SELECTIVE RHEOLOGICAL SEPARATION OF CLAYS

Abstract: A method for beneficiating a kaolin clay pigment to improve the rheological properties of a high solids suspension subsequently formed therefrom, wherein a 10 to 20% solids aqueous suspension of a kaolin clay (A) is subjected to a selective rheological separation, by mixing the suspension with from about .001% to 0.1% by weight of dry clay of a high molecular weight anionic polymer (B) and allowing the thereby treated suspension to separate into a sedimented phase (C) and a supernatant phase (D), substantially free of aggregates; separating (E) the supernatant phase containing the beneficiated kaolin pigment in suspension. The suspended product can then be conventionally processed, by reductive bleaching, floccing, filtering, washing, dispersing and drying.

Description: Selective Rhe ogical Separation -of Clays Background of Invention ' This invention relates generally to kaolin clays, and more specifically relates to a pro- cess for beneficiating a kaolin clay to improve the rheological properties of a high, solids sus¬ pension subsequently formed from the beneficiated clay, thereby rendering same more suitable for paper and paperboard coating applications. Kaolin clay coating pigments having very fine particle size and high brightness characteristics, are widely utilized in the coating of merchant grade papers and various types of paperboard where¬ in high gloss and smoothness of coating is required Typically, these pigments are applied as a high solids aqueous suspension, i.e., a suspension in¬ cluding from approximately 60-75% by weight of clay solids. The size distribution of prior art pigments used for such purposes are usually such that of the order of 90-100% by weight thereof are of less than 2 microns equivalent spherical diameter (E.S.D.) . Typically, further, the bright¬ ness characteristics, as measured by the standard specification established by TAPPI procedure T-646m-54, are f the order of at least 90. • Among the further qualities of a high solids coating clay slurry, which are of paramount impor¬ tance tor achieving high quality coatings, are the the viscosity characteristics of same. It may be be noted in this connection that the term "viscosity as used herein with respect to clay slurries, refers to such characteristics as determined by the procedures of TAPPI Method T 648 su-72, as revised in 1972. This method sets forth specific procedures for determination of both the "low shear" and "high shear" viscosity. The latter, i.e. the high shear viscosity, is considered of special importance in evaluating a high solids clay slurry for the aforementioned coating purposes. While numerous products are known and commer¬ cially available which are quite adequate (and in many instances of excellent quality) with, respect to brightness, and to a lesser extent, particle size distribution, the high shear rheological qualities of these coating clays are less than would be ideally sought for. Efforts have there¬ fore been made over the years to improve the rheo¬ logical properties of such clays; but by and large, little direct success has been achieved. In genera the rheological properties have been accepted as those which are inherent in the particular starting materials used. In accordance with the foregoing, it may be regarded as an object of the present invention, to provide a method for benefiσiating a kaolin clay to improve the high shear viscosity of a high, solids suspension subsequently formed from the beneficiated pigment. %r It is a further object of this invention to provide a method as aforesaid, which simultaneously improves the size characteristics of the clay, to markedly decrease the proportion of the clay parti- cles which may have deleterious size or shape characteristics. Summary of Invention Now, in accordance with the present invention, the foregoing objects and others as will become apparent in the course of the ensuing specification are achieved in a method wherein a 10 to 20% solids aqueous suspension of a kaolin clay is subjected to a selective rheological separation, by mixing the suspension with from about 0.001% to 0.1% by weight of dry clay, of a high molecular weight anionic polymer. The treated suspension is then allowed to separate into a sedimented phase, and a supernatant phase which is found to be substan¬ tially free of aggregates. The supernatant phase containing the beneficiated kaolin pigment in sus¬ pension is then separated from the sedinented phase. The suspended product of the process can then be conventially processed, e.g., bleached, flocced, filtered and washed, then re-dispersed and dried or mixed with previously prepared dry material, to yield a high solids (e.g. 60% to 75% solids) coat¬ ing slurry. In a typical procedure wherein the initial starting material is a crude sedimentary kaolin clay including from about 1-2% titania, the said OMPI crude is first subjected to a separation process to reduce the titania content to below 0.8% by weight — more generally the titania will be re¬ duced to the range of from about 0.2 to 0.8%. Where a froth flotation process is used for such purposes, the clay may be initially blunged and conditioned by forming an aqueous alkaline disper¬ sion of the clay (pH adjusted to about 7-10 with ammonium hydroxide). The dispersion may include as a deflocculating agent, various compounds known to be useful for such purposes. " A preferred agent for such purposes is sodium silicate. Other useful agents include a water soluble salt of a polyacrylic acid or polymethacrylic acid, preferably having an average molecular weight in the range of 500-10,000. Oleic acid or other collector agent is added during the