METHOD OF HEAVY METALS ESPECIALLY CADMIUM REMOVAL FROM SOLUTIONS WITH PHOSPHORIC ACID CONTENT

摘要

PCT No. PCT/NO89/00016 Sec. 371 Date Nov. 3, 1989 Sec. 102(e) Date Nov. 3, 1989 PCT Filed Feb. 24, 1989 PCT Pub. No. WO89/08075 PCT Pub. Date Sep. 8, 1989.The present invention relates to a method for removal of heavy metals, especially cadmium, from phosphoric acid containing solutions, primarily such solutions made by digestion of rock phosphate by nitric acid and subsequent removal of the main part of calcium from the mother liquor. The phosphoric acid solution is pre-purified for removal of sludge and insolubles and then partly neutralized with ammonia to pH 1.4-2 and cooled to 5 DEG -40 DEG C. Metal salts of dithio carbonic acid-O-esters are added for precipitating the heavy metals which then are separated from the solution. The solution is preferably neutralized to pH 1.6-1.8 and cooled to 10 DEG -20 DEG C. before precipitation of the heavy metals which then can be removed from the phosphoric acid solution by flotation and subsequent filtration.