US3852404A - Preparation of crystalline sulfides and selenides of cadmium zinc and mercury - Google Patents

Abstract

Well-ordered hexagonal crystalline forms of the sulfides, selenides or solid solutions of the sulfides and selenides of cadmium, zinc or mercury are produced by treating crude, amorphous precipitates of the sulfides, selenides or mixtures of sulfides and selenides with aqueous ammonium sulfide. The crystalline cadmium sulfide-containing precipitates are particularly useful as pigments.

Description

United States Patent [1 1 Daly Dec. 3,1974

[ PREPARATION OF CRYSTALLINE SULFIDES AND SELENIDES OF CADMIUM ZINC AND MERCURY James Ernest Daly, Hudson Falls, NY.

Hercules Incorporated, Wilmington, Del.

Filed: Oct. 24, 1972 Appl. No.: 300,028

Inventor:

Assignee:

References Cited FOREIGN PATENTS OR APPLICATIONS 2/1963 Great Britain 423/509 OTHER PUBLICATIONS Mellor: A Comprehensive Treatise on Inorganic & Theoretical Chemistry, Vol. 4, (1923), p. 588.

Allen and Crenshaw: Sulfides of Zinc, American Journal of Science, Series 34, 341-396 (1912).

Primary Examiner-Oscar R. Vertiz Assistant ExaminerHoke S. Miller Attorney, Agent, or Firm-l-Iazel L. Deming [5 7 ABSTRACT Well-ordered hexagonal crystalline forms of the sulfides, selenides or solid solutions of the sulfides and selenides of cadmium, zinc or mercury are produced by treating crude, amorphous precipitates of the sulfides, selenides or mixtures of sulfides and selenides with aqueous ammonium sulfide. The crystalline cadmium sulfide-containing precipitates are particularly useful as pigments.

6 Claims, N0 Drawings PREPARATION OF CRYSTALLINE SULFIDES AND SELENIDES OF CADMIUM ZINC AND MERCURY This invention relates to production of crystalline compounds from Group IIB and sulfur and/or selenium, and more particularly to a process for converting crude cadmium sulfide-containing precipitates into pigmentary grade materials.

Various methods have been proposed for converting crude cadmium sulfide-containing precipitates into pigments. One method involves heating the crude, usually in a non-oxidizing atmosphere, at elevated temperatures of about 400 to 700 C. (the so-called calcination treatment). Another method concerns heating the crude under pressure in aqueous medium in the presence of a small quantity of an alkaline-reacting salt at elevated temperatures and preferably at about 360 C. Still another method relates to heating an aqueous slurry of crude cadmium sulfo-selenide in the presence of 1,000 to 2,000 percent of an alkali metal hydroxide and 50 to 150 percent of an alkali or alkaline earth metal nitrate, sulfate, halide or aluminate at 90 to 160 C. It has also been proposed to purify compounds of Groups [l8 and VlA by heating the compounds in a water slurry of an alkaline earth halide in a flow of inert gas in a furnace at about l,000 C. until the impurities have reacted with the halide and been removed by the gas. These prior art treatments require high tempera tures, high temperatures and pressures or large amounts of alkali to promote the crystal growth and particle size development necessary for a good pigment. Thus, any advantages in lower processing conditions are offset by the high investments required for equipment, maintenance and recovery of chemicals.

Now, in accordance with the present invention, it has been found that crude amorphous precipitates of the sulfides, selenides or mixtures of the sulfides and selenides of cadmium, zinc, or mercury can be refined without the prior art disadvantages to give crystalline products which are of particular value as pigments for coloring materials in hues ranging from light yellow through the oranges to reds.

Accordingly, the present invention relates to a process for producing crystalline sulfides, selenides or solid solutions of sulfides and selenides of cadmium, zinc or mercury, which process comprises treating a crude, essentially amorphous precipitate of at least one sulfide, selenide or mixture of sulfides and selenides of cadmium, zinc or mercury with sufficient of an aqueous ammonium sulfide solution to provide a weight ratio of solution to precipitate of at least 1:] and a weight ratio of ammonium sulfide to precipitate of at least 0.02:1 until the precipitate is converted to the well-ordered hexagonal crystalline state, and then recovering the crystalline product so produced.

