Patented Feb. 11, 1947 2,415,792 UNITED STATES PATENT OFFICE 2,415,792 PSEPARATION OF POTASSUV FEERRCYANDE Rogers Gravel, Linden, N.J., assignor to Ameri can Cyanamid Company, New York, N. Y., a. corporation of Maine Application September 19, 1945, Serial No. 6,262 2 Clains. (CI. 23-2) The present invention relates to the prepara 2 tion of alkali metal ferri and ferrocyanides and details as hereinafter more fully described and specifically to K2Na25e(CN)6, KaNa,Fe(CN)6 and shown in the drawing in which the single figure Ese (CN)6 or any of then. is a flow sheet showing the preferred method The principal object of the invention is the of carrying out the invention. preparation of one or more of the above Sub 5 Referring now to the flow sheet, crude calcium stances from a cheap source of raw materials cyanide is placed in a heated extraction vessel as a complete cyclic process without undue waste to which water or wash liquor from a previous and without relying upon any other or related batch is added, in either case with the addi process to take values which would otherwise tion of an aqueous solution of ferrous sulfate be lost. 0 (FeSO4.7H2O), a 30 to 40% solution being pre The alkali metal ferri and ferrocyanides are ferred.place: As a result, the following reaction takes of particular value in the industry in that they are used extensively as photographic reagents and as intermediates in the production of iron blue complexes for pigments or the like. Considerable heat is developed as the reaction These complex iron cyanides may be readily progresses So that Only a small quantity of steam prepared from a cyanogen compound Such as is required to bring the temperature of the ex crude calcium cyanide and ferrous sulfate but traction menstruum to about 200 F. Which is due to the chemical afinity of the Fe(CN)6 radi 20 desired in order to bring about a complete and cal for the calcium, difficulty has heretofore been adequate extraction. The resulting slurry is encountered in forming the alkali metal salt. It filtered on a continuous filter of the Oliver type has been discovered that by judicious choice of or the like and the calcium sulfate sludge washed the intermediate alkali or alkaline earth metal with water at about 120° F. The Wash Water ferrocyanide, paying particular attention to its 25 from the cake may be returned to the extraction ease of formation and insolubility in the men Wessel for an additional cycle. Where desired stuum in which it is formed, a perfect and op and in order to improve the speed of filtration, erative process resultS. a small amount of calcium carbonate sludge, ob For instance, calciurn ferrocyanide may readily tained later in the process, may be added to the be formed by reacting a Solution of calcium 30 slurry before filtration although this is not cyanide with ferrous sulfate. One of the cal ?eCeSSaty. cium atoms only may be readily replaced by po This calcium ferrocyanide liquor contains some tassium through reaction with potassium chlo undesirable sulfate, usually about 0.3% calcu ride, for instance. The other calcium aton Can lated as potassium Sulfate. Since the sulfate not be replaced as Such with potassium even content of such liquors should be reduced to a though large quantities of potassium chloride are minimum to produce good final products, the added at this stage. On the contrary, however, liquors may be passed to a treating tank, sufi this remaining calciun aton may be readily re cient barium chloride added to precipitate the placed With sodium as by reaction with soda, ash Sulfate as barium Sulfate, and the sludge removed to form KNa2Fe(CN)6. This material may as by filtering. either be recovered as such in solid form or one The thus purified calcium ferrocyanide is then of its sodium atons may be then knocked Out transferred to a precipitation tank, heated to With chlorine to for in KgNa:Fe(CN)6 or this latter boiling with a steam coil and treated with an material may have its single Sodium aton re excess of solid potassium chloride with agita placed with potassium through reaction with tion. The calcium ferrocyanide liquor added to potassium chloride to fornia K3Fe(CN)6. While the precipitation tank contains about 6% of at first, blush this would appear to be a round calcium ferrocyanide and from 6 to 7% sodium about method of arriving at an end product, yet chloride, the latter having been present as an by so doing advantage is taken of the ability iiipurity in the crude calcium cyanide. of one material to replace another in a ferro At this stage, there may also be added the or ferricyanide while at the same time choosing mother liquor containing substantial quantities a material to be formed at that stage, which is of K3 Fe(CN)6 from a later part of the process more insoluble in the menstruum than the by and for the purpose of recovering values therein. products or impurities present there. Under the circumstances, approximately 20% of the ferrocyanide present at this stage may con The invention further contemplates additional 55 sist of ferrocyanide which has thus been recycled. 