Extraction of highly pure silica from local rice straw and activation of the left carbon for chromium (VI) adsorption

摘要

The main objectives of the present work is develop an efficient procedure for treating the rice straw (RS) to separate silica and activating the carbon left behind for Cr(VI) adsorption from its aqueous solutions. This has been possible by first digesting the RS with NaOH solution to dissolve the silica content followed by an acidification step to obtain silica gel which was dried at 110 C° and calcined at 750 C°. The determined optimum factors thereof have resulted in 85.5% silica leaching efficiency and a product purity of 99.8%. The separated silica has been specified through relevant chemical as well as via XRD and FTIR analyses. The residue left behind after silica extraction was then heat-treated for its activation before being applied for Cr (VI) adsorption. The relevant adsorption factors have included the effects of pH and the time as well as the effect of the initial Cr (VI) concentration. Using the optimum values of the latter, the prepared activated carbon was applied for chromium management from a titania waste solution assaying 650 ppm Cr species and it was possible to realize an adsorption efficiency exceeding 98%.