Eco-Friendly and Efficient Alumina Recovery from Coal Fly Ash by Employing the CaO as an Additive During the Vacuum Carbothermic Reduction and Alkali Dissolution
Zitao Rao, Wenzhou Yu, Haitao Yuan, Peng Wei, Fan Yang, Joseph Emmanuel Nyarko-Appiah
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Abstract
With the growing concern of environmental protection and waste recycling, recovery of high-value metal from coal fly ash (CFA) has attracted a lot of attention around the world. In our previous study, CaO was employed as an additive to react with mullite (3Al2O3·2SiO2) in CFA to produce CaO·xAl2O3, by which the extraction of alumina was strengthened tremendously. However, the dissolving mechanism of CaO·xAl2O3 in alkali liquor has not yet been conducted in in-depth research, which casts a shadow for the further progress of the process. In this paper, with the aim of clarifying the alkali dissolving mechanism as well as developing an eco-friendly alumina recovery process, the effect of CaO addition on the mineralogical transformation of CFA and the dissolving behaviors of CaO·xAl2O3 in alkali liquor were investigated thoroughly. The results show that the mullite in CFA can be converted to Fe-Si alloys and CaO·xAl2O3 with the addition of CaO. Additionally, it is proved that the liquid/solid ratio, the alkali concentration, and the dissolving temperature would be the most critical impactors to decide the extraction rate of alumina. Under the optimal conditions, the extraction rate of alumina attained 93.8% and the CaO can be recycled for cyclic utilization in this process.
摘要随着人们对环境保护和废物回收利用的日益关注，从粉煤灰（CFA）中回收高价值金属已引起世界各国的广泛关注。在之前的研究中，我们采用 CaO 作为添加剂，与 CFA 中的莫来石（3Al2O3-2SiO2）反应生成 CaO-xAl2O3，从而大大提高了氧化铝的提取率。然而，CaO-xAl2O3 在碱液中的溶解机理尚未得到深入研究，这为该工艺的进一步发展蒙上了阴影。本文以阐明碱溶解机理和开发生态友好型氧化铝回收工艺为目的，深入研究了 CaO 添加对 CFA 矿化转变的影响以及 CaO-xAl2O3 在碱液中的溶解行为。结果表明，添加 CaO 后，CFA 中的莫来石可转化为铁硅合金和 CaO-xAl2O3。此外，还证明液固比、碱浓度和溶解温度是决定氧化铝萃取率的最关键影响因素。在最佳条件下，氧化铝的萃取率达到了 93.8%，并且 CaO 可以在此过程中循环利用。
期刊介绍：
Journal of Sustainable Metallurgy is dedicated to presenting metallurgical processes and related research aimed at improving the sustainability of metal-producing industries, with a particular emphasis on materials recovery, reuse, and recycling. Its editorial scope encompasses new techniques, as well as optimization of existing processes, including utilization, treatment, and management of metallurgically generated residues. Articles on non-technical barriers and drivers that can affect sustainability will also be considered.
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