Abstract
Recent advances in high-tech applications have highlighted the growing demand on highly pure silicates like quartz. Therefore, purification of quartz ore was determined as the subject of this study performed by pyrometallurgical followed by hydrometallurgical processes. In this research, the effect of thermal treatment (TT) followed by oxalic acid (OA) bleaching of quartz was examined to have a better understanding on the relationship between Fe remaining in concentrate and colour response. The level of TT temperature was found to have a significant effect on the purification of quartz by OA. The maximum Fe rejection rate was observed to occur both for non-treated and TT quartz up to 250°C. TT between 400°C and 900°C showed poor purification performance: decreasing L* value, and increasing a* and b* values. It is important to note that further increase in TT temperature to 1100°C resulted in the poorest bleaching: Fe rejection rate decreased, but colour response improved providing the highest L* value and the lowest a* and b* values. This finding was explained by the formation of dissolution resistant iron silicates. Moreover, the rate of Fe removal from quartz ore and differences observed in its colour response by OA bleaching were explained by changes in crystalline structure and formation of microcracks.
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