Struvite from municipal wastewater applied for the recovery of iron oxide pigments from acid mine drainage: an experimental and geochemical modelling approach

The exploration of alternative acid mine drainage (AMD) treatment agents remains crucial, given the consistent rise in AMD release globally. Herein, a municipal wastewater (MWW)-derived byproduct, struvite, is investigated for the treatment of AMD, including the recovery of iron oxide pigments, where geochemical modelling is employed as a preliminary modelling prediction tool. The synthesis of struvite occurred through pH-controlled precipitation, where by adding a Mg-based reagent (MgO) was added in municipal wastewater effluent (MWWE). Then, the synthesized struvite was applied in AMD treatment, where the generation precipitation of Fe(III) occurred at pH > 3.5. A further valorization of Fe(III) was conducted; for iron oxide pigment production. MWWE treatment and recovery of struvite dominated byproduct formation became were successful, with the specific recovery of as phosphate and ammonium recovery reaching > exceeded 85%. Synthesis Struvite formation occurred under the following experimental conditions: Operational pH (optimized), running time and mixing speed of 9, 30 mins, and 200 rpm, respectively. X-ray diffraction (XRD) revealed struvite material of high crystallinity, with phases displayed at 2θ = 18.4, 32.7, 50.5, and 58.5°, corresponding to (010), (021), (004), and (022) miller indices, respectively. Application of struvite in AMD treatment displayed a 94.4% recovery of Fe(III). Goethite, hematite and jarosite were the main minerals predicted from PhreeqC interactive as the most thermodynamically stable iron oxide pigments under set experimental conditions. Iron oxide pigment production occurred at temperatures’; vis, 25, 100 and 850 °C, with 100 and 850 °C iron oxide pigments resembling commercially procured goethite and hematite, respectively. Overall, this study demonstrates the valorization of a municipal solid waste (containing struvite) in achieving both the treatment of AMD and recovery of iron pigment.