Document LKNwpM5y9wYM4eM922ERrwnGw

United States Patent .im Baak et al. [li] 3,965,241 [45] June 22, 1976 [54] LEACHING TREMOLITEIMPURITY FROM TALC [75] Inventors: N. Tryggve E. A. Baak, Marina Del Rey; Dwight L. Harris, Westlake Village, both of Calif. [73] Assignee: Cyprus Mines Corporation,West Los Angeles, Calif. [22] Filed: June 16, 1975 [21] Appi. No.: 587,175 [52] U.S. Cl.................................. 423/155; 106/306; 423/331 [51] Int.C l.2......................................... .. C01B 33/24 [58] Field of Search.................... 423/155, 167, 331; 106/306; 241/4; 252/450 [56] 1,598,256 2,576,653 References Cited UNITED STATES PATENTS 8/1926 Prutzman et al........................ 252/450 11/1951 Thomas........................ . 252/450 3,116,974 1/1964 3,305,302 2/1967 3,533,821 - 10/1970 3,806,043 4/1974 3,837,582 9/1974 3,932,194 1/1976 3,939,249 2/1976 Nikolai................................ 423/163 Heuer................................... 423/163 Lundquist............................ 106/306 Roe........................................... 241/4 Baak......................................... 241/4 Lamar................................... 106/306 Huege............................. 423/331 X OTHER PUBLICATIONS Abido, "Chemical Abstracts," vol. 78, 1973, 81311k. Primary Examiner--Edward J. Meros Attorney, Agent, or Firm--Nilsson, Robbins, Dalgarn & Berliner [57] ABSTRACT A process for removing tremolite impurity, from talc by subjecting finely ground talc to a combination of steps including froth flotation and pressure leaching with a strong acid at an elevated temperature. The re covered talc is characterized by a tremolite content of less than 1.0 percent by weight. 15 Claims, 1 Drawing Figure PLAIN TIFFS E X H IB IT CAM -243 U.S. Patent June 22, 1976 3,965,241 L & A C H T/AA&. M/A/07TSS p e & c e w r 7~e.EA\ac/T& /a/ ceacz-zea ta c-c, 3,965,241 12 certain physical properties of talc, as described, none LEACHING TREMOLITE IMPURITY FROM TALC of the foregoing references report a decrease in tremo BACKGROUND OF THE INVENTION lite, nor are they in fact particularly concerned with tremolite-containing talc. 1. Field of the Invention 5 This invention relates to the production of a high SUMMARY OF THE INVENTION purity talc from ore including a high proportion of It is a primary object of the present invention to undesirable impurities, such as asbestos in the form of provide an economical process for the production of a tremolite. high purity talc from talc ore containing tremolite as an 2. Description of the Prior Art 10 excessive impurity, i.e., greater than 1.0 percent tremo High grade talc in the form of powder has found wide lite. acceptance, for example as a grain coating agent, as a The present invention is particularly suitable for the filler in paper, plastic and rubber, and in the cosmetics production of high quality talc from talc ores such, for industry for application to human skin. For such uses, it example, as are found in the region of Gouverneur, is desirable to have the talc as free as possible of any 15 N.Y., and in certain regions of California. By virtue of irritating particles. In several instances, the use of talc the present invention, a high quality talc product may as talcum-powder or as a grain coating agent has been be economically produced from such ores. pointed out as a health hazard when ingested or in Generally stated, this invention provides a process haled; however, it has been hypothesized that the impu for preparing a high quality talc ore containing tremo rity tremolite in the talc is the harmful agent. Tremolite 20 lite as an excessive impurity by finely grinding the talc is known as a potential occupational hazard. Tremolite, ore and subjecting the ground talc to a combination of as well as other forms of asbestos, are described by the steps including froth flotation and pressure leaching American Conference of Governmental Industrial Hy with a strong acid at an elevated temperature. Specifi gienists as occupational carcinogens. Accordingly, a cally, the talc is subjected to a temperature of at least process for removing tremolite from talc would be 25 110C and a pressure of at least 1.5 kg/cm2 for a time desirable. Certain talc ores, such as, for example, those sufficient to reduce the amount of tremolite to less than found in the region of Gouverneur, New York and 1.0 weight percent of the talc, generally requiring at certain California talc ores, contain a substantial pro least 1 hour of pressure leaching. portion of tremolite. Such ores would therefore benefit While impurities other than tremolite, such as car from an effective process for removing tremolite from 30 bonates, can be removed effectively by acid-leaching talc. talc in