PASSIVE METAL REMOVAL SYSTEM UTILIZING ZEOLITE FOR INITIAL TREATMENT OF SEASONAL ACID ROCK DRAINAGE—NEW TECHNOLOGY FOR ENHANCING PASSIVE TREATMENT SYSTEMS

Efficacy of passive treatment systems for remediation of acid rock drainage (ARD) can be limited by the seasonal flux of discharge and metal concentrations that may not have been considered during treatment design. Drainage and metal variability can lead to surface passivation and flow bypass, thereby reducing the efficacy and life of a treatment system. In cases of highly variable ARD, complimentary treatment systems may assist in reducing metal concentrations and acidity to lessen the variability of hydrochemical conditions for downstream primary treatment systems. For this study, a prototype of a complimentary and modular passive treatment system was developed through the evaluation of three silicate substrates– bare silica fiber, functionalized silica fiber, and zeolite. The substrates were compared for their ability to remove Fe(II) under acidic conditions in static and kinetic sorption experiments. Zeolite was selected as the substrate for the treatment system based on its Fe-sorbing capabilities, high surface area to volume ratio, and high permeability. A prototype of the treatment system was deployed at an abandoned mine near Great Falls, Montana, where ARD was discharging to local creeks. Fe concentration and pH were monitored upstream, within, and downstream of the treatment system for 4 days. Fe removal by the treatment system ranged from 40-95% and pH (initially 2.7) increased to 4-5.5 as surface reactions reduced acidity.