複雑硫化鉱硫酸化焼鉱の選択還元焙焼

複雑硫化鉱の製錬に関する研究 (第6報)

抄録

Selective reduction of copper sulfate contained in sulfation-roasted calcine of complex sulfide are and leaching of zinc compounds (ZnO·E2ZnSO4, ZnO, ZnS) in the reduction-roasted calcine with 0.4N H₂SO₄were investigated.
If copper exists in a metallic state after the reduction, the copper will be left behind in leached residue by the leaching treatment, and then the separation of zinc from copper is to be attained only by the acid leaching of the reduced calcine. Furthermore, this method facilitates recovery of gold and silver beared in raw sulfide ores, because the gold and the silver will be allowed to behave together with the metallic copper in the leached residue when the copper is cast into moulds to prepare copper anodes for electrolytic refining.
However, if zinc sulfate in the sulfation-roasted calcine is converted into zinc sulfide during the reduction roasting, the leaching of zinc with 0.4N H₂SO₄may be hindered. Factors which have an effect on the conversion of the zinc sulfate were concentration of CO in a reducing gas-mixture composed of CO, CO₂and N₂, and reduction-roasting temperature. The degree of the conversion became higher with the greater CO-concentration and the higher reduction temperature. These conditions accelerated also formation of iron sulfide FeS from Fe₃O₄and SO₂which were produced in the reduction roasting: Fe₃O₄+10CO+3SO₂=3FeS+10CO₂
The iron sulfide evolved H₂S by a reaction with H₂SO₄ in the leach solution and the hydrogen sulfide promoted dissolution of the magnetite. Liberated Fe³⁺ion from dissolved magnetite attacked not only the zinc sulfide but also the metallic copper. Therefore, copper dissolution in the leaching treatment could not be avoided so far as the magnetite dissolved to any extent.
It was confirmed experimentally that the optimum conditions for the selective reduction roasting in a fluidized bed were as follows; the reduction temperature-500°C, the CO-concentration-20%(CO₂/CO=1.3) and roasting time 4hrs. The zinc extraction from the reduction-roasted calcine under those conditions with 0.4N H2SO4 was 92%, the copper dissolution 17% and the iron extration was 52%