Chromium (VI) Adsorption Study Using Bio-Adsorbent Material Derived from Tamarind-Seed Testa

Abstract

In this research, the chromium (VI) adsorption in potassium chromate (K2CrO4) and potassium dichromate (K2Cr2O7) was studied with the low-cost adsorbent derived from sweet tamarind seeds obtained from the food processing industry in Thailand. The tamarind-seed testa was prepared by decoloring the tamarind-seed husks in boiling water and 1% NaOH solution followed by bleaching in H2O2 solution. The major components found in the tamarind-seed testa were alkali hydrolysable, low molecular-weight carbohydrates. The study found that the adsorbent material derived from tamarind–seed testa could well adsorb chromium ions in both chromium compound solutions at pH 2. The adsorption took place rapidly within the first 4 hours and then gradually declined until reaching adsorption equilibrium in 12 hours. Adsorption of chromium (VI) from potassium chromate solution was superior to that from potassium dichromate. Chromium adsorption at pH 2 fitted well with Langmuir and Freundlich isotherms. The adsorption mechanism in both solutions was a monolayer chemical adsorption rather than multilayer physical adsorption. The adsorbent could almost completely remove chromium in potassium chromate (90% removal) while it could remove 57% chromium from potassium dichromate solution when the initial chromium concentration of 100 mg/l was employed.