Adsorption of toxic metals from landfill leachate using coconut husk biochar

Adsorption is an eco-friendly and cost-effective technique for removing heavy metals from contaminated aqueous environments using low-cost and readily available materials. This study evaluated the potential of coconut husk biochar for the removal of arsenic (As), nickel (Ni), chromium (Cr), and cadmium (Cd) from landfill leachate. The biochar was produced at pyrolysis temperatures of 350 ± 5 °C and 500 ± 5 °C and tested under batch adsorption conditions using adsorbent dosages of 0.50, 1.50, and 3.00 g per 100 mL of leachate at contact times of 30 and 60 min under mechanical agitation. The adsorption efficiency of As, Ni, Cr, and Cd increased with increasing biochar dosage, higher pyrolysis temperature (500 ± 5 °C), and longer residence time (60 min), with Cd and Cr showing the highest adsorption efficiencies (99.76 to 99.85%), Ni showing consistently high adsorption (93.28 to 95.22%), and As with relatively lower adsorption efficiencies (48.60 - 63.59%). Arsenic removal was generally enhanced at higher pyrolysis temperatures; however, biochar produced at 350 ± 5 °C demonstrated superior adsorption performance compared with biochar produced at 500 ± 5 °C under similar operating conditions, particularly at a dosage of 1.50 g and contact times of 30 and 60 min. In contrast, the removal efficiencies of Ni, Cr, and Cd consistently improved with increasing pyrolysis temperature, contact time, and adsorbent dosage. The Freundlich model's best fit for arsenic, chromium, and nickel was highlighted by their high K L and R 2 values and intriguing adsorption characteristics. Overall, the study demonstrates that coconut husk biochar is an effective, sustainable, and low-cost adsorbent for the removal of toxic metals from landfill leachate. Further research is recommended to optimise operational parameters and assess the feasibility of large-scale applications.