A ‘three in one’ complexing agent enables copper desorption from polluted soil, its removal from groundwater and its detection

Abstract

High groundwater concentrations of heavy metals such as copper are toxic to humans. Attenuated total reflectance – Fourier transform infrared spectroscopy (ATR-FTIR) demonstrated that the environmentally benign surfactant sodium lauryl lactylate (SLL) formed bidentate complexes with copper ions. CuSO4 increased the surface tension and the compressional rigidity of SLL films at air-water interfaces, providing additional evidence of SLL-Cu interactions. Here, we harness for the first time the formation of Cu-SLL complexes to achieve the three following objectives. First, SLL enabled the facile detection of copper in water samples, by enhancing the color of copper solutions (10−3 M copper concentrations could be detected with the naked eye). Second, SLL promoted the desorption of copper from model polluted soils. Therefore, SLL can be useful for surfactant flushing applications, in which surfactants are used to enhance the remediation of polluted aquifers through pump and treat. Third, SLL enhanced the treatment of water polluted with copper ions. Specifically, SLL favored the partitioning of Cu2+ into canola oil, purifying water. Therefore, canola oil could be used as liquid sorbent for the treatment of groundwater in SLL-enhanced pump and treat, in which polluted groundwater would be pumped and then treated at the surface. The safety of the proposed treatment can be improved by injecting fluids obtained with the biopolymer sodium alginate (Na-alginate) around the treated area. Na-alginate fluids (at 0.5 wt%) had low viscoelastic moduli before contact with Cu2+ (facilitating their injection) and gelled when intercepting Cu2+ ions (to allow their confinement inside the boundaries of the treated area).