Yushuang Li

Remediation of cadmium-contaminated soil by extraction with para-sulphonato-thiacalix[4]arene, a novel supramolecular receptor.

Batch extractions were conducted to evaluate the performance of para-sulphonato-thiacalix[4]arene (STC[4]A), a novel supramolecular receptor, for removing cadmium (Cd) from soil. The extraction mechanism was investigated by determination of the conditional stability constants (log K) of the STC[4]A-Cd complex. The influences of various variables were examined, including pH, contact time, and extractant concentration. The Cd extraction efficiency increased with increasing pH, reaching the maximum at pH 11 and then declining at higher pH values. This pH dependence was explained by the variation in the log K value of the STC[4]A-Cd complex along with pH change. When the STC[4]A dose was increased to an STC[4]A:Cd molar ratio of 2.5:1, Cd was exhaustively removed (up to 96.8%). The comparison experiment revealed that the Cd extraction performance of STC[4]A was almost equivalent to that of EDTA and significantly better than that of natural organic acids. STC[4]A extraction could efficiently prevent co-dissolution of soil minerals.

Removal of potentially toxic metals from soil by para-sulphonato-thiacalix[4]arene: competitive extraction and selectivity sequence

para-Sulphonato-thiacalix[4]arene (STC[4]A) is an emerging supramolecular receptor for enhancing the extraction of potentially toxic metals (PTMs) from soil. Batch extraction experiments were conducted to evaluate the competitive extraction of cadmium (Cd), copper (Cu), and lead (Pb) by STC[4]A from single- and multi-metal contaminated soils. The extraction capacity and selectivity mechanism were investigated by determination of the conditional stability constants (logK) of the STC[4]A–M complex via spectrophotometric titration and the metal speciation using sequential extraction. Under STC[4]A deficiency, the order of metal extraction efficiencies was Cd > Cu > Pb for single-metal contaminated soils, while the selectivity sequence of metal extraction was Cu > Cd > Pb for multi-metal contaminated soils. Spectrophotometric titration indicated that the logK values of the STC[4]A–M complex were in the order of STC[4]A–Cu > STC[4]A–Cd > STC[4]A–Pb and that the values governed the metal extraction selectivity of STC[4]A in multi-metal contaminated soils. Although the logK values for STC[4]A–Cd were intermediate, STC[4]A showed the largest extraction yield for Cd from single-metal contaminated soil due to its larger proportion of exchangeable fraction in soil. The effectiveness of STC[4]A washing appeared to be highly dependent on the metal–STC[4]A formation constants and the metal distribution in soil.