Sept. 12, 1972 G. VERONICA 3,690,819 PROCESS FOR THE PREPARATION OF POTASSIUM NITRATE Filed June 1, 1970 2 SapotgarSlaeo FIG.1

as as a as a a de as a did

Sept. 12, 1972 G. VERONICA 3,690,819 PROCESS FOR THE PREPARATION OF POTASSIUM NITRATE Filed June 1, 1970 2 Sheets-Sheet 2

Ca(NO, ) 40

Conversion to KNO Recycle solutior

Precipitation of calcium oxychloride

Decomposition of calcium oxychloride

ff Separation.

Waste Fig. 2 3,690,819 United States Patent Office Patented Sept. 12, 1972

2 3,690,819 solution some calcium hydroxide, which will combine with PROCESS FOR THE PREPARATION OF CaCl2 and will form a slightly soluble oxychloride, accord POTASSUMNTRATE ing to the reaction: Giacinto Veronica, 7 Via Dolores Bello, Novara, Italy (2) HO Filed June 1, 1970, Ser. No. 42,135 (CaCl2) -- (3Ca(OH)2) (C2 (3CaO.CaCl2·16H2O) Claims priority, application Italy, May 22, 1969, 17,178/69 The equilibrium solution (1), after completion of reac nt. C. C01b. 21/48 tion (2), is then capable of dissolving further calcium U.S. C. 423-397 6 Claims nitrate and potassium chloride to thus yield further potas sium nitrate as a solid phase. 0. The oxychloride thus obtained is then decomposed in a ABSTRACT OF THE DISCLOSURE subsequent stage with an excess of water, according to Process for making KNO3 from KCl and Ca(NO3)2 the reaction: salts, these salts being reacted in the presence of a (3) EO recycle solution to form solid KNO, the recycle solution (3CaO.CaCl216H2O) to (3Ca(OH)2) + (CaCl2) as containing Cat, Kt., NO, and Cl ions, separating the The lime obtained is recycled to (2), with the CaCl solu solid KNO at a temperature from about -10 to --20 tion representing the waste product of the process. C., and treating the mother liquor from which the KNO Although the above process has been known for quite has been precipitated with lime to thereby precipitate some time (1933), to date it has not proven to be of calcium oxychloride, CaCl23CaO 16H2O, to thereby re 20 convenient application in industry, due to the fact that the duce the calcium chloride content of the mother liquor. oxychloride precipitates in the form of very thin needles Improvement comprises effecting the precipitation of cal and thus results in slurries having poor characteristics of cium oxychloride in the presence of a solid phase made decantability and filterability. After filtering, the oxychlo up substantially of calcium oxychloride and not more than ride solid appears as a spongy mass that retains large 5% by weight of free lime at a temperature that is from quantities of the contact solution and retains useful salts from about 5 to 15 higher than the temperature of separa (calcium nitrate and potassium chloride), so that it be tion of the KNO3, and maintaining the concentration of comes necessary to use great volumes of washing water in chloride ions of the liquid phase within tS grams per order to recover these salts. Such washing results in an liter of the saturation concentration. excess of water being introduced into the cycle as com 30 pared to the amount of water removed from the cycle (as water of hydration of the oxychloride and the hygroscopic BACKGROUND OF THE INVENTION HO associated with the KNO3), so that it is necessary to resort to evaporation, to the extent of 1 to 2 parts of (1) Field of the invention evaporaed water for each part of obtained nitrate, accord The present invention relates to a process for the pro ing to German Pat. 572,722, mentioned previously. The duction of potassium nitrate. More particularly it relates necessity to evaporate, as well as the difficulty in handling to a process for preparing potassium nitrate from calcium a salt formed of fine crystals, render the process economi nitrate and potassium chloride. cally unprofitable. (2) Description of the prior art 40 SUMMARY OF THE INVENTION It is known that one can obtain potassium nitrate start The present invention provides a closed cycle for the ing from calcium nitrate and potassium chloride, as a preparation of potassium nitrate, according to the previ solid phase in an equilibrium solution in water, according ously specified reaction sequence, however avoiding evapo to the reaction: ration. (1) H2O 45 This invention also reduces to a minimum the require Ca(NOs) -- 2KCl - 2KNO3 + CaCl, ment of thermal energy for heating or cooling of the sys followed by the separation of the potassium nitrate at a tem during the various stages of the process. Moreover, temperature between -10° and +20° C., and preferably the invention ensures particularly high conversion yields, at about 0 C. both in K+ as well as in NO, obtained in the form of However, even when operating at this latter tempera technical potassium nitrate with a titer not less than 96% ture, the yield in precipitated KNO3 is only about 60%, with respect