Lead removal from aqueous solutions using biochars derived from corn stover, orange peel, and pistachio shell

Abstract

Biochar has been viewed as a cost-effective adsorptive material for heavy metals in water. In the present study, a total of nine different biochars synthesized from three different biomass types were studied: corn stover, organic peel, and pistachio shell at three pyrolysis temperatures (300, 450, and 600 °C). The efficiency of lead ion (Pb2+) removal by the biochars was investigated through batch adsorption experiments in parallel with physicochemical characterization of the biochars. Single-point Pb2+ adsorption at 10 mg L−1 showed that high-temperature corn stover biochar at 600 °C and low-temperature orange peel biochar at 300 °C performed the best in the Pb2+ removal (> 94%). Pistachio shell biochars were relatively poor at removing aqueous Pb2+ (20–35%). The efficiency of the Pb2+ removal increased with increasing pH (2–6) until a maximum adsorption of Pb2+ was observed at pH 6. Adsorption isotherms for Pb2+ were conducted using the best-performing biochars per biomass based on the single-point adsorption results. All isotherms were best described by the Langmuir model, and the Pb2+ sorption capacities were 25,000 mg kg−1 for corn stover biochar at 600 °C, 11,111 mg kg−1 for orange peel biochar at 300 °C, and 2500 mg kg−1 for pistachio shell at 600 °C. The physicochemical properties of biochars indicated that oxygen-containing functional groups and specific surface area were major parameters affecting aqueous Pb2+ removal. This study highlights that biomass type and pyrolysis temperature as well as solution pH are important in affecting the adsorption efficiency of Pb2+ from aqueous solution.