The main reactions of leaching strontium sulfide concentrate and brittle sulphur bismuth lead concentrate with Na 2 S solution are:
However, Na 2 S can be strongly hydrolyzed in water:
The NaHS produced by hydrolysis is oxidized by oxygen in the air to form sodium polysulfide Na 2 S 2 , thereby reducing the action of Na 2 S. Therefore, a certain amount of NaOH should be added to the Na 2 S leachate to inhibit the two types. Adverse reactions that affect leaching efficiency. Experiments have shown that in the case of adding NaOH, the amount of Na 2 S is slightly higher than the theoretical amount, and a high leaching rate can be obtained. Therefore, the leaching agent actually used is Na 2 S+NaOH. When Na 2 S is insufficient, NaOH also has a certain dissolution effect on Sb 2 S 3 , and the reaction is:
The Na 2 S+NaOH mixed solution also dissolves Sb 2 O 3 , and the reaction is carried out in two steps:
The high-valent oxides Sb 2 O 4 and Sb 2 O 3 do not dissolve in the Na 2 S solution. Associated metal antimony sulfide concentrate, in addition to Hg, and Ag, Cu, Pb, Fe, Zn, Ag and other immune Na 2 S dissolved in the solution, enriched in the slag during leaching. The leaching reaction of sulfides of Hg and As is as follows:
Sulfide of arsenic can also be dissolved by NaOH, but arsenic in the arsenopyrite (FeAsS) is insoluble.
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