US3337048A

US3337048A - Method for beneficiating clay by flotation

Info

Publication number: US3337048A
Application number: US415503A
Authority: US
Inventors: Mercade Venancio
Original assignee: Minerals and Chemicals Philipp Corp
Current assignee: Minerals and Chemicals Philipp Corp; Phibro Corp
Priority date: 1964-12-02
Filing date: 1964-12-02
Publication date: 1967-08-22
Anticipated expiration: 1984-08-22

Description

United States Patent 3,337,048 METHOD FOR BENEFICIATLNG CLAY BY FLOTATION Venancio Mercade, Metuchen, N.J., assignor to Minerals & Chemicals Philipp Corporation, Woodbridge, N.J., a corporation of Maryland No Drawing. Filed Dec. 2, 1964, Ser. No. 415,503 20 Claims. (Cl. 209-5) This invention relates to the beneficiation of clay and is directed especially to a process for floating finely-divided colored impurities from the clay.

Clay, especially kaolin clay, is widely used as a pigmentfor coating paper. For such use, the value of the clay is dependent upon its whiteness or brightness since this property affects the appearance of clay-coated sheet material. High-grade coating clays have brightness values of at least about 86-87% when the brightness is determined by a light reflectance method hereinafter described. Small differences in brightness values of clays represent significant differences in the utility of the clays. Thus, a clay that has a brightness of 91.0% is markedly superior to a clay having a brightness of 89.0% or even 90.0%.

Some clays, especially certain foreign primary kaolin clays, possess adequate brightness for paper coating use after being beneficiated only to the extent that coarse agglomerates and grit are removed. Other clays, such as the sedimentary kaolin clays, as exemplified by Georgia kaolin clay, normally contain an appreciable quantity of finely divided colored impurities which detract significantly from the usefulness of the clays. These sedimentary clays, after degritting and fractionation to remove oversize, have a brightness which is far below the brightness values of high grade coating clays.

The colored impurities that ness of sedimentary kaolin clays include ferruginous matter. This constituent can be removed at least in part from the clay by chemical bleaching methods, such as with hydrosulfurous compounds, which solubilize the ferruginous matter so that it can be removed from the clay. Sedimentary kaolin clays usually also contain anatase, which is a yellow titaniferous impurity that has a very detrimental effect on the clay brightness. This type substantially unaffected by the chemical by the clay industry. To remove colored titaniferous impurities, it has been necessary to employ froth flotation in the presence of flotation reagents which bring about the selective flotation of the titaniferous matter from the clay. The flotation beneficiated clay is then treated with chemical bleaching reagents to solubilize and eliminate a substantial amount of the undesirable feruginous matter. The flotation of the titaniferous matter from the clay can be achieved by dispersing the clay in water, incorporating a higher fatty acid, such as tall oil acids, aerating the system and withdrawing a froth which is a concentrate of the yellow titaniferous impurities originally associated with the clay. Especially good results have been obtained using ultraflotation, which is a particular type of flotation process. In this type of flotation process, described in US. 2,990,95 8 to Ernest W. Greene et al., a substantial amount of finely divided insoluble particulate matter, usually finely divided calcite, is incorporated into the aqueous clay dispersion along with the fatty acid collector reagent. The added particulate matter, which is also reagentized by the fatty collector reagent, enhances the flotation of the finely divided colored impurities and reports in the froth along with the colored impurities. Ultraflotation in conjunction with chemical account for the low brightbleaching has resulted in the commercial availability of 90% to 91% brightness Georgia kaolin clay from clay crudes having brightness values less than These results have been achieved with a type of discolored kaolin clay referred to in the field as white clay to distinguish it from gray clay which is similar to white clay in chemical composition but which, for reasons presently unknown, has a distinctly gray tinge.

To brighten white clay by flotation and chemical bleaching to optimum brightness values, it has been found that it is essential to achieve complete dispersion of the clay by means of sodium silicate before subjecting the clay to flotation. It has been necessary, however, to carefully control the quantity of sodium silicate used. Even a small excess of the sodium silicate has been found to affect adversely the results of the flotation operation. In many cases, adequate control of dispersant dosage has been difficult because of individual differences in the dispersant demand of different crudes, even crudes from different localities within the same mine.

In the case of gray clay crudes, it has been necessary to resort to preliminary chemical treatment of the clay in order to achieve the desired response of the gray kaolin clay crudes to the flotation process. As an example of such preliminary chemical treatment is the sulfidization treatment described in US. 3,072,255 to Ernest W. Greene et al. Even with the specialized chemical treatment of the gray clay, the overall results were not quite comparable to the best results achieved with the white variety of kaolin clay.