The process of the invention have been found to be applicable to any Group "B sulfide, selenide or mixture of sulfides and selenides and is of particular value when applied to the cadmium sulfide-containing precipitates. For example, the invention is particularly useful for refining cadmium sulfide, mixtures of cadmium sulfide and cadmium selenide, mixtures of cadmium sulfide and zinc sulfide and mixtures of cadmium sulfide and mercury sulfide. The invention is also useful for aging the pure cadmium pigments as well as the extended pigments such as those of the so-,called lithopone type.

The crude, essentially amorphous precipitates which are treated in accordance with the invention can be prepared by any of the known methods for producing the desired crude precipitates of cadmium, zinc or mercury sulfides, selenides or mixtures of sulfides and selenides, as for example by reacting aqueous solutions or suspensions of salts of cadmium, zinc and/or mercury with solutions of an alkali metal or alkaline earth metal sulfide and/or selenide. Typically, the cadmium, zinc or mercury salt is a nitrate, sulfate or halide. By the suitable choice of raw materials such as cadmium, zinc, mercury, sulfur and selenium, a series of crudes can be produced yielding a wide range of colored pigments with hues varying from light yellow through the oranges to the reds and maroons. 7

As stated, the method of the invention is a wet conversion process in which crude, amorphous precipitates of at least one sulfide, selenide or mixture of sulfides and selenides of cadmium, zinc or mercury are treated in the presence of aqueous ammonium sulfide until the precipitate is converted to the wellordered crystalline state which exhibits by x-ray diffraction a welldeveloped hexagonal crystal structure. The treatment can be carried out at any convenient temperature but will usually be conducted within the range of from about 0 C. to about 300 C. and preferably from about 20 C. to about 275 C. for periods of time ranging from less than about 1 hour up to several days or more. Longer times, of course, will be required to perfect crystallization at lower temperatures. Moreover, by the judicious selection of the conditions of time, temperature and ammonium sulfide concentration, series of products with varying degrees of transparency, strength and cleanness can be produced.

The amount of ammonium sulfide solution which is used in the practice of the invention is an amount sufficient to provide a weight ratio of solution to precipitate (dry crude) of at least 1:1 and a weight ratio of ammonium sulfide ((Nl-l S) to precipitate of at least 0.02:1. Preferably the ratio of solution to precipitate will range from 1.521 to 20:1 and most preferably from 2:1 to 10:1, and the ratio of ammonium sulfide to precipitate will range from 0.05:1 to 15:1 and most preferably from 0.1:1 to 10:1. The concentration of the ammonium sulfide in the treating solution can vary within relatively wide limits and usually will range from about 2 percent to about percent and preferably from about 5 percent to about 50 percent by weight of solution. Other ammonium salts and particularly such salts as the nitrates, sulfates or halides can also be present in the treating solution in varying amounts providing they do not detract from the advantages of the invention. The amount of such other salts used will usually vary from about 5 percent to about 25 percent by weight of the treating solution.

The crude precipitate which is treated in accordance with this invention can be freshly formed precipitate in the aqueous medium in which it is formed, a filter cake or press cake of the precipitate, or precipitate which has been filtered, washed and, if desired, dried and pulverized.

The treatment of the invention does not require agitation, grinding, milling, etc. However, such can be used, if desired, to insure intimate contact and to facilitate handling.

The products produced in accordance with the invention are crystalline, highly colored materials. The

cadmium sulfide-containing materials in particular are characterized by a broad range of properties exhibiting maxima in transparency, purity of masstone and tinctov rial strength and range in color from light yellow through oranges to the reds. They can be prepared in all of the desired hues for commercial pigment applications, as warranted.

The invention will now be illustrated by reference to the following examples in which all parts and percentages are by weight unless otherwise specified.

EXAMPLE VI A crude cadmium sulfide precipitate is prepared by adding 600 parts of a 9% aqueous solution of sodium sulfide at 60 C. over a period of minutes to 480 parts of an agitated, 34.1 percent aqueous solution of cadmium nitrate maintained at 50 C. Agitation is continued for 1 hour at 50 C. after which time the resulting slurry is filtered and the precipitate is washed to remove soluble salts, dried and pulverized. The dry crude (100 parts) is next combined with 640 parts of a 9 percent aqueous ammonium sulfide solution in a vessel, the vessel is closed and the contents are allowed to age for 16 hours at 30C. without agitation, after which time the aged product is recovered from the ammonium sulfide liquor, washed, dried and pulverized. The product is a highly transparent, golden yellow pigment which exhibits by x-ray diffraction the hexagonal crystal structure of cadmium sulfide. The product is a pigment of good coloring power and gives clean, intense tint tones.

