Enhancing Arsenic Phytoextraction of Dwarf Napier Grass (<i>Pennisetum purpureum</i> cv. Mott) from Gold Mine Tailings by Electrokinetics Remediation with Phosphate and EDTA

Abstract

In order to study the efficiency of arsenic (As) removal from gold-mine tailings by electrokinetic-assisted phytoremediation (EAPR), a constant direct current (DC) electric field of 1 V/cm (3 h per day) was applied to dwarf Napier grass (Pennisetum purpureum cv. Mott) seedling pots. Furthermore, the influence of the enhancing agent on As uptake was compared with the addition of PO43− at levels of 0.7 (P1), 1.4 (P2), and 2.8 (P3) mmol/kg, and ethylenediaminetetraacetic acid (EDTA) at levels of 2.5 (E1), 5 (E2), and 10 (E3) mmol/kg. The increase in the enhancing agent level resulted in a significant (p ≤ 0.05) decrease in aboveground biomass and SPAD values. This was due to the high levels of the enhancing agent inducing a high As concentration in the aboveground parts of the grass. The optimum level of P2 caused the labile As at the anode to form mainly in the charged species throughout the experiment. This caused P2 to have 2.62 µg/g of As in its aboveground parts, which was 38.93% of the total accumulated As. The optimum level of E1 returned a similar As concentration of 2.27 µg/g in the aboveground parts, which was 41.34% of the total accumulated As, corresponding to the highest translocation factor (TF). Moreover, As K-edge X-ray absorption near-edge structure (XANES) spectra of mine tailings at the anodes of P2 and E1 indicated that the oxidation of As(−I) to As(V) increased. This caused As in mine tailings to be more phytoavailable and also enhanced the translocation of As from the underground to the aboveground parts of the grass.