An object of this invention is to improve the effectiveness of froth flotation as a method for removing colored impurities from clay.

One specific object is to buffer the effect of sodium silicate dispersant in clay flotation so that the clay is not so sensitive to the quantity of alkali silicate dispersant and small amounts of excess dispersant will not adversely affect flotation results.

Another object beneficiated clays.

Still another important object is to provide a process for brightening gray kaolin clays to brightness values comparable to those of high grade white coating clays.

I have discovered a simple, yet remarkably elfective method for improving upon the response of clays, includ ing gray kaolin clay, to froth flotation.

Stated briefly, the present invention resides in dispersis to improve the brightness of flotation whereby a dilute stable hydrosol is formed by reaction between the metallic salt and the dilute sodium silicate. The clay pulp is dispersed with the hydrosol reagent before the pulp is subjected to froth flotation in the presence of flotation reagents selective to colored impurities in the clay. An essential feature of the process is that the quantity of salt that is incorporated into the solution of the sodium silicate is restricted to quantity which forms a stable hydrosol with quantity of polyvalent metal salt carying out my invention is a small to the quantity of sodium silicate less than about 2 pounds per ton of clay.

In accordance with a preferred embodiment of my invention, the aforementioned hydrosol dispersant reagent is used in combination with an alkaline carbonate cooperthat is employed in amount as compared that is used and is the sodium silicate. Thus, the i ive dispersant and the latter material is incorporated to a pulp of the clay before addition of the hydrosol spersant reagent.

The metal salts used in preparing the hydrosol reagent Intain metal cations of Group II or higher in the Periodic able. The Periodic Table referred to is the one appearing Kirk-Othrners Encyclopedia of Chemical Technology,

)1. 5, page 672. As is well known in the art, metal ions Group II or higher react with alkaline sodium silicate aqueous media with the formation of precipitates. In re dilute systems I employ, the reaction products remain )lloidally dispersed in the aqueous media, forming stable ispersions usually referred to as hydrosols. Chemicalthese hydrosols probably comprise complex silicates. .xamples of metal ions of Group II or higher are Zinc, ianganese, cadmium, lead, nickel, silver, magnesium, alcium and aluminum. Especially preferred are salts of ietals having amphoteric properties, e. g., salts of alulium or manganese. Manganous salts or manganic salts an be used although the former are preferred because f their lower cost. With white Georgia kaolin clays, I refer to use aluminum salts. On the other hand, man- ;anese salts appear to give somewhat better results than tluminum salts with gray kaolin clay.

The following table contains data illustrating the effect f addition of various quantities of aluminum sulfate to l dilute aqueous solution of brand sodium silicate a commercial solution reported to contain 9.16% Na O, 19.5% SiO and about 62% H O, weight basis). The lata represent results obtained by slowly adding a 1% [weight basis) aqueous solution of alum cate to 100 parts by Weight water) and allowing the compositions to stand for the periods of time indicated.

- precipitate is formed an anhydrous sodium silicate basis, usually 1.0 to 3.0 pounds anhydrous sodium silicate per ton with most clays. Using the 0 brand sodium silicate (which contains about 68% water) about 2.0 to 10.0, and preferably 3.0 to 6.0 pounds, of the commercial sodium silicate solution is used for every ton of clay. Metal salt is usually employed in amount ranging from about 0.1 to 2.0 pounds per ton of clay, with especially good results being obtained with 0.4 to 0.8 pound per ton. When too little metal salt is used, the effect of its presence may not be appreciable. With too much metal salt, a copious flocculent when the salt is incorporated with the sodium silicate solution and the metal salt is not so effective. Before addition of the hydrosol to the clay, I prefer to add an alkaline carbonate cooperative dispersant to the clay pulp in amount of 2.0 to 10.0 pounds carbonate per ton of clay. With white clays, ammonium carbonate is the preferred carbonate. With gray clays, sodium carbonate is preferred.

