China Nonferrous Metallurgy

The rotary kiln combined with hydrometallurgical process to recover silver from copper anode slime is used by a metallurgical plant. The obtained crude silver powder is of low grade, for which the silver converter process needs to be added, it will result in an increase of energy consumption and severe environmental pollution. In a bid to omit the silver converter process, a new hydrometallurgical process for silver separation is tested by the plant to replace the original silver separation process of ammonia leaching-hydrazine hydrate with the new hydrometallurgical silver separation process. Exploratory tests were conducted on silver separation with sodium sulfite-formaldehyde reduction-oxidative acid leaching process for impurity removal (silver separation with sodium sulfite-formaldehyde direct reduction process) and silver separation with sodium sulfite-decomplexation of silver separation solution-oxidative acid leaching for impurity removal-formaldehyde reduction process(silver separation with sodium sulfite-formaldehyde indirect reduction process). The results showed that the silver separation with sodium sulfite-formaldehyde indirect reduction process featured a sound stability, the grade of obtained crude silver powder reached 99.93% and the content of other impurities approached to zero. If the silver separation with sodium sulfite-formaldehyde indirect reduction process is substituted for the original process, it is estimated that the plant will increase benefits of at least 1386900 CNY. The regeneration and recycling of sodium nitrite solution from the test process is the key issue that needs to be tackled for the follow-up new process. It can not only solve the problem of production water volume expansion and but also lower the volume of wastewater treatment and consumption of sodium sulfite, which are of vital importance to further reduction of production cost.