SBIR-STTR Award

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. Publications and Presentations: Publications have been submitted on this project: View all 1 publications for this project Supplemental

Keywords:
small business, SBIR, sulfide mineral coating, acid rock drainage, ARD, heavy metals, chemical oxidation, base metal sulfides, armoring process, sulfide-oxidizing bacteria, mining industry, EPA., POLLUTANTS/TOXICS, Water, Scientific Discipline, Engineering, Chemistry, & Physics, Chemical Engineering, Analytical Chemistry, Chemicals, Chemistry, Environmental Chemistry, heavy metals, environmental contaminants, biological oxidation, acid mine drainage, sulfer oxide, acid rock drainage (ARD), mine drainage

Uncontrolled oxidation of sulfide minerals in mine wastes causes acid rock drainage (ARD) that contaminates receiving waters with acid and heavy metals. ARD is an enormous environmental problem, and the most significant environmental issue faced by the mining industry. Effectively dealing with ARD has been and continues to be a formidable challenge for which no global solutions exist. Existing technology for controlling ARD at the source by stopping oxidation of sulfide minerals still is rudimentary and aims to stop either chemical oxidation or biological oxidation, but not both. Both of these chemical and biological processes are important in the formation of ARD. Consequently, both processes must be controlled for a comprehensive solution to the problem. The overall goal of this Phase II research project is to develop a comprehensive solution to the ARD problem by rendering sulfide rock nonreactive to chemical and biological oxidation. The approach involves a combined treatment involving chemical coating and the use of thiocyanate, which is highly and selectively inhibitory to acidophilic microorganisms that catalyze ARD formation. Furthermore, the control of microbial activity may prolong the longevity of chemical coatings that are subject to failure under the severe ARD conditions caused by biooxidation. The specific goals of this Phase II project are to: (1) determine quantitatively the effectiveness of the combined treatment in preventing ARD from developing when applied to fresh waste rock or tailings; (2) determine the effectiveness of the combined treatment in controlling an existing ARD situation; (3) estimate the cost for this ARD treatment; (4) develop an engineering plan for application of the treatment at mine sites; (5) obtain preliminary information on the feasibility of producing a combined controlled-release product; and (6) determine if consolidated phosphate clay waste may be used as a source of phosphate rock. Phase II laboratory tests will be conducted with sulfidic rock from collaborating mining companies that are prepared to conduct field trials if the results are promising. Phase I results were encouraging, showing that the combined treatment could be highly effective both in preventing ARD and in controlling existing ARD. Phase I research and development involved laboratory-accelerated weathering tests employing sulfidic rock from a gold mine in Nevada. Preliminary estimates indicated that the combined treatment would be less costly than existing technology for ARD prevention and control. Furthermore, even where complete control was not obtained, the improvement in water quality with the combined treatment would result in a substantial reduction in capital and operating costs for conventional water treatment, and far less sludge would be produced. The combined treatment approach has the potential to greatly reduce the costs and environmental impacts from ARD. It has wide applicability to mining situations, including application to tailings and waste rock to prevent or treat ARD. It could be used by mining companies for ARD control during or following mining. The component chemicals of the combined treatment are readily available and inexpensive. In some cases, the components already are available at mining sites in process waste streams. Nonetheless, there also may be the opportunity to develop a combined controlled-release product. Supplemental

Keywords:
small business, SBIR, sulfide mineral coating, acid rock drainage, ARD, mine waste, water, heavy metal, oxidation, thiocyanate. Acidophilic microorganisms, biooxidation, tailings, mine sites, phosphate rock, sulfidic rock., POLLUTANTS/TOXICS, INDUSTRY, Water, Scientific Discipline, Wastewater, Industrial Processes, Chemicals, Environmental Engineering, Environmental Chemistry, heavy metals, thiocyanate, mining, acid mine drainage, oxidation chemistry, sulfide mineral coating, wastewater discharges, acid rock drainage