to the stoichiometric. and hence other operations must be carried out on the The invention also maintains substantially unaffected equilibrium solution in order to recover the remaining the above high yields, even when using raw materials of desired ions (Kh and NO). low purity, such as certain calcium nitrates and potassium For effecting such a recovery several processes are 55 chlorides of industrial production. known, such as, e.g., evaporation, or evaporation and According to my invention, calcium chloride is precipi precipitation of a double salt (KNO3 CaCl2.2H2O), tated from the mother liquor (containing KNO3) as cal which is recycled (British Pat. 1,007,297), or the use of cium oxychloride, CaCl-3CaO 16H2O, by the addition aliphatic alcohols which render the KNO3 insoluble of lime, at a temperature of from 5 to 15° C. higher than (German Pat. 606,385), etc. 60 the temperature employed in the separation of potassium According to German Pat. 572,722, in order to in nitrate, maintaining the chloride ion concentration in the crease the separation yield of potassium nitrate the method liquid phase within a range of from --5 to -5 g/liter to be followed is that of removing calcium chloride from with respect to its saturation concentration, in the presence the equilibrium solution. This is achieved by adding to said of a solid phase consisting of calcium oxychloride (ob 3,690,819 3 4 tained from previous processing) and of the minimum 1 show the course of the concentration in chloride ions quantity of free lime at most, equal to 5% by weight of throughout reaction (2), when operating at 10 C., in the solid phase). conditions of concentration of CaCl2, respectively lower In fact, it has been found that by operating under the than (FIG. 1a), greater than (FIG. 1b) and essentially above indicated conditions the oxychloride precipitates equal to (FIG. 1c) that of equilibrium at 10° C. The as coarse crystals, of a presmatic shape tending to a equilibrium concentration at 10° C. is represented by cubic shape, of a particle size of around 0.1 mm. easily the horizontal dotted line (63 g/liter of Cl). decantable and readily separable from the mother liquor The diagram reported in FIG. 1a was obtained starting (by filtering or by centrifuging). A small quantity of from a suspension whose liquid phase was in equilibrium washing liquid readily suffices for removing the useful 0. with calcium oxychloride at 10°C. To this was first added salts adhering to the oxychloride crystals. all the lime theoretically necessary for precipitating a certain quantity of CaCl2, and thereupon the CaCl2 solu BRIEF DESCRIPTION OF THE DRAWING tion was added over a time period of 100 minutes. The My invention will be best understood from the follow concentration of chloride ions increases gradually up to ing detailed description, taken in conjunction with the 5 reaching 65 g/liter. The calcium oxychloride crystals accompanying drawing, wherein: obtained are represented by photograph a and are quite FIGS. 1a, 1b, and 1c plot the chloride ion concentra" fine. tion for reaction (2) when operating at varying CaCl2 The diagram of FIG. 1b was obtained by adding to a concentrations with respect to the equilibrium concen suspension, the liquid phase of which was in equilibrium tration, with photographs a, b, and c, showing the nature 20 with oxychloride, first all the CaCl2 and then by grad of the resulting calcium oxychloride crystals; ually adding lime, still at 10° C. and over a period of FIG. 1d is a photograph of calcium oxychloride crys 100 minutes. The crystals are even finer than in the tals obtained when employing a minor amount of a tri previous case. (See photograph b.) valent metal salt; and The diagram of FIG. 1c was obtained by adding to FIG. 2 is a schematic diagram illustrating the process 25 the solution, having its liquid phase in equilibrium with of my invention. oxychloride, contemporaneously and gradually the CaCl2 solution and the lime, in stoichiometric quantities, and DESCRIPTION OF THE PREFERRED keeping close to the pre-existing equilibrium conditions. EMBODIMENTS Thereby there were obtained large crystals, as shown by Reaction (2) is conducted at a temperature from 5' 30 photograph c. to 15° C. higher than the temperature employed for According to the present invention, I have found that reaction (1), the separation of potassium nitrate. In this one may add to the solution small quantities (0.1-0.3 way one avoids precipitation of potassium nitrate that g/liter calculated as oxides) of trivalent metal salts of would otherwise occur due to the removal of water from such metals as Al, Fe, Cr. etc., preferably in the form of the liquid phase, this water removal being due to hydra 35 metal nitrates. Indeed, oxychloride crystals obtained in tion of the oxychloride. the