In putting my invention into practice, the hydrosol dispersant reagent is formed by diluting water-soluble sodium silicate with water and slowly adding a dilute aqueous solution of polyvalent metal salt until a suitable quantity of salt solution has been added. This condition is indicated by the development of a turbid but stable system which is free from flocs and exhibits the Tyndall phenomenon. The hydrosol formed by reaction of the metal salt and sodium silicate is then added with agitation to an aqueous clay pulp. Sufficient hydrosol is added to form a welldispersed pulp. It is desirable to formulate the system so that the clay solids content of the desired pulp will be about 10% to weight basis. The clay is agitated with the hydrosol for at least 10 minutes, preferably 30 to minutes, before incorporation of the collector reagent into the pulp. With pulps that are to be degritted and/or fractionated, it may be convenient to carry out EFFECT OF ADDITION OF ALUM TO A DILUTE SODIUM SILICATE SOLUTION Various anions can be present as the anionic constituent of the metal salt used in preparing the hydrosol reagent and the results that are achieved are substantially independent of the anionic constituent of the salt. Thus, the results obtained with aluminum sulfate have been found to be substantially equivalent to results with either aluminum nitrate or aluminum chloride when the various salts were used in amount to provide equivalent quantities of aluminum ions. Nitrates, chlorides, sulfates and acetates are especially recommended because of their low cost and availability. However, other salts can be employed. Mixed salts, such as ammonium alums can be used. Mixture of salts, such as, for example, a mixture of aluminum sulfate and manganese sulfate, can be employed. The use of hydrated salts is also fully within the scope of the invention and the term metal salt as used herein is intended to encompass hydrated metal salts.

The water-soluble sodium silicates employed in the preparation of the hydrosol reagent have a weight ratio of Na O to SiO ranging from 111.60 to 113.75. Excellent results have been obtained with sodium silicate having a Na O to SiO weight ratio of 1:322.

The sodium silicate is employed in amount ranging from about 0.5 to about 4.0 pounds per ton of clay on such steps after addition of the hydrosol and before incorporation of collector reagents.

The marked benefit of incorporating the metal salt into the sodium silicate dispersant solution before incorporating the dispersant solution into the clay is dramatically illustrated in the accompanying examples.

The flotation reagents used in carrying out the process of this invention include fatty acid reagents which are selective to the titania impurities in the clay. The flotation reagents used in ultraflotation are preferred. As mentioned in US. 2,990,958 to Ernest W. Greene et al., reagents for utraflotation concentration include, in addition to higher fatty acid, especially a mixture of resin acid and fatty acid (tall oil acids), a substantial quantity of finely divided auxiliary mineral, especially minus 325 mesh calcite and, preferably, an oil-soluble water-insoluble petroleum sulfonate salt. Additional quantities of sodium silicate can be incorporated into the pulp after addition of calcite if the addition of calcite results in flocculation of the pulp. Ammonium hydroxide can be used to adjust the pH to a desired level of about 8.0 to 8.5. The pH can be buffered, as by the addition of ammonium sulfate. Flotation is carried out in an alkaline pulp, producing a froth which is a concentrate of impurities in the clay intimately mixed with the finely divided mineral additive. The beneficiated clay, in the form of a dispersed pulp, reports in the machine discharge product. The recovery of beneficiated clay can be improved by refloating the froth product one or more times.

The following examples are given to contribute to a better understanding of the present invention and to illustrate its benefits.

Examples I to N, which follow, illustrate the application of my process to the flotation beneficiation of white sedimentary Georgia kaolin clay (Washington County clay). The minus 325 mesh fraction of this clay had a brightness of about 80% before being beneficiated by flotation and bleaching. In beneficiating the white clay, the following general dispersion and flotation procedures were used. In some cases, these procedures were modified as described in the examples. In describing the procedures, all reagents are reported on a weight basis and represent pounds per ton of dry clay unless otherwise indicated.

DISPERSIONWHITE CLAY Twelve hundred and fifty grams of dry clay Was diluted with soft water to 30% solids, weight basis, and transferred to a Fagergren flotation cell. When used, sodium carbonate or ammonium carbonate was added as a 5% (weight basis) aqueous solution and in amount to provide a desired quantity of the reagent, typically 2.0 to 6.0 pounds sodium or ammonium carbonate per ton of clay. The pulp Was agitated without aeration for 1 minute. A 5% aqueous solution of brand sodium silicate was prepared by adding parts by weight 0 brand (containing about 68% H O) to 100 parts by weight water. The 5% solution was added to provide the desired quantity of dispersant, typically 3.0 to 8.0 pounds 0" brand per ton of clay. When sodium or ammonium carbonate was used, the dilute sodium silicate solution was incorporated immediately after agitating the pulp for a minute with the carbonate. After addition of the sodium silicate solution, the pulp was agitated for 30 minutes in the Fagergren flotation cell and the pH recorded. The slip was then degritted by passing it through a 325 mesh screen.

