Remediation of hexavalent chromium in water and soil by pristine and chemically modified pine barks: Effects and mechanisms

Chemical modification can greatly improve the adsorption performance of materials. In this study, pristine pine bark (PB) was modified by phosphoric acid (PA-PB), dodecyl trimethylammonium bromide (DTAB-PB) and cetyl trimethylammonium bromide (CTAB-PB) to test their influence on remediating hexavalent chromium [Cr(IV)] contamination in water and soil systems. Under the optimal experimental conditions in solution, the reduction/adsorption capacities and removal rates of Cr(IV) follow the order of CTAB-PB > PA-PB > DTAB-PB > PB, with CTAB-PB showing the highest capacity of 88.1 mg g(-1). Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS) indicated that adsorption coupled with reduction were the responsible mechanisms for Cr(IV) removal by pristine and modified PB, and modification with CTAB greatly improved Cr(IV) removal, especially the reduction of Cr(IV). When CTAB-PB and PB were applied in soil for a 30-day microcosm experiment, more than 93 % of Cr(IV) was converted into Cr(III) at four different addition levels (2, 5, 10, and 15 wt%) with CTAB-PB exhibiting a faster immobilization rate than PB. In conclusion, CTAB-PB showed better performance than PB and is a promising material for the remediation of Cr(IV) contamination in water and soil.