Metals and sulphate removal from acid mine drainage in two steps via ferrite sludge and barium sulphate formation

• Simultaneous removal of metals and sulphate decreased magnetic moment.
• Increasing pH and heat improved the degree of crystallite of the ferrite.
• Ferrite sludge and sulphate were removed from AMD separately.
• Addition of ferrite seeds enhanced rate of metal removal and magnetic moment.
• AMD could be used as a resource for production of commercially valuable chemicals.

In this work, primary test of ferrite formation by coprecipitation method from pure Fe(NO3)3⋅9H2O and FeSO4⋅7H2O were evaluated at different pH and temperature by continues stirring using magnetic stirrer. The optimized method was applied on simulated and real acid mine drainage (AMD). The impact of simultaneous removal of metals and sulphate on the magnetic moment of ferrite sludge and addition of ferrite or ferrite sludge seeds into real AMD samples were also investigated. The XRD results of synthesised ferrite from pure binary salts confirmed that presence of heat and increased pH improved the degree of crystallite of ferrite. During neutralization of AMD using sodium hydroxide, gypsum was not precipitated in the absence of calcium hydroxide or barium ions. Consequently, the two step processes were applied; whereby metals are removed in the first step via ferrite sludge formation using sodium hydroxide and followed by treatment of the filtrate with barium chloride or barium hydroxide for complete sulphate removal as barium sulphate precipitate. From the analysis results, the ferrite sludge produced separately from sulphate showed higher magnetic moments than produced simultaneously. In the pH range of 7–8.5, at temperature of 60 °C, 93%, 12%, and 28%, and 99.6%, 57.5% and 47.5% of Fe, Mn and Co were removed from real AMD; in the absence and presence of ferrite seeds in 20 min reaction time, respectively. Furthermore, the rate of metal removals and magnetic moments of synthesised ferrite sludge were increased in the presence of ferrite seeds. Generally, these results indicated that AMD could be used as a resource for production of commercially valuable chemicals, which in turn could help to offset the cost of treatment.