Effective remediation of Cr(VI) using coconut coir-derived porous biochar: application of kinetics and isotherm approaches

Abstract

Biochar-based chromium adsorption is a relatively new and affordable method for remediation of hazardous metal species from contaminated environments. Coir fiber is an agricultural waste produced from coconut processing industry. This study focused on the synthesis of coconut coir-based biochars and evaluated their Cr(VI) removal efficiency. Biochar samples were prepared under different pyrolysis temperatures (300-700 degrees C) and characterized using Thermogravimetric, Carbon-Hydrogen-Nitrogen-Sulfur-Oxygen and Brunauer-Emmett-Teller surface area analyzer. Following a screening process to determine the efficacy of removing Cr(VI) of all biochar samples, coconut coir biochar prepared at 400 degrees C (CBC400) showed relatively better (similar to 90%) Cr(VI) removal. The effects of various physicochemical factors such as pH, initial metal concentration, treatment time, and adsorbent dosage on Cr(VI) removal process are investigated and optimized. It was also found that at 50 mg/L initial Cr(VI) concentration, the CBC400 can remove 40.3 mg (q(max)) Cr(VI) per 1 g adsorbent dosage within 24 h under optimum condition. It was demonstrated that Cr(VI) adsorption using CBC400 has a good fit with Langmuir isotherm and pseudo-second-order kinetics model. The interaction between Cr(VI) ions and biosorbent were well established by characterising prior and post-Cr(VI)-treatment of biochar samples using scanning electron microscopy with energy-dispersive X-ray spectroscopy, X-ray diffraction and Fourier transform infrared spectroscopy. From the overall findings of the study, it was concluded that CBC400 can be suitably applied for Cr(VI) removal with possible safe disposal in cost-effective and environmentally safe way. [GRAPHICS] .