ULTRAFLOTATIONWHITE CLAY A portion of the pulp containing 750 grams of the degritted clay (dry clay basis) was diluted with 250 ml. soft water. 112.5 grams of minus 325 mesh calcite having an average particle size of about 5 microns (Drikalite) was added and agitated without aeration for 1 minute. The pulp in the conditioner was at about solids, weight basis. Forty-five ml. of a 5% ammonium sulfate solution was added and the pulp conditioned for V2 minute. An'emulsion of the following composition was then added to the pulp and conditioned for 17 minutes: 250 ml. of soft water, ml. of a 2 /2% aqueous solution of ammonium hydroxide, 137 drops of a mixture of equal parts of crude tall oil acids and a solution of neutral calcium petroleum sulfonate in mineral oil (Calcium Petronate). After 5 minutes conditioning time had elapsed, 111 drops of lubricating oil (Eureka M) were added. The

Reagent: Pounds/ton Calcite 300 (NH SO 6.0 NH OH 2.0 Tall oil acids Aqueous emulsion 4.5 Calcium Petronate {4.5 Eureka M oil 8.0

the pH of the pulp at the end of conditioning was typically 8.5-8.8.

The conditioned pulp was subjected to aeration and froth flotation in a 1000 cc. Air Flow flotation cell, removing a froth product for 10 minutes. The froth product was refloated three times without addition of reagents, producing three products: a froth product (F.P.); a first machine discharge product (MD1); and combined machine discharge product (MD-2, 3,. 4). MD-l typically contained about 6.5% solids and MD-Z, 3, 4 about 2.5% solids. The machine discharge products were analyzed by a standard chemical method for TiO and, in some cases, they were also analyzed chemically for Fe O Brightness values of products were determined by TAPPI Standard Method T-646 m-54, as described on pages 159A and A of the October 1954 issue of TAPPI (a monthly publication of the Technical Association of the Pulp and Paper Industry). The method measures the light reflectance of a clay sample and thus gives a quantitative indication of its brightness or whiteness.

BLEACHING-WHITE CLAY The machine discharge products were flocced by addition of sulfuric acid in amount to reduce the pH to 2.5. The flocced clay was bleached with zinc hydrosulfite solution, following typical practice of the industry. The clay was then filtered. The brightness of the clay after being bleached Was measured and compared to the brightness of the clay after flotation but before bleaching for the purpose of determining the further improvement in brightness resulting from the chemical bleach.

Example I To illustrate the desirable effects of incorporating a small quantity of polyvalent metal cations into a sodium silicate dispersant solution, a series of ultraflotation tests was made with samples of the 80% brightness white Georgia kaolin clay crude using sodium. silicate dispersant solution with and without addition of alum to form a hydrosol. In these tests the sodium silicate dosage was varied over a relatively wide poundage (3 to 8 pounds 0 brand sodium silicate per ton of clay). Also, tests were made with the pH of the clay dispersion increased by incorporation of sodium carbonate or ammonium carbonate to the clay slip before addition of the sodium silicate solution or hydrosol formed by addition of a metal salt to a 5% 0 brand sodium silicate solution. The results are summarized in Tables I, II and III.

TABLE I.EFFECT OF ADDING ALUM TO SODIUM SILICATE DISPERSANT SOLUTION Slip Treatment, lbs/ton Properties of MD-l 0" Brand 1 Unbl. Br., T102, wt. FeaOs, wt. Na CO; (NH4) 1003 Sodium Alum pH 1 percent percent percent 7 Silicate 1 Wet basis (including water present in the commercial solution). 3 pH of dispersed Slip before addition of flotation reagents.

8 Unbleached brightness.

TABLE II.EFFECT OF PRESENCE OF ALUM ON QUANTITY OF SODIUM SILICATE EMPLOYED IN DISPERSING CLAY 1 Wet basis.

TABLE IIL-EFFECT OF VARIATION OF QUAN- TITY OF ALUM AT CONSTANT QUANTITY OF SODIUM SILICATE Slip Treatment, lbs/ton Unbleached Brightness AF 9 Brand oi MD-l, (NH4) 10 0; Sodium Alum Percent Silicate 1 Wet basis.

