LABORATORY EVALUATION OF SELENIUM TREATMENT USING ZERO-VALENT IRON (ZVI) UNDER OXIC CONDITIONS

Selenium (Se) occurs naturally in many rocks and sediments and is therefore present in a variety of environmental settings. Although a nutrient at low concentrations, elevated Se concentrations can negatively impact water quality, ecosystem function, and human health. Many anthropogenic activities including mining and industrial manufacturing operations can contribute elevated Se concentrations to surface and groundwaters.

The release of Se via sulfide mineral oxidation within waste rock and tailings represents a considerable risk to water quality in mining environments. The development of pragmatic and cost-effective techniques for limiting Se concentrations in mining effluents is therefore vital for reducing environmental impacts of mining operations. Iron oxy-hydroxides can play a dominant role in trace metal partitioning in the environment. Their natural abundance, reactivity, and moderately high surface areas have drawn the attention of the scientific community with respect to the attenuation of Se via adsorption under transient flow conditions. However under continuous flow conditions, available reactive surface sites are quickly saturated and thus this technique is unviable in the remediating Se-contaminated waters. Recently, zero-valent iron (ZVI) has been considered for the removal of Se from water via reductive and adsorptive processes. Treatment systems that utilize ZVI to promote Se attenuation have proven effective at the laboratory scale under experimental conditions of limited relevance to the mining industry.

In this study, we examined mechanism and rates of removal of dissolved Se(VI) by ZVI in abiotic batch experiments conducted under oxic and circumneutral pH conditions at ambient temperature. The experiments were conducted using a range in input solutions containing 1 mg L^-1 Se(VI) and/or SO₄ and NO₃using a solid-to-solution ratio of 1:100. Aqueous and solid samples were analyzed (ICP-MS, IC, XRD, BET, SEM, TEM, Raman spectroscopy, Mössbauer spectroscopy, etc.) to determine Se treatment efficiencies and mechanisms. Preliminary results indicate that ZVI can efficiently remove Se under these experimental conditions.