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A mechanism to convert Fe(III) to Fe(II) by a reduction process could be a solution to the problem of selective separation of metals in extraction processes by using the ion-exchange process. The aim of this research was to reduce Fe(III) to Fe(II) present in leachate from nickel mining waste. Reducing agents used were sodium dithionite and sodium metabisulfite. The potential was decreased in order to quantify the minimum reducing agent that was necessary for conversion. Reaction time, pH, stirring speed and temperature were also studied. Results indicated dithionite was a better reducing agent than metabisulfite and complete conversion was possible by reducing the potential to 590mV at pH 0.5-2 and 240mV at pH 2.5. Stirring speed had no influence on the reduction process at 2 hours; however, conversion decreased after 24 hours, perhaps due to oxygen present in air. The analyses were conducted by ion chromatography and voltammetry.

The processing of laterite ores for nickel and cobalt production is increasing to meet the global demand for these metals. Sulphuric acid is used as a leaching agent, and metals present in the solution may be recovered by many different processes, such as ion exchange. The main problem with nickel limonite layer leach solution is the high concentration of iron, which decreases the efficiency of resin adsorption of nickel and cobalt. The removal of iron by oxidation and precipitation results in nickel, copper, and cobalt losses (co-precipitation). The aim of this work was to investigate the chelating resin extraction to recover copper from a leachate combined with a pre-reduction process, in order to increase the resin's efficiency and to increase its pH above 2.00. The following three synthetic solutions were studied: first, a solution prepared with Fe(III); the second solution was prepared with Fe(II); and the last solution was prepared with Fe(III) using a reducing process. Batch experiments were performed to study the influence of pH and temperature, and column experiments with three solutions were compared in order to verify suitable conditions to recover Cu(II) in a fixed-bed column process.

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