UNITED STATES PATENT OFFICE 2,643,196 PROCESS for PREPARING PURE CADMUM RED PGMENT Benjamin W

Patented June 23, 1953 2,643,196

UNITED STATES PATENT OFFICE 2,643,196 PROCESS FOR PREPARING PURE CADMUM RED PGMENT Benjamin W. Allan and Frank O. Rummery, Baltimore, Md., assignors to The Glidden Com pany, Cleveland, Ohio, a corporation of Ohio No Drawing. Application March 11, 1949, Serial No. 81,023 5. Claims. (C. 106-301) 2 This invention relates to pure cadmium sul to coprecipitate an oxidic cadmium compound foSelenide red pigments, and to an improved and a crude cadmium sulfoSelenide pigment. process for preparing such red pigments. It is a further object, to provide an improved In preparing cadmium red pigments it is cus Cadmium red pigment by calcining a crude red tomary to dissolve selenium in an alkali metal pigment in the presence of an intimately dis or barium sulfide solution, and then to react persed OXidic cadmium compound, the intimate this selenium-containing solution with a soluble dispersion being achieved by coprecipitation of cadmium salt. When the cadmium Salt is Suit the respective components from aqueous solution. ably selected in view of the metal ions present It is yet another object to reduce or avoid in the sulfide Solution, an unextended (i.e., pure) Selenium losses during the calcination of cad crude pigment may be formed by the reaction. mium red pigments by having an oxidic cad The crude pigment is separated from the bal mium compound more intimately dispersed ance of the reaction mass, Washed and dried, if throughout the calcination mass than hereto desired, and then calcined under non-oxidizing fore. conditions, During the calcination the cad 5 These and other objects will be perceived from mium, sulfur and selenium are induced to unite the following description of the invention. into a pigmentary product which exhibits the We have found that numerous advantages ac desired shades of red. Crue from calcining a crude cadmium red pig During the calcination it is desirable to have ment maSS which has had an oxidic cadmium present an oxidic cadmium compound, such as 20 Compound coprecipitated with it and hence in cadmium oxide, hydroxide, carbonate, etc., timately dispersed through it. Selenium losses since the presence of such compound has been during calcination are reduced or substantially found to effect a reduction in the amount of eliminated, lower calcining temperatures are selenium which is otherwise copiously volatilized possible, and greater uniformity and control out of the calcination charge. In One proposal 25 of Shade from batch to batch are achieved. of the prior art the oxidic cadmium compound These advantages spring largely from the inti was prepared separately from the crude cad macy of the mixture and the carefully selected mium sulfoselenide pigment, and was then mixed proportions of oxidic cadmium compound to or blended into the crude pigment before the Selenium, and are in contrast with results se latter was calcined. The separate preparation cured When the oxidic compound is prepared of the oxidic cadmium compound in pigmentary 30 Separately and then mixed or blended with the grades and States, and the blending thereof crude pigment. We have found that coprecipi with the crude SulfoSelenide pigment involves tion of the oxidic cadmium compound and the considerable expense in time, labor and equip Cadmium Sulfide, preferably in the presence of ment, and in addition has not been found to Selenium, produces the necessary intimacy of produce as uniform a calcination mixture as is 35 mixture, and is furthermore a practical, com deemed desirable. This invention is directed to mercial method which may be adapted to the the avoidance of the separate preparation of the present commercial methods for producing crude oxidic cadmium compound and to the avoid cadmium pigments. Coprecipitation eliminates ance of a separate mixing or blending step. In the former need of separately preparing the accordance with the preferred embodiment of 40 Oxidic compound in a pigmentary quality and this invention, the oxidic cadmium compound State, and avoids the expenses incident to the is formed in the presence of, and simultaneously time, labor and equipment for so preparing and with, the