SBIR-STTR Award

The proposed research will evaluate a novel agent for its potential to: (1) control acid rock drainage (ARD) at its source, and (2) stop ARD once it starts. The agent in low concentrations is a potent toxicant to acidophilic pyrite-oxidizing bacteria. These bacteria play a major role in the formation of ARD from sulfidic mine tailings. The toxicity of the agent appears to be specific to the acidophiles; it has low toxicity to other forms of life. Thus, the agent could be applied safely in the environment. The research will establish the concentration of the agent required to prevent formation of ARD and the concentration of the agent required to stop ARD once it has begun. The effectiveness of the agent in preventing ARD from sulfidic waste rock will be evaluated in laboratory humidity cell tests. Three samples of waste rock will be tested so that the dose of the agent required to prevent ARD can be correlated with the sulfide content (acid-forming potential) of waste rock. Compared with available technologies, the agent may be a much more potent, less expensive, and more easily applied technology for controlling ARD.The agent has the potential to be a more effective, less expensive, and long-term inhibitor of pyrite-oxidizing bacteria than is offered by available technology. It could be applied both to source material and to existing piles of mine waste that produce ARD. If this agent is effective in preventing ARD, it will be a major breakthrough in the control of ARD, which is threatening the environment and the economic viability of the mining industry worldwide. The agent would help to protect the thousands of miles of streams adversely affected by ARD, and it would significantly lower costs, amounting to billions of dollars worldwide, and increase the effectiveness of treating ARD.Supplemental

Keywords:
small business, SBIR, wastewater treatment, engineering, chemistry

The generation of acid rock drainage (ARD) is the most serious long-term economic and environmental issue facing the mining industry in the United States today. ARD also is an international problem of the highest priority for the mining industry. ARD is associated with the mining of coal, copper, other base metals, and precious metals. ARD is caused by the exposure and weathering of sulfide rock, chiefly the oxidation of pyrite (iron disulfide) in rocks and ores. The ARD process releases acid and heavy metals into receiving streams and groundwater. Certain acid-loving (acidophilic) bacteria are known to accelerate the oxidation of pyrite 10- to 20-fold or more over the background chemical oxidation rate. Consequently, stopping the activity of these organisms has been viewed as key to combating ARD. Existing technology for inhibiting these bacteria in active and abandoned mines has met with limited success and is not widely used. This proposal describes the development of a new technology for stopping the activity of sulfide-oxidizing bacteria in mining wastes. This approach uses a biocide that is highly and selectively toxic to sulfide-oxidizing bacteria at extremely low concentrations. The Phase I research employed three sources of sulfide rock from U.S. mines. Small-scale, short-term accelerated weathering tests showed the biocide could prevent formation of biocatalyzed ARD and also could stop active biocatalyzed production of ARD. The biocide is relatively nontoxic to other forms of life and is not listed on aquatic toxicity or human health standards. The biocide is stable in acidic environments where sulfide oxidizing bacteria grow, but is readily biodegraded under normal environmental conditions. A Phase II research objective is to demonstrate the effectiveness of the biocide in longer-term, larger-scale columns containing waste rock. These tests will establish the biocide dose, method(s) of application, and time period of effectiveness. These results will be used to produce engineering specifications for a field trail. Another objective in Phase II is to produce and evaluate the effectiveness of slow release forms of the biocide. The results of Phase II will: (1) demonstrate to potential clients the feasibility of using the biocide, (2) identify the options for applying the biocide to prevent or stop ongoing ARD, (3) provide expected performance criteria (dose, frequency) for field trials, and (4) provide prototype slow release product(s). Several major hard rock mining companies have expressed strong interest in the research and some have pledged funds to augment the project. The proposed Phase II option will involve a pilot field trial of the technology, beginning during the second part of the Phase II research. A successful field demonstration is an important step in commercialization of the technology.