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AMELIORATION OF ACID MINE DRAINAGE USING REACTIVE MIXTURES IN PERMEABLE REACTIVE BARRIERS
Citation:
McNeil*, M S. AND R T. Wilkin*. AMELIORATION OF ACID MINE DRAINAGE USING REACTIVE MIXTURES IN PERMEABLE REACTIVE BARRIERS. GSA Annual Meeting, Reno, NV, 11/9-18/2000.
Description:
The generation and release of acidic drainage from mine wastes is an environmental problem of international scale. The use of zero-valent iron and/or iron mixtures in subsurface Permeable Reactive Barriers (PRB) presents a possible passive alternative for remediating acidic groundwater contaminated by heavy metals. A series of batch studies were carried out to evaluate the performance of various types of zero-valent iron and/or reactive media for the amelioration of acid mine drainage (AMD). Fisher iron, Connelly iron, and mixtures of Fisher iron, calcium sulfide (30 % - 50 % grout), and natural zeolite (clinoptilolite) were exposed to an AMD solution. Experimental results show that all zero-valent iron mixtures remove metals from solutions to concentrations near detection limits of ICP-OES analytical methods. Within 100 hours, solution pH increases from 2.3 to steady, near-neutral values (5.5-7); alkaline pH was reached using Fe?-CaS mixtures. The pH increase correlates with the decrease in metal concentrations and the rate of pH increase is proportional to the reactant mass (surface area). Concentrations of total iron increase from initial values of 3 mM to final values after 500 h of 20 mM (zero-valent iron) and 10 mM (zero-valent iron + clinoptilolite). Substantial amounts of Fe and Al hydroxides precipitate as pH increases. Such precipitates likely serve as sorption sites for transition metals; they also could lead to decreased PRB longevity, pore clogging, and remedial failure. Concentrations of total iron decrease to below detection limits after reaction with Fe -CaS mixtures. Attempts to remobilize metals by oxidation with air-saturated water were unsuccessful indicating that zero-valent iron mixtures are stable sinks for metal contaminants.
This is an abstract of a proposed presentation and does not necessarily reflect EPA policy.
Geological Society of America, Abstracts with Programs (Reno, NV), v. 32, p. A284, 2000