United States Patent (19) 11 3,967,930 Sadan (45) July 6, 1976
Total Page：16
File Type：pdf, Size：1020Kb
United States Patent (19) 11 3,967,930 Sadan (45) July 6, 1976 (54) SEPARATION OF COMPLEX POTASSIUM 1,589,680 6/1926 Burnham.......................... 23/303 X SALTS FROM BRINE EVAPORTES 3,003,849 0/1961 Veronica ....... ............ 23/304 X 3,365,278 1/1968 Kelly et al...... ... 23/302 X 75 Inventor: Abraham Sadan, Salt Lake City, 3,499,725 3/1970 Scarfi et al..... ... 23/302 X Utah 3,615,259 10/1971 Neitzel.................................. 23/298 73) Assignee: NL Industries, Inc., New York, 3,642,454 2/1972 Nylander.............:. 23/298 X N.Y. w Primary Examiner-Morris O. Wolk 22 Filed: Nov. 18, 1974 Assistant Examiner-Barry I. Hollander (21) Appl. No.: 524,485 (57) ABSTRACT 52) U.S.C..................................... 23/296; 23/298; Evaporite minerals comprising mixtures of relatively 23/300; 23/302 R; 23/303; 423/179; 42.3/55 coarse salts are treated in a manner such that certain 51) Int, C2 a so we w as so a sa v BOD 9/04; COD 5100 of said salts are converted by recrystallization to very 58 Field of Search.................. 23/296, 297, 295 S, finely divided form and then separated from the 23/298, 299, 302 R, 303, 304,300; 4231551, coarse salts by size classification such as elutriation, 79 the treatment being especially useful in a process for s the recovery of potassium sulfate from marine evapo 56) References Cited rite mixtures such as kainite and halite. UNITED STATES PATENTS 6 Claims, No Drawi 476,873 12/1923 Burnham.................. ......... 23/295 S s, No Urawings 3,967,930 1 2 and inexpensive separation step; and its application to SEPARATION OF COMPLEX POTASSIUMSALTs a process for recovering potassium sulfate from mixed FROM BRINE EVAPORITES salts deposited from marine brines. More particularly, the method of this invention is especially applicable to the treatment of salt deposits, BACKGROUND OF INVENTION sometimes hereinafter referred to as harvest salts, de By far the largest sources of potassium salts are ma rived from Great Salt Lake brines and comprising es rine brines and the evaporite salts formed by the evapo sentially a mixture of kainite (MgSO, KCL3HO) and ration of marine brines. These brines are found world sodium chloride, and is characterized by two relatively wide and have been formed under various conditions so 10 simple process steps identified as a recrystallization their compositions are quite varied. Most potassium step and a separation step. As applied to the recovery salts are recovered as potassium chloride since this of potassium values from these salt mixtures it has now compound is frequently found unaccompanied by more been discovered that when the double salt kainite is than one or two other salts in major proportions. In heated above 80°C, it is changed into a salt mixture such cases, the separation of a commercially pure po- 15 comprising essentially langbeinite (2MgSOKSO), tassium chloride is relatively inexpensive. However, carnallite (KClMgCl,6HO), and brine; and that when potassium salts are widely used as a fertilizer and for the transformation is effected rapidly, as for example this use there is a strong preference for potassium sul by heating the salts well above 80°C, the langbeinite, fate over potassium chloride, especially with crops such carnallite mixture comes down in the form of relatively as citrus fruits and tobacco. In fact, the demand is great 20 fine crystals, whereas the sodium chloride remains enough that potassium sulfate is frequently manufac unaffected, that is to say comprises relatively coarse tured from potassium chloride at considerable expense. crystals. As the result of this crystal size differential, Potassium sulfate can be recovered also from many separation of the finely divided langbeinite and carnall natural deposits of salts or from many salt mixtures ite crystals from the relatively coarse sodium chloride obtained by evaporation of natural brines. However, 25 crystals can be affected using any known means for potassium sulfate production from such sources is usu separation according to particle size as for example ally complex because of the presence of many other hydraulic classification, screens and the like. However, salts in significant proportions. Indeed, in such salt the preferred method of separation is be elutriated as mixtures the potassium is almost always present chemi hereinafter described. cally combined with another salt in a "double salt;" for 30 Once the relatively finely divided langbeinite and instance, as langbeinite, kainite or glaserite, which salts carnallite have been separated from the sodium chlor are representative of a large group of double salts con ide the langbeinite and carnallite may then be pro taining potassium. Many schemes have been presented cessed, according to known methods, for recovering its for separating potassium sulfate from various