Pure lead chromate pigment - prepd by pptg chromate particles in presence of excess chromate ions and removing excess chromate ions

摘要

Pure lead chromate pigment is prepd. by (a) forming an acidic lead chormate suspension at ambient temp. by adding an aq. soln. of lead ions to an aqs. soln. of chromate ions, precipitation being effected in the presence of excess of chromate ions in the suspension; (b) heating the suspension at the rate of at least 1.5 degrees C/min. to 60 degrees C; (c) maintaining the suspension at 60 degrees C for a period sufficient to stabilise the lead chromate precipitate; (d) pptg. the excess chromate ions at pH 5.5-6.5 by adding an aqs. soln. f lead ions; (e) separating the lead chromate particles from the soln; and (f) converting the separated particles into a pigment. The separated mother liquor is practically free of Cr(VI) ions, and thus does not cause pollution. high quality pigments are obtd. with a good resistance to light, heat and industrial atmospheres, and low lead content.