Assessing the Influence of NaCl on the Reduction of a Siliceous Laterite Nickel Ore Under Caron Process Conditions
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UCTION
THE two main mineral sources of nickel are sulfide ores and lateritic ores.[1–3] Sulfide ore accounts for 60 pct of the world’s nickel production, but on the other hand, lateritic ore is the most common ore, i.e., approximately 70 pct of the nickel mineral reserves are lateritic ores.[1–5] There are two main types of lateritic ores, namely (i) limonitic and (ii) saprolite. These two typologies have specific mineralogical phases that render the extractive process necessary for nickel production from one type of ore unsuitable when applied to ore of the other typology.[3,6–9] The Caron process was developed for the processing of the oxidized fraction of the nickel lateritic deposit (limonitic ore) and does not apply to the other fraction of the deposit (saprolite ore), mainly due to the low VICTOR DE ALVARENGA OLIVEIRA is with the Thermal Analysis Laboratory, Department of Metallurgical and Materials Engineering, Universidade Federal de Ouro Preto, Ouro Preto, Minas Gerais, CEP 35400-000, Brazil. Contact e-mail: [email protected] CLA´UDIO GOUVEˆA DOS SANTOS is with the Polymer Analysis Laboratory, Department of Chemistry, Universidade Federal de Ouro Preto, Ouro Preto, Minas Gerais, CEP 35400-000, Brazil. EDUARDO DE ALBUQUERQUE BROCCHI is with the Department of Chemical and Materials Engineering, PUCRio, Rio de Janeiro, CEP 22454900, Brazil. Manuscript submitted September 6, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS B
extraction values obtained when using this fraction. This can be explained by the fact that, in saprolite lateritic ore, most of the nickel is found in the crystalline network of silicate minerals (chlorite and magnesium aluminum silicates) and the thermal decomposition of these minerals promotes the formation of refractory phases such as enstatite and forsterite. These phases are responsible for the low values of nickel recovery in the Caron process. The presence of a characteristic exothermic peak in the differential scanning calorimetry (DSC) curve of lateritic ores, between 700 C and 820 C, has been reported by several authors as evidence of forsterite formation during thermal treatment or reduction of these nickel ores.[10–12] Several studies have been carried out aiming at reducing these ores and subsequently separating the reduced metal phase from unreduced oxides at a later stage of magnetic separation.[13–17] Although these works show an increase in the contents and good values for nickel recovery, the reduction temperatures used by the authors are always above 1100 C. This means that, despite the lower temperatures used by the authors compared to those of the RKEF process, yet a lot of energy has to be spent just to heat until 1100 C a raw material with low nickel content (< 3 pct). In addition, the formation of forsterite also leads to low recovery values of nickel, as can be inferred by some of these reports.[13–17]
Thus, in order to promote a better separation of the reduced metal phase of the different oxides present in the ore, and thus improving the recovery values of
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