Biogeochemistry of the treatment of mining-impacted water in mining legacy sites: integrating aqueous phase and solid phase analyses to elucidate efficiencies and mechanisms
Citation:
Al-Abed, S., P. Pinto, P. Potter, AND J. McKernan. Biogeochemistry of the treatment of mining-impacted water in mining legacy sites: integrating aqueous phase and solid phase analyses to elucidate efficiencies and mechanisms. 257th ACS National Meeting & Exposition: Mar 31 – Apr 4, 2019, Orlando, FL, Orlando, Florida, March 31 - April 04, 2019.
Impact/Purpose:
Abandoned mining sites generate important amounts of metal and sulfate contaminated mining-influenced water. This study introduced the integration of analytical work (on aqueous and solid phases), complemented with chemical equilibrium models to evaluate the performance of anaerobic reactors and to elucidate the mechanisms involved in metal and sulfate removal. This approach helped to determine several parameters that are helpful in the design of field-scale systems, as substrate amount, mass and composition, hydraulic retention time, impact of dissolved oxygen in the influent, etc. Since there are more than half a million abandoned mining sites in the U.S., the proper understanding of the mechanisms and involved parameters will help to optimize the resources required to treat these waters and increase the efficiency of passive systems. This research is useful for the scientific community and consulting firms involved in treating this water, the decision-makers on a number of sites, EPA regions that are dealing with these sites, and all who are studying new approaches on mine water remediation.
Description:
There are over half a million abandoned mine sites in the U.S. potentially emanating mining-influenced water, contaminating streams and soils in adjacent areas. These sites present major challenges for their remediation, including: seasonal inaccessibility, rough terrain, lack of energy sources, high acidity, and metal concentrations (e.g. Fe, Al, Cu, Zn, Mn, Cd, etc.). To appropriately evaluate mining-impacted water treatment techniques that can provide the best cost benefit with the desired effluent quality, decision-makers usually rely on bench-scale and pilot-scale tests before designing field-scale reactors. Traditionally, the focus has been on metal removal efficiency to determine the feasibility of the proposed treatment, but it is difficult to replicate the high efficiencies of bench-scale tests with field-scale reactors. The integration of aqueous phase analytical chemistry (e.g. pH, alkalinity, elemental composition, anions, sulfides, etc.) with solids analysis (e.g. elementary composition, speciation by XPS and XANES, etc.) and chemical equilibrium models (e.g. Visual Minteq) provide the tools to evaluate metal removal while elucidating the involved mechanisms. The benefit of this approach is that the impact of several variables (e.g. substrate volume, mass and composition, hydraulic retention time, dissolved oxygen content in the influent, etc.) can be evaluated for metal and sulfate removal; this way, the variables that have the highest impact on effluent water quality are known and considered so the most effective field-scale reactors can be installed. Case studies of passive reactors using actual mine water from abandoned mine sites will be used to demonstrate the benefits of this approach.