity: 2360 cps. pH At Time of Viscosity Measurement: 7.8 Clay Mineral Gontent — Expanding Clays: 6% Mica (fine grain, like illite): 2% Kaolinite: 92% 202702 A second (treatment) sanple of the same crude clay was degritted in the manner just described. After degritting, this sanple was adjusted to a solids content of 35%; then a 10% aqueous solution of potassium carbonate was added to the clay in an amount sufficient to provide 0.2% of K2OO3, based on the solids content of the slurry. The resulting mixture was slowly blended for six hours, then flocced with sulfuric acid to a pH of about 3.0 to 3.5. The slurry was filtered, and the filter cake was dried in a 105° C. oven. The dried clay was divided into three fractions, each of which was then heated in an oven for two more hours. The oven temperatures during the additional heating step and the lew shear viscosities of the resulting clays were as follows: Fraction 1 Oven Temperature 105° C.

Low Shear Viscosity 2000 cps. 2 150° C 1200 cps 3 200° C 785 cps 202702 1. A process of reducing the low shear, slurry viscosity of a kaolinitic clay that is contaminated with degraded illite, conprising the steps of: a) intimately admixing the clay with a source of cationic potassium, and b) heating the potass ion-treated clay to a tenperature in the range of . 100 to 300 ° C. 2. The process of claim 1 wherein the clay is acknixed with . 1 to 10 pounds of the potassiun source (calculated as cationic potassiun) per ton of the clay (dry weight basis). 3. Hie process of claim 1 wherein the potassium-treated clay is heated to a temperature in the range of 120 to 200° C. 4. Hie process of claim 1 wherein the source of cationic potassiun used is one or more ccnpounds selected fron the group consisting of potassium hydroxide, potassiun bicarbonate, potassiun carbonate, potassiun sulfate, potassiun chloride, and potassiun citrate.

. The process of claim 1 wherein the source of the cationic potassium is potassiun bicarbonate. 6. Hie process of claim 1 wherein the admixture of the clay and the source of cationic potassiun is blended for 6 to 24 hours prior to the heating step. 7. Hie process of claim 1 wherein the source of cationic potassium is dissolved in water prior to being mixed with the clay.

Claims (1)

1. WHAT WE CLAIM IS: 202702 8. The process of claim 7 wherein the solution of the source of cationic potassiun has a concentration of 1 to 20 weight percent, calculated as cationic potassiun. 9. The process of claim 1 wherein the kaolinitic clay that is mixed with the source of cationic potassium is a fraction of which at least 50 percent of the particles (based on the weight of the clay) have equivalent spherical diameters of less than 2 microns. ^ ( 10. The process of claim 1 wherein the clay that is mixed with the source of cationic potassiun is in the form of an aqueous slurry containing 25 to 35 weight percent solids. 11. The process of claim 1 wherein the clay being treated has a low shear, slurry viscosity prior to the treatment of at least 1000 centi-poises, as determined by TAPPI Procedure No. T 648 su-72 with the pH of the slurry at the point within the range of 6 to 8 at which the slurry exhibits the lowest lew shear viscosity. 12. A process of reducing the low shear, slurry viscosity of a kaolinitic clay that is contaminated with 2 to 15 percent of one or more expanding clays, based on the weight of solids in the clay, wherein at least 50 weight percent of said expanding clay contaminant is made up of degraded illite, comprising the steps of: a) intimately acknixing an aqueous slurry of the clay, containing 25 to 35 weight percent solids, with a source of cationic potassiun selected fron the group consisting of potassiun hydroxide, potassiun bicarbonate, potassiun carbonate, potassiun sulfate, potassiun chloride, and potassium citrate, the ratio of the ingredients being 1 to 10 pounds of the potas- 2027C2 sium source (calculated as cationic potassium) per ton of the clay (dry weight basis); b) blending said mixture for 6 to 24 hours; c) filtering the blended mixture to obtain a filter cake containing 58 to 65 weight percent solids; and d) heating and stirring the filter cake in a pressure vessel maintained at a temperature in the range of 120 to 200°C for 1/2 hour to 5 hours, while allowing sufficient water to evaporate from the filter cake to adjust its solids content to 60 to 70 weight percent. * 13. The process of claim 12 wherein the potassium source is potassium bicarbonate, which, in step (a), is admixed with the clay in an amount of 0.05 to 0.2 percent, based on the dry solids weight of the clay. 14. The process of claim 13 wherein, in step (d), th« filter cake is heated and stirred for 1 to 2 hours, and the pressus vessel is maintained at 120 to 190°C. 15. A process according to claim 1 of reducing the low shear, slurry viscosity of a kaolinitic clay that is contaminated with degraded illite as hereinbefore described with reference to any one of the examples. - 21 -