conditioning process. Reference may be had to U.S. Patent No. 3,974,067 for further details of flotation procedures which may be utilized in this aspect of the invention. Further aspects of flotation treatment of the aforementioned type can be found in numerous places in the prior art, including in Cundy, U.S. Patent No. 3,450,257; and in U.S. Patents No. 2,990,958 and 3,138,550. The purpose of the froth flotation in the fore¬ going sequence is to remove titania; and accordingl other techniques can be utilized in place of, or to supplement flotation, including by passing the slur- ry in relatively dilute form (typically at about ' 30% solids) through a high intensity magnetic field e.g. via a magnetic separator of the type disclosed in Marston, U.S. Patent No. 3,627,678. Such device comprises a canister packed with stainless steel wool, at which enveloping magnets are capable of providing a high-intensity field of 12 kilogauss or higher. Reference may further be had in the above connection to the cited U.S. Patent No. 3,974,067 to Alan J. Nott, which patent is assigned to the assignee of the present application. In this paten a method is disclosed for brightening a kaolin clay to remove discoloring contaminants, including titan ia, by subjecting the clay as an aqueous slurry to a froth flotation treatment, and subsequently to a magnetic separation in a slurry-pervious ferromag¬ netic matrix of the type described in the aforemen¬ tioned patent to Marston. The fraction obtained from the previously des- cribed process is, if necessary, diluted to less than 20% solids by weight (preferably to 10% to 15% solids), and is then subjected to the central step of the present process, i.e. to a selective rheological separation, utilizing an appropriate high molecular weight anionic polymeric flocculant. Typically the said anionic polymeric flocculant is added at a dose in the range of from about 0.001% to 0.1% by weight (of dry clay in the suspension), with agitation just sufficient to completely dis- perse the polymer throughout the clay slip. Within minutes (typically less than 5 minutes per inch of slurry depth) , the slip is found to separate into two phases: a fluid and dispersed supernatant phase, and a flocculated, sedimented phase. The supernatant phase, which includes the beneficiated kaolin, is readily separated from the sediment and may be processed separately. The subsequent treatment of this separated phase is then relatively conventional, and may typically include acid flocculation, bleaching with sodium hydrosulfite, filtration, washing, redispersing, and drying or mixing with previously beneficiated dry material. When a high solids slurry based upon the re-- fined clay of the supernatant phase is examined from a rheological viewpoint, it is unexpectedly and surprisingly found to have extremely low values of high shear viscosity relative to the starting clay, and particularly relative to the clay in the sedimented phase. Examination of the beneficiated clay by electron microscopy estab¬ lishes that it is substantially free of aggregates, which structures have apparently been relegated to the sedimented phase by the process of the inven- tion. As will be discussed further hereinbelow, this is hypothesized to be at least one of the mechanisms repsonsible for the remarkable improve¬ ments enabled by the invention. In a further aspect of the invention it is found that where the starting dilute suspension includes a 100% less than 5 micron clay, the frac¬ tion of clay recovered in the supernatant phase has extremely fine particle size. Typically 90% to 100% by weight of the particles thereof have an E.S.D. less than 2 microns. Thus the process of the invention also serves to beneficially alter the size characteristics of the suspension as to improve the coating properties of the clay. It is important to observe here that the size separation which occurs as an incident of the polyrαe treatment, and which is normally highly beneficial, can in no way fully account for the remarkable rheo- logical improvements yielded by the invention. Thus and as will be hereinafter illustrated, a given kao¬ lin clay can be classified by centrifuging to pro¬ vide a fraction having a size distribution as above; yet such fraction will lack the rheological charac- teriscs yielded when the same clay is processed by the method of the invention. The anionic polymeric flocculants which are ad¬ vantageously used in the method of the invention, ar preferably characterized by charge densities of 25% or higher and a molecular weight of over 10 . Typi¬ cal such molecular weights are, e.g., of the order o 10 to 15 million. Typical such compounds utilizable in the invention include highly anionic polymers suc as polyacrylaπides or derivatives of same. Among the compounds of this type commercially available and utilizable in the invention are those produced by Nalco Chemical Company, Oak Brook, Illinois, and commercially available in the U.S. under designa¬ tion such as Nalco 7873, and Nalco 9UD120; and the Percol 156 product, produced by Allied Colloids Incorporated, Ridgewood, New Jersey. It may be noted here that in Rowland, U.S. Patent No. 2,981,630, poly-aliphatic-hydroxy poly¬ mers or carbohydrate polymers, and most especially water suspensible derivatives such as manno-galacta are disclosed for separating a clay suspension into components having different viscosities by select¬ ively flocculating one or more said components. In this teaching, however, the low viscosity component is precipitated, while the more viscous fraction re mains in the supernatant liquid. There is no indic tion that high shear rheology is improved. The mec anism of the Rowland disclosure is belived to