2 Difierence between unbleached brightness of beneficiated product and head.

Data in Table I show that while the results were generally better when the pH of the clay dispersion was in- :reased by addition of sodium carbonate or ammonium :arbonate, in all instances the addition of alum to the sodium silicate dispersant solution to form a hydrosol resulted in brighter clay products having lower TiO contents than when the sodium silicate was employed without alum addition. Thus, using a mixture of alum with sodium silicate to form a hydrosol, the flotation beneficiated clay had an excellent unbleached brightness of 87.8% and contained only 0.18% TiO versus an unbleached brightness of only 84.9% with a relatively high T102 content of 0.26%.

Data in Table II show that the use of alum with sodium silicate obviated the normal tendency of the sodium silicate to decrease the brightness of the clay product very significantly when the silicate poundage was inthe white clay dispersion and flotation procedures described above were carried out with addition of alum at various points of the process. In all cases, 25 ml. of a 5% ammonium carbonate solution was added to 1250 grams of the Washington County crude previously blunged in water to 30% solids and the dispersant composition was then added to the carbonate-treated slip and conditioned for 1 minute.

In one experimental test, representing a preferred sequence of processing, the alum was incorporated by mixing 100 ml. of 5% 0 brand sodium silicate solution (5 parts by weight 0 brand to 100 parts by weight water) with 25 ml. of 1% alum solution for 30 minutes, adding the resulting stable hydrosol to the clay pulp and agitating without aeration for 30 minutes. Another test, also representing a preferred processing sequence, was carried out in the same way but the conditioning time was minutes. In still another test, the sodium silicate and alum were added separately. In that case after addition of ammonium carbonate solution to the 30% solids clay pulp and one minute conditioning, 100 ml. of the 5% solution of 0 brand sodium silicate was added and the pulp conditioned for one minute. Twenty-five ml. of 1% aqueous alum solution was then added and conditioned for 29 minutes. In other tests, alum was added either after the calcite carrier and before addition of emulsified fatty acid reagent or after the emulsified fatty acid reagent. In all cases the pulp was degritted over a 325 mesh screen after the dispersant treatment and before being reagentized for ultrafiotation concentration with calcite carrier and emulsified fatty acid reagent. The pH of the pulps were about 8.1 after dispersion and degritting. After addition of the emulsified flotation reagents, the pH of the pulps were 8.5i0.l.

Analyses were made on MDl and on composites of MD-l and MD-Z, 3, 4 (indicated as MD-l-4), with the results summarized in Table IV. The data in this table show that the titania flotation was markedly more eflicient when the alum was mixed with the sodium silicate to form a hydrosol before the clay was dispersed with the sodium silicate than when the same quantity of alum was added after the clay had been dispersed with the sodium silicate. In all cases, flotation of titania was improved somewhat by incorporation of the alum. The data therefore demonstrate the beneficial eflect of alum on the flotation of titania from a sodium silicate dispersed clay pulp and the desirability of incorporating the alum with the sodium silicate to form a hydrosol before the sodium silicate is employed to disperse the clay.

TABLE IV.EFFECT ON FLOTATION OF METHOD OF ALUM ADDITION TO CLAY PULP Slip Treatment, lbs/ton MD-l MD-1-4 0 B and Method of Alum Addition P t P t P t P t ercen ercen ercen ercen (NHi) 2003 fl ll A12(SO4)a.18HzO Wt. T103 Wt. TiOa Silicate 1 2.0 8.0 0. 4 Alum and sodium silicate added 47. 9 0.15 91. 0 0.17 as mixture (Hydrosolfl 2.0 8.0 0. 4 Alum and sodium silicate added 41. 7 0.15 87. 7 0. 16 as mixture (Hydrosol). 2.0 8. 0 0. 4 Sodium silicate added first 48. 5 0. 19 91. 8 0. 20

followed by alum after one minute. 2.0 8.0 0. 4 Alum added after calcite flota- 51. 4 0.20 92. 2 0. 20

tion reagent. 2.0 8.0 0. 4 Alum added after emulsified 44. 4 0.19 89. 4 0.20

fatty acid flotation reagent. 2.0 8.0 Control, no alum added 51. 3 0.23 91.8 0.22

1 Wet basis. 2 Conditioned for 30 minutes. 3 Conditioned for 60 minutes.

creased with this particular clay crude to values in excess of about 5 pounds 0 brand per ton of clay.

Data in Table III show the desirable effect on clay brightness of incorporating alum into the dispersant solution in amounts of 0.24 to 1.6 pounds per ton of clay.

