Abstract
Mine-impacted water, including acid mine drainage (AMD), is a global problem. While precipitation of dissolved metals and neutralization of acidity from mine-impacted water is accomplished relatively easily with lime addition, removal of sulphate to permissible discharge limits is challenging. This paper presents a high-level comparison of four sulphate removal technologies, namely reverse osmosis, ettringite precipitation, barium carbonate addition, and biological sulphate reduction. Primarily operating costs, based on reagent and utility consumptions, are compared. Each process is shown to be subject to a unique set of constraints which might favour one over another for a specific combination of location and AMD composition. Access to and cost of reagents would be a key cost component to any of the processes studied. The total cost calculated for each process also depends on the type of effluents that are allowed to be discharged.
Highlights
Acid mine drainage (AMD) arises when pyrite comes into contact with oxygenated water where surfaces have been exposed during mining operations
High or low [SO4] influent when monovalents can be tolerated in product
While reverse osmosis is the only process that is industrially applied in South Africa for sulphate removal from acid mine drainage, the generation of brine as a waste justifies consideration of alternative process options for the treatment of AMD
Summary
Acid mine drainage (AMD) arises when pyrite comes into contact with oxygenated water where surfaces have been exposed during mining operations. The pyrite undergoes oxidation in a two-stage process; the first stage produces ferrous sulphate and sulphuric acid, causing the dissolution of metals from surrounding surfaces, while the second stage produces orange-red ferric hydroxide (Johnson and Hallberg, 2005; McCarthy, 2010; van Rooyen and van Staden, 2020). The resultant AMD contains high concentrations of dissolved metals, sulphates, and acidity. This paper presents a high-level comparison of four sulphate removal technologies that have received attention in South Africa over the past years. These technologies are reverse osmosis (RO) (physicochemical), the SAVMIN process involving ettringite precipitation (chemical), sulphate removal with barium carbonate addition (chemical), and biological sulphate reduction (biological). The need for sulphate removal AMD typically contains high concentrations of dissolved metals and sulphates, along with low pH values. The sulphate is partially removed, and the gypsum-saturated water, containing sulphate concentrations
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