Removal of copper(II) from aqueous solution by pine and base modified pine cone powder as biosorbent

Pine cone, a popular agricultural waste in South Africa has been studied for its potential application as a biosorbent in its raw and sodium hydroxide modified form. Surface modification were carried out using sodium hydroxide solution of concentration ranging from 0.01 to 0.15 mol L −1and the samples characterized. Batch kinetics were carried out on the biosorption of copper(II) from aqueous solution using the prepared samples and varying biosorption parameters such as solution pH, dose and biosorption temperature. The results revealed that pine cone surface was modified by sodium hydroxide treatment, carboxylic and phenolic functional groups were mostly affected as seen from Boehm's titration and FTIR analysis. Surface modification reduced pH PZC from 7.49 to 2.55 and also increased the internal surface of pine cone powder. Copper(II) biosorption studies revealed that optimum solution pH and biosorbent dose for copper(II) removal was pH 5 and 8.0 g L −1, for the untreated and treated samples. Copper(II) uptake followed the pseudo-second order kinetic model and the intraparticle diffusion model. Copper(II) removal increased with NaOH modification and higher NaOH concentration. Biosorption temperature was found to increase copper(II) uptake for all samples indicating that copper(II) biosorption is endothermic in nature. Activation energy computed from the pseudo-second order rate constant increased with NaOH modification from 18.22 to 21.39 kJ mol −1. The thermodynamic parameters of activation (Δ G*, Δ H* and Δ S*) were computed using Erying equation and the results show that the reorientation step is mostly entropy controlled at the activation state and the contribution of entropy to the reorientation step of activation tends to decrease with NaOH washing and with increase in NaOH concentration.