Development and Characterization of Biosorbents To Remove Heavy Metals from Aqueous Solutions by Chemical Treatment of Olive Stone

Olive stone is an agroindustrial waste, which has been used as precursor for the development of new biosorbent materials for lead ions removal. Chemical treatments of biosorbent were studied to analyze their effects on physical-chemical properties and lead removal. Chemical treatment of olive stone can remove lignin and holocellulose and increase the porosity or surface area. A detailed description of the changes on chemical, physical, and textural properties is presented in this study. Acid treatment improved cellulose hydrolysis, increased surface area and average pore volume, and decreased pore diameter of the olive stone. Also, the acid-base properties of the solids were well described by simplified chemical equilibrium models. Concretely, treatment of olive stone by acids developed negatively charged groups in the acidic pH range. Consequently, olive stone chemically modified with acids has a much lower pH(ZPC) value indicating that the biosorbent surface becomes more negative due to dissociation of weakly acidic oxygen-containing groups. Lead biosorption properties of chemically modified olive stone were improved compared to a native one. For example, after basic treatment with NaOH, the maximum biosorption capacity of lead increased from 6.32 to 38.02 mg/g.