dilute or concentrated acids at temperatures Talc is hydrated magnesium silicate, Mg3[Si4O10] from room temperature (for calcite) up to 80C (for (OH)2, a layer type lattice with relatively well satisfied magnesite), the decomposition of tremolite in mineral valence bonds within the layer lattice and is relatively acid does not occur appreciably until temperatures inert in many environments. Its platy, inert type of 35 above 100C and pressures above atmospheric are structure, has made it a safe, useful powder for dusting obtained. The rate of decomposition is dependant upon or coating surfaces. Tremolite, on the other hand, is a temperature and increases with temperature above the fibrous or bladed type of amphibole, having the for normal boiling point. The talc mineral is relatively mula Ca2Mg5(Sis0 22) (OH)2, has less saturation of the unaffected in the range of temperature and pressure surface bond, is more reactive, and has been a concern 40 hereinafter described. for health reasons, as pointed out above. An essential feature of the present invention which is Many physical processes for separating talc from critical to the successful separation of the tremolite tremolite and other undesirable impurities, such as from the talc and the consequent production of a cos dolomite, calcite, quartz, chlorite, mica, etc. have been metic grade product, is the combination of froth flota tried and have been effective, albeit in many cases costs 45 tion and pressure-acid leaching operations. In this re of processing the ore have been high. Selective mining gard, it has been found that froth flotation alone will and/or hand sorting of lumps of ore which can be dis not afford a satisfactory separation of the tremolite tinguished visually can be done and aids to visual sort impurities from the talc, nor will pressure acid leaching ing, such as fluorescent effects, have also been used. alone result in a satisfactory product. The froth flota See, e.g., U.S. Pat. No. 3,837,582 to Baak, On the other 50 tion operation may be conducted before or after pres hand, when the talc and the tremolite in the ores are sure acid leaching of the ground talc or may be con very finely disseminated, physical separation processes ducted both before and after the leaching step. Each are less effective and satisfactory amounts of tremolite froth flotation may be conducted as a single step opera are not removed. tion or, advantageously, the concentrate can be re It is known that leaching of talc with a strong acid, 55 slurred for one or more successive operations. such as a mineral acid, can improve certain of its physi The invention will be better understood when details cal properties such as its brightness, wettability and thereof are considered in conjunction with the ap surface area. See, e.g., U.S. Pat. No. 2,576,653 to pended drawing. Thomas which describes mineral acid treatment of a slurry of finely ground particles of a clay, such as talc, 60 BRIEF DESCRIPTION OF THE DRAWING under broadly defined conditions which can include The FIGURE is a plot of tremolite content in talc open vessel heating, refluxing, or heating in a closed versus pressure acid leach time for various tempera vessel under steam pressure. Other patents which may tures in accordance with the present process. be of some interest in this regard are U.S. Pat. No. 3,533,821 to Lundquist, U.S. Pat No. 3,271,323 to 65 DETAILED DESCRIPTION Whittmore, U.S. Pat. No. 2,574,895 to Stecker, U.S. Initially, the talc ore is crushed or ground to a parti Pat. Nos. 1,598,255 and 1,598,256, both to Prutzman cle size of minus 20 Tyler mesh, and preferably below et al, and U.S. Pat. No. 89,438 to Sell. While benefiting minus 100 mesh, or finer. For cosmetic purposes, the 34 ore should be ground to a particle size of 100 percent other hand, if such minor decreases in surface area are minus 100 mesh and 98 percent minus 200 mesh. not of a major consideration, then sulfuric acid can be Thereafter, the finely ground talc can be subjected used. directly to a pressure acid leaching process followed by Generally, a moderate acid concentration is used, a froth flotation operation in one or more steps with the 5 between that which is considered a dilute solution and concentrate washed, filtered and dried to yield the a strong solution. For example, with hydrochloric acid, desired product. Alternatively, the finely ground talc usually supplied commercially in the range of 36-38 can be initially subjected to a froth flotation operation weight percent, an optimum solution would be ob in one or more steps with the concentrate subsequently tained by diluting the acid with about an equal amount combined with a strong acid and pressure leach. Since 10 of water to obtain about 18-20 weight