Effect of arsenic-antimony mineral on cyanide leaching
2020-08-18 17:08Introduction：Effect of arsenic-antimony mineral on cyanide leaching Arsenic in gold ores exists in the form of sulfides (realgar, orpiment , arsenopyrite, etc.). Arsenic minerals are extremely harmful to the leaching of gold and silver, sometimes makin
Effect of arsenic-antimony mineral on cyanide leaching
Arsenic in gold ores exists in the form of sulfides (realgar, orpiment , arsenopyrite, etc.). Arsenic minerals are extremely harmful to the leaching of gold and silver, sometimes making them impossible to carry out. Realgar(As2S3) and orpiment(As2S2) are highly soluble in alkaline cyanide:As2S3＋6Ca(OH)2=Ca3(AsO3)2+Ca3(AsS3)2+6H2O
Ca3(AsS3)2+ 6Ca(OH)2= Ca3(AsO3)2+6CaS+6H2O
2CaS+2O2+H2O=CaS2O3+ Ca(OH)2
2CaS+2NaCN+O2+2 H2O=2NaCNS+2 Ca(OH)2
Ca3(AsS3)2+6 NaCN+3O2=6 NaCNS+ Ca3(AsO3)2
As2S3+3 CaS= Ca3(AsS3)2
6As2S2+3O2=2As2O3+4As2S3
6As2S2+3O2+18 Ca(OH)2=4 Ca3(AsO3)2+2 Ca3(AsS3)2+18H2O
Arsenopyrite is difficult to dissolve in cyanide solution, but it produced Fe2(SO4)3 、As(OH)3and As2O3 etc during oxidation, In the absence of free base, As2O3 can react with cyanide to form HCN：
As2O3+6NaCN+3H2O=2Na3AsO3+6HCN
Arsenate and thioarsenate in solution can form a covering film on the surface of gold and silver, which hinders the dissolution of gold and silver. Therefore, arsenic-bearing ore is difficult to be leached directly by cyanidation, which is usually treated by oxidation roasting and then cyanide leaching.
Stibnite is a common antimony mineral in gold-antimony ore. It does not directly interact with cyanide, but it can dissolve well in alkali and form antimonates and thioantimonates:
Sb2S3+6NaOH=Na3SbS3+Na3SbO3+3H2O
2Na3SbS3+3NaCN+3H2O+3/2O2= Sb2S3+3NaCNS+6NaOH
The sulfides of antimony are dissolved again in alkali, which further absorbs oxygen. These reactions can only end when all the sulfides of antimony become oxides.
Antimonates and thioantimonates can also form thin films on the surface of gold and silver, which hinders the dissolution of gold and silver. Therefore, it is very difficult for gold and antimony ore to be leached directly by cyanide, which usually needs to be oxidized and roasted first, then cyanide leaching.
