Highly efficient Cd(II) removal using macromolecular dithiocarbamate/slag-based geopolymer composite microspheres (SGM-MDTC)

The Si-O-Si moiety present in low-cost, easy-to-prepare geopolymers forms a part of the skeletal structure and does not participate in adsorption. In this work, a novel composite adsorbent (SGM-MDTC) was synthesized by grafting macromolecular dithiocarbamate (MDTC) on slag-based geopolymer microspheres (SGM), and the Si-O-Si in SGM was activated to enhance the Cd(II) adsorption performance of the geopolymer adsorbent. The SGM-MDTC was synthesized successfully and characterized using the XRD and FT-IR techniques. The Si-O-Si unit present in SGM was activated after anchoring MDTC. The activation was confirmed using the XPS technique. It was observed that the morphology of SGM and SGM-MDTC changed significantly, and the specific surface area of SGM increased from 52.99 to 72.36 m(2)/g following the process of MDTC anchoring. The effects of pH, the dosage of SGM-MDTC, contact time, and initial concentration during static adsorption on the adsorption performance of Cd(II) on SGM-MDTC were studied. It was observed that the process followed the pseudo-second-order kinetics, Langmuir, and Sip models and was primarily controlled by the process of intra-particle diffusion. The adsorption capacity of the synthesized SGM-MDTC (205.8 mg/g) material was nearly twice as high as that of SGM (106.7 mg/g) under conditions of static adsorption. Dynamic adsorption is more suitable for practical application than static adsorption. The adsorption capacity of SGM-MDTC was as high as 382.8 mg/g. This revealed that the synthesized SGM-MDTC material exhibited excellent Cd(II) purification performance and high application value.