EXAMPLE 2 The procedure of Example 1 is repeated except that in this example the washed precipitate (400 parts of pulp containing 100 parts of crude on a dry basis) is not dried or pulverized, but is combined with 340 parts of a 17 percent aqueous ammonium sulfide solution in the vessel. The crystalline product of this example is a highly transparent, golden yellow pigment and is substantially identical with the product of Example 1.

EXAMPLE 3 The procedure of Example l is repeated except that in this example the slurry containing the cadmium sul- -fide precipitate is cooled to 30 C. and transferred directly to the vessel without filtration, washing, drying and pulverizing, and, therein, the slurry is combined with 516 parts of a 24 percent aqueous solution of ammonium sulfide. The crystalline product is a transparent golden yellow pigment which is substantially identical with the product of Example 1.

EXAMPLE 4 The procedure of Example 1 is repeated except that the vessel contents are aged for 16 hours at 70 C. The product of this example is a golden yellow pigment similar in hue, but cleaner by reflected light and less transparent than the product of Example 1.

EXAMPLE 5 The procedure of Example 1 is repeated except that the 100 parts of dry crude are combined witha solution prepared by dissolving l 12 parts of ammonium sulfate and 66 parts of sodium sulfide in 462 parts of water. The crystalline product of this example is a highly transparent golden yellow pigment which is substantially identical with the product of Example 1.

EXAMPLE 6 A dry crude cadmium sulfide precipitate is prepared as in Example 1 and the crude (100 parts, dry weight) is pebble milled with 640 parts of an 18 percent aqueous solution of ammonium sulfide for 48 hours at 30 C., after which time the product is recovered as in Example l. The crystalline product is a golden yellow pigment which is similar in hue but more opaque than the product of Example 1. The product of this example is characterized by unusually high tinctorial strength and cleanness.

EXAMPLE 7 A crude precipitate of a mixture of cadmium sulfide and zinc sulfide is prepared by adding 487 parts of an aqueous solution containing 148 parts of cadmium nitrate and 18.6 parts of zinc nitrate at 25 C. over 10 minutes to 500 parts of an agitated aqueous solution containing 58 parts of sodium sulfide maintained at 50 C. Agitation is continued for 1 hour at 50 C. after which time the resulting slurry is filtered and the precipitate is recovered in the manner of Example 1. The dry crude (100 parts) is next combined with 1,140 parts of a 10.5 percent aqueous ammonium sulfide solution in a vessel, the vessel is closed and the contents are aged without agitation for 16 hours at C., after which time the product is recovered according to the manner of Example 1. The product is a highly transparent, primrose yellow pigment having high tinctorial strength and clarity. The product exhibits by xray diffraction a hexagonal crystal structure and is a solid solution of cadmium sulfide and zinc sulfide.

EXAMPLE 8 A crude precipitate of a mixture of cadmium sulfide and mercury sulfide is prepared by adding an aqueous solution previously prepared by combining 575 parts of a 9 percent sodium sulfide solution and 54 parts of a 30 percent mercuric nitrate solution at 60 C. over 10 minutes to 1,810 parts of an agitated 8, percent aqueous solution of cadmium nitrate maintained at 60 C. Agitation is continued for 1 hour at 60 C. after which time the crude precipitate is recovered in the manner of Example l. The dry crude parts) is next combined with 400 parts of a 55 percent aqueous solution of ammonium sulfide in a vessel, the vessel sealed and the vessel contents aged for 142 hours at 30 C., after which time the aged product is recovered in the manner of Example 1. The product is a highly transparent deep orange pigment having high tinctorial strength. The product exhibits by x-ray diffraction a hexagonal crystal structure and is a solid solution of cadmium sultide and mercury sulfide.

