Facile synthesis of halloysite-bentonite clay/magnesite nanocomposite and its application for the removal of chromium ions: Adsorption and precipitation process

Here we report the synthesis of halloysite-bentonite clay/magnesite nanocomposite, using ball milling and calcination. It was identified that the synthesized nanocomposite enjoys the synergistic properties of both materials, i.e. clays and magnesite, and hence was assessed in terms of chromium ions removal from real tannery wastewater. To identify the optimum conditions for chromium ions removal the one factor-at-a-time (OFAT) method was applied in the design of the batch experiments. The examined parameters include mixing time, dosage, concentration, and pH, while state-of-art analytical techniques were used. Specifically, to identify the morphological properties and the elemental composition of the synthesized nanocomposite, before and after it reacted with the chromium ions, HR-SEM-EDS was used. XRD was used to identify mineralogical compositions, while BET was used to determine surface areas. ICP-MS and multi-parameter probe were employed for water quality analyses. The removal of chromium ions, post the adsorption process, was confirmed using HR-SEM-EDS. The optimum conditions for chromium ions removal were identified as 60 min contract, 0.5 g of dosage at 0.5 g: 500 mL S: L ratio, and 300 mg L−1 chromium ions concentration. The reaction was observed to be independent of pH (1–10). At optimum conditions, the nanocomposite practically removed chromium ions from all examined water matrices, i.e. real tannery wastewater, fortified tap water, groundwater, mine water, and synthetic solution. The adsorption capacity was observed to be 199 mg g−1. Regarding the regression analysis, the adsorption kinetics seem to follow the pseudo-second-order (PSO) than the pseudo-first order (PFO) model. In addition, the adsorption data better fitted the Langmuir than the Freundlich adsorption isotherm. In a nutshell, the synthesized nanocomposite was found to be very promising for chromium ions removal from wastewater and possibly for other contaminants, such as heavy metals, which will be examined in future works of our group.