A High-Efficiency Alkali Circulation Process for Alumina Extraction from High Alumina Fly Ash via Improved Hydro-Chemical Method

The present article is focused on extraction alumina from high alumina fly ash using an improved hydro-chemical method with high-efficiency alkali circulation and mild reaction conditions. The alumina leaching behavior and corresponding reaction mechanism of the process were systematically investigated. The results revealed that the alumina extraction efficiency reached 50.7% in the low alkali process with alkali concentration of C(Na2O) = 230 g/L, and the total alumina extraction ratio reached 92.4% in the high alkali process with alkali concentration of C(Na2O) = 380 g/L. The presence of Ca leads to the formation of katoite (Ca2.93Al1.97Si0.64O2.56(OH)(9.44)) during the low alkali process, which reduces the alumina extraction rate. Isomorphism occurs in the high alkali process and generates iron-containing hydrated garnet (Ca-3(Fe0.87Al0.13)(2)(SiO4)(1.65)(OH)(5.4)), which improves the alumina extraction rate, The improved hydro-chemical process proposed in this paper not only has milder reaction conditions, but also the cycle efficiency is > 330% higher compared with the hydro-chemical method of the existing literature.