GB774709A - Process for removing arsenic compounds from phosphoric acid - Google Patents

Abstract

774,709. Purifying phosphoric acid by electrodeposition of arsenic. KNAPSACK-GREISHEIM AKT.-GES. Aug. 31, 1954 [Sept. 2, 1953], No. 25312/54. Class 41. Arsenic is removed from phosphoric acid by electrodeposition in the presence of dissolved copper, which is codeposited with the arsenic, and 0.5 to 50 parts by weight of added iodine per 100 parts of copper, the ratio of copper to arsenic being between 0.2 to 1 and 5 to 1. The copper may be anodically dissolved or it may be added as a soluble salt such as the chloride, bromide, sulphate, nitrate, or acetate, preferably as the phosphate, either directly or as a concentrated aqueous solution. The iodine may be added as a 0.1 N solution or as hydriodic acid or its soluble salts. Cuprous iodide may be used to add both components. Typically electrolysis is effected between a platinum gauze anode 7 and a surrounding copper gauze cathode 8 in a brick-lined double-wall cell 3 heated to 90‹ C. by liquid passed in the space between the walls, with an applied potential of 3 volts at a low cathode current density the reaction mixture which is stirred being either treated batchwise or passed steadily through the cell from pipe 4 to pipe 5 at a rate so that the reaction mixture is changed every 30 minutes. In the modified cell (not shown) employed in the examples concentric copper gauze cathodes are disposed on opposite sides of the anode.