Enhanced removal of trace mercury from surface water using a novel Mg2Al layered double hydroxide supported iron sulfide composite

Mercury contamination poses a serious threat to the ecological system and human health. Yet, removal of mercury at parts per billion (ppb) level in surface water is difficult to achieve. This study developed a Mg2Al layered double hydroxide supported iron sulfide composite (FeS@Mg2Al-LDH) and investigated its removal effectiveness and mechanisms of mercury from surface water. FeS was successfully soldered onto Mg2Al-LDH via surface complexation and surface adsorption. The composite (FeS:Mg2Al-LDH mass ratio of 1:1) at 20 mg/L effectively removal 89.4% of 110 mu g/L mercury at pH 7.0 within 72 h. A pseudo-second-order kinetic model well simulated the sorption kinetic data and a Sigmoidal Langmuir isotherm model perfectly fitted the sorption isotherm data with a maximum monolayer sorption capacity of 116.96 mg/g. X-ray powder diffraction (XRD), Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS) analyses suggested that mercury was removed via chemical precipitation, ion exchange, and surface complexation. The supporting material Mg2Al-LDH greatly enhanced the antioxygenic and pH-resistant properties of FeS, and the composite offered high selectivity for mercury. FeS@Mg2Al-LDH and immobilized mercury remained stable over 6 months. This study demonstrated the potential and viability of FeS@Mg2Al-LDH for efficient removal of aqueous mercury.