June 29, 1971 U. E. G. NETZEL 3,589,871 METHOD FOR THE PRODUCTION OF HIGH-GRADE KAINITE Filed June 10, 1968 4. Sheets-Sheet . - I r I-III-II Tr CONCENTRATION OF MgSO vs MgCl2 CONCENTRATION IN A TYPICAL SUMMER BRINE OF THE GREAT SALT LAKE (UTAH) EVAPORATED AT 25°C. O IO 2O 3O 40 5O 6O 7O 8O 90 IOO MOLES, MgCl2 / IOOO MOLES H2O - I - I - T -- I -TIt CONCENTRATION OF K2Cl2 vs MgCl2 CONCENTRATION | A/G N A YPCAL SUMMER BRINE OF THE GREAT - SALT LAKE (UTAH) EVAPORATED AT 25° C. - - - d O O 2O 3O 4O 5O 6O 7O 8O 90 OO MOLES MgCl, / IOOO MOLES H.O. 60 I-I-I I CONCENTRATION OF Na2Cl2 vs MgCl2 CONCENTRATION || IN A TYPICAL SUMMER BRINE OF THE GREAT A/G 50 SALT LAKE (UTAH) EVAPORATED AT 25° C. 3 O O O 2O 3O 40 5O 6O 70 8O 90 OO MOLES MgCl2 / IOOO MOLES H2O INVENTOR. ULRICH E. G. NETZEL ATTORNEYS June 29, 1971 U. E. G. NEITZEL 3,589,871 METHOD FOR THE PRODUCTION OF HIGH-GRADE KAINITE Filed June 10, 1968 4. Sheets-Sheet 2 A/G 4. CONCENTRATION CURVES FOR GREAT SALT LAKE BRINE FOR JULY 2O MOLES MgCl2 / IOOO MOLES H2O A/G 5. CONCENTRATION CURVES FOR GREAT SALT LAKE BRINE FOR OCTOBER 28 - - ----u- - - - r m-m-- - - ---T-- - - - - - - 26 IIIMgSO4. 24 H-H -v-H-I-H -|--|--|----------------- No.2 Cl2 -- ---- - is 22 -- K2Cl2. - - T f n d O O 3. O - T (u) O O O 2O 3O 4O 5O 60 7O 8O 90 OO MOLES MgCl2 / IOOO, MOLES H2O INVENTOR. ULFRICH. E. G. NETZEL, BY Aft:- ATTORNEYS June 29, 1971 U. E. G. NETZEL, 3,589,871 METHOD FOR THE PRODUCTION OF HIGH-GRADE KAINITE Filed June 10, 1968 4. Sheets-Sheet S A/G 6 A/G 7 GREAT SALT LAKE BRINE OF COMPOSITION A BRINE OF COMPOSITION C H.O KAINTE POND SALT POND I NaC BRINE OF COMPOSITION B BRINE OF COMPOSITION D MIXING CARNALLTE POND BRINE OF COMPOSITION BD BRINE OF COMPOSITON H2O NOC and SAL POND I So"; O STORAGE POND (WINTER COOLING) BRINE OF COMPOSTION C BRINE OF COMPOSITION K H2O KAINTE POND MgSO4 7H2O BITTERNS STORAGE BRINE OF COMPOSITION D H2O CARNALLTE CARNALLITE POND NOC MgSO4 7H2O BITTERNS INVENTOR. ULRICH E. G. NETZEL BY Eit:-ce--4---- ATTORNEYS June 29, 1971 U. E. G. NETZEL 3,589,871 METHOD FOR THE PRODUCTION OF HIGH-GRADE KAINITE Filed June lo, l968 4. Sheets-Sheet 4 A/G 6 BRINE OF COMPOSITION C KANITE POND BRINE OF COMPOSITION D CARNALLITE POND I CARNALLITE POND II CONVERSION TO KANITE (EVAPORATION) BRINE OF COMPOSTON E EVAPORATION POND STORAGE POND (CARNALLITE) (WINTER COOLING) BRINE OF COMPOSITION K BTTERNS STORAGE INVENTOR. ULRICH E. G. NETZEL, "g it:- ATTORNEYS 3,589,871 United States Patent Office Patented June 29, 1971 1. 2 which is relatively high in potassium content is isolated in 3,589,871 this fashion. Such a procedure is in fact impractical, how METHOD FOR THE PRODUCTION OF HIGH-GRADE KANETE ever, because the loss of potassium to the low-grade Ulrich E. G. Neitzel, Ogden, Utah, assignor to Great precipitate represents too substantial a percentage of the Salt Lake Minerals and Chemicais Corporation, New 5 total potassium in the brine, e.g., 40 percent or more, York, N.Y. much more than has heretofore been recognized. Filed June 10, 1968, Ser. No. 735,840 U.S. Patent 1,593,038 teaches the recycle of magnesium Int. C. B01d 9/00, C13k 1/10 chloride bitterns, i.e., the residual liquor obtained from U.S. C. 23-298 21 Claims a Solar pond precipitation process, to a potassium-sat O urated liquor to force potassium chloride out of solution. This patent is directed, however, to the treatment of ABSTRACT OF THE DESCLOSURE chloride brines which contain little, if any, sulfate. It is Natural brines, such as those from the Great Salt Lake further known from Indian Patent No. 67,461 to extract of Utah, are subjected to evaporation in a pond until potassium chloride from a mixture of sodium chloride, they are saturated with potassium salts. The brine is then 5 magnesium sulfate, and potassium chloride with hot mag transferred to a mixing pond wherein it is mixed with a nesium chloride bitterns and to then cool the hot solution second brine which contains a higher molar ratio of mag to obtain carnallite. It is also known to mix bitterns brine nesium to potassium. The thus-adjusted brine is subjected containing a high concentration of MgCl, with bitterns of to pond evaporation to precipitate sodium chloride until lower MgCl2 concentration to precipitate a mixed salt it is again saturated with respect to potassium salts. The 20 containing about equal amounts of potassium chloride brine is then transferred to another pond wherein it is and sodium chloride at lower brine densities than would subjected to further evaporation to precipitate kainite. The be required to precipitate the mixed salt by evaporating kainite is precipitated until carnallite begins to form, at the low-MgCl2 bitterns brine. which time the brine is transferred to another pond