Removal of sulphates acidity and iron from acid mine drainage in a bench scale biochemical treatment system

Abstract

The focus of this study was to develop a simple biochemical system to treat acid mine drainage for its safe disposal. Recovery and reuse of the metals removed were not considered.

A three‐step process for the treatment of acid mine drainage (AMD), proposed earlier, separates sulphate reducing activity from metal precipitation units and from a pH control system. Following our earlier work on the first step (biological reactor), this paper examines the second step (i.e. chemical reactor). The objectives of this study were: (1) to determine the increase in pH and the reduction of iron in the chemical reactor for different proportions of simulated AMD, and (2) to assess the capability of the chemical reactor. A series of experiments was conducted to study the effects of addition of alkaline sulphidogenic liquor (ASL) derived from a batch sulphidogenic biological reactor (operating with activated sludge and a COD/SO₄ ratio of 1.6) on the simulated AMD characteristics. At 60‐minute contact time, addition of 30% ASL (pH of 7.60–7.76) to the chemical reactor with 70% AMD (pH of 1.65–2.02), increased the pH of the AMD to 6.57 and alkalinity from 0 to 485 mg l⁻¹ as CaCO3, respectively and precipitated about 97% of the iron present in the simulated AMD. Others have demonstrated that metals in mine drainage can be precipitated by bacterial sulphate reduction. In this study, iron, a common and major component of mine drainage was used as a surrogate for metals in general. The results indicate the feasibility of treating AMD by an engineered sulphidogenic anaerobic reactor followed by a chemical reactor and that our three‐step biochemical process has important advantages over other conventional AMD treatment systems.

Keywords:

• sulphates
• sulphides
• tailings pond treatment

Acknowledgements

This work was partially funded by the EJLB Foundation of Montreal whose contribution is acknowledged with appreciation. The authors also thank the personnel of Toronto’s main wastewater treatment plant for their cooperation and assistance.