crude cadmium sulfoselenide as a re mixing the oxidic cadmium compound with a Sult of its coprecipitation therewith from aque calcination maSS. In view of these numerous ous solutions. By So coprecipitating these de 45 advantages of a coprecipitation method, it is sired compounds to produce the desired calcina apparent that the latter method offers many tion mixture, intimate dispersion of the oxidic features and effects which are commercially compound throughout the crude cadmium pig desirable. ment is obtained, and the separate preparation The invention is applicable particularly to and subsequent intermixing steps of the desired 50 the unextended or pure cadmium red pigments. ingredients of the calcination mass are avoided. AS is well known, such pigments are produced By calcining Such intimate mixture, an improved by incorporating a proportion of selenium with cadmium pigment is obtained, and losses of a crude cadmium sulfide pigment mass. The selenium are minimized. Selenium may be incorporated in such mass by Accordingly, it is an object of this invention 55 two alternative methods, one being to dissolve 2,643,198 3 4. the selenium in an alkali-metal or barium Sul The portions enclosed in brackets represent a ?ide solution and then to strike this solution single strike solution, but in the interest of clar with an aqueous solution of a cadmium Salt to ity, the portions thereof which are involved in produce a pure cadmium sulfoSelenide precipi the formation of the oxidic cadmium compound tate. The other method involves first preparing are represented separately from the portions a pure cadmium sulfide precipitate and Subse which react with the bulk of the cadmium Salt quently, but prior to calcination, adding thereto to form cadmium sulfoSelenide. In all of the and mixing therein the desired quantity of above equations, the selenium may be present in Selenium. The present invention may be ap a variable amount; accordingly, the symbol Se plied to each of these methods, but for reasons O is used to signify that selenium is present but is of commercial expediency we particularly pre not necessarily present in atomic proportions. fer the first of said methods; namely, that in The above equations illustrate that the various which the selenium is dissolved in the aqueous reactants are selected so that cadium Sulfo sulfide strike liquor, so that the oxidic compound Selenide and the oxidic cadmium compounds are is coprecipitated with the cadmium sulfide in the 5 the only insoluble products which are formed. presence of Selenium. The other reaction products, being Soluble, can In accordance with our preferred method of be removed from the precipitates by washing. operation, we strike a soluble cadmium salt solu During the Subsequent calcination of the crude tion with a previously prepared aqueous alkaline pigment obtained from the strike, other reactions Sulfide Solution containing Seleniuin and an 20 occur between the oxidic cadmium compound, oxidic compound of an alkali or alkali-earth part to all of the selenium and part of the cad metal, the latter oxidic compound being chosen mium sulfide to produce the final pigment. in view of the cadmium Salt which is being used Without being restricted to the theory there indi So that cadmium SulfoSelenide and an oxidic cated, we believe that the following reactions are cadmium compound are the only in Soluble prod 25 typical: ucts of the subsequent strike reactions. For ex acCdS--2Se--CdCO3-> ample, if a cadmium nitrate solution is to be 2CdSe--SO2-CO-- (ac-1) CdS struck, the sulfide solution may be composed of acCdS-3Se--2CdCO3-> sodium, potassium or lithium sulfide containing . . 3CaSe--SO2-4-2CO2-- (ac-1) CaS Selenium dissolved therein, and either or any of 30 sodium, potassium, lithium or barium hydroxide, acCdS--2Se--Cd(OH)2-> or sodium, potassium or lithium carbonate. 