Reductive Leaching of Iron and Magnesium out of Magnesioferrite from Victorian Brown Coal Fly Ash

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• 作者：Teck Kwang Choo ; John Cashion ; Cordelia Selomulya ; Lian Zhang
• 刊名：Energy & Fuels
• 出版年：2016
• 出版时间：February 18, 2016
• 年：2016
• 卷：30
• 期：2
• 页码：1162-1170
• 全文大小：531K
• ISSN：1520-5029

文摘

This paper for the first time reports the reductive leaching of an iron-rich brown coal fly ash composed principally of a chemically resilient magnesioferrite (MgFe<sub>2sub>O<sub>4sub>) matrix. The simultaneous mobilization of Fe and Mg out of magnesiorferrite here aims to produce abundant Mg<sup>2+sup> that can convert into high-purity MgCO<sub>3sub>, through a mineral carbonation process for CO<sub>2sub> capture, and abundant Fe<sup>2+sup>/Fe<sup>3+sup> that can convert into value-added high-purity Fe-rich compounds such as FeOOH. Sulfur-bearing compounds, including Na<sub>2sub>S, Na<sub>2sub>S<sub>2sub>O<sub>4sub>, and FeS<sub>2sub>, were used as reductants, on the basis of the fact that S is one of the inherent elements in fly ash that has a Fe-reductive capability. Synchrotron-based X-ray absorption near-edge spectroscopy was used to quantitatively determine the speciation of Fe (Fe<sup>2+sup> or Fe<sup>3+sup>) and S (SO<sub>4sub><sup>2–sup> or S<sup>2–sup>) in the leachate produced. Leaching with Na<sub>2sub>S<sub>2sub>O<sub>4sub> and FeS<sub>2sub> was found to produce the most Fe<sup>2+sup> (more than 70% of total eluted Fe) in the leachate at 200 °C. Increasing the leaching temperature is beneficial in increasing the reactivity of FeS<sub>2sub>, leading to a greater amount of Fe<sup>2+sup> produced at 200 °C, whereas Na<sub>2sub>S<sub>2sub>O<sub>4sub> reached its best performance at 100 °C. This is due to a quicker dissolution of Na<sub>2sub>S<sub>2sub>O<sub>4sub> into the leachate to promote the reduction of inherent Fe<sup>3+sup>-bearing ash matrix in the liquid phase, whereas FeS<sub>2sub> mainly remains as a solid, which is less reactive. None of the mechanisms involved affected the total Mg<sup>2+sup> cations eluted. Increasing the molar ratio of S to Fe from 0.125 to 0.5 completely reduced all aqueous Fe<sup>3+sup> present to Fe<sup>2+sup> for both reductants. Concurrent with this was an incremental change in total aqueous Fe amount when Na<sub>2sub>S<sub>2sub>O<sub>4sub> was used. No significant increase in total Fe eluted was observed when FeS<sub>2sub> was used. The fate of S differs for both cases, with S mostly mobilized in the leachate when Na<sub>2sub>S<sub>2sub>O<sub>4sub> was used while predominantly being in the solid leaching residue in the case of FeS<sub>2sub>. In light of this, the use of FeS<sub>2sub> is more promising on a large scale, although it is less active.