Pilot-scale neutralisation of underground mine water

Traditionally acid mine water is neutralised with lime (Ca(OH)₂). Limestone (CaCO₃) is a cheaper alternative for such applications. This paper describes an investigation aimed at demonstrating that underground mine water can be neutralised with limestone in a fluidised-bed. The contact time required between the limestone and the acid water, chemical composition of water before and after treatment, and economic feasibility of the fluidised bed neutralisation process are determined. A pilot plant with a capacity of 10k1/h was operated continuously underground in a gold mine. The underground water could be neutralised effectively using the limestone process. The pH of the water was increased from less than 3 to more than 7, the alkalinity of the treated water was greater than 120 mg/l (as CaCO₃) and the contact time required between mine water and limestone was less than 10 min (the exact contact time depends on the limestone surface area). Chemical savings of 56.4% can be achieved compared to neutralisation with lime.