Valorisation of acid mine drainage waste for synthesis of ferric ammonium sulfate (FAS)

Green and sustainable production of secondary products from waste sources is needed for a global circular economy. The primary aim of this work was to produce ferric ammonium sulfate (FAS) from acid mine drainage (AMD). AMD with a Fe content of approximately 240 mg/L was used as a matrix to model FAS formation under different solution concentrations of Fe and S (as ferric sulfate and sulfuric acid). This approach offered the benefit of identifying boundary conditions for FAS synthesis from wastes, so that the results of this study can be applied to many different AMD compositions. Results showed that increased Fe concentrations were associated with higher crystal yields and more selective crystallisation. Fe, S, and Al were more selectively incorporated over other elements present in AMD, however, XRD analysis did not show additional Al-bearing alum products. FAS was produced for AMD solutions where Fe was above 2500 mg/L, which demonstrates that FAS could be formed from iron-rich waste solutions.