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In this article, a leaching study, carried out on a quartz sample to obtain high-purity silica sands, has been presented. A leaching process by using oxalic acid to remove low iron content from the ore under study and to obtain a material suitable for fiber optic production has been evaluated. A characterization study has been carried out to establish the location of the iron impurities on the ore:  77 g/t was the maximum iron contamination, whereas, a final iron content <10 g/t (as Fe) has to be achieved for the application considered. The effect of the grinding process on the iron extraction yield has been established; the maximum iron extraction yield obtained with the ore as-is was about 45−50%, whereas extraction yields greater than 80−90% can be obtained after grinding the ore in different experimental conditions. An empirical model was evaluated to correlate the iron extraction yield obtained after 3 h of leaching at 80 °C, with 3 g/L of oxalic acid and 10% (w/v) of ore concentration, as a function of the average particle diameter of the ore after grinding. An iron extraction yield of about 98−100% can be obtained with an average particle diameter of about 20 μm. A schematic flowsheet of the process has been proposed considering the obtained experimental results and the results obtained in the literature for the waste treatment aspects. The experimental results have shown the technical feasibility of this process for the production of high-purity silica sands.

In the present work a preliminary study of iron removal from a yellow kaolin supplied by ECC International (Europe) Ltd. was performed using mainly oxalic and ascorbic acids in sulfuric acid solutions. The aim of the initial phase of research was to determine the effects of the main factors which can potentially influence the iron-removal process. Two-level fractional factorial experimentation was thus utilized to establish the main factors having an influence on the iron removal and to define a subsequent experimental test design. The factors involved in this study were:  temperature, concentration of oxalic and ascorbic acids, mineral concentration, mixing conditions, and concentration of the sulfuric acid. The experimental results shown that the effect of oxalic and ascorbic acids and of the temperature are the most important. In the investigated conditions, the maximum iron extraction yield was 43−45% after 3−4 h of treatment indicating a limit of iron removal for the mineral. Further study is in progress to define the best operative conditions considering the economic point of view.

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