FR2574807A1 - CADMIUM PIGMENTS OR THE SOLUBILITY OF CADMIUM IN DILUTED HYDROCHLORIC ACID IS LIMITED - Google Patents

Abstract

A. CADMIUM PIGMENTS OR THE SOLUBILITY OF CADMIUM IN DILUTED HYDROCHLORIC ACID IS LIMITED. B. CHARACTERIZED IN THAT THEY CONTAIN, AS A COMPOUND OF HARDLY SOLUBLE ZINC, IN A PROPORTION OF 0.2 TO 5 BY WEIGHT, THE ZINC SALT OF 2,4,6-TRISMERCAPTO-S-TRIAZINE RESPONDING TO THE ZN FORMULA (CNS). C. THE INVENTION RELATES TO CADMIUM PIGMENTS WHERE THE SOLUBILITY OF CADMIUM IN DILUTED HYDROCHLORIC ACID IS LIMITED.

Description

Cadmium pigments o the solubility of cadmium in

  dilute hydrochloric acid is limited.

  The invention relates to cadmium pigments where the solubility of cadmium in dilute hydrochloric acid is reduced by a content of a compound of the invention.

  zinc, containing sulfur, hardly soluble.

  The term "cadmium pigments" should be understood to mean cadmium sulfides and sulfoselenides which have the crystalline structure of the hexagonal wurzite network and the characteristic particle size distribution for pigments. Cadmium sulphide is yellow; it is formed, by incorporation of Se ions, mixed crystals in cadmium sulphide whose shade passes, with the increase of the selenium content, to orange and

red, to purple.

  The. cadmium pigments are used

  preferably for coloring plastics.

  If we consider the toxicity of cadmium, it is desirable to

  than the proportion soluble in the acids of these pig-

  finely divided fractions, especially in hydrochloric acid

  diluted drique, and consequently also in the acid of the stomach,

  so as to exclude to a large extent an insalu-

  in case of oral absorption of powder of these pigments

during their handling.

  The dyestuffs of cadmium halides have already been described in DE 24 48 338, in which the solubility of cadmium in dilute hydrochloric acid is decreased, in which this solubility has been reduced by means of inorganic sulphides. precipitated on these pigments among which zinc sulfide. This precipitation is effected by sending gaseous hydrogen sulphide or by the addition of organic compounds giving off H2S in an aqueous suspension of pigment

containing a zinc salt.

  A disadvantage of this process lies

  in that, or else the hydro-

  toxic sulphide gaseous gene, or one operates with substances emitting sulphide ions, so that one can not avoid also a certain nuisance due to gases containing hydrogen sulphide. Since excess hydrogen sulphide must be used, it is necessary to take

  special provisions for the protection of

rations.

  For the same reason, cost measures

  its for purifying the air that escapes inevitably

  and other precautions for the protection of the environment

  are necessary because the filtrate is saturated

  H2S must be rendered harmless before being rejected.

  The technical expense and the time to spend for the treatment by this process are, therefore,

important.

  These deficiencies will be overcome according to the invention by cadmium pigments where the solubility of cadmium in dilute hydrochloric acid is

  decreased by means of a zinc compound content

  containing sulfur which is difficult to dissolve, characterized in that

  that these pigments contain, as a compound of zinc contained

  from 0.2% to 5% by weight of sulfur,

  the zinc salt of 2,4,6-trismercapto-s-triazine satisfies

  with the formula Zn3 (C3N3S3) 2. The cadmium pigments recommended according to the invention have a content of

  this zinc compound from 0.4 to 0.8% by weight.

  Another object of the invention is a

  process for the production of cadmium pigments

  the zinc compound containing sulfur. It consists in intimately admixing an aqueous slurry of the relevant cadmium pigment with a corresponding slurry of Zn3 (C3N3S3) 2, maintaining a weight ratio of cadmium pigment to the zinc compound of 100: 0.2 to 5, more preferably 100: 0.4 to 0.8, and then filtered and dried. The aqueous suspensions of the pigment and organic zinc compound are neutral and substantially free of electrolyte, so that the acid-stabilized pigment, separated from the joined and mixed suspensions, remains in original purity and we can thus remove the

wash with water.

