Sulfate removal from acid mine water from the deepest active European mine by precipitation and various electrocoagulation configurations.

Sulfate removal from mine or process water is a key issue in the mining industry. In this paper, precipitation with lime (calcium oxide) was integrated with electrocoagulation for sulfate removal from Pyhäsalmi/Finland mine water. Sulfate precipitation with calcium oxide decreased the sulfate concentration from 13,000 mg/L to 1600 mg/L. Various current densities were applied to the pre-treated mine water with various electrodes and aluminium and iron anodes. It was found that 25 mA/cm was the best tested current density for both anode types. At the second stage, this current density was used for different iron and aluminium anodes in various monopolar and bipolar configurations. It was found that this hybridisation is effective for sulfate removal, and that a bipolar configuration showed better results than the monopolar configuration. The best result was gained from 25 mA/cm with a two aluminium and two stainless steel anode-cathode configuration and calcium oxide pre-treatment to reach pH 12. The removal efficiency reached 84.4% and 63.8% with aluminium anodes in bipolar and monopolar configurations, respectively. This setup was able to decrease sulfate concentrations from 13,000 mg/L to 250 mg/L, which meets mine water discharge limits. Kinetic studies showed that iron and aluminium anodes obey pseudo-second order kinetic. Finally, the energy consumption was calculated.