Chemical modified tannins from Pinus patula bark for selective biosorption of gold in aqueous media

Abstract

Recovery of precious metals such as gold has been of great importance for the metallurgical industry, however the methods used usually involve high costs and/or high levels of contamination, therefore recent research has been dedicated to search for new methodologies for the recovery of these metals. In this work, a modified adsorbent from the tannins of the Pinus patula bark (AT) was prepared for recover of Au (III) using sulfuric acid as a crosslinking agent. Infrared spectroscopy allowed to determine the OH groups (3400–3660 cm−1) of the AT and observe the structural change after adsorbing to the gold (bands between 1380 and 1465 cm−1 by oxidation of OH). By means of BET analysis it was found that it presents a surface area of 4172 m2/g and 1–10 µm particle size by SEM experiments. AT showed selectivity to Au over others metals with adsorption of gold above 99% in lowest concentrations of HCl (0,1–5N) and 10–19% adsorption for Cu (II), Fe (III), Zn (II), Ni (II) under experimental conditions. Au (III) adsorption isotherm data were better described by Langmuir model (r=0,9855) in concentration range studied describing monolayer formation. The maximum adsorption capacity for Au (III) was reached at 666,67 mg L−1 of adsorbent. Proposed mechanism indicates the adsorption of gold on the surface of AT and the subsequent reduction to Au 0, which was also observed by optical microscopy. Compared with activated carbon (98,79%), tannins (85,47%) and bark (76,94%), prepared adsorbent had a higher adsorption capacity (98.79%).