mixtures potassium values as potassium sulfate using for exam of these salts. One type of separation process depends 35 ple a solubility type process such as outlined in Volume on solubility relationships which are complex and gen 16, pages 383 and 455 of the Kirk Othmer Encyclope erally give poor yields. Another group of separation dia of Chemical Technology, 2nd edition. processes may be termed mechanical; flotation and tabling are examples. In the case of potassium sulfate, a PREFERRED EMBODIMENT OF THE INVENTION mechanical type of separation step is frequently com: 40 By way of illustrating a preferred embodiment of the bined with a solubility process step in order to make the invention the following description details its applica latter more efficient. Mechanical methods of separa tion to the recovery of potassium values in the form of tion usually have reasonably good yields. However, the double salt kainite substantially free of sodium they usually require grinding the salt mixture and inas chloride from harvest salts derived from Great Salt much as the salt mixture frequently must be ground 45 Lake brines. extremely fine, the grinding step becomes quite expen It is well known of course that these naturally occur sive. ring lake brines are quite concentrated. Relatively pure So, in general, it may be said that there are many sodium chloride is commonly recovered from the lake kinds of deposits from which potassium sulfate may be brine by solar evaporation. If, following recovery of the recovered; and there are many known processes or 50 sodium chloride, the brine is pumped to another pond combinations of processes which can be used in such and further evaporated a potassium-containing mixture recovery. However, all such processes that have been of salts will precipitate. The composition of this mix tried commercially have significant drawbacks. It is ture is affected by the way the evaporation is done and desirable, therefore, to provide a simple and economi principally by the extent of evaporation, that is to say, cal process for separating certain double salts contain- 55 the percentage of water removed; and a generally ac ing potassium from other salts occurring in brine evap ceptable evaporating process such as described in U.S. orites; and to use this novel separation process in an Pat. No. 3,432,031 will effect precipitation of a mixture improved process for recovering potassium sulfate of salts consisting largely of sodium chloride and kai from mixed salts formed by solar evaporation of marine nite with minor amounts of other salts. brines. 60 However, the greatest difficulty encountered in ef. fecting a clean separation of these several salts is due to SUMMARY OF INVENTION the presence of the sodium chloride. One method of In its broadest aspects the instant invention relates to separating sodium chloride from kainite is disclosed in treatment of brine evaporites in the form of mixtures of U.S. Pat. No. 3,432,031, Ferris, Mar. 11, 1969, various kinds of relatively coarse salts in a manner such 65 wherein the salt harvested from a solar evaporation that certain selected salts are converted by recrystalli pond is ground, crushed, ball-milled and then treated zation to relatively fine crystals which may then be with an organic flotation agent to float off a substan cleanly separated from the remaining salts by a simple tially pure kainite salt. Another known process directed 3,967,930 3 particularly to the recovery of potassium sulfate from sium salts including langbeinite, about 90% of which salt brines is disclosed in U.S. Pat. No. 3,082,063, Devi had a particle size in the range from 5 to 50 microns; dalli et al., Mar. 19, 1963, according to which kainite and 28% essentially sodium chloride about 90% which obtained from concentrated salt brines is converted to was between 150 and 1500 microns. The slurry at 30% schoenite plus solid sodium chloride in a solution of 5 solids was then fed into the middle of an elutriation magnesium chloride; followed by floating the solid column measuring about 12 inches in diameter and 5 schoenite from the solid sodium chloride and then feet high into the bottom of which a magnesium chlor heating the schoenite with water to convert it to solid ide brine (28% MgCl) was introduced at a velocity of potassium sulfate in a solution of potassium sulfate and about 2.5 feet per minute whereby the finely divided magnesium sulfate, the latter being recycled to treat O potassium salts were carried upwardly into and dis additional kainite. However, the mother liquor from charged from the top of the elutriation column as a the schoenite contains appreciable quantities of sulfate dilute elutriate of about 10% solids; and the coarse and hence when the mother liquor is sent to waste these sodium chloride crystals, which had settled to the bot sulfate values are lost. The recoveries of potassium tom of the column, were periodically removed.