Adsorption of hexavalent chromium from aqueous solutions by bio-chars obtained during biomass pyrolysis

In this study, bio-chars were evaluated as a potential adsorbent for the removal of Cr (VI) ions from aqueous solutions. The effects of some important parameters including initial pH (1.5–7), adsorbent dose (0.2–5 g/L), contact time (5–900 min) and initial Cr (VI) ion concentration (5–75 mg/L) were tested on the removal of Cr (VI) ions from aqueous solution in batch experiments. Maximum adsorption capacities of the tested bio-chars under the certain experimental conditions determined as optimal were 3.53 mg/g for NCBC, 3.97 mg/g for NZCBC and 6.08 mg/g for ACBC, respectively. Results of the kinetic and isotherm modeling studies revealed that the adsorption data fitted well with a pseudo-second order and Langmuir model. In among the tested bio-chars, the bio-char (ACBC) was largely equivalent to activated carbon: AC (9.97 mg/g) in terms of adsorption capacity. All results indicated that the bio-chars had higher adsorption capacity than some chars and activated carbons reported previously, and also that these bio-chars could be used successfully as low-cost adsorbents for the removal of chromium ions from aqueous solutions under the tested experimental conditions.