Recovery and synthesis of Polycationic Dimetals from acid mine drainage and their respective application in the removal of Arsenic, Chromium and Congo Red Dye from toxic industrial effluents.

Abstract

Water contamination is one of the leading challenges faced by the global community. This is due to the escalating population growth and anthropogenic activities which have led to water supply being inversely proportional to demand for fresh water. In this study, the recovery of Fe-polymeric species from authentic acid mine drainage and their respective applications in the removal of pollutants from wastewaters were explored. The synthesis of polycationic dimetal iron/aluminium nanocomposite (PDFe/Al nanocomposite) was executed through fractional precipitation followed by and processed through calcination and vibratory ball milling, while the efficiency of the material was determined through adsorption of arsenic (As(V)), chromium (Cr(VI)) and Congo red dye (CR) on a batch experimental set-up. Parameters optimised included: agitation time, adsorbent dosage, temperature, pH, and initial adsorbate concentration. Experimental results revealed that optimum conditions that are suitable for the removal of As(V) from an aqueous system are: 150 mg/L of As(V) concentration, 1 g adsorbent and 60 min equilibration time. As(V) removal was independent of pH and temperature. Cr(VI) was effectively removed at 50 mg/L initial Cr(VI) concentration, 3 g nanocomposite dosage, initial pH = 3 of solution, 180 min equilibration time and temperature = 45 ºC. Optimum conditions for removal for CR adsorption are: 100 mg/L initial CR concentration; 0.5 g PDFe/Al nanocomposite; 20 minutes agitation time; 3 – 8 initial CR pH; and temperature of 35 ºC. Under optimised conditions, As(V), Cr(VI) and CR showed >99,9%, >95% and >99%, respectively. The adsorption capacities (qe) of As(V), Cr(VI) and CR were found to be 105 mg/g, 4.166 mg/g and 25 mg/g, respectively. Adsorption kinetics followed the pseudo-second-order as opposed to pseudo-first-order behaviour, therefore confirming chemisorption for all chemical species. Regeneration study of the material showed that the adsorbent can be reused more than four times on the adsorption of As(V), Cr(VI) and CR. This study demonstrated that valorisation of waste material by recovering valuable di-metals and employing them to curtail the impact of problematic pollutants is feasible. As such, this double-edged study demonstrated the exceptional potential of the synthesised material to remove As(V), Cr(VI) and CR from aqueous system.