(514m) Exploration of Iron Functionalized Biochar and Activated Carbon for Cr(VI) Aqueous Sequestration

Qhubu MC¹, Ramuhashi T¹, Nomngongo PN², Mtunzi FM¹, Klink MJ and V.E Pakade^1*

¹Vaal University of Technology, Department of Chemistry, Private Bag x 021, South Africa, 1900

²University of Johannesburg, Department of Chemistry, South Africa, 000

Hexavalent chromium (Cr(VI)) is toxic and carcinogenic to humans and plants. Its sources in nature include discharge from electroplating, chrome mining, paints and pigment, leather tanning, and textile industries. Methods such as chemical precipitation, reverse osmosis, ion exchange, adsorption and coagulations have been used for the removal of Cr(VI) from the environment. Among these, adsorption methods have enjoyed widespread acceptance due to their simplicity, cost effectiveness and fine-tuning of functional groups on the surface of adsorbents. To that extent, numerous adsorbents have been developed from synthetic polymers, biomass, clays, and natural polymers. Even though these adsorbents have shown promising applications but there has been challenges with regards to Cr(VI) removal. One of those challenges is the highly oxidative nature of Cr(VI) which tend to get reduced to its trivalent form (Cr(III)) during adsorption leading to incomplete removal of total chromium. Our studies have thus focused on developing adsorbents for the removal of both forms of chromium, sequentially or simultaneously. Various modifications of Macadamia nutshells and mango kernels have been explored for the removal of chromium and adsorption performance improved following ligand immobilization.

In this study, the adsorption efficacy of iron functionalised biochar and activated carbon-silica composites were explored as a cost-efficient adsorbent for the removal of chromium (VI) from aqueous solutions. Magnetic adsorbents were achieved by co-precipitation of Fe²⁺ and Fe³⁺ over activated carbon (AC) derived from Macadamia nutshells. Silica-coated activated carbon were prepared by coating the magnetized activated carbon (AC-Fe₃O₄) with tetraethylorthosilicate (TEOS) and subsequently reacted with 3-glycidaloxypropyltrimethoxysilane to introduce the epoxy group to yield AC-Fe₃O₄-SiO₂-epoxy. Triethylamine and N,N’-dimethylformamide (DMF) were utilized for the quaternization of AC-Fe₃O₄-SiO₂-epoxy to yield AC-Fe₃O₄-SiO₂-N⁺(CH₂CH₃)₃^-. Iron functionalized biochars were produced by solid-phase reduction of pyrite. All materials were characterized by several analytical techniques and their Cr(VI) removal was explored in aqueous solution by studying functional parameters such as the effect of pH, time, adsorbent and adsorbate concentrations.