Precipitation of iron from concentrated chloride solutions: Literature observations, challenges and preliminary experimental results

The removal of iron is necessary during the purification of leachates from zinc bearing ores prior to electrowinning due to its negative impact on both product quality and current efficiency. Whilst precipitation down to acceptable levels is readily achieved, the challenge lies in producing an easily filterable precipitate which is relatively pure (for resale and/or reuse). Crystalline hematite is an iron precipitate which potentially fulfils these requirements. Some work has been presented in literature on precipitation of hematite from sulphate solutions and dilute chloride solutions, however no work has been found on the selective precipitation of hematite from concentrated halide solutions. This technical note presents some preliminary observations on the selective formation of hematite from a leachate which originated from the zinc recovery process developed by Intec Ltd. The process is novel in the use of a mixed halide leachant over the traditional sulphide leachant, with the advantages of operation at low temperatures and atmospheric pressure, and that the leachant may be regenerated and recycled. The solution contains relatively high chloride/bromide concentrations which makes direct extrapolation from literature reports difficult.