Repurposing of sludge generated from the treatment of acid mine drainage

Abstract

This study had a two-pronged approach, the first part of which involved assessment of the potential to precipitate different ochres from acid mine drainage (AMD) by using various neutralising agents. This was achieved through computational simulations using the PHREEQC geochemical modelling code. Inferences could then be drawn from the simulations as to which neutralising agents (or a mix thereof) were suitable, taking into account the predicted treated water quality, types of ochres formed and their predicted yields. NaOH and MgCO3 were found to be the most suitable neutralising agents for this purpose, producing ochres with colours varying from yellow to orange and red. Other colours such as green and blue could also be produced following addition of ferrous cyanide to the neutralisation reaction. Naturally, such colourations occur at tailings sites as a result of the presence of cyanide that is used as a lixiviant in gold extraction. The ochres were tested in simple artwork and were found to perform as their commercial counterparts. Further testing of their applicability as paint pigments for building purposes remains possible and should be considered in future studies. The second part of the study was based on exploring the potential to repurpose high density sludge (HDS) generated from AMD treatment plants by taking advantage of the ferric hydroxide (Fe(OH)3) and/or goethite (FeOOH) contained in its matrix that can act as an adsorbent for conditioning of AMD. This AMD would mainly be in mine voids and shafts. Another potential use of HDS as an adsorbent was focused on the adsorption of phosphate from agricultural type and sewage type of water with the aim of applying the phosphate-laden sludge as an amendment for mine tailings on which woodlots are planted for phytoremediation.