Lead removal from contaminated water using biochar and biomass of olive wast in bath adsorption systems: isotherms and kinetic studies

Nowadays, regarding the effects of contaminants on general health of human and other living beings, identification of effective ways to removal of toxic contaminants from the water is undoubtedly essential. At present, using low-cost locally-available wastes, like biochar, as sorbent materials to removal heavy metals (HMs) from water is preferred than other costly ways. The main objectives of this study were to assess the Pb sorption from water solutions by the biochar derived from olive kernel, the effect of contact time, solution reaction, the initial solution concentration, the sorbent levels, the isotherms and the kinetic of Pb removal process.

The biochar was produced from olive kernel in one hour at 600˚C at oxygen-absence conditions and injection of N2 gas. The biochar properties were determined using Scanning Electron Microscope (SEM), Fourier Transform Infra-Red Spectrometer Spectrum. The carbon, nitrogen and hydrogen contents and specific area were determined using CHN Elemental Analyzer and Methylene-blue, respectively. The effects of contact time (from 0.5 to 16 hours), solution pH (from 2 to 8), sorbent contents (from 0.2 to 10 g.lit-1) and Pb concentration (from 25 to 2500 mg.lit-1) on Pb removal from water solution were studied. The sorption isotherms was studied using Langmuir and Freundlich isotherms.

Based on results cation exchange capacity of olive kernel biochar and olive biomass were 57.42 and 8.12 Cmol kg-1, respectively. Specific surface for olive kernel biochar and olive kernel biomass was 13.2 and 3.92 m2 g-1, respectively. The results obtained from SEM confirmed that the produced biochar has more porosity compared with the olive kernel. Carbon percentage in the produced biochar was 1.5 times of carbon percentage in olive kernel biomass. It was observed that 31 to 71 % of total Pb was removed from water solution by amended biochar during the time. The maximum sorption was observed after 8 hours. It seems that Pb sorption is influenced by solution pH; so that with increment of solution reaction until 5, the sorption content was significantly increased. The optimum sorbent content for used biochar was 4 g lit-1. The results showed that Pb sorption was best modeled by Langmuir isotherm. According to the results of correlation coefficients of kinetic models, Pseudo-second order function had the best performance.

Considering its low costs, production of olive kernel biochar is suggested as a good sorbent for Pb removal. These findings may present some useful information for environmental management in respect of Pb removal, especially at the surroundings of Pb-processing factories and polluted areas of Zanjan province.