2CdSe--SO2--H2-- (ac-1) CdS Barium carbonate or mixtures of oxidic com acCdS-4-3Se--2Cd(OH)2 > pounds of alkali metal and barium which by 3CdSe--SO2-2H2O-- (ac-1) CdS metathesis yield barium carbonate cannot be It will be understood that exceSS Selenium Over used because barium carbonate is in Soluble and the molar proportions indicated in these re hence unable to effect the precipitation of the actions may be used. The reactions of other desired oxidic cadmium compound. When a Oxidic cadmium compounds, such as cadmium solution of cadmium sulfate is to be struck to oxalate, cadmium formate, cadmium tartrate, make a pure red pigment, alkali-earth metal ions etc., are comparable, and the fundamental con must be essentially absent in both the Sulfide Sideration common to all is the concept of co component and the oxidic component since even precipitating cadmium sulfide and an oxidic Small amounts of alkali-earth metal ions from cadmium compound in the presence of selenium, such sources or any other sources may produce and then calcining the coprecipitate to bring a precipitation of alkali-earth metal Sulfate about a reaction between the three components along with the desired crude cadmium pigment. (1) the oxidic cadmium compound, (2) part of The following tabulation shows the various oxidic the cadmium sulfide, and (3) part to all of the compounds which can be used in the indicated selenium. During the calcination a part of the strike systems for producing pure red pigments: cadmium sulfide may not enter into the afore mentioned reaction directly, as the equations Cd(NO3)2--alkali metal Sulfide Solution con 50 illustrate, but such portions may nevertheless be taining Se: influenced by the calcination and by the result (a) NaOH, Na2CO3, KOH, K2CO3, Li2CO3 or ing reaction products in Such manner that pig mixtures mentary and desired color qualities are imparted (b) NaOH, KOH, LiOH, Ba(OH)2 Ca(OH)2 to the entire calcination charge. The infillence or mixtures 55 of the reaction and/or reaction products on the Cd(NO3)2--barium sulfide solution containing mass as a whole is manifest in two prominent Se: ways: (1) pigmentary qualities are developed in (c) NaOH, KOH, LiOH, Ba(OH)2 Ca(OH)2 the mass at lower calcination temperatures than or mixtures would be needed if the Oxidic compound were not CdSO4--alkali metal sulfide solution containing 60 coprecipitated with the cadmium sulfide in the Se: presence of selenium, and (2) the selenium is (d) NaOH, KOH, LiOH, Na2CO3, K2CO3, used more efficiently in developing desired color Li2CO3 or mixtures tones and qualities; that is, selenium losses by Typical strike reactions involved in the practice volatilization are reduced, and deeper colors are of the invention are: obtainable, indicating that the selenium can be E. Na2S--Ser-2NaOH CdS. Se- 4NaNO3+Cd(OH), an -> a Cd (NO3)2 --LaNa2S--Se a CdS-Ser-2cNaNO3 2cd(NO), +I Bas-Se-Ba(OH), am -> at Cd(NO3).--LBaS --Se a CdS-S-I-rBa(NO), 2cdso. -- Na:S-Se-K:COs CdS-Se-- Na2SO --KSO--CdCO an -> a CdS () --LaNa2S--Se a CdS-Se-acNaSO4

2,643,196 5 6 induced to combine with the cadmium sulfide mind that the shade of red in the finished pig more effectively than in prior art methods. ment is determined largely by the ratio of Sele It has long been known that the red shades nium to cadmium Sulfide. LOW ratioS (i. e., low of cadmium sulfoselenide pigments are due to Selenium content) produce the orange colors Some sort of combination between the Selenium 5 and light reds, While high ratioS (high Sele and the cadmium sulfide. It is yet, So far as We nium content) produce the maroons and deeper are aware, a matter of speculation whether the Shades. Because of the effective manner in combination is strictly chemical, or physical, or which the present invention utilizes the Sele physico-chemical, and when we speak of the nium, prior art ratioS can be followed only selenium being combined with the cadmium Sul 10 roughly, and a perSon skilled in the art Who fide, we do not want to be restricted by any Seeks to produce a particular shade of red will theory regarding the manner in Which the COm realize that he must conduct a few trials to de bination has been effected or exists. For Our termine the precise ratio which he should use to present purposes of explaining the invention in produce the particular shade desired. Pref such manner that One skilled in the art may erably, however, the molar ratio of Selenium to practise it, selenium may be regarded to be com Cadmium Sulfide should be less than about 3:1. bined with cadmium sulfide when the finished The Subsequent examples give the proportions pigment has an orange or red color and can be Which We employ for a light red, a medium red shown by chemical analysis to contain the three and a very deep maroon. These examples may elements cadmium, Sulfur, and Selenium. 