Novel thio-kaolinite nanohybrid materials and their application as heavy metal adsorbents in wastewater

Abstract A new clay nanohybrid adsorbent material was obtained by grafting the compound 3,6-dithia-1,8-octanediol (HO(CH2)2S(CH2)2S(CH2)2OH) onto the internal aluminol surfaces of both the urea- and dimethylsulfoxide (DMSO) precursors of two kaolinite clay minerals: the Source clay KGa-1b and a Portuguese clay sample collected from the Clays of Taveiro formation. All samples were characterised by X-ray diffraction and solid-state 13C cross-polarisation nuclear magnetic resonance (CP-MAS NMR) spectroscopy. Initial materials and final products were also characterised by thermal gravimetric analysis (TGA) and Fourier-Transform infrared (FTIR) spectroscopy. The results describe nanohybrid materials that are resistant to hydrolysis and exhibit different grafting fashions. The potential application of these materials as a heavy metal adsorbents was tested in ZnCl2 solutions as well as in zinc-spiked raw wastewater. The first assessment of the zinc adsorption capacity of the Source clay KGa-1b was made. Zinc concentrations were analysed concomitant with other metal species by inductively coupled plasma mass spectrometry (ICP-MS), demonstrating variable adsorption capacities of the different clay samples, and a consistently greater zinc removal in the wastewater system compared to simple zinc solutions. Measured concentrations of concomitantly analysed metals reveal a potentially worrying release of certain heavy metal species from some of the clay samples as a result of zinc adsorption.