presence of such salts in the solution tend more to Such a crystallization would, obviously, involve a con wards a cubic shape, since there is favored the develop sumption of washing water much greater than the quan ment of face 010 to the detriment of face 100, as may be tity of water necessary and sufficient for the removal of seen from the photograph d, which shows said crystals. only the adhering lye. The rise in temperature on passing 40 As appears from a comparison between photograph d from reaction (1) to reaction (2) is spontaneous, due and photograph c, crystals obtained in the presence of to the positive enthalpy of reaction (2), and therefore trivalent metal salts turn out to be larger and more cubic it is not necessary to provide external heat to obtain the than those crystals obtained in the absence of such tri above mentioned thermal temperature difference: on the valent metal salts. contrary, sometimes it may be necessary to somewhat 45 Reaction (3) is carried out without any external addi cool down the reaction temperature. tion or removal of heat. The reaction is conducted along During the reaction one must avoid the occurrence of the same principles illustrated in connection with reaction either appreciable oversaturation or undersaturation of (2), that is, by feeding the oxychloride and the water CaCl in the liquid phase, with respect to the concentra inside an equilibrium slurry with a solid phase of tion value foreseen by the equilibrium with the solid 50 Ca(OH)2, using such flow rates and such ratios as to phase, 3CaO.CaCl216H2O, at a given temperature. maintain substantially constant the conditions of the The concentration at equilibrium also depends on the equilibrium itself. nature of the solid phase; in fact, a solid phase consisting In this way one obtains a well crystallized lime, with of oxychloride and free lime permits a concentration of the advantage of a smaller requirement in water for the CaCl in the liquid phase considerably lower than the 55 cycle, because its water content is only about 25-30% concentration that would occur when the solid phase as against that of about 50% for normal slaked lime. consisted substantially of only oxychloride. A concen Moreover, the use in reaction (2) of well crystallized lime tration of from 60 to 70 g/liter in chloride ions in the reduces the solid-liquid exchange surfaces, on whose inter mother liquor is sufficient for preserving the above indi face the reaction occurs, reducing in proportion the num cated conditions for the whole temperature range from 60 ber of nuclei of oxychloride produced in a given time 10° to 20° C. at which the precipitation of the oxychlo unit. However, it is desirable that the particle size of the ride is preferably carried out. lime should not exceed 0.2 mm., so as not to excessively A preferred form of execution of reaction (2) is that retard reaction (2). of continuously introducing, as two separate streams, the The process of this invention will now be described in lime and the liquid phase of reaction (1) inside a sus 65 further detail, with respect to a preferred embodiment, pension in equilibrium according to (2), maintained at and with reference to FIG. 2. a constant temperature, and regulating the rate of addi FIG. 2 schematically illustrates the process of this in tion of the reactants, so that the concentration of CaCl2 vention. The reaction is carried out in three stages, identi in the liquid phase remains substantially constant with fied by reference characters I, II, and III, respectively. time. That is, it is preferred to meter the reactants in 70 Stage I: To a recycle solution 8-1-9 (described in such a manner as to maintain the concentration of chlo greater detail hereinafter), this recycle solution contain ride ions essentially constant. ing primarily Catt, Kt., NO and Cl- ions, and being In any event, one operates in such a manner that said withdrawn from Stage II and added to zone 3 of Stage I, concentration will not differ by more than 5 g./liter from were added, via lines 1 and 2, respectively, calcium nitrate the saturation concentration. The three diagrams of FIG. 75 and potassium chloride in such amounts and proportions 3,690,819 5 6 as to result in the formation of a solid phase consisting ing then sprayed on the salt gathered in the centrifuge. substantially of KNO. The solid KNO3 is separated in The liquid phase obtained in this stage (recycle water zone 4, as by filtration or by centrifugation, and is then 8--9, consisting of the mother liquor 8 from the precipita discharged via line 5. The liquid phase passes via line 17 tion of the oxychloride plus the washing water 9) is re into Stage II. If desired, one can subject the separated turned to Stage I. solid to washing and then add the washings to the mother Stage III: The