Patent ID: 8557124
Filing Date: 2013-10-15
Classification: C02F

Abstract:
1. A process for treating acid mine drainage containing dissolved metals, dissolved calcium, and dissolved sulphates, which process includes in a first treatment stage, adding magnesium hydroxide to the acid mine drainage, for neutralization of the acid mine drainage and for reaction with dissolved metals in the acid mine drainage, thereby to cause the metals to be precipitated as metal hydroxides or metal oxides; removing precipitated metal hydroxides and metal oxides from the acid mine drainage; thereafter, in a second treatment stage, adding barium hydroxide to the acid mine drainage, with the barium hydroxide reacting with dissolved sulphates in the acid mine drainage to produce barium sulphate which precipitates out, and with dissolved magnesium to produce magnesium hydroxide; removing precipitated barium sulphate from the acid mine drainage as a sludge; treating the sludge so as to convert the barium sulphate to barium hydroxide via barium sulphide by reacting the barium sulphate with coal in accordance with reaction (2) thereafter reacting the barium sulphide with steam under pressure, in accordance with reaction (3) and thereafter reacting the barium oxide with water, in accordance with reaction (4) wherein reaction (2) is effected in a kiln, and wherein the mole ratio of C:BaSO 4 is about 1:3 to cater for heat that is required in reaction (2) which is endothermic; removing precipitated magnesium hydroxide from the acid mine drainage; recycling the precipitated magnesium hydroxide to the first treatment stage; in a third treatment stage, adding carbon dioxide to the acid mine drainage, with the carbon dioxide reacting with dissolved calcium in the acid mine drainage, to cause the calcium to be precipitated as calcium carbonate; and removing the precipitated calcium carbonate from the acid mine drainage.