Adsorption of mercury onto 3-ureidopropyltriethoxysilane grafted empty fruit bunches biosorbents

Abstract

Mercury is among the heavy metal with high toxicity levels that are commonly released into environment. Heavy metals are persistent, nonbiodegradable and accumulates overtime, reaching health concering concentration. In this study, biosorption studies of mercury and methylmercury onto oil palm empty fruit bunch fibre (OPEFB) were performed to investigate the biosorption performances. In addition, OPEFB was further functionalised by 3-ureidopropyltriethoxysilane via grafting through hydrolisis method. These biosorbents were then characterised by scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR), point of zero charge (pHpzc) and cation exchange capacity (CEC). Batch biosorption experiments were performed to evaluate the effects of several parameters such as ligand concentrations, initial pH, initial concentrations, contact time and temperature. The results indicated that the biosorption performance of Hg (II) and CH3Hg (I) sorption significantly changed with the changes in the aforementioned parameters. Highest biosorption capacity of 156.99 mg/g was recorded for Hg (II) sorption onto treated sorbent while CH3Hg (I) sorption did not show any improvement even when tested upon treated sorbent. Biosorption of both metals onto treated and untreated biosorbents was best fitted to Langmuir isotherm model while, pseudo-second order model was chosen to represent all the biosorption data obtained in this study. Mercury metal selectivity study was conducted for each sorbent for Pb, Zn, and CH3Hg (I) in an individual batch biosorption test. Regeneration ability of treated biosorbent in Hg (II) sorption that was completed for four cycles still performs better than untreated biosorbent despite experiencing gradual reduction in sorption capacity.