Example 11 To illustrate the desirability of adding polyvalent metal Example III This example illustrates the use, also in accordance with this invention, of a manganese salt additive to a sodium silicate dispersant in the flotation beneficiation of the Washington County clay.

The previously described white clay dispersion pro cedure was modified as follows: ammonium carbonate as salt as a mixture with the sodium silicate dispersant, a 5% aqueous solution was added to a 30% solids aqueous pul of the clay and conditioned for twominutes. The ammonium carbonate was used in amount of 2 pounds (NH CO per ton of crude. In accordance with this invention, a stable hydrosol obtained by thoroughly mixing 50 ml. of a 1% aqueous solution of MnSO .H O with 100 ml. of a 5% aqueous solution of brand sodium silicate was added to the clay pulp at room temperature. The pulp then contained sodium silicate in amount of 8.0 pounds of 0 brand per ton of crude clay and MnSO .H O in amount of 0.8 pound per ton of the crude clay. After addition of the hydrosol, the clay pulp was conditioned for 30 minutes. The pulp was immediately degritted through a 325 mesh screen and subjected to the ultraflotation procedure previously described. The combined machine discharge products (MD14) were fractionated by sedimentation to produce a fine size fraction. This fine size fraction was flocced with sulfuric acid to a pH of 1.5 and thickened by sedimentation. A sample was obtained for brightness. The remainder was bleached with zinc hydrosulfite and analyzed for brightness.

The fine size fraction of MD-14 had an excellent brightness of 88.9% before bleaching, representing an increase of 8.1% in brightness from the crude. Hydrosulfite bleaching increased the brightness to 90.9%.

Example IV This example illustrates the use of a magnesium salt in forming the hydrosol dispersant reagent.

The procedure of Example III was repeated with another sample of the Washington County crude, except that in dispersing the clay a 1% aqueous solution of MgSO -7H 0 was added with agitation to the solution of O brand sodium silicate and the resulting hydrosol was added to the ammonium carbonate treated clay pulp and conditioned for 30 minutes. The sodium silicate was used in amount of 8.0 pounds 0 brand per ton of crude and MgSO4-7H O was used in amount of 0.5 pound per ton of crude. The previously described ultraflotation reagents and flotation conditions were used. The combined machine discharge products of the ultraflotation test (tMD14) were flocced and bleached. The product had a brightness of 87.4%, as compared to a brightness of only 86.0% for a similar test in which no polyvalent salt was added to the sodium silicate dispersant. The bleached MD-14 contained 0.19% Ti0 as compared to the 0.22% TiO content of the bleached MD-1-4 of the similar test without addition of metal salt to the sodium silicate dispersant solution.

A comparison of the results of this example with results of Examples I and II indicates that manganese and aluminum salts were considerably more effective than the magnesium salt when incorporated with the sodium silicate clay dispersant to form a hydrosol.

Example V The following example illustrates the benefits of incorporating a polyvalent metal salt in a sodium silicate dispersant in the flotation beneficiation of a gray kaolin clay from Georgia.

The same procedures employed in dispersing and floating the Washington County clay were used with the gray kaolin clay with the following exceptions. Sodium carbonate was incorporated into the clay pulp as a 5% aqueous solution in amount of 8.0 pounds per ton of clay crude and conditioned for 30 minutes before addition of the solution of sodium silicate (or hydrosol). Addition of the sodium carbonate increased the pH of the clay pulp to about 5.8. Sodium silicate was used to disperse the sodium carbonate treated pulp in amount of 5.0 pounds 0 bran-d per ton of clay. Also, with the gray clay, the dispersed clay pulp was fractionated before ultraflotation by means of a Tollhurst centrifuge and a fine fraction recovered as an aqueous pulp. The quantity of flotation reagents used with the pulp of the Reagent: Pounds/ton Calcite (minus 325 mesh) 600 (NH4)2SO4 NH OH I- 3.0 Tall oil acids 6.2 Calcium Petronate Aqueous emulslon 6.2 Eureka M oil 8.0

Conditioning time was 30 cedure was the same used with the white clay.

