GB325641A - Improved method for preparing white lithopone from incompletely purified zincic solutions - Google Patents

Abstract

325,641. Bidaine, M. Dec. 27, 1928. Pigments.-A method of producing white lithopone from incompletely purified zinc solutions in which a substance or substances are precipitated on the lithopone, is characterized by the precipitation of substances which are blue or greenish blue or acquire such colour on calcination, whereby the yellow or reddish yellow tint imparted to the lithopone by the impurities are complemented. The process may be effected in various ways from zinc solutions which may have been purified by known processes in such a way that certain quantities of nickel and cobalt are left in solution, giving a yellow tint to lithopone precipitated therefrom. (1) The colouring substance or substances may be added in the form of a salt or salts to the zinc solutions before their precipitation with barium sulphide, and precipitated with the lithopone. (2) The precipitated lithopone may be mixed with the salts &c. in solution and the colouring material precipitated by a suitable agent. (3) The salts &c. in solution may be added to the finished lithopone after wet grinding and before filtration, are precipitated, and the manufacture finished as usual. In examples (1) chromium sulphate is added to the zinc sulphate solution and the whole precipitated with barium sulphide whereby chromium hydroxide is formed on the lithopone. On calcination green chromium oxide is formed. (2) To the precipitated lithopone a small quantity of zinc and cobalt sulphates in solution are added. After agitation, the salts are precipitated as a pink aluminate which becomes greenish blue on calcination. (3) Sodium or potassium ferrocyanide solution is added to the finished lithopone before filtration, and precipitated with a ferric salt. Ferrous ferricyanide may be similarly precipitated on the lithopone. Specification 225,523 is referred to.