Using the thiomolybdate-loaded D201 resin derived from the W and Mo separation process as the scavenger of Cr(VI), Cu(II), and Pb(II)

Heavy metals (HMs) are recalcitrant and persistent in the environment, posing long-term detrimental effects to ecosystems and public health. Adsorption is an available method to sequester HMs from environmental media. Expensive tetrathiomolybdate (MoS4 2-) salts have been widely used to modify materials, showing favorable performance in removing HMs. Instead of using such a costly reagent, applying the W and Mo separation process to load thiomolybdate (MoOxS4-x 2- ) on a strong basic resin D201 as the scavenger of Cr(VI), Cu(II), and Pb(II) was proposed in this study. Assisted by the orthogonal experiment, the optimal separation conditions, i.e., pH = 7, ns/ nMo = 8, [Mo]0 = 2 g/L, and solid/liquid ratio of 30, with desirable removal rates for Cr(VI) and Cu(II) were achieved. Compared with the control group (MoS4 2--loaded D021, MSD201), the resin (WMD201) collected from the optimized W and Mo separation conditions showed a comparable capacity and similar mechanism for the adsorption of the three HMs. The adsorption kinetics and isotherm results of metals on WMD201 were well fitted by the pseudo-second order and Langmuir modes, respectively. Increasing the initial pH from 1 to 4 resulted in a significant rise for the uptake of Cr(VI) and Pb(II). Different from Cu(II) and Pb(II), which were sequestered mainly by forming complexes with MoOxS4-x 2- and/or S2-, the removal of Cr(VI) was partially attributed to ion exchange and reduction. These results suggest that using W and Mo separation processes to functionalize materials as the efficient scavengers of HMs is feasible.