20 serve as guides to one who desires intermediate On this basis it will be understood that the Shades, provided he employs the same molar foregoing calcination reactions expreSS Our ratioS of Selenium to Oxidic cadmium compound. theory that at least a part of the selenium is in It will be understood from Equations A and B duced to combine with cadmium to form cadmi above that it is this latter ratio which promotes um Selenide. The reactions may be Written in the effective use of the Selenum. The higher the a simplified form by omitting the cadmium Sul ratio is, the more nearly one approaches the fide which does not react directly with Selenium prior art and the less efficiently is the selenium and the oxidic cadmium compound: used. However, the oxidic cadmium compound A. CdCO3-CdS.--2Se->2CdSe--SO2-CO should not be leSS than about A2% by Weight of 30 the crude pigment. When the oxidic cadmium B. 2CdCO3--CdS-3Se->3CdSe--SO2-4-2CO2 Compound is proportioned approximately stoi We express no theory as to the Way in Which the chiometrically to the total Selenium, on the basis cadmium selenide so formed ultimately combines of Equations A or B, the selenium is employed with any balance of the cadmium Sulfide to form very effectively. We accordingly prefer to use a red pigment, nor do we express any theory as 35 Se: CodO ratios of between 3:2 and 2:1. to the manner in which any exceSS Selenium may After One has Selected the approximate ratio contribute to the final red color. Accordingly of Selenium to cadmium sulfide, on the basis of we propose that reactions A and B, and others the shade of red he desires, and has also se comparable thereto, account in part for the more lected the desired proportion of oxidic cadmium effective use of Seleniuin. Which occurs as a 40 Compound, On the basis of Equations A or B, or result of our intentional incorporation in the otherwise, he is ready to formulate the strike calcination charge of a coprecipitated Oxidic Solutions which Will yield the desired crude pig cadmium compound, by illustrating that under ment maSS. One Strike Solution is prepared to such conditions, at least a part of the Selenium contain the total quantity of cadmium desired is induced to form a cadmium Selenide com in the crude pigment. Any soluble cadmium pound, and oxygen derived from the oxidic Compound can be used in preparing this solu cadmium compound is united with Sulfur derived tion and the Specific gravity of the solution may from the cadmium sulfide to form Sulfur dioxide. be varied widely. However, a moderately con The proportions represented in Equation A are centrated Solution is preferable to avoid the preferred because they result in the formation handling of large volumes of Solution. The other of reducing conditions during calcination. Strike Solution is formulated with a soluble sul In summary, the invention involves the fun fide, Selected as indicated above in view of the damental steps of (1) coprecipitating cadmium Soluble cadmium compound being employed, and sulfide and an oxidic cadmium compound, pref is made up to contain enough combined sulfur erably in the presence of Selenium, thereby and dissolved Selenium to give the ratios of sele producing an intimate mixture of the compo nium and Sulfur to cadmium oxide which are nents, and (2) then calcining the intimate mix desired in the crude coprecipitated pigment ture under conditions which convert the co .a.SS. The alkaline-reacting oxidic compound precipitated mass to a pigmentary state. The which by reaction with part of the cadmium improvements which We have observed to flow 60 Sait Solution produces the desired oxidic cad from these steps are: mium precipitate is also included in this strike 1. A more effective use of the selenium Solution, after which the solution is farther ad d. Reduced losses of Selenium. justed, if necessary, with water additions to b. Deeper colors for given ratios of selenium bring it to any convenient specific gravity. to Sulfur in the uncalcined pigment. 