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United States Patent Office Patented Apr 3,244,476 United States Patent Office Patented Apr. 5, 1966 1. 2 3,244,476 . and water are driven of according to the following METHOD OF PRODUCING CRUDE SODAASH reaction: FROM CRUDE TRONA WITH SELECTIVE 2(NaCOs: NaHCO2HO)->3Na2CO3 +5H2O+CO LewisPULVERIZATION K. Smith, Covina, Calif., assignor,- . by mesne assign The conversion of the sodium bicarbonate to sodium car ments, to Intermountain Research & Development bonate by the removal of carbon dioxide and water from Corporation, Cheyenne, Wyo, a corporation of the crude trona produces porous crystals of soda ash Wyoming while the high calcining temperature sinters the shale and No Drawing. Filed Jan. 9, 1963, Ser. No. 250,225 other insoluble materials. The net result is that the soda - 5 Claims. (Cl. 23-63) ash (soluble) fraction is softened while the shale (in The invention relates to a method of processing trona O soluble) fraction remains at substantially the same hard to produce a crude calcined trona having a high Na2CO3 ness. Advantage is taken of this difference in hardness content and a low content of insoluble materials which of the soda ash and shale after calcining to effect separa is suitable for use as crude soda ash in many processes tion of the desired fraction from the undesired fraction. where refined soda ash is presently used. The process of the invention comprises calcining crude In Sweetwater County and adjacent counties in Wyo trona to change the sodium sesquicarbonate to porous ming there are large deposits of trona which consists es soda ash, beneficiating the calcined crude trona so that sentially of sodium sesquicarbonate the porous soda ash is broken to a smaller size than the (NaCO-NaHCO2HO) shale, screening the beneficiated crude trona so that the 20 shale and other insolubles are retained on the screen and contaminated with shale and small amounts of other im discarded and recovering the soda ash with a low in purities. The trona has the following approximate soluble content which passed through the screen. composition: The beneficiation can be effected in a number of ways, Constituent: , Percent such as by preferential crushing, air blasting or the like. Na2CO3 ------------------------------- 43.5 25 For purposes of illustration, preferential crushing with NaHCO3 ------------------------------ 36.11 multiple roll crushers is used. HO ------------------ mm - - --------... 13.14 The shale after calcination is approximately five times Na2SO4 ---------------------- 0.02 harder than the soda ash. The relative hardness was . NaCl ------------------------ - - determined by placing particles of calcined trona or sin- . 30 tered shale on the balance pan of a thirty pound ca Fe2O3 ----------- - - - - - - - - - - - - - - - - - - - --- 0.14 pacity spring balance and the particles were crushed by Organic matter ------------------------- 0.30 applying a slowly increasing pressure with a quarter inch Shale and other insolubles ---------------- 6.70 tool steel rod until the respective particles were broken. The Wyoming trona can be processed to produce a re or pulverized. The results are summarized in Table I. fined soda ash therefrom by a number of different proc 35 Visual observation of the crushed particles showed that esses such as described in the Pike Patent No. 2,639,217, the calcined trona was broken to a smaller size than the the Seaton et. al. Patent No. 2,770,524 or the Bauer et sintered shale. al. Patent No. 2,962,348. In general these processes in volve dissolving crude trona or crude calcined trona, TABLE I-RELATIVE HARDNESS OF CALCINED TRONA AND SHALE separating the insoluble material and other impurities from the solution, evaporating and cooling the solution 40 to crystallize therefrom sodium carbonate values in dif -6-8Mesh Calcined -4 +6 Mesh Calcined ferent forms and calcining the said crystals to produce Trona Trona soda ash. Due to their complicated nature these proc Trona Shale Trora Shale esses, are expensive and make the production of soda ash 45 Fraction, Fraction, Fraction, Fraction, from Wyoming trona expensive. Pounds 1 Pounds i Pounds Pounds 1 It is an object of this invention to provide a relatively 2.0 6.0 16.0 inexpensive process for the production of crude soda ash 2.6 >30 from crude trona which can be used in some of the proc 2.6 9, 5 . 5.0 esses which now utilize refined soda ash. 50 5.4 17.5 It is another object of the invention to increase the 2.5 4.5 3.0 17.5 percentage of soda ash and decrease the amount of in 2.0 1.5 soluble materials in crude soda ash made from calcined 3.6 19.0 crude "trona. 