The adsorption characteristics of gold onto 3 aminopropyltriethoxysilane grafted coconut pith

Abstract

Increased use of gold in the various industries has raised significant quantities of such compounds into environment. Gold is persistent and non-biodegradable. Precious metal (gold) becomes serious threat to human health in the form of ionic compounds. They can cause damage to nervous system, skin problem, cancer, kidney problem, bone marrow and hearing damage. Also their high price and limited sources makes it economical to recover them. In this study, coconut pith was investigated for the biosorption studies of Au(III). The chemical modification of coconut pith was done using 3-aminopropyltriethoxysilane. The Scanning Electron Microscopy (SEM) results reveal that the surface of grafted coconut pith (GCP) has cracks and coarse surface as compared to virgin coconut pith (VCP) which shows smooth surface. These cracks and irregularities help to increase the biosorption on the interior and surface of GCP. The Fourier Transform Infrared (FTIR) spectroscopy shows different silanization bonds on GCP; Si-O-Si (1032 cm-1), Si- CH2 (1411cm-1) and NH2 (1569.56 cm-1) which were absent in VCP. The effect of different parameters such as pH, contact time, temperature, and initial Au(III) concentration on biosorption was studied. The optimum conditions for biosorption of Au(III) onto GCP and VCP were at Au(III) concentration of 500 ppm, pH 4, contact time of 360 minutes, and temperature of 60 oC. The highest biosorption capacity of 262.19 mg/g was recorded for Au(III) biosorption onto GCP biosorbent at pH 4 and dosage of 1 gm/ml. The biosorption of Au(III) onto VCP and GCP biosorbents was best fitted to the Langmuir isotherm model while the pseudo-second order model was found to best describe experimental data. Au(III) biosorption selectivity of the GCP was better compared to VCP. The regenerability of GCP and VCP biosorbents in gold (III) biosorption was completed in three cycles revealing excellent durability of GCP as compared to VCP.