First full-scale application of barium carbonate as an effective dispersed alkaline substrate for sulfate removal from acid mine drainage

A full-scale passive treatment plant using barium carbonate (BaCO₃), the mineral witherite, as a Dispersed Alkaline Substrate (DAS) for strongly contaminated acid mine drainage was implemented for the first time globally at Mina Concepción, located in the Iberian Pyrite Belt (SW Spain). The plant was monitored over a 105-day period, covering the wettest months of the hydrological year and with a mean flow around 4 L s^-1. The AMD treated in the plant exhibits a high strength, with an average sulfate concentration around 1500 mg L^-1 and net acidity close to 1000 mg L^-1 as CaCO₃ equivalent. According to the above, the loading rate for SO₄ and Fe was around 400 and 80 kg day^-1, respectively. The treatment process produced an alkaline effluent with low metal content. Nearly complete removal of most metal(loid)s was achieved, with significant sulfate decrease to below 500 mg L^-1 in the alkaline outflow of the barium carbonate tank. Barium carbonate demonstrated superior performance compared to magnesia, particularly in enhancing alkalinity and lowering net acidity and concentrations of sulfate and manganese. The high efficiency attained by the plant after the barium carbonate treatment is evidenced by compliance with environmental water quality standards for most contaminants.