A further variation was that after the flotation beneficiated gray clay was flocced with sulfuric acid, it was oxidized by treatment with a solution of potassium per manganate before being bleached with zinc hydrosulfite. The permanganate treatment was carried out by adding a 1% aqueous solution of potassium permanganate to the machine discharge product in amount of 5 pounds KMnO per ton of clay and agitating for 60 minutes. In some tests, the permanganate treatment and zinc hydrosulfite treatments were carried out at about F. The use of a permanganate treatment before reducing bleach in the brightening of clay is disclosed and claimed in a copending US. patent application, Ser. No. 330,634, filed Dec. 16, 1963, by James B. Duke, which is a continuation-in-part of Ser. No. 236,685, filed Nov. 9, 1962, now abandoned.

A series of tests was run with various quantities and types of metal salts incorporated into a 5% aqueous solution of O brand sodium silicate before the dispersant solution was added to a pulp of the gray clay and the pulp subjected to froth flotation and bleaching. A control was run without addition of metal salt to the sodium silicate dispersant solution.

When no metal salt was added in the control experiment, the brightness of the flotation beneficiated, bleached gray kaolin clay was 90.6%, as compared to a brightness of only 79.8% for a similar size fraction of the crude. In one test, a 1% alum solution was mixed into the 5% sodium silicate solution to form a hydrosol and the hydrosol was conditioned with the gray clay pulp for 20 minutes. This addition corresponded to the use of 5.0 pounds per ton of 0 brand sodium silicate and 0.4 pound per ton of Al (SO -18H O. The Ti0 content of the bleached beneficiated clay in this test was 0.28%, which was appreciably less than the 0.32% TiO content of the bleached beneficiated clay in the control experiment. Using the hydrosol formed by adding alum to the sodium silicate dispersant solution, product brightness was 91.2%, a value comparable to that of the best imported kaolin clays and the best beneficiated domestic white kaolin clays. In another test, a 1% solution of MnSO -H O was incorporated into the dilute sodium silicate solution and the resulting hydrosol employed in amount to provide 0.4 pound MnSO -H O per ton of clay and 5.0 pounds of 0 brand sodium silicate per ton of clay. Clay brightness after bleaching and flotation was 91.5% when this hydrosol was used to disperse the clay before flotation; These results show, therefore, that the gray clay could be beneficiated to a greater extent when a pulp of the clay was dispersed with a hydrosol before flotation and bleaching.

I claim:

1. In a process for brightening discolored clay which comprises pulping the clay with water, dispersing the pulp by addition of sodium silicate thereto, and subjecting the dispersed pulp to froth flotation in the presence of an anionic flotation reagent in an alkaline flotation circuit, the improvement which comprises incorporating a water-soluble polyvalent metal salt into a dilute aqueous solution of the sodium silicate clay dispersant before minutes and the flotation prohe sodium silicate is incorporated into the clay pulp, the mount of polyvalent salt being suflicient to form a stable iydrosol with said dilute sodium silicate.

2. The process of claim 1 wherein said polyvalent salt s a salt of a metal having amphoteric properties.

3. The process of claim .2 wherein said polyvalent salt 5 an aluminum salt.

4. The process of claim 2 wherein said polyvalent salt s a manganese salt.

5. The process of claim 1 wherein the said polyvalent salt is a magnesium salt.

6. The process of claim bonate is incorporated into dispersed by addition of the solution of sodium having incorporated therein said metal salt.

7. The process of claim 1 wherein said clay is sedimentary kaolin clay.

8. The process of claim 1 wherein said clay is sedimentary gray kaolin clay.

9. The process of claim 1 in which said sodium silicate is used in amount ranging from about 0.5 to about 4.0

1 wherein an alkaline carsaid pulp before said pulp is silicate pounds anhydrous sodium silicate per ton of said clay and said metal salt is used in amount ranging from about 0.1 to about 2.0 pounds per ton of said clay.

10. In a process for the froth flotation of kaolin clay containing finely-divided titaniferous mineral as a colored impurity wherein a pulp of the clay is dispersed with sodium silicate and the dispersed pulp is subjected to froth flotation in an alkaline circuit with added minus 325 mesh calcite and a higher fatty acid selective to both said titaniferous mineral and said auxiliary mineral, producing a froth which is a concentrate of said titaniferous mineral intimately associated with said auxiliary mineral and a machine discharge product which is a clay of reduced titania content, the improvement which consists in incorporating into a dilute aqueous solution of the sodium silicate dispersant before a pulp of the clay is dispersed with said sodium silicate, a small amount, less than 2 pounds per ton of said clay, of a water-soluble polyvalent metal salt said amount being sufiicient to form a stable hydrosol with said sodium silicate.