solid phase is withdrawn from Stage II liquor of the KNO, as by adding such washings to the via line 18, and is decomposed in zone 10 with water liquid phase in line 17. that is added via line 19, preferably at room temperature Since, ordinarily calcium nitrate is introduced in the and in such quantity as to obtain an equilibrium solution. form of the tetrahydrate, the volume of the resulting O This equilibrium solution, after a contact time of from liquid phase is greater than that of the starting recycle about 1 to 3 hours, is discharged via line 12 and desir solution, primarily because of the addition of water from ably has a content of from 80 to 100 g/liter of CaCl. the tetrahydrate. If required, it is, however, also possible to obtain more The mixture of Stage I may be prepared from hot re concentrated solutions, either by increasing the tempera actants, but it must then be cooled down in order to ob ture, or at room temperature, by first carrying out a tain a satisfactory yield upon separation of the KNO3, 5 decomposition in the presence of a solid phase of lime taking into consideration its high thermal coefficient of and oxychloride, and then by completing separately the solubility. A temperature of from -10° to -20° C., and decomposition. Solid Ca(OH)2 is separated from the preferably between 0 and 10 C., has been found to be CaCl2 solution in zone 11. most satisfactory. 20 A portion of the solution in line 12 thus obtained serves If the calcium nitrate employed has been obtained as a for the washing of the oxychloride, via line 14. The re result of treatment of phosphate rocks with KNO3 followed maining portion of the solution is discharged through line by separation of calcium nitrate by cooling (e.g., Odda 15, and is considered as waste with respect to this process. process or the like), it thus contains impurities such as It contains the foreign salts adhering to the oxychloride phosphorus and fluorine (which impurities, upon passing 25 along with virtually all of the calcium chloride present into the subsequent stage, would hinder the regular therein; moreover, it is essentially saturated with growth of the oxychloride crystals). In such case, the first stage of the process is modified in the sense that Ca(OH) initially there is added only calcium nitrate. This dis with a content of about 2 g/liter at room temperature. solves completely (without the need of heating), and the 30 Said solution removes the K+ and NO ions not re resulting solution is then treated with that quantity of covered in the process, as an average in the proportion lime necessary for precipitating the above mentioned of from 3% to 4% and from 5% to 6%, respectively, impurities, which are then eliminated by filtering. To the with respect to the starting reactants, KCl and Ca(NO3)2. resulting clear solution is then added potassium chlo The yields amount to 96-97% in K+ and to 94-95% ride. It is possible to use KCl of a technical grade (60%- 35 in NO. Slightly lower yields may be obtained where it 62% KO) wherein the chief impurity is NaCl. Once has been necessary to initially purify the calcium nitrate the operational conditions are attained, the sodium ion used, although the small quantities of K+ and NO ions is substantially eliminated together with the calcium chlo removed during such purification may be utilized at ride discharge solution via line 15, so that the potassium another point, for instance, in the nitric acid treatment nitrate will not contain more than 0.2-0.3% by weight 40 of NaO. of phosphate rocks to form the initial calcium nitrate. Stage II: Solution 17, coming from Stage I together In order to further illustrate this invention, the follow with washing water, if any, from the washed KNO, is ing illustrative examples are given. All parts are by weight admixed in zone 6 with lime which enters . . . via line 13 unless otherwise stated. (from the decomposition of the oxychloride carried out EXAMPLE 1. in Stage III), along with a small additional quantity of 45 lime via line 16 in order to balance out losses due to The initial solution withdrawn in line 17, this solution solubilization. The total quantity of lime is adjusted, ac amounting to 1000 liters or 1340 kg, was obtained in the cording to the stoichiometry of reaction (2), to the separation at 0°C. of solid KNO. The solution was of the quantity of the new CaCl2 originated in Stage I, which following composition: corresponds to the KNO3 produced. It is desirable to 50 216.5 g/liter of CaCl2, 116 g/liter of Ca(NO) and operate in such a manner that the free lime, after 150 g/liter of KNO. This solution was fed in 2 hours precipitation, does not exceed 5% by weight of the into a slurry, the liquid phase of the slurry being in equi solid phase of calcium oxychloride that is formed. librium with solid