Waste biomass derived highly-porous carbon material for toxic metal removal: Optimisation, mechanisms and...

Toxic elements, lead, and copper are often found in wastewater discharged from industries such as mining. The discharge of untreated effluent poses severe environmental challenges and sorption methods using agricultural waste materials are proposed as an efficient and cost-effective solution. For this research, activated sunflower material (ASM) was prepared from abundantly available agricultural sunflower waste residues and utilised to remove Pb²⁺ and Cu²⁺ ions from an aqueous medium. To begin, we examine variables that may have an impact on the adsorption process, such as pH, contact time, adsorbent dose, and initial concentration using Box-Behnken Design (BBD) to find optimal conditions. Maximum removal efficiency was found at a pH of 5, contact time of 180 min, and initial concentration of 50 mg/L for Pb²⁺ and 150 mg/L for Cu²⁺. Additionally, adsorbent dose differed by element, for Cu²⁺ it was 200 mg, whilst for Pb²⁺ it was 124 mg. Features of activated carbon such as morphology, elemental composition, textural properties, and surface functionalities were characterised using SEM-EDS, BET, FTIR, and XPS. The adsorption equilibrium data were analysed by Langmuir, Freundlich, and Dubinin-Radushkevich isotherm models. It was found that the obtained results for Pb²⁺ adsorption were better described with the Freundlich isotherm model. Maximum adsorption capacities for Pb²⁺ and Cu²⁺ were 91.8 mg/g and 20.5 mg/g, respectively. Furthermore, kinetic studies confirmed that the adsorption process followed a pseudo-first-order kinetic model for Pb²⁺, but for Cu²⁺ all applied kinetic models fitted experimental data with the same values of the correlation coefficient (R² = 0.99). After comprehensive analysis using the methods mentioned above, ASM was tested for the removal of Cu²⁺ from mining wastewater sample, and the obtained removal efficiency was 98.6% ± 2.0%. The results of desorption experiments conducted, confirm that ASM has good potential to be reused for the purpose of removing Cu²⁺ from wastewater.