Preparation of high purity AlCl3·6H2O crystals from coal mining waste based on iron(III) removal using undiluted ionic liquids

Abstract

Abstract This study reported an environmentally benign approach to iron(III) extraction using undiluted Aliquat 336. This technique was then applied for iron(III) removal from coal mining waste (CMW) hydrochloric acid leach liquor to produce high purity aluminum chloride. The extraction behavior, loading capacity, selectivity, and stripping of iron(III) were investigated within synthetic solutions and compared with those obtained from Cyphos IL 101. The results showed that iron(III) can be quantitatively extracted using Aliquat 336 with high efficiency and high selectivity against aluminum(III), calcium(II), magnesium(II) and potassium(I). The maximum loading capacity of iron(III) in Aliquat 336 was 100.7 g L−1, which is higher than that in Cyphos IL 101. Iron can be more effectively stripped from Aliquat 336 rather than Cyphos IL 101 when using 0.5 M H2SO4 as the stripping solution. The regeneration of the IL phase and their reuse in subsequent extractions of iron from CMW leach liquor were further examined. The extraction efficiency of iron(III) decreased after Aliquat 336 and Cyphos IL 101 had been recycled for six and three cycles, respectively. High purity AlCl3·6H2O crystals were prepared under vacuum evaporation from the raffinate after iron removal, where the iron content in the AlCl3·6H2O crystals was less than 0.005%.