Passivation process and the mechanism of packing particles in the Fe0/GAC system during the treatment of ABS resin wastewater.

This study provides mechanistic insights into the passivation of the packing particles during the treatment of acrylonitrile-butadiene-styrene (ABS) resin wastewater by the Fe0/GAC system. The granular-activated carbon (GAC) and iron chippings (Fe0) were mixed together with a volumetric ratio of 1:1. GAC has a mean particle size of approximately 3-5 mm, a specific surface of 748 m2 g(-1), a total pore volume of 0.48 mL g(-1) and a bulk density of 0.49 g cm(-3). The iron chippings have a compact and non-porous surface morphology. The results show that the packing particles in the Fe0/GAC system would lose their activity because the removal of TOC and PO4(3-) for ABS resin wastewater could not carried out by the Fe0/GAC system after 40 days continuous running. Meanwhile, the availability of O2 and intrinsic reactivity of Fe0 play a key role on the form of passive film with different iron oxidation states. The passive film on the surface of iron chippings was formed by two phases: (a) local corrosion phase (0-20 d) and (b) co-precipitation phase (20-40 d), while that of GAC was mainly formed by the co-precipitation of corrosion products with SO4(2-) and PO4(3-) because SO4(2-) and PO4(3-) would not easily reach the Fe0 surface. Therefore, in order to avoid the occurrence of filler passivation, high concentrations of SO4(2-) and PO4(3-) in wastewater should be removed before the treatment process of the Fe/GAC system.