  In general, the process according to the invention brings the following advantages: - The substances used emit no sulphurous ion

and are not toxic;

  - In the operation, no harmful substance escapes

  to the environment, so the precautions

  protection which might correspond to it

  feels; - All commercially available cadmium pigments will be positively influenced in their solubility in acids (determination according to DIN

  53 770), by a simple mixture with the suspension of

  neutral hibitor followed by filtration and drying and without special washing operation;

  - No precipitation operation on the cadmium pigment

  mium concerned has to be carried out; - The process requires only a slight manipulation and a

low energy expenditure.

  The zinc compound, used next

  the invention-for the stabilization, of the trismecapto-s-

  triazine (TMT) is manufactured, in a known manner by double reaction of TMT with a zinc salt, a solution of the sodium salt of TMT being reacted with a solution of zinc sulfate, and the precipitate being separated most of the sodium sulphate, which has formed and is in the solution, by two washes

  in a settling operation.

  The cadmium pigments to be treated according to the process of the invention will be

  manufactured as follows: The yellow pigment of

  mium is made by the reaction of cadmium sulphate with sodium sulphide in aqueous solution, washing, and drying the corresponding precipitate, then calcination at

  530 C. The red cadmium pigment is manufactured by reaction

  cadmium carbonate with a solution of sulpho

  sodium selenide, washing and drying the precipitate formed, followed by calcination at 580 C. The yellow and red pigments thus produced are then subjected to a treatment.

with dilute sulfuric acid.

  Pigments made in this way

  contain 0.6 to 0.1% by weight of soluble calcium

  According to this DIN document, 10 g of chalcogenide is stirred in 150 ml Erlenmeyer flask with 150 ml of 0.1 N HCl for 15 minutes at 23 ° C., inverting the bottle. Then, the suspension is allowed to stand for 10 minutes. Then the solution is filtered while settling on a membrane filter

  (pore size 0.15 P). Five minutes later, the filter

  is completed. Determination of Cd in the filtrate

  occurs with the atomic absorption photometer.

  The manufacture of the zinc compound suspension of the TMT, of which-. use in the

  method of the invention is described with reference to the examples

  following steps is carried out as follows: In a stainless steel container of a container of 300 liters, 100 liters of cold water completely demineralized and introduced, with vigorous stirring, 50 1 of zinc sulfate solution having a content of 100 g zinc / l, as well as 74 1 of a commercially available solution, at 15%

  of trisodium salt of 2,4,6-trismercapto-s-triazine.

  As the product of the reaction, a hard soluble precipitate forms, which corresponds, within the limits of the current technical tolerance, to the composition Zn3 (C3N353) 2, and sodium sulphate under

form of solution.

  To remove most of this sodium sulfate, the precipitate is washed, repeating two

  decantation, with completely demineralized water

  read, and then supplemented to a volume of 280 1.

  The suspension made in this way has a solids content of Zn3 (C3N3S3) 2 of 50

  g / 1. Before taking the quantity of Zn3 (C3N3S3) 2

  written for the treatment of the pigment in question, the

  The suspension is homogenized by vigorous stirring.

Example 1

  To a neutral aqueous suspension which contains 400 kg of cadmium red pigment in a total volume of 1.6 m 3, 16 l of a suspension of Zn 3 (C 3 N 3 S 3) 2, the content of which is

solid material is 50 g / l.

  The two suspensions are stirred together vigorously for 30 minutes, filtering the material

  solid in a filter press, and dried at 110 C.

  The proportion of acid soluble cadmium according to DIN 53 770 is, in the finished product

to 0.007% by weight.

