Biochar synthesis from sweet lime peel for hexavalent chromium remediation from aqueous solution.

Sweet lime (Citrus limetta) peel biochar was obtained by slow pyrolysis of raw biomass at 450 °C with 5 °C/min heating rate. Proximate and ultimate analysis, physico-chemical characterization of the biochar was done. Batch adsorption experiments for Cr(VI) removal were performed with varying pH, biochar dose, contact time and initial Cr(VI) concentrations. It took 8-24 h to reach the equilibrium at 30 °C for varying Cr(VI) concentrations. The biochar was found to possess higher adsorption capacity (100 mg/g) than the adsorbents reported in several previous studies. Langmuir adsorption isotherm and pseudo second order model best explained the experimental data, suggesting monolayer adsorption as the dominant mechanism. Chemical interaction, ion exchange of solute and sorbate ions and physical adsorption also contributed into Cr(VI) adsorption process. Further, Cr(VI) adsorption was found to be a multistep process. The findings suggested that sweet lime peel biochar can be utilized as a low cost and efficient alternative for Cr(VI) removal, which could be useful for aqueous solutions, as well as to promote overall protection against soil and water degradation and pollution.