Selenium extn. from materials contg. silver - by oxidn. in presence of nitrate and leaching to selenious acid

摘要

Se extn. from starting materials contg. Se and Ag, esp. metallurgical intermediates such as anode sludges, takes place by an oxidising leaching process. The starting materials in acid aq. phase are (1) oxidised in the presence of gaseous O2 and, w.r.t. Se oxidn. to H2SeO3, substoichiometric nitrate ion quantities, but >=2g/l., and (2) leached with Cl- and/or Br- ions in >= stoichiometric quantities w.r.t. Ag content of starting materials. Separation of dissolved Se from soln. is pref. achieved by introducing SO2. Generation of nitrous gases is prevented by adding urea before SO2 introduction. Process is partic. suitable for processing anode sludges after extn. of Cu and/or Ni, e.g. with H2SO4 in presence of air. Process is economical, with high degree of decompsn., e.g. 95% calc. on initial Se and high Se concn. in leaching agent.