diffe fundamentally from the present invention, with the distinctions being partially due to the chemically distinct nature of the polymers used in the two instances. It may be further noted, that it has heretofor been known to utilize high molecular weight anionic polymeric flocculants of the general type used in the present invention, including certain polyacryl- amides, in the course of treatment of clay slurries to effect certain separations in same. However, it is noteworthy to observe that such prior art treat- ments have considered solely the utility of such flocculants for removal of discoloring contaminants from the clay slurry. None have taught the utility or application of the said flocculants for the sep¬ aration of clay fractions from clay fractions, wher in such fractions are further, possessed of markedl different rheological properties. Reference may be had in the foregoing connec¬ tion to U.S. Patent No. 3,808,021 to R. N. Maynard wherein a kaolin slurry which has previously been refloσculated by use of excess peptizing agent, is treated with an anionic high molecular weight poly¬ mer to form floes of purified kaolin clay, which settle, leaving titanium and iron contaminants in suspension. Reference may also be had to the same inventor's U.S. Patent"No. 3,857,781, wherein a similarly reflocculated and aged kaolin ' slurry, is treated with an anionic high molecular weight poly¬ mer in the presence of specified inorganic salts. In this instance, the floes which settle out from the suspension include the titanium and iron contam inants, leaving the brightened- kaolin in suspension. The precise mechanisms at work in achieving the highly beneficial results yielded by the present in¬ vention are, at present, only imperfectly understood While applicant does not intend to be bound by any theory of the invention, evidence thus far gathered (in part by use of scanning electron photomicros- copy) suggests that the highly anionic polymer func¬ tions in the present invention to selectively floc- culate aggregates of very minute kaolin platelets, thereby removing these elements from the suspension to render same substantially free of aggregates, and leaving substantially discrete kaolin platelets remaining in the suspension, with the highly im- proved rheological properties being thereby yielded. In the terminology set forth in the preceding paragraph, applicant intends the phrase "aggregates" to refer to two types of kaolin structures wherein groups of kaolin platelets are associated. In the type "A" aggregate, the clay platelets are substan¬ tially arranged in neatly stacked, one-atop-the- other order. In the type "B" aggregate, the stacks of platelets are skewed, i.e., a relatively complete overlap between successive overlying platelets is absent. In this type "B" aggregate a certain amount of edge-to-edge contact in the platelets thus occurs An analogy might be made with a deck of ordinary playing cards. If the deck is perfectly squared off the arrangement is comparable to the "A" aggregate. If the same deck is spread out or skewed about, then an arrangement results which is more nearly akin to the type "B" aggregate. In any event, in the instance of both the type "A" and 'B" aggregates, it will be clear that, in comparison to the situation where relatively small numbers of platelets are bound to each other, or where platelets are substantially free from one another, one effectively has an increased collec¬ tion of platelet edges relative to outwardly acces- sible faces. In view of the known fact that kaolin platelet faces carry negative charges, while the edges thereof carry positive charges, it will be clear that the aggregates will possess a higher proportion of positive-to-negative charge than will isolated platelets or small collections of plate¬ lets. Therefore, using an anionic high molecular weight polymer, the aggregates are attracted to the long-chain polymer, which polymer tends to tie up a large number of such aggregates, in consequenc of which the resultant floes settle out of the sus¬ pension. In accordance with a further aspect of the in¬ vention, it is found that the benefits of the pre¬ sent process are applicable to a kaolin clay which has already been highly refined, i.e., refined to the extent of being of relatively fine particle siz and which by virtue of low titania and iron content already constitutes a highly whitened and brightene pigment. Thus, it is possible; in accordance with this aspect of the invention, to utilize as a "star ing material" the already highly brightened and pur ified pigment produced by prior art processes, whic may have included flotation and/or magnetic separa¬ tion treatment of crude kaolins and/or various clas sification and bleaching steps — to have already resulted in a pigment of relatively good coating qualities. By use of the present invention, howeve i.e., by subjecting such materials to a selective rheological separation by the method of the inven- tion, the high shear viscosity is greatly improved and the size distribution properties, i.e. the fineness of the clay, may be substantially further improved. Brief Description of Drawings FIGURE 1 herein is an electron photomicrograph of a clay suspension, representing the supernatant phase resulting from treatment of a kaolin clay by the process of the present invention; FIGURE 2 is a further electron photomicrograph, showing type "A" aggregates which have accumulated in the sedimented phase resulting from treatment of a kaolin clay by the process of the invention; FIGURE 3 is a yet further electron photomicro¬ graph, showing type "B" aggregates which have acumu lated in the sedimented phase resulting from treat¬ ment of a kaolin