percent acid. carbonates can be decreased by flotation prior to Generally, at least 5 weight percent acid should be used leaching, thereby minimizing acid requirements, initial and a concentration as high as 40 weight percent, or flotation is preferred. Thereafter, the product can be higher, can be used. directly washed, filtered and dried, or, if a product of Froth flotation techniques for talc are well known, extreme purity is desired, the leached concentrate can 15 but in the present invention a preferred technique is to be again subjected to a froth flotation operation in one use a relatively dilute slurry, e.g., having a solids con or more steps. tent of less than about 15 percent by weight, most The pressure leach operation, whether directly on preferably 10 percent or less by weight of the slurry, as ground ore or on a flotation concentrate, is advanta described in Baak U.S. Pat. No. 3,837,582. Addition geously conducted in a closed vessel at steam pressure 20 ally, as known, a small amount of a water-soluble at the particular temperature selected. Such a vessel frother may be added, up to about 0.2 pounds of can be a Teflon-lined bomb of a size sufficient to hold frother per ton of solids in the slurry, to improve sepa the quantity of materials utilized. Alternatively, one ration of the talc from gangue material and to other could use any method for subjecting the slurry of talc wise generally improve the froth flotation operation. and leaching acid to a suitable pressure. 25 Any well known commercially available frother may be In particular, the finely ground talc is slurried with a used and particularly useful frothers are methyl isobu moderate aqueous solution of a strong acid, placed in a tyl carbinol or isopropanol. Where isopropanol is used, closable vessel, such as a bomb, whereupon the vessel it is generally desirable to add a small amount of so is closed, heated to a temperature above 100C, prefer dium silicate to the slurry to further improve separation ably to a temperature of at least 110C. Although an 30 of talc. The slurry is then aerated and a first concen upper temperature limitation is not as critical, there is trate withdrawn. It has been found desirable to conduct no particular advantage in heating above 250C and by the froth flotation in a series of steps whereby the con operating within that range, one can avoid excessive centrate from a prior step is reslurried and refloated, decomposition of the talc. When using a closed vessel, generally without addition of any reagents. A series of and steam pressures generated thereby, the resultant 35 three flotation steps can be used to insure virtually pressures would be from 1.5 kg/cm2to 40 kg/cm2. Pres complete removal of the tremolite and residues al sures in excess of the foregoing can be applied from an though a flotation operation incorporating two steps is external source, but are generally not required. generally sufficient to provide a talc product in which The pressure-acid leaching step is conducted for a the tremolite content is less than 1%. The froths may be time sufficient to reduce the amount of tremolite to less 40 processed in a conventional manner by thickening, than 1.0 percent of the weight of the talc, as deter filtration, washing and drying. mined for a particular talc sample by analysis. Of An additional advantage of the process of the inven course, higher temperatures and pressures generally tion as described above is that fibrous magnesium sili require a shorter reaction time, but usually at least 1 cates such as serpentine are also substantially reduced hour. The pressure-acid leaching step can be con 45 in content and for the most part removed with the ducted for extended periods of time if it is desired to tremolite. Furthermore, as an economic advantage, reduce the level of tremolite to very small amounts, one can omit entirely the usual chlorine treatment, but, generally, heating for more than 5 days does not since the acid leach will remove all micro-organisms. result in significant incremental decreases in tremolite In order that those skilled in the art may better un content. 