11. In a process for the froth flotation of sedimentary kaolin clay containing colored impurities wherein a dispersed aqueous pulp of the clay is subjected to froth flotation in an alkaline circuit in the presence of added minus 325 mesh calcite and tall oil, the improvement which consists in preparing the dispersed aqueous pulp of clay by adding a material selected from the group consisting of ammonium carbonate and sodium carbonate to an aqueous pulp of the discolored clay, and dispersing the resulting pulp by adding an aqueous dispersion medium obtained by mixing an aqueous solution of a mineral acid salt of a polyvalent metal having amphoteric properties with a dilute aqueous solution of sodium silicate, said salt being employed in small amount as compared to the amount of said sodium silicate and being sufiicient to form a stable hydrosol therewith.

12. The process of claim 11 in which said metal salt is an aluminum salt.

13. The process of claim 12 in which said metal salt is aluminum sulfate.

14. The process of claim 11 in which said salt is a manganous salt.

15. The process of claim 14 in which said salt is manganese sulfate.

16. A process for separating colored titaniferous matter from Georgia kaolin clay which comprises:

forming an aqueous pulp of said clay,

incorporating an alkaline carbonate into said pulp in amount within the range of from about 2 to about 10 pounds per ton of said clay,

dispersing said pulp by adding a stable hydrosol formed by mixing a dilute aqueous solution of sodium silicate having a Na O to SiO weight ratio within the range of from 1:1.60 to'l:3.75 with a small amount of a water-soluble salt of a polyvalent metal having amphoteric properties, said hydrosol being used in amount to provide from about 0.5 to about 4.0 pounds of anhydrous sodium silicate and from about 0.1 to about 2.0 pounds of said salt per ton of said clay,

and subjecting the dispersed pulp to froth flotation in the presence of flotation reagents selective to the flotation of titaniferous matter in the clay, producing a froth which is a concentrate of titaniferous matter originally associated with the clay, and a machine discharge product which is a concentrate of clay of reduced titania content.

17. The process of claim 16 in which said salt is an aluminum salt.

18. The process of claim 17 in which said salt is a manganous salt.

19. A process for which comprises:

forming an aqueous pulp of said clay,

incorporating sodium carbonate into said pulp,

dispersing said pulp by adding a dilute aqueous solution of sodium silicate to which has been added a small amount of a water-soluble salt of an amphoteric metal, the amount of said salt being suflicient to form a stable hydrosol with said sodium silicate solution,

subjecting said dispersed pulp to froth flotation in the presence of reagents selective to colored impurities in said clay, producing a froth which is a concentrate of colored impurities originally in the clay and a machine discharge product which is a concentrate of clay of increased purity,

and chemically bleaching the machine discharge product.

20. The process of claim 19 wherein said salt is a manganese salt that is used in amount ranging from 0.4 to 0.8 pound per ton of said clay and said sodium silicate is used in amount ranging from 0.5 to about 4.0 pounds brightening gray Georgia kaolin clay of anhydrous sodium silicate per ton of said clay.

References Cited UNITED STATES PATENTS 2,408,656 10/1946 Kirk 252-313 2,569,680 10/1951 Leek 209-5 X 2,657,183 10/1953 Bechtold 252--313 2,794,783 6/1957 Podschus 252-313 2,894,628 7/1959 Duke 209-166 2,990,958 7/1961 Greene 209-466 3,072,255 1/1963 Greene 209166 HARRY B. THORNTON, Primary Examiner.

FRANK W. LUTTER, Examiner.

R. HALPER, Assistant Examiner.

Claims

1. IN A PROCESS FOR BRIGHTENING DISCOLORED CLAY WHICH COMPRISES PULPING THE CLAY WITH WATER, DISPERSING THE PULP BY ADDITION OF SODIUM SILICATE THERETON, AND SUBJECTING THE DISPERSED PULP TO FROTH FLOTATION IN THE PRESENCE OF AN ANIONIC FLOTATION REAGENT IN AN ALKALINE FLOTATION CIRCUIT, THE IMPROVEMENT WHICH COMPRISES INCORPORATING A WATER-SOLUBLE POLYVALENT METAL SALT INTO A DILUTE AQUEOUS SOLUTION OF THE SODIUM SILICATE CLAY DISPERSANT BEFORE THE SODIUM SILICATE IS INCORPORATED INTO THE CLAY PULP, THE AMOUNT OF POLYVALENT SALT BEING SUFFICIENT TO FORM A STABLE HYDROSOL WITH SAID DILUTE SODIUM SILICATE.