65 From what has just been described, it will be 2. Lower calcination temperatures. understood that four strike components are in 3. Avoidance of the costs heretofore involved in Wolved, one being the soluble cadmium salt which a. Separately preparing the Oxidic cadmium is prepared as a first strike solution, the other compound. three being Selenium, an alkaline-reacting oxidic b. Subsequently mixing the said oxidic com 70 component and a Soluble sulfide, being combined pound into a crude cadmium Sulfide-Selle into a Second strike solution. nium mass for calcination therewith. The two strike solutions may be reacted in any desired sequence, as cadmium first, cadmium sec 4. Cleaner and brighter colors. Ond, Simultaneously, or otherwise. We particu In practising the invention, one must keep in 75 larly prefer a simultaneous strike in which the

2,648,196 7 8 two solutions are poured together at a slow con Flake Sodium sulfide was dissolved and filtered trolled rate and are mixed with good agitation. to remove impurities. A typical Solution resulted This type of strike is particularly effective in which contained sulfide ions equal to. 32.2 g/1. giving accurate control of the particle size of the To 55.5 gallons of this solution were added 11.4 crude pigment mass. The strikes may be carried pounds of Na2CO3 and 9.7 pounds of Se. out at room temperatures or in a heated condi This mixed solution, and 40.0 gallons of a pure tion but we prefer to avoid temperatures in the Solution of CdSO4 which contained 177.3 g./l. Cd, strike slurry above about 70° C. Warm to hot were added simultaneously to 10 gallons of water strikes are beneficial to pigment qualities when at 60° C., and the above mentioned solutions were light reds or orange pigments are being prepared, O added at such rates that the pH-4- value of the While cold or room temperature strikes are ad slurry was maintained at 9.0 to 9.5. There was vantageous to the deeper shades. The Strikes formed a raw pigment which contained 67.3 should preferably be conducted so as to maintain pounds of CdS, 10.6 pounds of CdCO3, and 9.7 a pH in the strike slurry of between about 7.0 pounds of Se. and 10.0 and we particularly prefer a pH between 5 The precipitate was filtered and washed to about 9.0 and 9.5. remove soluble salts and then was dried at below After the strike has been completed, the Strike 100° C., and crushed in preparation for cal slurry is filtered and the crude coprecipitated pig cination. ment mass is washed to remove soluble Salts. Any The crushed raw pigment was calcined at ten conditioning agent(s) which may be desired to 20 peratures between 400° C. and 700° C. in its own assist the development of pigmentary qualities atmosphere and quenched in water. There was during the calcination may then be added to the very little loss of selenium by volatilization dur pigment mass in any convenient manner, Such as ing the calcination. by repulping the filter cake and adding the con The produce had excellent tinting strength and ditioning agent(s). The crude conditioned pig 25 color quality, and good grinding properties in oil ment mass may then be dried and ground pre and enannel vehicles. paratory to calcining it. The crude pigment may be calcined in any Suit Eacample 2-Medium red pigment able furnace at temperatures between about 400° C. and 700° C. During calcination a non-oxidiz 30 In this instance the following reaction was ing atmosphere is desirable, and it may be either employed to effect the precipitation: . mixed solution CdS. Se--Cd(OH)2+ Ba(NO3)+2KNOs -> stilla Cd (NO3)2 BaS-I-Se. CdS. Se --Ba(NO3), substantially neutral or mildly reducing. Strong 35 A Warm, filtered Solution of BaS was prepared ly reducing atmospheres should, however, ice whicin contained 27.4 g/l. Sulfide ion. 69.4 gal avoided as they may interfere with the desired ions of the barium. Sulfide solution were treated elimination of sulfur which is accomplished in Clair with 10.4 pounds of KOH and 18.3 pounds of process by reaction of cadmium sulfide with the granular selenium. When this solution was added oxidic cadmium compound. The non-Oxidizing 40 to 41.3 gallons of a pure Solution of Cd(NO3)2 atmosphere may be supplied from external containing 177.3 g/l. Cd, a precipitate was formed sources, or may be generated in situ, as when the which contained 