Otostegia persica biomass as a new biosorbent for the removal of lead from aqueous solutions

Biosorption characteristics of Pb(II) ions from aqueous solution were studied using some residues of solvent-extracted Otostegia persica known as goldar residue biomass. The effects of contact time (0–120 min), the initial pH 3–8, biomass dosage (0.53–2.6 g/L) and the initial lead concentration (5–25 mg/L) on biosorption were investigated. The maximum adsorption capacity of 17.3 mg/g at pH 5.5, the initial lead concentration of 25 mg/L and goldar residue biomass dosage of 1.06 g/L were obtained. The results of equilibrium adsorption were studied through different isotherm models of Langmuir, Freundlich, Temkin, Halsey, Scachard and Dubinin–Radushkevich. Different kinetic models including pseudo-firstorder, pseudo-second-order and intraparticle diffusion were applied. The pseudo-second order described the adsorption kinetics data properly. Thermodynamic investigation at temperatures ranging from 25 to 45 °C showed a reduction in both the possibility of adsorption and randomness at the solid–solution interface of goldar residue. Fourier transforms infrared analysis confirmed the presence of several functional groups on the surface of the goldar residue biomass during lead adsorption. O. persica residue biomass showed good properties to use as a new biosorbent for removal of low concentrations of lead ions from water.

Keywords
Biosorption; Otostegia persica; Lead ions; Adsorption kinetics; Adsorption isotherm