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UBC Theses and Dissertations

Kinetics of leaching galena concentrates with ferric fluosilicate solution Chen, Alan Airong


A new hydrometallurgical leaching process, which dissolves galena concentrates with acidified ferric fluosilicate solution, has been investigated for the selective extraction of lead and zinc from the galena concentrates. The process of leaching galena concentrates avoids the generation of sulfur dioxide and lead dust emissions and is capable of treating complex sulfide and low-grade flotation concentrates. The leaching of Pine Point galena concentrates by ferric fluosilicate solutions was studied under various experimental conditions in the temperature range 20 to 95°C. Temperature had a pronounced effect on the dissolution of the concentrates. The rates of lead leaching are very rapid over the temperature range 38 to 95°C. The reaction rates for the dissolution of galena were found to be controlled by surface chemical reaction. The apparent activation energy of the leaching reaction was calculated to be equal to 62.1 kJ/mole which is consistent with a chemical reaction control mechanism. The SEM micrographs show that the elemental sulfur reaction product formed in the leaching of the galena concentrate is fairly rough and appears to be quite porous on the particle surface. It is a non-protective product layer. The fluosilicate lixiviant may dissociate at high temperatures. Some white precipitates were found in the leached residue which were generated in the course of reactions at above 65°C. The initial contents of Pb2+, H+, and Fe3+ in the lixiviant do not have a significant effect on the lead extraction under the experimental conditions in the study. The insensitivity of the leaching rates to the leaching variables probably arises from an electrochemical mechanism involving adsorption of ferric ions on cathodic sites, isolated from anodic sites where the leaching takes place. During the course of the galena leaching, zinc extraction is much lower than lead extraction, especially at temperatures below 65°C. Separation of lead and zinc by selective leaching seems to be feasible and effective. Therefore, the ferric fluosilicate leaching system appears to have great potential to treat both conventional lead sulfide concentrates and complex sulfide concentrates, such as the McArthur River concentrates. The solubility of lead salt in fluosilicate medium is relatively high, and easily meets the concentration requirement for the subsequent aqueous electrolysis operation.

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