The waste electrolyte contains 250 to 300 g/l of gold . Commonly used recovery methods are replacement method and reduction method.
Professional big size CNC EDM Sinker machine manufacturer, the worktable fixed type. We supply best quality CNC EDM Sinker Machine quality and best price and best after service
Worktable Fixed CNC EDM Sinker Worktable Fixed CNC EDM Sinker,CNC EDM Sinking Machine,CNC EDM Sinker,big size CNC EDM Sinker Suzhou Simos CNC Technology Co., Ltd. , http://www.edm-machines.com
Replacement: replacing zinc powder, the reaction is:
2HAuCl 4 +3Zn=2Au↓+3ZnCl 2 +2HCl
Before using zinc powder to replace the waste electrolyte, it should be boiled and the nitrate should be washed to avoid gold returning. At the time of replacement, the pH is 1 to 2, so as to avoid the solution of zinc salt water to 30 g, which prevents the precipitation of gold.
Reduction: ethylene sulfite can be used iron sulfate or reduction reactions are of formula:
3FeSO 4 +HAuCl 4 = Au↓+FeCl 3 +Fe 2 (SO 4 ) 3 + HCl
Na 2 SO 3 +2HCl=2NaCl+H 2 O+SO 2 ↑
2HAuCl 4 +3SO 2 +6H 2 O=2Au↓+8HCl+3H 2 SO 4
In addition to precious metals, ferrous sulfate has almost no reduction effect on other metals, so it is beneficial to improve the purity of the reduced gold. However, the reduction reaction of ferrous sulfate is slow, the reaction is not thorough, and the tail liquid needs to be further treated with zinc powder.
If the waste electrolyte contains nitric acid, it should be heated and boiled before reduction to remove free nitric acid. Large particle sponge gold can be obtained by appropriate heating during reduction. In order to enhance the reduction of sponge gold, it has been proposed to add 0.3 g/L of polyethylene glycol as a coagulant to the solution. 