Removal of arsenate in acid mine drainage by a permeable reactive barrier bearing granulated blast furnace slag: Column study

Immobilization of arsenate in groundwater impacted by acid mine drainage was investigated using a permeable reactive barrier (PRB) column bearing granulated blast furnace slag (GBFS) to compare with iron granules which are commonly used. Sorption capacity of arsenate onto the GBFS was quite lower than iron granules in the amount of sorbed arsenate per unit surface area of sorbents (mmol/m²) at the equilibrium, Q′, in two orders of magnitude in batch tests, however, the amount of sorbed arsenate per unit amount of sorbents (mmol/kg) at the equilibrium, Q, were comparative to each other, because of much higher porosity in the GBFS. Results of column performance showed that 15 mg/L of As was decreased to be less than 0.4 mg/L for more than 18 pore volumes (pv) in the GBFS-PRB by sorption, co-precipitation and presumably formation of hydrated calcium arsenate, and less than 0.04 mg/L for more than 17pv in the iron bearing PRB probably by co-precipitation with iron (oxyhydro)oxides. Additionally 15 mg/L of Mn²⁺ ions was also decreased to less than 0.3 mg/L and 0.03 mg/L, respectively, in iron bearing and the GBFS bearing PRB columns, probably caused by sorption and precipitation of oxides and carbonates. The GBFS has advantages to compensate its low reactivity with high porosity, to facilitate the industrial handling with low density, and to utilize industrial wastes for more valuable applications, emphasizing a potential of alternative reactive materials instead of iron granules in PRB for immobilization of arsenic and manganese in acid mine drainage.