In the quest for sustainable solutions to combat environmental pollution, particularly the pervasive issue of chromium contamination in water bodies, a groundbreaking study has emerged. Focused on the adsorptive removal of hexavalent chromium [Cr(VI)], this research leverages the modification of biochar, a renewable carbonaceous material derived from plant and animal waste. The study introduces two modified biochars: one treated with ferric chloride (FBC) and the other with both ferric chloride and chlorapatite (FBCP), aiming to enhance the adsorption capacity under weakly acidic conditions.

Employing a variety of analytical techniques, including scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD), the study elucidates the adsorption mechanisms of Cr(VI) by FBC and FBCP. These mechanisms include reduction, physical adsorption, ion exchange, and functional group complexation. The adsorption process was revealed to be a spontaneous and endothermic reaction, fitting well within the pseudo-second-order kinetic model and the Langmuir model, indicating a monolayer chemical adsorption predominance.

Remarkably, the FBC and FBCP exhibited significant improvements in the maximum saturated adsorption capacities for Cr(VI), achieving 4.06 and 6.48 times the capacity of unmodified biochar, respectively. Notably, FBCP’s inclusion of phosphate ions further enhanced pollutant removal efficiency through co-precipitation with Cr(III), underscoring the synergistic benefits of the dual modification.

This research not only highlights the potential of biochar as a cost-effective, efficient, and environmentally friendly adsorbent for Cr(VI) removal but also sets a new benchmark in the development of advanced materials for wastewater treatment. The innovative approach of combining ferric chloride and chlorapatite modification opens new avenues in the resource utilization of waste, addressing the dual challenges of environmental pollution and waste management.