oxychloride (the liquid phase of the The quantity of water of hydration of the oxychloride slurry contains: 113 g/liter of CaCl; 182 g/liter of is such as to counterbalance the water introduced into 55 Ca(NO3)2; 164.5 g/liter of KNO; and 5-10 g/liter of the cycle (1) with the calcium nitrate, (2) with the minor constituents), maintained at 10 C., together with a lime, and (3) with the washings. mixture of 375 kg. of recycle lime Ca(OH)2 content: In order to reduce the washing of the oxychloride, it 70.5% and 11 kg. of make-up lime Ca(OH)2 content: is essential that this intermediate salt be obtained in the 50%. form of well developed crystals that retain relatively little 60 The mixture of recycle lime and make-up lime is fed of the contact solution; otherwise, by limiting the wash as suspension into solutions coming from the filtering of ing water in order to balance the cycle, one would en previously precipitated oxychloride, of other preparations counter too large a loss of useful ions that had remained of KNO3 and having the above-said equilibrium composi adhering to the oxychloride. tion (1 part by weight of lime in 1.5 parts by weight of Operating according to the previously described condi 35 solution). tions, the precipitation of the oxychloride is completed The lime suspension was maintained at 15-20 C. in in from about 1 to 3 hours. Thereafter the resulting slurry order to avoid reactions between the two phases. is fed to a thickener. Thereupon the settled salt is separ During the precipitation of the oxychloride it is neces ated, as by filtering or, preferably, by centrifuging as in sary to eliminate part of the heat due to the exothermic zone 7, and is then washed in zone 7 with a portion (via 0. nature of the reaction, which can be economically carried line 14) of the exhaust solution (via line 12) which is out by exploiting the endothermic nature of the decom withdrawn from Stage III. position reaction. Once the precipitation of the oxychloride A preferred embodiment for washing comprises in had been completed, the slurry was decanted and centri troducing a part of the washing liquid into the settled fuged, and the thickened slurry was then washed in zone slurry to be centrifuged, the remaining part of liquid be 75 7' (FIG, 2). 3,690,819 7 8 In this manner, from the 1000 liters of solution with The liquid phase 8 in equilibrium with the above men drawn via line 17, there were obtained, 1125 kg. (875 tioned oxychloride, together with the washing liquid 9, liters) of recycle solution (via lines 8-9) having the forms the recycle water (via lines 8-1-9); this amounts to same composition as that of the liquid phase of said 1105 kg. (855 liters) and shows a composition in g./liter slurry, and 772 kg. of oxychloride having the following 5 of: CaCl2=101; Ca(NO3)2=190; KNO3=172; lime and percent composition by weight; CaCl2=17.05%; other minor constituents=7.5 and H2O=821. In the above mentioned solution (8-1-9) were dissolved Ca(NO)=0.9% at 10 C. 317 kg. of calcium nitrate (resulting from the treatment of phosphate rock with nitric acid) and having KNO3=0.8%; Ca(OH)=36.5%; HO=46.1%. l0 the following composition, expressed in weight percent: The 875 liters of recycle solution (lines 8-1-9) were Ca(NO)=63.8; free HNO3=2.0; PO= 1.0; F=0.25; recycled to Zone 3, the temperature being maintained at HO=31.5. To the resulting solution were then added 10 C., and there were added 272 kg. of pure 13 kg. of recycle lime for the precipitation of the impuri ties which were gathered as 38 kg. of a precipitate of the Ca (NO3)2.4H2O 5 following composition expressed as weight percent: Cas 14.3; C1-3.9; KO=4.0; NO3=13.2; PO5=8.1; and 161 kg. of pure KCI, via lines 1 and 2, respectively. F=1.0; HO=50.0. In order to speed up the reaction of double salt exchange, After filtering the above mentioned precipitate, there mild heating was effected, up to about 15-20° C. On cool were added to the filtrate 188 kg. of technical KCl (titre: ing down the slurry to 0° C. and one separating the pre 20. 97 weight percent KCl; main impurity-NaCl). After hav cipitated KNO3, there were obtained 1308 kg. (955 liters) ing carried out the double-exchange reaction, the slurry of solution (withdrawn via line 17) and 250 kg. of salt. was cooled down to 0° C., and the potassium nitrate (258 This salt had the following composition, expressed as kg.) was separated and washed (with 35 kg. of water), weight percent: Cls=1.3; Cass=1.7; K2O=41.0; and showed the following composition, in weight percent: 25 Ca-0.5; C1-1.2; Na=0.3; KO=42.8; NO3=58.1; NO=57.1 HO-4.2, corresponding to 96.1% of KNO3 on a dry HO=5.6. Upon washing the salt with 30 kg. of water, its basis. composition was expressed as weight percent: Cl=0.7; The liquid phase 17 thus obtained (equilibrium Solu Ca=1.0; KO=43.0; NO=58.5; HO=4.0, which cor tion at 0° C. plus washing) corresponded in composition responds to 96.5% KNO3 on a dry basis. 