Mechanisms at Different pH for Stabilization of Arsenic in Mine Tailings Using Steelmaking Slag

The mechanisms at different pH for the stabilization of arsenic (As) in mine tailings (MTs) using steelmaking slag were investigated using laboratory experiments. Two types of steelmaking slag were used in the experiments. Ca-slag has high pH and high calcium oxide content due to its short period of aging. In contrast, Fe-slag is oxidized for a long time and is richer in Fe than in Ca. The As-contaminated MTs were taken from a tailing-storage dam around an abandoned gold mine in Korea. The tailings had an average As concentration of 2225.3 mg/kg. The As-removal batch experiment was performed to investigate the As-removal characteristics of the steelmaking slag. From SEM/EDS analyses after each batch experiment, Ca-As bearing precipitates were broadly found on the surface of Ca-slag particles and the final pH of the solution increased to 12.3. However, for Fe-slag, the As was locally found as forms adsorbed to the surface of Fe and Mn oxides contained in the Fe-slag particles. The final pH of this solution was 8.4. The efficiency of removal of As from water using the Ca-slag was >97% and that with Fe-slag was 79%. This suggests that As ions in solution were removed by Ca-(co-)precipitation (which occurs comprehensively on the Ca-slag surface), or by restrictive adsorption of Fe- and Mn-oxides (on limited parts of the Fe-slag). To determine the efficiency of As-extraction reduction from MTs using steel slags, arsenic-extraction batch experiments with two slags were performed under acidic conditions, simulating the leaching environment formed around a mine tailing storage dam. The As concentration in the extracted solution was decreased by 69.9% (even at pH 2) after the addition of 5% Fe-slag. However, when 5% Ca-slag was added, the As concentration decreased by 42.3% at pH 2. These results suggest that Fe-rich steel slag can be more effective than Ca-rich steel slag as a stabilizer for As in contaminated mine tailings at low pH.