and is To produce potassium sulfate product, it is desirable to subjected to additional evaporation to precipitate carnal 2 5 provide a processing plant with a feed which contains lite. Some of the kainite-depleted brine is recycled to the an as-high-as-possible concentration of potassium and an mixing pond. After carnallite has precipitated, in the as-high-as-possible concentration of sulfate, but as little evaporation pond, the residual brine is transferred to deep as possible of the other constituents in the brine, partic storage and subjected to winter cooling to precipitate ularly sodium, chloride, magnesium, and water of hy additional carnallite. The precipitated carnalite is con 30 dration. The plant feed should also contain as high a per verted to kainite by contacting it with kainite-saturated centage as possible of the potassium values in the initial brine. brine. None of the prior art processes adequately achieves these objectives. The aforedescribed patents, for example, BACKGROUND OF THE INVENTION produce products which contain no sulfate. Field SUMMARY OF THE INVENTION The present invention avoids the precipitation of This invention relates to the recovery of potassium potash-lean fractions and produces kainite of high grade, values from brines. It is specifically directed to the re i.e., a crystal product which contains a high percentage of covery of kainite from natural brines, such as those of 40 kainite and little sodium chloride. In this fashion suitable the Great Salt Lake in Utah. feed material for a potassium sulfate plant is obtained State of the art without discarding previously precipitated potassium. The It is known to evaporate natural brines to cause the kainite product contains an increased percentage of the precipitation of potassium-containing salts. Efforts have potassium initially present in the natural brine. Preferred been made to obtain potash fertilizers and other com embodiments of the invention involve the recovery of mercial compounds from natural brines taken from the carnallite from the kainite-depleted brines and subse Great Salt Lake of Utah, but none of these efforts has quent conversion of the carnallite to kainite. According been commercially successful. Potassium is present in to these embodiments, substantially all of the potassium the brine in very small amounts, considerably below 1 initially present in the natural brine is recovered as kainite. percent by weight, whereas other, less desirable con According to this invention, natural brines containing stituents, such as magnesium, sodium, chloride, and dissolved sodium, potassium, magnesium, chloride, and sulfate are present in larger amounts. sulfate in proportions such that schoenite crystallizes from When natural brines are exposed to solar evaporation solution prior to kainite as the brine is evaporated are for sufficient time to concentrate the brines beyond the subjected to mixing and evaporation steps in a sequence saturation level of the dissolved potassium salts, the 5 5 selected to avoid the precipitation of schoenite. A natural precipitate formed is a complex mixture of salts. The brine is subjected to evaporation until it is substantially total precipitate contains a very small amount of potas saturated with respect to potassium, i.e., until schoenite sium, on the order of only a few percent. Because potas either begins to or is about to begin to precipitate from sium is present as a mixture of a variety of potassium solution. The composition of the brine is then adjusted by minerals, further processing of the precipitate to recover 60 mixing magnesium chloride solution therewith to increase potassium sulfate or potassium chloride is necessarily the ratio of magnesium to potassium in the brine. When complicated. In addition, the transport of the low-grade this mixture is evaporated, sodium chloride precipitates mixture from the solar ponds to the processing plant is until there is produced a residual brine which is again expensive. saturated with respect to potassium. Sufficient magnesium It is further known that the precipitate formed by the chloride is preferably added to the schoenite-saturated evaporation of natural brines contains a lower proportion brine during the mixing step to adjust the composition of potassium during the initial stages of precipitation, in of the brine to the kainite region of the phase diagram creasing in grade during subsequent precipitation. Thus, descriptive of the particular brine. Thus, continued evapo it has been proposed to evaporate the brines until the low ration of the residual brine results in the crystallization grade precipitate has been formed and then to remove the 70 of potassium in the form of kainite.