30 and quantity to the initial solution from which the process The washing solution (45 liters) added to the 955 liters was commenced. The yield amounted to 95.3% in K and of the mother liquor at 0° C., restores the volume and 93.6% in NO-. These yields do, however, increase to, composition of the initial solution. The oxychloride was respectively, 96.5% and 96.7%, where one uses the pre decomposed with about 1200 kg. of water, resulting in cipitate obtained in the purification, for instance, by re 375 kg. of lime for recycle and about 1400 liters of waste 35 cycling it back to that initial stage of the process wherein solution (withdrawn via line 12) of which 140 liters were the calcium nitrate is obtained. used for the washing of the oxychloride. The oxychloride was decomposed with about 1300 kg. The conversion yield in KNO amounted to 97.2% for of water, thereby obtaining 381 kg. of lime Ca(OH)2 K+ and 94.7% in NO. content: 71.5% and 1700 kg. of waste Solution (with The precipitated calcium oxychloride showed substan 40 drawn via line 12). tially a cubic shape and had the following size distribu Modifications and variaitons can, of course, be made tion: without departing from the spirit and Scope of the inven Percent tion. Above 0.25 mm. ------9 Having thus described my invention, what I desire to From 0.25 to 0.15 mm. ------15.9 45 secure by Letters Patent and hereby claim is: From 0.15 to 0.09 mm. ------38.9 1. In a process for making KNO3 from KCl and Ca(NO) salts, said salts being reacted in a reaction ZO From 0.09 to 0.06 mm. ------0.2 in the presence of a recycle Solution to form solid KNO3, Less than 0.06 mm. ------Balance said recycle solution containing Cat", Kt., NO, and EXAMPLE 2 50 Cl- ions, separating said solid KNO3 at a temperature The precipitation of the oxychloride was carried out from about -10 to +20 degrees C. treating the mother under similar conditions as described for Example 1, with liquor from which said KNO3 has been precipitated with the difference that the recycle solution used (withdrawn lime to thereby precipitate calcium oxychloride, via lines 8-9) contained also a small quantity of alumi num nitrate, namely, 0.24 g. /liter expressed as Al2O3. The 55 CaCl-3CaO 16H2O lime used consisted of 368 kg. of recycle (via line 13) to thereby reduce the calcium chloride content of said 71.5% lime, the remainder being water and of 33 kg. mother liquor, separating Said precipitated calcium oxy of make-up (via line 16) 50% lime). The oxychloride chloride from said mother liquor, and recycling the thus thus obtained, after washing with 120 liter of waste Solu 60 obtained recycle solution to said reaction Zone, the im tion (via line 14), weighed 785 kg, and showed the fol provement comprising effecting said precipitation of cal lowing composition, expressed as weight percent: cium oxychloride in the presence of a solid phase made up substantially of calcium oxychloride and not more than CaCl2=17.9 5% by weight of free lime at a temperature that is from 65 about 5 to 15 degrees C. higher than the temperature of Ca(NO)=0.5; KNO3=0.4; Ca(OH)2=35.9; separation of the KNO3, and maintaining the concentra HO=45.0 tion of chloride ions of the liquid phase Within 5 grams per liter of the saturation concentration. It showed the particle size distribution: 2. The process of claim 1, wherein said separation of Percent 70 KNO is effected at a temperature of from about 0 to Above 25 mm. ------2.3 10° C. From 0.25 to 0.16 mm. ------15.0 3. The process of claim 1, wherein said precipitation From 0.16 to 0.09 mm. ------44.1 of oxychloride is effected at a temperature of from about From 0.09 to 0.06 mm. ------16.7 10 to 20 C. and with a concentration of chloride ions Less than 0.06 mm. ------Balance 75 in the liquid phase of from 60 to 70 grams per liter. 8,690,819 9 O 4. The process of claim 1, wherein to the solution from References Cited which is precipitated said oxychloride there is added a trivalent metal salt wherein the trivalent metal is Al, Fe, UNITED STATES PATENTS or Cr, said salt being present in an amount of from about 2,594.723 4/1952 Berteaux------23-295 0.1 to 0.3 g/liter, expressed as the corresponding metal 5 3,361,522 1/1968 Fiatt ------23-102 oxide, O in said trival 1 FOREIGN PATENTS 5. The method of claim 4, wherein said trivalent meta 572,722 3/1933 Germany. salt is a nitrate. 6. The process of claim 1, wherein the source of said OSCAR R. VERTIZ, Primary Examiner Ca(NO) is impure due to the presence of PO, F , 10 G. A. HELLER, Assi SiFi, or Mg+ ions, and wherein said source is treated, A. Ad , Assistant Examiner prior to reaction with KC, with lime to thereby precipi- U.S. C. X.R. tate said ions. 423-472; 23-304