Removal of Hexavalent Chromium from Aqueous Solution Using Olive Tree Bark as Natural Adsorbent

Abstract

This study examined the adsorption behavior of olive bark as a natural adsorbent to remove chromium (Cr) from aqueous solution by packed bed column technique (PBC) based on Box – Wilson design. This study involved the preparation of two batches of olive bark pieces. The first batch is raw pieces of bark with no treatment with chemicals. Strips of bark were taken from an olive tree and were cut into pieces by an agricultural scissor, some were cut into small pieces 4-6mm in size and other into big pieces 8-10mm in size. They were washed with distilled water to remove dirt from the sample and then dried in an oven at 100 °C for 2 hours. For the second batch, the strips of bark were also cut into small and big pieces and washed with distilled water. But then were modified by acid / base treatment, then they were dried in an oven. Next, each of the small and big pieces of the untreated batch were packed separately in three different columns about 3/4 of its length. Each column has a certain pH of chromium aqueous solution and contact time, same was done for the pieces of the treated batch, then, the chromium solution after treatment was collected in test tubes to measure its concentration by using atomic absorption spectroscopy. The best performance towards chromium removal was achieved with small particle treated olive bark, which showed a removal efficiency of 84.2% for Cr at pH 5.4 and contact time 4 hr. Statistical study showed significant differences in removal efficiency at the level of probability (p ≤ 0.05). The analysis of the infrared device (FTIR) proved the presence of active groups in the olive bark after treatment, which are responsible for bonding Cr from chromium aqueous solution. FE-SEM analysis showed the morphological changes on the olive bark surface before and after treatment of chromium aqueous solution.