clay by the process of the inven¬ tion; and FIGURE 4 is a graph plotting percentage of clay flocculated against polymer dose-rate for several polymers of differing degree of ionic charge and molecular weight. Description of Preferred Embodiment The invention is further illustrated by the following Examples: EXAMPLE I In this Example the selective rheological separation method of the present invention was practiced, utilizing as starting material samples obtained from a plant processing stream normally ^UR£ utilized to produce a high quality, fine particle size, and highly brightened coating clay from a mixture of relatively fine particle size sedimen¬ tary soft Georgia kaolin crudes. The mixture of crudes initially included by weight approximately 1.5% titania and .75% of iron expressed as Fe2θ3« These crudes, in the usual plant processing procedure, are subjected to blunging, refining, and conditioning as aforementioned, and, thence, to a froth flotation, which reduces the titania content to between 0.2 and 0.4%. A product from such processes was diverted from the plant proces¬ sing stream for use in the present Example. Nor¬ mally such material would proceed through the con- ventional flocculating, bleaching, filtering, and redispersion steps, which would result in a final product brightness exceeding 90%. The size distri¬ bution resulting from this conventional processing would generally be such that 95% by weight of the particles are of less than 2 microns E.S.D. Initially, a sample (A) was so diverted, and processed as to constitute a control. In partic¬ ular, the said sample was flocced with H2S04, then reductive bleached, and then filtered and washed. The filter cake was dispersed and the sample was then screened, and spray—dried. A second portion of the above starting material was diluted to 11.0% solids using deionized water. The diluted slip was then treated with .01% of an anionic acrylamide polymer, viz. the Nalco 9UD120 - polymer. The treated suspension was allowed to age 5 minutes per inch of slip. After aging, the sedi¬ ment (Sample B) and supernatant (Sample C) phases were separated by siphoning off the supernatant phase. The recovery of clay in the supernatant phase totaled approximately 54.5%. The sediment (Sample B) and the supernatant phase (Sample C) were then individually flocced with H2SO4 to pH 3.0, bleached with .35% sodium hydrosulfite, filtered, washed and then spray dried. In Table I, hereinbelow, the re¬ sults yielded for each of the three samples A, B, and C are set forth. More specifically, surface area, PSD, and viscosity data is tabularized for each of the said samples: O OMMPPII TABLE I SAMPLE SURFACE PARTICLE SIZE DISTRIBUTION (PSD) VISCOSITY* AREA (in microns) Brookfield High Shear High Shear m 2/g _ιo -5 -2 -1 -1/2 -1/4 in cps in in cps at 20 rpm Dyne-cm X 10^ A 19.43 100 100 95 8b 74 53 380 18 (i.3380 rpm 101.7 (control) li 19.11 100 100 90 73 56 35 540 18 @620 rpm 554.5 (sediment) C 25.58 100 100 100 96 88 64 510 6.2 ©4400 rpm 26.9 (supernatant) *Viscoaity measurements are in accordance with TAPPI Method T648 su-72 (revised-1972) . To be noted in Table I is that a most substan¬ tial improvement in all significant coating charac¬ teristics has been achieved in the sample C , which has been processed in accordance with the invention. This in comparison to sample A, which sample already represents a very high quality product. Thus, the considerable improvement in particle size distribu¬ tion (PSD) is evidenced by the much higher surface area achieved in sample C. The PSD shows that 96% by weight of the sample C particles are of less than 1 micron E.S.D. / with 100% less than 2 microns, as compared to the 86% and 95% control sample A. Also to be noted is the extremely fine particle sizes in sample C: 88% by weight are less than 1/2 micron E.S.D. and 64% by weight are of less than 1/4 micron E.S.D., as compared to 74% and 53% for the same pro¬ perties in sample A. But perhaps the most dramatic and startling im¬ provement may be noted in the viscosity data. Here it is emphasized that it is the high shear viscosity which is of particular significance for present (coating) purposes. And in this instance, it is see that the high shear viscosity in centipoise for sam¬ ple C is of the order of 1/3 of that sample A. It should, incidentally, be pointed out that the in¬ crease in Broo field viscosity, which sample C dis¬ plays in comparison to sample A, is not considered of significance for present purposes. Table I also illustrates that the separated sed imented phase (sample B) indeed possesses properties OMPI for coating purposes which are of comparatively less value than those of the control sample, and far inferior to those of sample C. Thus, it will be evident, in accordance with the invention, that a true selective separation of clay from clay has been effected, with the separated fractions having markedly different properties in regard to viscosit properties as same are measured by the critically important high shear viscosity test, and also dif- ferent properties as respects the PSD and surface area. The electron photomicrograph of FIGURE 1, shows a portion of the supernatant phase recovered from a selective rheological separation conducted on sa - pies processed in accordance with the procedure set forth in this Example. The photomicrograph (which incorporates a size scale) clearly depicts the sub¬ stantial absence of aggregates in the supernatant phase, which is thus seen to be comprised essen- tially of individual clay platelets. The electron photomicrograph of FIGURE 2, shows a portion of the sedimented phase recovered from the said selective rheological separation. Again in this instance, the scale of