Sulfide Mineral Coating Process To Control Acid Rock Drainage

Acid rock drainage (ARD) is a significant environmental problem. ARD is caused by chemical and biological processes (i.e., the oxidation of sulfide minerals in mine tailings and waste rock) and characterized by acidic water containing heavy metals. Existing technology for combating ARD consists of treating the acidic effluents or isolating problematic tailings or waste rock, but it does not attack the problem at the source. Little Bear Laboratories, Inc., has made significant progress in developing a process to stop the biological component of ARD. However, abiotic, chemical oxidation remains problematic, especially with base metal sulfides. ARD cannot be eliminated unless both the chemical and biological components of sulfide oxidation are arrested. This research project will test the feasibility of stopping ARD by applying a novel process that coats or armors sulfide mineral particle surfaces to stop further chemical oxidation and neutralizes acidity. The armoring process may be used in combination with treatment to stop the biological oxidation of sulfide minerals. The objective of this project is to determine the effectiveness of the armoring process in: (1) preventing ARD from developing, and (2) mitigating an existing ARD problem. Solid and soluble forms of the armoring agent at different concentrations will be applied to waste rock or tailings in accelerated-weathering, laboratory-scale (1 kg) humidity cell tests. The test system will be biologically active (i.e., sulfide-oxidizing bacteria will be added to the waste rock). In this manner, it can be determined whether sulfide mineral coating alone is effective in stopping ARD, or if coating also requires treatment to stop the activity of microorganisms. Test results will be used to provide a preliminary estimate of treatment costs and process efficiency in stopping chemically and biologically catalyzed ARD. If successful, the process would be a major breakthrough in the control of ARD¿a comprehensive solution stopping both chemical and biological oxidation of sulfides. The process could be applied to source material, to existing piles of mine waste producing ARD, and for closure of spent heap leach pads. It would significantly lower the costs and increase the effectiveness of treating ARD. These costs amount to billions of dollars worldwide. The process would help to protect the thousands of miles of streams adversely affected by ARD. Not only does ARD threaten the environment, but also the economic viability of the mining industry worldwide.