Treatment of wastewater using ferric chloride synthesized from Fe(III) recovered from acid mine drainage

Acid mine drainage (AMD) is an iron-rich acidic wastewater that poses grave environmental risks, but also presents opportunities for resource recovery. Here, ferric iron (Fe(III)) was facilely recovered from AMD and subsequently used for ferric chloride (FeCl3) production for water coagulation. To avoid the problem of high sulfate co-precipitation that is encountered with calcium (Ca)- and sodium (Na)-based agents, magnesium oxide (MgO) nanoparticles (derived from thermally activated cryptocrystalline magnesite) were used to selectively precipitate and recover Fe(III) from AMD. State-of-the-art instruments (i.e., HR-FIB-SEM-EDS) shed light on the characteristics and composition of the recovered material, confirming that Fe(III) was recovered, along with minor concentrations of aluminum (Al), Ca, Mg, and sulfate. This material was then reacted with hydrochloric acid (HCl) towards FeCl3 synthesis, which was then employed for water and wastewater coagulation-flocculation-settling treatment. Optimum conditions for South African river water treatment included 0.2 mL/L (v/v ratio), 100 rpm mixing speed, and 5 min contact time. Turbidity, Fe, and Al removals exceeded 99%, meeting the South African drinking water (SANS 241) standards. Most notably, the performance of the AMD-synthesized FeCl3 was on par with commercially available FeCl3, with no meaningful statistical differences being observed. Furthermore, and initial reagent-only cost analysis suggested costs less than half of those for commercially available FeCl3, thus, presenting a new sustainable waste-to-resource approach. Results also highlighted that AMD-synthesized FeCl3 can be safely employed by the water and wastewater industry to underpin sustainability and address price and availability (supply instability) concerns which surround commercial coagulants/flocculants. Furthermore, through AMD beneficiation, i.e., Fe(III) recovery, and partial acidity correction, water reclamation opportunities from AMD can be further pursued. Overall, resource recovery from waste and their reuse for treating other wastes can introduce sustainable paradigms and promote the United Nations (UN) sustainable development goals (SDGs).