1 mole of CdCOI) 2 per 4 moles proportions of the crude pigment correspond to of Se. those of Equation A above. When the pigment The precipitate was formed by adding the has been suitably calcined, it may be quenched in mixed solution composed of BaS, KOH and Se water directly from the calcining chamber. The 45 at 70° C., to the solution of Cd(NO3)2, at 25° C., quenched pigment may then be filtered, dried, slowly, with rapid agitation. The only heat in and ground. - troduced into the reaction cane by way of the We have found that pure red pigtinent. prepared heated barium liquor and the heat of the reaction in accordance with this invention has high tint itself. The final pH-- of the slurry was 8.0. The ing strength, good texture, gloss and grinding 50 precipitated raw pigment was filtered and washed properties and possesses clean, bright color qualir to remove soluble Salts. The precipitate Was then ties. ried rapidly at 90° C. in an oven, and crushed in The following examples illustrate the invention, preparation for calcination. but it will be undel'stood that many departures The raw pigment was calcined in a gas-fired may be made from the examples in accordance 55 rotary kiln, in a non-oxidizing atmosphere at with the principles stated hereinabove. temperatures between 400° C. and 700° C., quenched in Water, and Washed. - Eacample 1.-Light red pigment The resulting pigment was of high tinting The precipittalion reaction is as follows: Strength, Soft, With good texture, good gloss, and good grinding properties. - mixed solution - 2CdSO -- Na2S--Se--Na2CO3 CdS. Se--CdCO3-2Na2SO4 In this instance the loss of selenium during the axiary -> ww. calcination was slightly greater than in Example a ColSO4--acNa2S--Se acCdS. Se-- acNa2SO4 1, but not excessive. The calcination reaction which is desired is as follows: Eacample 3.-Very deep maroon pigment The lowest molar ratio of Se to CdC consistent (CdS) --CdS.--2Se--CdCO3-> with the preferred conduct of the invention was - 2CdSe--SO2--CO-- (CdS) utilized in the instant example to minimize the The CCS enclosed within parentheses indicates volatilization of Se during the calcination, i. e., the large excess of CdS which is present beyond 70 3 moles of selenium to 2 moles of cadmium hy the direct requirements of the reaction. droxide. mixed solution 4KOE -:) CdS-Se+2cd(OH)2+2KSO-- Naso, a CdSO NaS--3(Se) aCdS. Se --acNaSO

2,643,196 9 10 A volume of 38.0 gallons of a purified Solution the selenium being present in Sufficient quantity of sodium sulfide which contained 36.1 g./l. Sul to provide a molar ratio of Selenium to cadmium fide ion, was treated with 23.4 pounds of KOH oxide of at least 3 to 2, and the cadmium Sulfide and 21.5 pounds of granular Se. being present in Sufficient quantity above a molar A solution of pure cadmium sulfate was pre ratio of CdS : Se of 1 to 3 to produce the desired pared which contained 1744 g/l. Cd. The pH-i- shade of red, at least the cadmium sulfide and of the solution was 5.7. 41.6 gallons of this Solu the oxidic cadmium compound in Said maSS haW tion were used for the precipitation of the raw ing been formed in situ and coprecipitated as the pigment. direct insoluble products of a single strike be The precipitation was made in the cold under O tween: (a) an aqueous Solution of a cadmium constant agitation. The above Solutions Were salt as one strike component, and (b) a mixed added simultaneously to 10 gallons of Water SO aqueous solution as the other strike component, that the pH value Was maintained in the range said mixed solution containing a Soluble oxidic 9.0 to 9.5 throughout the entire 100-minute alkaline-reacting compound Whose anion forms precipitation. No external heat was introduced with cadmium ions an insoluble oxidic cadmium into the reaction. The final pH-- value was 9.2. compound, and a soluble sulfide whose cations The precipitate contained 51.75 pounds of CdS, yield water-soluble compounds When combined 26.5 pounds of Cd. (OH)2, and 21.5 pounds of Se. with the anion of said cadmium Salt. The precipitate was Washed, dried rapidly be 2. The method as claimed in claim i wherein low 90° C., and crushed in preparation for cal 20 the selenium is incorporated in said coprecipitat cination. ed mass by dissolving it