Removal and recovery of heavy metals from soil with sodium alginate coated FeSSi nanocomposites in a leaching process

Leaching technology has been widely applied to remove heavy metals (HMs) from soil, although the synchronous recovery of multiple HMs during the leaching process was rarely studied. In this study, we synthesized silicon sulfuretted nanoscale zero-valent iron (FeSSi), which was coated with sodium alginate (SA) to form the gel beads (SA-FeSSi). The specific surface area of FeSSi (101.61m(2)/g) was significantly increased by adding SiO2 seeding. The SA stabilization reduced the aggregation of FeSSi. The removal efficiency for cadmium (Cd), lead (Pb), nickle (Ni) and chromium (Cr) by SA-FeSSi in solution reached 80.10 %, 99.96 %, 66.80 % and 80.46 %, respectively. The removal kinetics was well fitted with the pseudo-second-order model. Leaching experiments showed that the recovery efficiency of HMs from solution (Rr/w) and soil (Rr/s) reached to the ranges of 59.79 %-98.70 % and 25.94 %-62.67 % with the addition of 0.3 g SA-FeSSi. Moreover, the leaching conditions including pH, temperature, adsorbent dosage, leaching agent concentrations, leaching time and leaching cycles were also investigated. Our results suggested that SA-FeSSi had an excellent HMs removal capacity and the recovery of HMs during the leaching process by SA-FeSSi could be a potential pathway to reuse the metal resources from soil.