Example 2

  To an aqueous-neutral solution, which contains 350 kg of yellow cadmium pigment in a total volume of 1.6 m3, is introduced at a temperature of 20 to 250C, 28 1 of an aqueous suspension of Zn3 (C3N353) 2 with

  a solids content of 50 g / l.

  both suspensions are shaken

  seems, energetically, for 30 minutes and ended

as in Example 1.

The proportion of soluble cadmium

  the acid according to DIN 53770 amounts to 0.006% by weight.

Example 3

  To a neutral aqueous suspension which contains 400 kg of cadmium red pigment in a total volume of 1.6 m 3, 48.1 of an aqueous suspension of Zn 3 (C 3 N 3 S 3) 2 was introduced at a temperature of 20 ° C.

  the solids content is 50 g / l.

  15.The two suspensions are shaken vigorously for 30 minutes, one with the other, and

completed as in Example 1.

  The proportion of soluble cadmium in

  the acids according to DIN 53 770 are 0.002% by weight.

Example 4

  In a neutral aqueous suspension which contains 350 kg of yellow cadmium pigment in a total volume of 1.6 m 3, 42 l of an aqueous suspension of Zn 3 (C 3 N 3 S 3) 2 are introduced at a temperature of 20 to C.

  the solids content is 50 g / l.

Both suspensions' are agitated

  together vigorously for 10 minutes, and are terminated

born as in example 1.

The proportion of soluble cadmium

  the acid according to DIN 53 770 amounts to 0.003% by weight.

Example 5

  To a neutral aqueous suspension which contains 400 kg of cadmium red pigment in a total volume of 1.6 m 3, 64 l of an aqueous suspension of Zn 3 (C 3 N 3 S 3) 2, having a temperature of 20 to 25 ° C., are added. a

  solids content of 50 g / l.

  The two suspensions are stirred together for 50 minutes, energetically, and terminated as

in example 1.

The proportion of soluble cadmium

  the acid according to DIN 53 770 amounts to 0.001% by weight.

Example 6

  To a neutral aqueous suspension which contains 350 kg of yellow cadmium pigment in a total volume of 1.6 m 3, 56 1 of an aqueous suspension of Zn 3 (C 3 N 3 S 3) 2 having a temperature of 20 to 25 ° C. is added at a temperature of 20 to 25 ° C.

  solids content of 50 g / l.

  The two suspensions are intimately mixed

  for 30 minutes and finish their treatment as

in example 1.

  The proportion of acid-soluble cadmium according to DIN 53770 in the finished product is

amounts to 0.001% by weight.

Example 7

  In a pulverulent aqueous suspension which contains 350 kg of yellow cadmium pigment in a total volume of 1.6 m 3, 350 l of an aqueous suspension of Zn 3 (C 3 N 3 S 3) 2 having a temperature of 20 to 25 ° C. are added at a temperature of 20 to 25 ° C.

  - solids content of 50 g / l.

  Both suspensions are shaken energetically together and their treatment is terminated as

in example 1.

The proportion of soluble cadmium

  the acid according to DIN 53 770 amounts to 0.001% by weight.

Claims (3)

R E V E N D I C A T I 0 N S   1>) Cadmium pigments with a solution   of cadmium in dilute hydrochloric acid reduced by a content of a zinc compound containing sulfur which is not readily soluble, characterized in that it contains   as a compound of zinc which is difficult to dissolve   portion of 0.2 to 5% by weight, the zinc salt of 2,4,6-   trismercapto-s-triazine corresponding to the formula Zn3 (C3N3S3) 2.   2) Cadmium pigments according to claim 1, characterized by a content of 0.4 to 0.8% by weight of the compound Zn3 (C3N3S3) 2.   3) Process for producing cadmium pigments containing a zinc compound containing   sulfur according to one of claims 1 and 2, characterized   in that an aqueous suspension is intimately mixed   may be agitated, the cadmium pigment con-   surrounded, with a corresponding suspension of the compound Zn3 (C3N3S3) 2, maintaining a ratio by weight between the cadmium pigment and the zinc compound of 100: 0.2 to   5, or better 100: 0.4 to 0.8 and then filtered and dried.