in the said mixed aqueous Calcinations in the range 400-700° C. in a non Solution prior to the Said strike. oxidizing atmosphere produced pigments of ex 3. The method as claimed in claim 1. Wherein cellent tinting strength and color. the selenium is incorporated in the crude pige Paint grinds were easily prepared and resulted 25 ment mass by intimately dispersing it into the in products of high gloss and good texture. coprecipitated mixture of cadmium Sulfide and In the foregoing examples, a Small excess of oxidic cadmium compound after said coprecip the oxidic alkaline-reacting compound has been itated mixture has been formed. used over that amount needed to precipitate the 4. The method of making a cadmium Sulfo desired quantity of oxidic cadmium compound. 30 selenide pigment which comprises the Steps of: This is desirable practice, and is especially desir providing a coprecipitated crude pigment maSS able when the cadmium Sulfate Solution contains composed essentially of cadmium Sulfide, an in nitrates as a result of the use of nitric acid or Soluble oxidic cadmium compound and Selenium, ammonium nitrate during the dissolution of the the oxidic cadmium compound being present in cadmium metal. The excess alkaline-reacting 35 sufficient quantity to provide at least 42% of compound aids in neutralizing the acidity which Cadmium oxide by weight of the crude pigment is caused by Such nitrates. mass, the selenium being present in Sufficient We have pointed out above that while we prefer quantity to provide a molar ratio of Selenium to incorporate selenium in the crude pigment to cadmium oxide of at least 3 to 2, and cadmium mass by dissolving it in the soluble sulfide solu 40 sulfide being present in Sufficient quantity above tion, it is also practicable to Omit the Selenium a molar ratio between CdS and Se of 1:2 to pro during the coprecipitation, and to add it to the duce the desired shade of red in the finished crude pigment mass at a later state prior to cal pigment, Said coprecipitated mass being formed cination. Such subsequent addition of Selenium in situ as the direct insoluble products of a usually involves an extended grinding operation single Strike between (d) an aqueous Solution of which introduces extra costs and When conducted a cadmium salt as one strike component, and on a commercial Scale usually fails to give as in (b) a mixed aqueous Solution as the other strike timate a mixture as can be Secured by COprecip component, Said mixed Solution being composed itating the oxidic cadmium compound and the of a soluble oxidic alkaline-reacting compound cadmium sulfide in the presence of selenium 50 Whose anion forms With cadmium ions and in which has been dissolved in the Sulfide strike So soluble oxidic cadmium compound, a soluble lution. For these reasons we have exemplified alkaline Sulfide, and dissolved selenium, and be the latter process as being the best mode of ap ing Substantially free of cations which yield plying the principles of our invention. in Soluble SaltS When combined With the anion of It Will be understood that numerous other 55 Said cadmium salt; and calcining said crude pig variations of the process are possible Within the ment maSS in a non-oxidizing atmosphere at scope of the following claims without departing temperatures between about 400° C. and 700° C. from the principles of our invention. until converted to pigment. Having now described our invention, What We 5. The method as claimed in claim 4 wherein claim is: 60 the molar ratio of Selenium to cadmium oxide 1. The method of making a cadmium Sulfo is between about 3:2 and 2:1. selenide pigment, which method comprises: cal BENJAMIN W. ALTAN. cining in a non-oxidizing atmosphere at tem FRANK O. RUMMERY. peratures between about 400° C. and 700° C., an intimately mixed crude pigment maSS composed 65 References Cited in the file of this patent essentially of cadmium sulfide, and in Soluble UNITED STATES PATENTS oxidic cadmium compound and Selenium, the Number Name Date oxidic cadmium compound being present in Suffi 2,134,055 Meister ------Oct. 25, 1938 cient quantity to provide at least Az% of cad 2,48,194 Drucker ------Feb. 21, 1939 mium oxide by weight of the crude pigment mass, 70 2,248,408 Juredline ------July 8, 1941.