the photomicrograph is set forth in the Figure. The very large body appear ing at the right center of the photomicrograph, is a type "A" aggregate, consisting of neatly stacked in¬ dividual platelets. Among other features to be note is the occurrence of the small negative plates at- tached to the positive edges of this large aggregate FIGURE 3 is a further electron photomicrograph which shows another portion of the sedimented phase recovered from the selective rheological separation. In this photomicrograph, a large type "B" aggregate is very clearly depicted. The skewed relationship of the individual platelets which comprise this ag¬ gregate may be clearly seen. EXAMPLE II In this Example the selective rheological sep- aration method of the invention was practiced, again utilizing as starting material specimens diverted from a plant production stream normally utilized to produce a high quality fine particle size and highly brightened coating clay from a mixture of fine par- ticle-sized sedimentary soft Georgia kaolin crudes. A first said specimen of the floated and re¬ fined slip, was processed exactly as was sample A in Example I, i.e. in this Example the resulting sample A served as a control in exactly the manner of sam- pie A in Example I. A second said specimen was diluted to 11.0% solids using deionized water. The diluted slip was then treated with .0075% of the aforementioned Nalco 9UD120 polymer. This was then allowed to stand un- agitated for 1 hour. Afterwards, the supernatant phase and the sediment phase were separated by si¬ phoning off the supernatant phase. The supernatant phase (sample B) was flocced to 3.0 pH using H2SO4, then bleached with .35% sodium hydrosulfite, fil¬ tered, washed, dispersed and dried. A portion of the sediment phase obtained from the above procedure (sample C), was treated as was sample B in Example 1. A further portion of the sediment from the se¬ lective rheological separation step of this Example was also treated with gaseous ozone, by bubbling th ozone as a fine dispersion through a well-agitated suspension of the sediment. This further sample (D) was then processed exactly as was the sediment in sample C. In Table II hereinbelow, the results yielded for each of the five samples A, B, C, and D are set forth. More specifically, there is tabularized sur¬ face area, PSD, and viscosity data for each of the said samples. TABLE II SAMPLE SURFACE PARTICLE SIZE DISTRIBUTION (PSϋ) VISCOSITY AREA (in microns) Brookfield High Shear High Shear m 2 /g -10 -5 -2 -1 -1/2 -1/4 in cps in in cps . at 20 rpm Dyne-cm X 10^ t o % I A 22.63 100 96 87 76 66 47 450 18 Θ1880 rpm 182.8 (Control) B 26.70 100 100 99 93 85 68 790 18 (33160 rpm 108.7 (Supernatant) C IB.66 99 95 71 53 44 32 690 18 @280 rpm 1227.8 (Sediment) D 18.17 100 96 71 52 41 30 580 18 @280 rpm 1227.8 (Sediment & Ozone) The data of Table II clearly supports the find ings of Table I, and further illustrates the remark able improvement in high-shear viscosity which is yielded by practice of the presenent invention. The objective of the ozone treatment in prepar ing sample D was to destroy the organic polymeric flocculant in order to demonstrate that the rela¬ tively poor rheology of the sedimented phase is not due to residual effects of the polymeric flocculant. Comparison of sample C with sample D in Table II, will bear out that this is indeed the case; i.e. this further confirms that a true rheological separ¬ ation is achieved by the process of the invention. EXAMPLE III The present Example illustrates that sim¬ ple classification of particle size by sedimenta- ■ tion, in no way results in a product having viscosit characteristics similar to those yielded by the selective rheological separation technique of the present invention. In this Example, a floated No. 2 clay fraction was diverted from the plant processing stream. A first said sample thereof (A) was pro¬ cessed as were the (A) samples in prior Examples. A further sample (B) of the starting material was processed as was sample A, except that the pro¬ duct was refined to 90% less than 2 micron fraction by centrifuging prior to floccing, bleaching, filtra OMPI tion, washing, redispersion and spray-drying. Sub¬ sequently, the viscosity, PSD, and surface area wer determined for the sample. A further sample (C) of the starting material was processed as sample B, except the sample in this instance was cut by the centrifuge to 98% less than 2 microns. A further portion of the original sample was diluted to 11.0% solids, then subjected to a selec- tive rheological separation by treating with .0075% of the aforementioned Nalco 9UD120 polymer (0.25% weight/volume solution) . The sample was then al¬ lowed to sit and age quiescently for 5 minutes per inch of slip. After aging, the supernatant phase was siphoned off into a separate container, leaving the sediment undisburbed. A portion (sample D) of the supernatant phase was flocced to a 3.0 pH using a 10% weight-to-volume solution of sulfuric acid, then bleached using 0.35% by weight sodium hydrosulfite, then allowed to age for 30 minutes, filtered, and washed. The filtered cake was dispersed as with prior samples, then screened, diluted and spray-dried, after which the said characteristics for prior samples were deter- mined. A portion of the sediment phase sample (E), was flocced to a 3.0 pH using sulfuric acid and bleached, filtered and washed as with prior samples. Following filtration the filter cake was dispersed as with prior samples, screened, spray dried and ~ the aforementioned viscosity, PSD, ans surface area characteristics determined. In Table III hereinbelow, the results yielded for each of the samples (A through E) of this Exam¬ ple are set forth: TABLE III SAMPLE SURFACE PARTICLE SIZE DISTRIBUTION (PSD) VISCOSITY AREA (in microns) m 2 /g -10 _5 _2 -l -1/2 -1/4 Brookfield High Shear High Shear in cps in in cps at 20 rpm Dyne-cm x 105 A 18.83 98 94 81 71 57 36 210 18@2380 rpm 144.4 (Control) 18.79 100 99 89 79 65 43 270 18@2280 rpm 150.7 (Centrifuged) 0 22.61 100 100 99 95 83 56 580 1802200 rpm 156.2 (Centrifuyed) D 24.29 100 100 99 96 86 64 500 9.2Θ4400 rpm 39.9 (Supernatant) Ε 12.31 95 U3 57 42 29 17 250 100420 rpm 010.5 (Sediment) Notes: All test procedures are as in Example I. The data in Table III further illustrates that the remarkable improvement in viscosity characteristics yielded by the present invention, are in no way dependent solely upon the particle size distribution changes achieved by the inventio EXAMPLE IV In this Example, selective rheological sep¬ arations in accordance with the invention were effected at substantially lower polymer concentra- tions than in prior examples. An initial sample of plant floated fine No. 1 fraction clay slip was flocced with acid, filtered, washed, then dispersed and spray-dried. This mater¬ ial constituted a control sample (sample A). A portion of the slip above described, was treated with 0.001% by weight of dry clay of the aforementioned Nalco polymer 9UD120. The treated material was allowed to separate, and the dispersed supernatant phase was recovered, flocced, bleached, filtered, washed, dispersed and dried as was the control sample A. The resulting material is ident¬ ified as sample B. A third sample (C) was prepared as described for sample B, except that the polymer dose was 0.002%. A fourth sample (D) was prepared as were the previous samples, except that the polymer dose was 0.003%. OMPI ~ Table IV sets forth the resulting measurement data for the samples, where the measured parameters are as discussed in prior Examples. It will be particularly noted that the polymer dose is effec¬ tive over the entire range utilized in these Exam¬ ples: OMP TABLE IV Particle Size Uistribtion Viscosity c m % < stated size (_u) Brookfield Hercules H Sample Brightness Recovery ~ « % 5 1 1/2 1/4 cps dynesørp cps A 90.3 99 94 07 73 44 430 1002820 122 | (Control) B 89.6 82 100 98 92 73 53 390 11.804400 51 ( .001% polymer) C 89.7 74 100 98 92 79 58 410 11.304400 49 (.002% polymer D 90.1 73 100 98 95 84 60 420 7.704400 33 ^ " 1 ( .003% polymer) EXAMPLE V Whereas many of the prior Examples herein utilize relatively fine particle sized input materials for treatment by the selective rheo- logical process of the present invention, this Example considers treatment of somewhat coarser materials. In particular, samples of a No. 2 grade plant floated slip, as described in the prior Example, were classified to (A) 83; (B) 93; and (C) 100% finer than 2 microns. These samples A, B, and C, were subsequently flocced, bleached, * filtered, washed, dispersed and dried. In each instance brightnesses, particle size distribution and viscosities were determined, whereby to serve as controls. Utilizing further portions of plant floated slip which had been classified to 83% less than 2 microns, further samples D, E, F, and G were prepared by treating such slip portions with the Nalco polymer 9UD120, then allowing the slip to separate, recovering the supernatant phase, then floccing, bleaching, filtering, washing, dispers¬ ing and drying — as in the controls. The polymer doseages were D — 0.001%; Ξ — 0.003%; F — 0.005%; and G — 0.0075% Nalco 9UD120 by weight of the dry clay. The resulting data is se forth in Table V, from which it will be evident that the selective rheological separation of the invention is fully effective with the coarser slip. To be - OMPI noted is that the high shear vicosity character¬ istics are substantially better for all of sam¬ ples D, E, F, and G, as compared even to control sample C. Also to be observed is that the size distribution for the samples D through G indicates coarser materials than e.g., control sample C; but nonetheless highly significant improvements in viscosities are evidenced. This again demonstrates that the rheological improvements yielded by the invention are in no way a simple consequence of the size separation which is an incident of the present selective rheological separation process. r OMPI TABLE V Particle Size Distribution Viscosity % < stated size (u) Brookfield Hercules Sample Brightness Recovery 5 2 1 1/2 1/4 cps dynesørpm cps % A 89.9 85 97 83 74 61 41 280 1801920 179 (83%<2m) B 91.1 70 100 93 80 70 52 630 1801600 215 I (93%<2m) C 90.6 40 100 100 100 96 67 1060 1801400 246 (100%<2m) D 90.4 72 100 90 80 67 46 480 1803000 115 (.001% polymer) , E 90.6, 67 100 94 84 71 48 520 1803320 104 ( .003% polymer) F 90. 7 65 100 96 87 73 47. 620 1803300 104 ( . Uϋ-i'i. jjυ Lyiiiυr) G 90.9 63 100 97 88 74 57 600 1803620 95 ( .0075% polymer) EXAMPLE VI In this Example, three different polymers were evaluated, to determine the effects of the ionic charge and molecular weight upon the selective rheological separation process of the present invention. In particular, the steps of the process were carried out using a nonionic, a moderately anionic, and a very highly anionic polymer. Pursuant to the above, a sample product was diverted from the plant processing stream, and was treated with three different polymers, viz. Nalco 7871, a nonionic polymer with average mole¬ cular weight of 8 million; with Nalco 8UD574, a 100% anionic polymer, further characterized as having an average molecular weight of 15 million; and with Nalco 9UD120, a 26% anionic polymer, which has been described in prior Examples. Differing dosage levels of the three poly- mers were utilized in order to generate the curves of Figure 4 herein, which shows the rela¬ tionship between the specific polymer dose and the percentage of flocculation of the treated clay suspension. Thus, in the first instance, a floated No. 2 clay fraction product was diluted to 11% solids, and 500 ml (58.9 g) of such product was treated with a 0.25% solution of the aforemen¬ tioned 7871 polymer, utilizing dose rates of .0025%, .005%, .01%, .03%, .04%, .05%, .1%, .15%, V-- „ * OMPI .2% and .225% — all by weight of dry clay. The supernatant phase was siphoned off, then flocced, filtered and washed. The cake was dispersed for particle size distribution analysis, as described for the previous Examples. A further such specimen was treated as des¬ cribed above, but with the Nalco 8UD574 polymer, also at various dosage rates. A further sample was treated as above, but with the Nalco 9UD120 polymer. In Tables VI(A), VI(B), and VI(C), data is tabulated for the three runs, i.e., using the different polymers: - JR »-_, i - i OM " TABLE VI(A) Nonionic Polymer/Nalco 7871 PARTICLE SIZE DISTRIBUTION (%) (in microns) DOSE% RECOVERY (% of clay -5 -2 -1 -1/2 -1/4 treated) . 0 100 95 82 72 58 38 .0025 86. 7 .005 87.2 98 91.0 82 68 42 .01 78.6 .03 63.9 04 60.0 05 51.8 10 20.7 100 96 84 70 36 15 16.6 20 6. 9 225 3. 6 100 98 96 90 44 OMP ' TABLE VI(B) 100% Anionic Polymer/Nalco 8UD574 PARTICLE SIZE DISTRIBUTION (%) (in microns) DOSE % RECOVERY -5 -2 -1 -1/2 -1/4 (% of clay treated) .0 100 95 82 72 58 38 .000625 58.0 .00125 53.7 .0025 44.9 100 99 98 88 60 .005 " 36.1 .01 23.9 100 99 98 92 65 .02 22.1 .04 21.8 100 100 99 95 66 .05 21.5 .10 17.5 100 100 99 98 80 .11 10.9 -$ J B.E__ OMPI TABLE VI(C) 100% Anionic Polymer/Nalco 8UD574 PARTICLE SIZE DISTRIBUTION (%) (in microns) DOSE % RECOVERY -5 -2 -1 -1/2 -1/4 (% of clay treated) .0 100 95 82 72 58 38 .000625 67.6 99 94 86 72 48 .00125 59.1 .0025 56.7 .005 50.7 .01 50.1 .03 46.1 100 99 98 94 62 .04 43.2 05 40.8 075 36.2 10 18.5 100 98 97 94 74 11 0.0 r- OMP In each instance the dosage, recovery, per¬ centage flocculated of the solids, and the particle size distribution for the supernatant phase is set forth. Figure 4 plots the percentage by weight of dry clay flocculated against the polymer dose rate (on a semi-log scale) for the data tabulated in each of the aforementioned Tables, thus showing the effects on flocculation of each of the three polymers. From these plots it is readily seen that the nonionic polymer is non-selective, as the percent floccula¬ tion increases at a rate proportional to dose rate. However, it is equally clear that the 26% an¬ ionic and 100% anionic polymers were selective — as is shown by the plots of dose rate verus floc- culation. It is readily seen that with the 26% anionic polymer, a plateau was obtained, where fur¬ ther increase in dose resulted in very little ad¬ ditional flocculation. This plateau was particu- larly evident in the range of from about 0.006 to 0.03% by weight of the polymer. A relatively broad plateau and higher recovery are clearly advantageous under commercial processing conditions. Among other things, the broad plateau- implies that dosage is not extremely critical over a fairly wide range. OMPI EXAMPLE VII In this Example, the effects of selective rheo logical separation pursuant to the invention were compared for two very different polymers, viz., the substantially nonionic Nalco polymer 7871 previousl referenced in Example IV, and the 26% anionic Nalco polymer 9UD120. Each of these polymers are class¬ ified as flocculants. Samples of a fine No. 1 clay fraction were di- verted from the plant processing line as referenced in the earlier Examples. A first such sample (A), was flocced to 3.0 pH using sulfuric acid, then bleached with 0.35% by weight sodium hydrosulfite, filtered, and washed with deionized water. The re- suiting filter cake was dispersed and spray dried. Following spray drying, PSD, surface area, and vis¬ cosity characteristics were determined for the re¬ sultant product. A further sample (B) of the original fraction was diluted to 11% solids. The diluted slip was then treated with 0.02% of the mentioned Nalco 7871 polymer, based on dry clay. The polymer was mixed into the sample by pouring the trated slip from one container to another several times. The treated slip was then allowed to stand unagitated for 5 minutes per inch of slip. After this, the super¬ natant phase was siphoned off into a separate con¬ tainer, flocced to 3.0 pH using sulfuric acid, and bleached with 0.35% sodium hydrosulfite and allowed to age for 30 minutes, then filtered and washed. OMP IP The filter cake was dispersed, screened, diluted and spray-dried, all as in the instance of Sample A, and thereupon the same characteristics of PSD, surface area, and viscosity were determined. The same procedure as was used for Sample B was used for a third sample (C); but in this in¬ stance, the treating polymer was the aforementioned anionic Nalco 9UD120 at a dose rate of 0.0075%. In Table VII hereinbelow, the data obtained pursuant to the above procedures for the three sam¬ ples, A, B, and C, is tabulated: SUBSTITUTE SHE . ^ f OMPI TABLE I c π PRODUCT SURFACE t PARTICLE SIZE DISTRIBUTION (PSϋ) VISCOSITY AREA (in microns) • 1 m^/g Brooktield High Shear High Shear -10 -5 -2 -1 -1/2 -1/4 in cps in in cps at 20 rpm Dyne-cm X 10 5 A 22.2 100 100 96 88 78 57 340 1803780 rpm 90.9 ~ n (control) B 2222..5544 110000 110000 9966 8899 777 52 370 1804200 rpm 81.8 (non-ionic) C 24.93 100 100 9b 98 92 69 380 5.804400 rpm 25.2 b NOTES: Supernatant phase recovery for Sample B was 86.5%; for Sample C, 54.1% Test procedures are all as in prior Examples. The data of Table VII establishes that the product B of treatment with the non-ionic poly- ' meric flocculant, differs very little, if at