2,415,792 4. 3. to reoxidize any ferricyanide which may have The quantity of KCl added represents an excess been reduced to ferrocyanide in the evaporation of about 30% above the theoretical required for proceSS. The mother liquor contains about 12% the calcium ferrocyanide liquor used, based on of total chloride calculated as chlorine. The the following reaction: evaporated liquor, containing any crystals which have separated during the evaporation, is then The calcium ferrocyanide liquor contains re cooled under vacuum to about 60° F. and the re ducing substances which ordinarily will reduce Sulting slurry filtered so as to collect the crude most of the ferricyanide to the ferro state. Any crystals of KaNa,Fe(CN)6. They may be further ferricyanide not so reduced may be converted O purified by recrystallization from water if desired. by adding amounts of sodium hydrosulfide solu The crude crystals contain only about 4% water tion as required. The bulk of the ferrocyanide and Small amounts of chlorides and ferrocyanides is precipitated as the sparingly soluble calcium as impurities. When dried, the product contains potassium ferrocyanide and may be recovered by 102% to 103% of ferricyanide calculated as potas filtration, the cake being washed with a small 5 sium ferricyanide equivalent to 97 to 98% cal amount of Water. The washings and the filtrate culated as the double salt, with 0.3% to 0.6% containing the calcium chloride, the excess po chloride calculated as chlorine, and 0.3% to 0.6% tassium chloride and the Sodium chloride de ferrocyanide calculated as as Fe(CN)6. The rived from the crude cyanide and recycled mother liquor from the formation of crude and purified liquor, are discarded. 20 crystals of KaNa,Fe(CN)6 may be recycled, as pre The cake of calcium potassium ferrocyanide is viously mentioned, to the solution of calcium fer then transferred to a heated mixer equipped with rocyanide for recovery of the values therein. an agitator and silurried with weak liquor Ob Where it is not desired to produce crystals from tained from a previous mixer batch. Soda ash the K2NaFe(CN)6 liquor but on the contrary to Solution in slight excess as determined by test, is convert it to KFe(CN)6, the crude KNaFe(CN)6 added according to the following reaction: liquor Containing about 31% equivalent of K3Fe(CN)6 may be treated with 0.5 to 0.6 lb. of solid KCl to each pound of equivalent KFe(CN)6 present according to the following reaction: and the whole mass heated to boiling by means 30 of a steam coil or the like. The resulting slurry is filtered to recover the precipitated calcium car bonate which is washed with water sufficient to It may then be evaporated until about 6% of the yield the volume of weak liquor necessary for pre weight has been removed as water. The resulting paring the next batch. About 15% of the ferro Solution, including any Crystals which have sepa cyanide present in any batch at this stage con rated during the evaporation, is then Cooled to sists of liquor recirculated in this way. about 60° F. and the crystals of K3Fe(CN)6 sepa The mother liquor from the filtrate contains rated as by filtration. The product consists es K2Na2Fe(CN)6, having a content of about 31% sentially of K3Fe(CN)6 with about 4% of water Calculated as K3Fe(CN)6 and may be used as such 40 and small amounts of chlorides and ferrocyanides in the arts, or evaporated and the crystals re aS impurities. Actually it contains from 100 to COWered for use. 1.01% of ferricyanide calculated as K3Fe(CN)6, In the event that it is not desired to recover with 0.3 to 0.6% chloride calculated as chlorine, K2 Na2Fe(CN)6, this mother liquor may then be and 0.3 to 0.6% ferrocyanide calculated as transferred to a chlorinating tank, cooled to about 5 EFe(CN)6. Where desired, the crystals may be i00° F. and oxidized by passing chlorine therein further purified by recrystallization from water. to at such a rate that the temperature does not From the above it will be apparent that a self exceed 120° F. In the chlorinating tank, the foll contained process has been designed for the lowing reaction occurs: preparation of K2Na2Fe(CN)6, K2 NaFe(CN)6 and 50 K3Fe(CN)6 or any of them, recycling values into 4.