Continuous pilot scale assessment of the alkaline barium calcium desalination process for acid mine drainage treatment

The alkaline barium calcium (ABC) desalination process for acid mine drainage treatment was evaluated at pilot scale. Experimental continuous sulphate removal was performed and regeneration of barium carbonates from barium sulphide/calcium carbonate sludge was conducted by using CO2 gas at room temperature. The effect of process parameters was evaluated and it has been shown that it is possible to remove sulphate to very low levels in continuous mode using barium carbonate. Sulphate was removed from 2250 to 200 mg/L in 90 min using a Ba2+ to SO42− molar ratio of 1:1. When the removal process was carried out for longer than 90 min a residual SO42− concentration of 100 mg/L remained in the treated water using a Ba2+ to SO42− molar ratio of 1:1, and this residual SO42− lies within acceptable drinking water limit of 400 mg/L and also ensures that no residual toxic barium is present in the treated water. Moreover; the regenerative barium carbonate process, involving the conversion of BaS to BaCO3 in the carbonation step has been assessed. The production of BaCO3 and H2S by treating aqueous slurry of BaS with CO2 was also evaluated. The CO2 flow rate had an impact on the BaCO3 morphology. BaCO3 was recovered from the pilot scale bubbling column reactor using 5% BaS at a CO2 flow rate of 14.4 m3/day and demonstrated effective sulphate removal ability during AMD treatment compared to commercial BaCO3. The quality of barium carbonate generated was also preliminary assessed.