2.0 12.5 It is a further object of the invention to provide a 5 5 2 2.7 215.3 process in which the change in the relative hardness of the soluble and insoluble fractions of crude trona brought about by calcination of the crude trona is utilized to effect a better separation of the soluble and insoluble fractions of the trona, the soluble fraction consisting of 60 2 Sodium carbonate and the insoluble fraction consisting of undesired shale, silica, etc. The units of SE represent the force required to shatter the These and other objects and advantages of the inven particlesAverage. of calcined troma and slaale. - tion will become obvious from the following detailed de scription. The shale before calcination has an actual compres During the calcination of crude trona, carbon dioxide sive strength of about 3225 p.s. i. while the compressive 3,244,476 3. 4. strength of the crude trona before calcination is about crusher gave a high degree of recovery of alkali values 7500 p.s. i. The actual compressive strengths of the cal with a high degree of removal of the insoluble material. cined trona and shale were determined as being about 652 p.s. i. and about 2780 p.s. i., respectively, by an aver Example II age of eight tests. These figures again show that the calcined shale is about five times as hard as the calcined The example shows the effectiveness of the beneficiation trona. process on trona containing various amounts of insoluble The calcination of the crude trona can be effected at material. temperatures between 200 and 800° C. However, the The crude trona was calcined at about 400 C. and a temperature range of 400 to 800° C. is preferred as a large sample of -6+8 mesh calcined trona was obtained. large percentage of the organic impurities present in the 0. The sample was split into five equal parts and then vary ing quantities of -6+8 mesh calcined shale were added peratures.crude trona is removed by volatilization at these tem to four of the samples. Each sample was passed through The size of the mesh of the screening of the benefici the roll crusher four times and the crushed samples were ated particles will vary depending upon the size of the then screened into a --20 mesh fraction and a-20 mesh particles of crude trona after beneficiation, but it will fraction. The various fractions were analyzed as before usually vary between about 3 mesh and about 40 mesh, and the results are summarized in Table III. preferably about 20 mesh. The screen is preferably a ton-cap or tie-rod screen of the vibrating type when using TABLE III roll crushers for the beneficiation. 20 The multiple roll crushers can have a series of pairs A. B C D E of rolls or merely one pair of rolls. If only one pair Percent of insolubles in feed------- 3, 10 4.58 7.62 9.91 13, 61 of rolls is present, the calcined trona may have to be run Percent of total feed in.--20 mesh through the crusher more than once. At least one of fraction ------------------------- 28, 4 31.8 32.4 34.5 3.0 Percent of total feed in -20 linesh each pair of rolls should be softer than the calcined 25 fraction------------------------- 71.6 68.2 67.6 65, 5 63.0 shale so that the softer calcined trona will be crushed Percent of insolubles in --20 nesh fraction------------------------- 5.19 8.91 17.30 22.14 29.71 while the sintered shale will be compressed into the Percent of insolubles in -20 mesh cushioned roll and not be crushed. A preferred com fraction------------------------- 2,27 2.56 2.99 3, 47 4.5 mercial roll crusher is one in which the rolls are at least Percent of original alkali content in -20 nesh fraction.------- -- 72.2. 69, 6 7.0 70.2. 69.9 10 inches in diameter and are covered with rubber ap Percent of insolubles removed in proximately half an inch thick, the rubber being such 30 . --20 mesh fraction.--------------- 47.6 61.9 73.5 77.1 80.8 that 100 pounds per square inch pressure is required to compress the rubber 0.15 inch. In the following example there are described several As can be easily seen from Table III, the recovery of preferred embodiments to illustrate the invention. How 35 the total alkali values is fairly constant regardless of the ever, it should be understood that the invention is not insoluble content of the calcined trona feed. There is a intended to be limited to the specific embodiments. sharp increase in the percent of total insoluble removed as Example I the percent of insolubles in the calcined trona feed in CreaSeS. Crude trona as mined was calcined at a temperature 40 By the process of calcining the crude trona to convert of about 400° C. and a large sample of -10--18 mesh the sodium sesquicarbonate component to soda ash and calcined trona having an insoluble content of 16.60% soften the crystals thereof, preferential crushing of the was obtained for the following runs.
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