all, ' , from the control product A. Particle size distri- bution was substantially not affected, nor was rheology by treatment with the non-ionic polymeric flocculant. On the other hand, the anionic polymer yielded a selective separation treatment, resulting in the recovery (product C) , of a product with ex- tremely desirable rheological characteristics, i.e., with a very low high-shear viscosity; the very fine size characteristics are also deemed most desirable for coating purposes. While the present invention has been particularly set forth in terms of specific embodiments thereof, it will be understood in view • of the instant disclosure, that numerous variations upon the invention are now enabled to those skilled in the art, which variations yet reside within the scope of the present teaching. Accordingly, the invention is to be broadly construed, and limited only by the scope and spirit of the claims now appended hereto. SUBSTITUT

Claims: Claims 1. A method for beneficiating a kaolin clay pigment to improve the rheological properties of a high-solids suspension subsequently formed there- from; said method comprising the steps of: forming said kaolin clay pigment into a dilute aqueous suspension having from 10% to 20% solids by weight; and performing a selective rheological separation upon said dilute suspension by mixing same with from about 0.001% to 0.1% by weight of dry clay, of a high molecular weight anionic polymer, and allow¬ ing the thereby treated suspension to separate into a sedimented. hase and into a supernatant phase which is substantially free of aggregates; and separating the supernatant phase containing the beneficiated kaolin in suspension. 2. A method in accordance with claim 1, wherein the clay to be beneficiated contains less than 0.8% by weight of titania. 3. A method in accordance with claim 2, wherein the clay of said dilute aqueous suspension has a particle size distribution such that substan¬ tially 100% by weight are of less than 5 microns E.S.D. 4. A method in accordance with claim 1, wherein said polymer comprises a polyacrylamide or derivative thereof. 5. A method in accordance with claim 4, wherein said polymer has a charge density of at least 25% and molecular weight greater than 10 7 . 6. A method in accordance with claim 5, wherein said molecular weight is in the range of 10 to 15 million. 7. A method in accordance with claim 4, wherein the suspension subjected to said rheolog¬ ical separation has a solids content in the range of from 10% to 15%. 8. A method for beneficiating a crude sedi¬ mentary kaolin clay which includes over 1% by weight titania to produce a clay pigment which yields improved rheological properties in a high solids coating suspension subsequently formed therefrom; said method comprising the steps of: blunging and dispersing said crude clay to form an aqueous suspension thereof; subjecting said suspension to a separation step fee—reduce the titania content thereof below 0.8% by weight of the dry clay; subjecting a substantially 100% less than 5 micron fraction of the clay from said separation step as a dilute aqueous suspension of less than 20% solids by weight of dry clay, to a selective rheological separation, by mixing said dilute sus¬ pension with from about 0.001% to 0.10% by weight of dry clay of a high molecular weight, anionic polymer, and allowing the treated suspension to T __x OMP separate into a supernatant and a sedimented phase; and separating the said supernatant phase con¬ taining the beneficiated kaolin clay pigment in suspension. 9. A method in accordance with claim 8, wherein said anionic polymer comprises a poly- acrylamide or derivative thereof. 10. A method in accordance with claim 9, wherein said suspension subjected to said selec¬ tive rheological separation includes from 10% to 20% solids by weight. 11. A method in accordance with claim 8, wherein said separation step for reducing said titania is effected by froth flotation. 12. A method in accordance with claim 8, wherein the said supernatant phase recovered from said selective rheological separation, is bleached to further reduce the iron content thereof, and flocced, filtered and redispersed. 13. A method for producing a refined coating clay pigment having fine particle size, and dis¬ playing extremely low viscosity when dispersed in a high-solids coating slurry; said method co - prising the steps of: blunging, dispersing, and conditioning a crude kaolin clay including from 1% to 2% by weight of discoloring titania, to form an aqueous suspension of same; subjecting said blunged, dispersed, and con¬ ditioned suspension to a froth flotation to reduce the titania content thereof below 0.8% by weight of the dry clay; diluting a 100% less than 5 micron fraction from said flotation step to form an aqueous sus¬ pension including from 10% to 20% solids by weight; treating said dilute suspension with from about 0.0075% to 0.1% by weight dry clay of a high molecular weight anionic polymer, and allowing the treated suspension to separate into a supernatant and sediment phase; and separating the said supernatant phasse, there¬ by recovering in said phase a beneficiated kaolin pigment, which pigment is substantially free of aggregates, and exhibits very low viscosity char¬ acteristics when dispersed as a high-solids slurry. 14. A method in accordance with claim 13, wherein said polymer comprises a polyacrylramide or derivative thereof, which has a charge density of at least 25% and a molecular weight of over 1Q 7 . BSTf rjTS' CFW«_,_ OMPI

Inventors: TURNER RALPH E
Applicants: ANGLO AMERICAN CLAYS CORP, ANGLO-AMERICAN CLAYS CORP
Application year: 1981
Main classification: B03B1
IPC codes: B03D3, C02F1, C09C1, D21H19