Laboratory and Pilot-Scale Studies on the Treatment of Acid Rock Drainage at A Closed Gold-Mining Operation in California

Abstract

Acid rock drainage from a closed gold-mining operation in northern California was studied first in the laboratory and then on the pilot scale to determine the technical feasibility of passive u-eatment. The drainage has a pH of 3.8, and concentrations of Cu, Fe, Mn, Ni, and Zn of 140, 190, 28, 0.93, and 40 mg/L respectively. The laboratory studies concentrated on the question of whether local organic and soil materials could be used to support sulfate reduction in a passive treatment system. Samples were incubated at laboratory temperatures for a period of 4 weeks. Soil and wood processing wastes from the immediate vicinity proved to be too acidic to maintain a large population of sulfate reducers. The most reasonable material for sulfate reduction was a mixture of equal amounts by weight of cow manure, planter mix soil, and limestone chips. The final solutions had pH's of 6.5 to 6.9, and average Cu, Fe, Mn, Ni, and Zn concentrations of 0.02, I, 5, 0.05, and 0.1 mg/L, respectively. Based on the laboratory results, a pilot system was constructed that consisted of a lined steel container filled with a substrate volume that measured 2 by 3 by 12 m. The substrate mixture was the same as used in the laboratory tests. Raw manure from a dairy farm was mixed into the substrate for the sulfate-reducing bacterial (SRB) inoculum. Loading of the system was based on the estimate that 0.3 mo! sulfide per cubic meter of substrate per day would be generated, and the inflow of heavy metals should not exceed the sulfide generated. Using these principles, the flow was set at approximately 800 mL/min. Over the course of 9 months, the pilot system achieved removal of Cu and Ni below the effluent standards of 1.0 and 0. 7 mg/L. Dissolved Zn concentrations in the effluent averaged approximately 0.1 mg/L, compared with an effluent standard of 0.02 mg/L. Dissolved Fe concentrations in the effluent varied with the seasons, reaching a minimum of 1 mg/Lin the summer and rising to a maximum of 120 mg/Lin the winter. There is a significant increase in concentrations of Fe in unfiltered waters. This implies that, in a full-scale system, a settlingpolishing pond will be needed.

Preliminary Evaluation of Locally Available Organic Substrates for Vertical Flow Passive Treatment Cells in Potosí, Bolivia

“…SRB increased through the time of experiment in all reactors exposed to discharge A. Additionally, the characteristic smell for H 2 S was observed in cow and llama manure reactors but not in brewery waste reactors. longer exposure times to determine optimal substrate for AMD remediation (Waybrandt et al, 1998;Wildeman et al, 1994a;Wildeman et al, 1994b;Waybrandt et al, 2002;Zagury et al, 2006). Even though these authors do not agree on a minimum time for assessing substrate performance, Zagury et al (2006) found that a minimum time of 70 days was needed to compare single substrates performance against different substrates mixes.…”

“…Even though these authors do not agree on a minimum time for assessing substrate performance, Zagury et al (2006) found that a minimum time of 70 days was needed to compare single substrates performance against different substrates mixes. Other authors have shown that a time of 28 to 52 days was enough to analyze metal removal and sulfate reduction rates (Wildeman et al, 1994a;Wildeman et al, 1994b;Gilbert et al, 1999). In addition, it has been observed that at lower temperatures the oxidation-reduction potential increased (Wildeman et al, 1994a), which may decrease the rate of sulfate reduction and metal removal (Neculita et al, 2007).…”

Biotratamiento de contaminantes de origen inorgánico

“…Las mayores aplicaciones de este procedimiento se encuentran en el tratamiento de aguas de mina (54 y 55). La eliminación de estos contaminantes inorgánicos es efectiva mientras que las bacterias y las condiciones experimentales den lugar a la reducción del sulfato (56).…”

Sulfate Reduction - Decreases in Substrate Reactivity and the Implication for Long-Term Treatment

“…As a result of these reactions, metals can be removed from solution and alkalinity can be generated. Many systems have been installed which use compost or other organic waste to generate an anaerobic environment and provide a source of organic carbon (Hedin et al, 1991;Wildeman et al, 1994;Gusek, 1998). Complex organics present in the substrate are microbiologically degraded to simpler organics which are utilized by the sulfate reducing bacterial.…”

“…Numerous studies have documented the ability of sulfate reduction to treat both coal and metal mine drainage, but many of the early studies were conducted for only one to two years (Hedin et al, 1991;Filas et al, 1992;Straub and Cohen, 1992;Dvorak et al, 1992;Wildeman et al, 1994). Initially, the results were impressive; pH increased from under 4 to over 7 and typical trace metal removal exceeded 90%.…”