A technique for selective extraction of ions of gold and silver from hydrochloric solutions with tributylphosphate

Abstract

Extraction is studied by tributylphosphate (TBP) of ions of gold and silver from hydrochloric solutions during the portional and single time feed of extractant in dependence of the initial concentration of metal ions, temperature, concentration of hydrochloric acid, the ratio of organic (О) and water W phases О:W. The initial solutions contained soluble complex chlorides of gold and silver. When dissolving metal chlorides in the solution of common salt and hydrochloric acid, water soluble coordinate compound are formed that contain complex anions [AuCl 2 ] – , [AuCl 4 ] – , [AgCl 2 ] – , [AgCl 3 ] 2– , [AgCl 4 ] 3– , et al. As an extractant we used the tri-butyl ether of phosphoric acid (С 4 Н 9 О) 3 РО hat belongs to oxygen containing neutral extractants. The formation of coordinate (complex) compounds of TBP and metal polychlorides may be treated as the process of solvation of the extracted metal salt by the extractant. For selective extraction of ions of gold and silver from their hydrochloric solutions by tributylphosphate it is run feeding the extractant portionally to the solution at the minimal time of contact between the solution and the extractant; it helps extracting gold almost completely with the few first portions of the extractant at concentrations of 2n HCl 240 g/dm 3 NaCl and the temperature t = 60°С. Meanwhile the extraction of silver is kept to a minimum. Silver is extracted almost completely after the extraction of gold is over; it is done with tributylphosphate as well at concentrations of 3n HCl, 240 g/dm 3 NaCl and the temperature t = 20°С.