A Novel Combination of Anaerobic Bioleaching and Electrokinetics for Arsenic Removal from Mine Tailing Soil

This study provides evidence that a hybrid method integrating anaerobic bioleaching and electrokinetics is superior to individual methods for arsenic (As) removal from mine tailing soil. Bioleaching was performed using static reactors in batch tests and flow conditions in column test, and each test was sequentially combined with electrokinetics. In the bioleaching, indigenous bacteria were stimulated by the injection of carbon sources into soil, leading to the mobilization of As with the concurrent release of Fe and Mn. Compared with the batch-type bioleaching process, the combined process showed enhanced removal efficiency in the equivalent time. Although the transport fluid bioleaching conditions were inadequate for As removal, despite long treatment duration, when followed by electrokinetics the combined process achieved 66.5% removal of As from the soil. The improvement of As removal after the combined process was not remarkable, compared with single electrokinetics, whereas a cost reduction of 26.4% was achieved by the reduced duration of electrokinetics. The As removal performance of electrokinetics was significantly dependent on the chemical species of As converted via microbial metal reduction in the anaerobic bioleaching. The synergistic effect of the combined process holds the promise of significant time and cost savings in As remediation

Equilibria, kinetics, and spectroscopic analyses on the uptake of aqueous arsenite by two-line ferrihydrite

<div><p>Arsenite sorption from aqueous solutions was investigated using two-line ferrihydrite at room temperature, as a function of solution pH and arsenite loading. The isotherms, pH envelopes, and kinetics of arsenite sorption were characterized and its mechanism was elucidated via X-ray absorption spectroscopic studies. Arsenite sorption showed only slight pH dependence with a sorption maximum centered around pH 8.0. The Langmuir isotherm is most appropriate for arsenite sorption over the wide range of pH, indicating the homogenous and monolayer sorption of arsenite. The kinetic study demonstrated that arsenite sorption onto two-line ferrihydrite is considerably fast and the equilibrium is achieved within the reaction time of 3 h. X-ray absorption near-edge structure spectroscopy elucidated a slight change in oxidation state of arsenite for the initial concentration of 13.35 mM at pH 4. The extended X-ray absorption fine structure (EXAFS) spectroscopy results indicate that types of surface complexes of arsenite appeared to be very similar to those proposed by the previous studies in that the bidentate binuclear corner-sharing (²<i>C</i>) complex is predominant at all the surface loadings. However, our EXAFS results suggest that regardless of pH, the mixed complexes of ²<i>C</i> and bidentate mononuclear edge-sharing surface complex (²<i>E</i>) as well as the ²<i>C</i> complex are favoured at low and intermediate surface loadings, but only the ²<i>C</i> complex is dominant at high surface loading. Overall, the EXAFS results support the efficient removal of arsenite by the two-line ferrihydrite through the formation of highly stable inner-sphere surface complexes, such as ²<i>C</i> complex.</p></div