50 derstand how the present invention may be practiced, One can use any strong acid which results in a soluble the following examples are given by way of illustration reaction product, but which will not unduly attack the and without limitation. talc. In this regard, hydrofluoric acid would not be suitable as it will attack any silicate. Phosphoric acid EXAMPLE I can be used with talc containing small amounts of cal 55 A California talc ore containing about 15 percent cium carbonate, but with large amounts of calcium tremolite and a small amount, several percent, of car carbonate undesirable calcium by-products are formed bonates, is pulverized in a grinding mill to 100 percent which may be entrapped with the talc. While such minus 200 mesh. The sample is separately subjected to strong organic acids such as perchloric acid and chloro- a froth flotation operation in which the talc ore is slur acetic acid can be used, such are generally not econom 60 ried with deionized water to make up a slurry of about ical for commercial processes. Accordingly, it is pre 10 percent solids to which a drop of frother is added. ferred to use a strong mineral acid such as hydrochloric The slurry is aerated and a concentrate obtained which acid, nitric acid and sulfuric acid, most preferably ei is then washed, filtered and dried. Separate samples of ther hydrochloric acid or nitric acid. The use of sulfuric the concentrate, each weighing 3 grams, are placed in acid may result in a slow decrease in surface area over 65 Teflon-lined bombs with 10 milliliters of 18 weight a long period of time, e.g. a year or more, and it may be percent hydrochloric acid. The bombs are closed and hypothesized that carbon dioxide is entrapped in the the slurries are heated in an electric oven at different surface of the talc leached with sulfuric acid. On the temperatures and for different periods of time for vari 3,965,241 56 ous samples, from 110up to 210C for from 60 minutes Sample number 2 shows the best elimination of trem to 1400 minutes. The pressures at which the samples olite by pressure-acid leaching for 72 hours at 130C. are heated can be estimated from steam tables for The present invention thus affords an improved pro water and are shown in the following table: cess for economically producing high grade talc, such 5 for example as may be used in cosmetic applications, Temperature I10C 120C 130C 150C 180C 2!0C Absolute pressure, kg/cm2 1.5 2.0 2.7 4.8 10.2 19.4 from talc ore of the type mined in the Gouvemeur, N.Y. region, or in certain regions of California, which type is characterized by relatively high contents of tremolite. The normal cosmetic grind of talc produced 10 in accordance with the invention can be used as a dry lubricant of white color in place of graphite or molyb denum disulfide, both of which have adverse colors. In addition, talc produced by the process of the invention The tremolite content is determined on the washed may also be used in the preparation of paint, paper, residue from each test sample from X-ray diffraction 15 textiles, ceramic compositions, rubber, plastics, and patterns and X-ray spectrometry data. various other applications by means well known to Referring to the FIGURE, the tremolite content for those skilled in the art. various samples run at various temperatures is plotted It should be understood that while the present inven with the analyzed amount of tremolite on the abscissa versus the pressure-acid leach time in minutes on the 20 tion has been described in considerable detail with respect to certain specific embodiments thereof, it is ordinate. The data shows that tremolite is effectively not to be considered limited to those embodiments, but removed to a low level for each sample. Thus, for sam may be used in other ways without departure from the ples treated at 150C, a tremolite content of substan spirit of the invention or the scope of the appended tially less than 1.0 percent is obtained after 500 min utes. For a sample treated at 130C, a tremolite content 25 claims. What is claimed is: of less than 0.3 percent is obtained after 1000 minutes 1. A process for the preparation of high purity talc of treatment. In each case, the talc content is found to from talc ore containing tremolite as an impurity, be only slightly affected as confirmed by residue recov which comprises: eries of 83 percent and higher. EXAMPLE II 30 crushing said talc ore to provide finely ground talc of a particle size of minus 20 mesh; combining said finely ground talc with a strong acid; A New York talc ore is ground to a fine particle size leaching said talc by subjecting said combination of and then screened through a 200 mesh screen. The talc and acid to a temperature of at least 110C at oversized materials are repulverized and rescreened 35 repeatedly to secure 100 percent minus 200 mesh ma a pressure of at least 1.5 kg/cm2 for a time suffi cient to reduce the amount of tremolite in said talc terials as a flotation feed. A flotation pulp is prepared to less than 1.0 weight percent; by slurrying the talc ore in deionized water to make up prior or subsequent to said leaching step, forming a a slurry of 10% solids. To assure complete wetting, the dilute aqueous slurry of said talc and subjecting pulp is mixed at a high speed for at least 30 minutes. 