EXAMPLE 9 A crude precipitate of a mixture of cadmium sulfide and cadmium selenide is prepared by adding a solution of sodium sulfide and sodium selenide (previously prepared by dissolving 14 parts of selenium in 425 parts of a 10.1 percent aqueous solution of sodium sulfide at 60 C.) over 10 minutes to an agitated slurry of cadmium carbonate and cadmium nitrate maintained at 50 C., the slurry having been prepared by reacting 430 parts of a 35 percent aqueous solution of cadmium nitrate with 260 parts of a 3.5 percent aqueous solution of sodium carbonate at 25 C. Agitation is continued for 1 hour at 50 C., after which time precipitate is removed by filtration. The precipitate is washed to remove soluble salts, dried and pulverized. 100 parts of 5 the pulverized crude precipitate is mixed with 500 parts of a 24 percent aqueous solution of ammonium sulfide in a pressure vessel equipped with an agitator, the vessel is sealed and the contents are agitated for 4 hours at 250 C. under about 1,000 pounds per square inch pressure, after which time the pressure is released and the product recovered in the manner of Example 1. The product is a medium red pigment exhibiting by x-ray diffraction a hexagonal crystal structure and is a solid solution of cadmium sulfide and cadmium selenide.

What I claim and desire to protect by Letters Patent is:

1. A process for converting a crude, essentially amorphous precipitate of cadmium sulfide, or a mixture of cadmium sulfide and cadmium selenide, zinc sulfide 0r mercury sulfide into a pigment having an x-ray diffraction pattern characteristic of the hexagonal crystalline structure, which process comprises treating said crude,

essentially amorphous precipitate with sufficient of an aqueous solution containing from about 5 percent to about 55 percent by weight of ammonium sulfide to provide a weight ratio of solution to precipitate of at least 2:1 and a weight ratio of ammonium sulfide to precipitate of 0. 1 :1 to 10:1 at a temperature from about 20 C. to about 275 C. for a period of time ranging from about 1 to about 6 days until said precipitate is converted to the well-ordered hexagonal crystalline state and recovering the crystalline pigment so produced.

2. The process of claim 1 wherein the pigment is cad-' mium sulfide.

3. The process of claim 1 wherein the pigment is a solid solution of cadmium sulfide and cadmium selenide.

4. The process of claim 1 wherein the pigment is a solid solution of cadmium sulfide and zinc sulfide.

5. The process of claim 1 wherein the pigment is a solid solution of cadmium sulfide and mercury sulfide.

6. The process of claim 1 wherein the recovered crys-

Claims (6)

1. A PROCESS FOR CONVERTING A CRUDE, ESSENTIALLY AMORPHOUS PRECIPITATE OF CADMIUM SULFIDE, OR A MIXTURE OF CADMIUM SULFIDE AND CADMIUM SELENIDE, ZINC SULFIDE OR MERCURY SULFIDE INTO A PIGMENT HAVING AN X-RAY DIFFRACTION PATTERN CHARACTERISTIC OF THE HEXAGONAL CRYSTALLINE STRUCTURE, WHICH PROCESS COMPRISES TREATING SAID CRUDE, ESSENTIALLY AMORPHOUS PRECIPITATE WITH SUFFICIENT OF AN AQUEOUS SOLUTION CONTAINING FROM ABOUT 5 PERCENT TO ABOUT 55 PERCENT BY WEIGHT OF AMMONIUM SULFIDE TO PROVIDE A WEIGHT RATIO O SOLUTION TO PRECIPATE OF AT LEAST 2:1 AND A WEIGHT RATIO OF AMMONIUM SULFIDE TO PRECIPITATE OF 0.1:1 TO 10:1 AT A TEMPERATURE FROM ABOUT 20*C. TO ABOUT 275* C. FOR A PERIOD OF TIME RANGING FROM ABOUT 1 TO ABOUT 6 DAYS UNTIL SAID PRECIPITATE IS CONVERTED TO THE WELL-ORDERED HEXAGONAL CRYSTALLINE STATE AND RECOVERING THE CRYSTALLINE PIGMENT SO PRODUCED.

2. The process of claim 1 wherein the pigment is cadmium sulfide.

3. The process of claim 1 wherein the pigment is a solid solution of cadmium sulfide and cadmium selenide.

4. The process of claim 1 wherein the pigment is a solid solution of cadmium sulfide and zinc sulfide.

5. The process of claim 1 wherein the pigment is a solid solution of cadmium sulfide and mercury sulfide.

6. The process of claim 1 wherein the recovered crystalline pigment is washed, dried and pulverized.