Langmuir and Hill model fitting to Pb(II), Cd(II) and Zn(II) sorption by five plant-based biochars

This file contains the raw data and the script for analysing the sorption capacities of five plant-based biochars for Cd(II), Zn(II) and Pb(II). Sorption capacity was measured using a constant quantity (1.25 mg.L-1) of biochar. Metal solutions were prepared in the range commonly present in the soil pore water of contaminated soils: from 0.05 to 10 mg.L-1 for Cd(II) and Zn(II) and from 0.5 to 50 mg.L-1 for Pb(II). As the biochar did not reach its maximum sorption capacity within that range additional concentrations up to 50 mg.L-1 were used for Cd(II) and Zn(II) and up to 85 mg.L-1 for Pb(II). Sorption experiments were carried out at an initial pH 5 for Pb (II) sorption, pH 6.5 for Cd(II) and pH 7.5 for Zn(II). The metal adsorption experiments were performed using a batch equilibration technique in triplicates. Stock solutions (1000 mg.L-1) of Zn(II), Cd(II), and Pb(II) were prepared in deionized water from Zn(NO3)2.6H2O, Cd(NO3)2.4H2O and Pb(NO3)2 (GR grade, Fisher Scientific, USA). The experiments were conducted in 50 mL polyethylene centrifuge tubes, the mixture was agitated at 120 rpm on a reciprocating shaker at 22 ⁰C ± 2 ⁰C. Replicate tubes for each biochar were destructively sampled, and filtered using 0.45 µm syringe filters. The filtrates were acidified with 1% (v/v) HNO3 (Fisher, TraceMetalTM grade) and Cd(II), Pb(II) and Zn(II) concentrations determined by ICP-MS (PerkinElmer, Sciex Elan DRCII). The experimental data was fit to Langmuir and Hill sorption isotherm models.