Granular activated carbon/pyrite composites for environmental application: Synthesis and characterization

Abstract

The goal of this study was to produce a reactive granular activated carbon (GAC) coated with pyrite (FeS2) for environmental remediation, which would combine both functions of GAC adsorption and FeS2 reduction reactions. GAC–FeS2 composite materials have been successfully prepared via sequential processes, i.e., incipient wetness iron impregnation, transformation into hematite (Fe2O3) by calcination at 300°C and sulfurization by calcination at 400°C. The point of zero charge (pHPZC) of GAC washed with nitric acid (HNO3) decreased to improve the drawing of iron ionic species into the pores of GAC and the results of FTIR confirmed the predominance of carboxylic acid groups which cause a negative charged GAC surface. XRD results indicated that the calcined composites are transitional GAC–Fe2O3 and final GAC–FeS2. The obtained FeS2 crystallite size calculated using Scherrer formulae was around 31–34nm and SEM/SEI showed FeS2 had an angular shape. The existence of FeS2 in GAC gave rise to a significant reduction of BET surface and pore volume. However, even though these reductions may result in the decrease of adsorption capacity when compared to the virgin GAC, the coated reactive FeS2 may result in the abiotic transformation of adsorbates such as trichloroethylene (TCE) and this would compensate for the loss of adsorption. Furthermore, the preliminary results of TCE experiments on GAC–FeS2 adsorption/dechlorination revealed that the composite initially accumulated and confined TCE on GAC and gradually dechlorinated TCE by embedded FeS2.