Cassava stem biochar (CSB) for chromium removal from produced water: sustainable adsorption and environmental implications

Abstract BACKGROUND Produced water, a byproduct of oil and gas extraction, often contains elevated levels of heavy metals, including chromium, posing significant environmental and health risks. Cassava stem biochar (CSB) was prepared by pyrolysis of cassava stem and its potential has been investigated for the removal of chromium (Cr) from produced water. Batch adsorption experiments were conducted to evaluate the adsorption capacity of CSB under various conditions of pH, contact time, initial produced water concentration, adsorbent dosage, agitation speed, temperature and particle size. RESULTS From the experiment results, it was found that CSB showed good adsorption capacity of chromium ions from produced water. The adsorption process was found to be highly pH‐dependent, with maximum removal efficiency observed at a pH of 4.0. Equilibrium data were fitted to the Freundlich isotherm models, indicating multilayer adsorption on a heterogeneous surface. The kinetic data demonstrated that the adsorption process followed pseudo‐first‐order as well as pseudo‐second‐order kinetics, suggesting a physisorption and chemisorption mechanism. The thermodynamic parameters, including changes in enthalpy (ΔH), and entropy (ΔS), were evaluated to gain insights into the spontaneity and feasibility of the adsorption process. The negative ΔH values indicated that the adsorption of Cr onto CSB was non‐spontaneous and exothermic in nature. The negative ΔS value suggested the adsorption is feasible. CONCLUSION This comprehensive study demonstrates the potential of cassava stem biochar as an effective and environmentally friendly adsorbent for the removal of chromium from produced water. © 2024 Society of Chemical Industry (SCI).