40 said slurry to at least one froth flotation; and Flotation consists of a 2 stage operation, i.e., rougher recovering a high purity talc. flotation and a cleaner flotation. Methyl isobutyl carbi 2. The process of claim 1 in which said talc is crushed nol is added into the pulp just prior to the pumping of to provide a particle size of 100 percent minus 100 the pulp into the flotation cell at about 0.15 pounds per mesh and 98 percent minus 200 mesh. ton of solids in the slurry. The feed rate of the pulp to 45 3. The process of claim 1 in which said strong acid is the rougher cell is about 45 pounds per hour. Following a strong mineral acid. aeration, the concentrate is collected, re-slurried with 4. The process of claim 3 in which said strong mineral deionized water to make a dilute pulp of about 10 acid is hydrochloric acid. percent solids and then is froth floated in the cleaner 5. The process of claim 1 in which said temperature cell. The concentrate from the cleaner cell is then 50 is in the range of 110-250C, said pressure is in a range washed, filtered and dried and is found to contain of 1.5-40 kg/cm2 and said leaching step is conducted about 1.5 weight percent tremolite. for at least 1 hour. Separate samples of the flotation concentrate are 6. A process for the preparation of a high purity talc treated by a pressure-acid leaching bomb technique as from ore containing tremolite as an impurity, which in Example I under temperatures and pressure which 55 comprises: vary from 110to 160C for time varying from 390 crushing said talc ore to provide a finely ground talc minutes to 4320 minutes as shown in the following of a particle size of minus 20 mesh; table. The amounts of tremolite remaining in the forming a dilute aqueous slurry of said crushed talc; treated samples are estimated by X-ray diffraction and subjecting said slurry to at least one froth flotation; are shown in the table. 60 removing the froth formed during the final froth flotation step to obtain a talc concentrate; Sample Time, min. Temp., C % Tremolite in residue combining said talc concentrate obtained from said final froth flotation with a strong acid; I 1110 2 4320 3 390 4 480 110 130 160 160 0.75 leaching said talc by subjecting said combination of 0.1 0.3 65 talc concentrate and acid to a temperature of at 0.2 least 110C at a temperature of at least 1.5 kg/cm2 for a time sufficient to reduce the amount of tremo lite in said talc to less than 1.0 weight percent; and 3,965,241 78 washing said leached talc and drying to recover a a pressure of at least 1.5 kg/cm2 for a time suffi high purity talc. cient to reduce the amount of tremolite in said talc 7. The process of claim 6 in which said talc is crushed to less than 1.0 weight percent; to provide a particle size of 100 percent minus 100 subsequent to said leaching step, forming a dilute mesh and 98 percent minus 200 mesh. 5 aqueous slurry of said leached talc; 8. The process of claim 6 in which said strong acid is subjecting said slurry to at least one froth flotation; a strong mineral acid. removing the froth formed during the final froth 9. The process of claim 8 in which said strong mineral flotation step; and acid is hydrochloric acid. 10. The process of claim 6 in which said temperature 10 recovering a high purity talc from said floated froth. 12. The process of claim 11 in which said talc is is in the range of 110-250C, said pressure is in the crushed to provide a particle size of 100 percent minus range of 1.5-40 kg/cm2 and said leaching step is con 100 mesh and 98 percent minus 200 mesh. ducted for at least 1 hour. 13. The process of claim 11 in which said strong acid 11. A process for the preparation of a high purity talc from talc ore containing tremolite as an impurity, 15 is a strong mineral acid. 14. The process of claim 13 in which said strong which comprises: mineral acid is hydrochloric acid. crushing said talc ore to provide finely ground talc of 15. The process of claim 11 in which said tempera a particle size of minus 20 mesh; ture is in the range of 110-250C, said pressure is in combining said finely ground talc with a strong acid; leaching said talc by subjecting said combination of 20 the range of 1.5-40 kg/cm2 and conducted for at least 1 hour. said leaching step is talc and acid to a temperature of at least 110C at ***** 25 30 35 40 45 50 55 60 65 UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. : 3,965,241 DATED INVENTOR(S) : June 22, 1976 n . Tryggve E. A. Baak and Dwight L. Harris It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below: Col. 1, line 7, insert -- talc-- before "ore". Col. 2, line 19, insert -- from talc-- before "ore". [SEAL] Attest: Signed and Sealed this Eleventh Day of January 1977 RUTH C. MASON Attesting Officer C. MARSHALL DANN Commissioner o f Patents and Trademarks