Chromate reduction by waste iron from electroplating wastewater using plug flow reactor

Hexavalent Chromium Reduction with Zero-Valent Iron (ZVI) in Aquatic Systems

“…XRD analysis conducted by Chen et al (2007) to examine the remaining species onto ZVI particles after Cr(VI) reduction at pH 2 indicated the presence of Fe 3 O 4 and, probably, of FeS 2 ; however, when the pH was even lower, the iron oxide layer was not formed since iron was dissolved in solution ). In a subsequent study, Chen et al (2008) reported the presence of Fe 2 O 3 , Fe 3 O 4 , FeOOH, Cr 2 O 3 and mixed iron-chromium complex, Cr 2 FeO 4 , at the surface of exhausted ZVI. Mineralogical examination conducted by Jeen et al (2007) on the ZVI-bearing reactive materials derived from long-term column experiments revealed that whilst the major reaction product in the columns receiving solution 10 mg/L Cr(VI) was magnetite-maghemite, for the columns receiving solution 10 mg/L Cr(VI)+500 mg/L CaCO 3 , the main products were iron aragonite and hydroxycarbonate.…”

“…Another explanation of the faster initial Cr (VI) reduction could be the existence of a Cr(VI) sorption phase (Geng et al 2009a;Ponder et al 2000), whilst the slowing of the rate, at later times, could occur due to a physical mechanism (occlusion of the ZVI) rather than chemical (Ponder et al 2000). In poorly buffered systems, decreases in the reduction rates with time could also be caused by the increase of pH with up to about 3 units over the course of the reaction (Ai et al 2008;Chang 2005;Chen et al 2008;Gheju and Iovi 2006). According to Guha and Bhargava (2005), the second period was followed by a third fast-rate period.…”

Hexavalent chromium reduction with scrap iron in continuous-flow system. Part 2: Effect of scrap iron shape and size

“…Recycling of waste materials has both environmental benefits (preventing the pollution associated with producing virgin materials, reducing odors and congestion associated with the transportation of disposable wastes, decreasing the amount of landfilled materials) and socio-economic benefits (savings in material and energy costs, increase of products competitiveness in the international marketplace and generating employment for collection and recycling activities). Although scrap iron can be a potentially useful reducing material for treating Cr(VI) contaminated wastewaters, to the authors knowledge there are only a few references in the literature concerning the use of this waste material for the reduction of Cr(VI) to Cr(III) [45][46][47][48][49][50][51], comparing with the numerous papers that studied the Cr(VI) removal by adsorption on waste materials [52]. The kinetics of Cr(VI) reduction with iron waste was evaluated in two batch studies [45,46] and in one flow-trough study [47].…”

“…The reduction of Cr(VI) by steel wool was studied under continuous conditions [49]; unfortunately, in this study, the Cr(VI) feed solution was saturated with air, which makes the experimental results difficult to compare with other studies. A more recent paper reported the continuously reduction of hexavalent chromium with cast iron waste, under very strong acidic conditions, and obtained the minimum hydraulic retention time (HRT) at different pHs [50]. In our previous study [51] we investigated the effect of H + concentration on the Cr(VI) reduction by scrap iron, in continuous system, over the pH range of 2.00-7.30.…”

Immobilization of nanoscale Fe0 in and on PVA microspheres for nitrobenzene reduction

“…Fe 0 has been used for the treatment of water contaminated with different types of organic and inorganic compounds, such as chlorinated solvents [1][2][3][4][5], nitroaromatic compounds [6][7][8][9][10], nitrate [11][12][13][14][15], and heavy metal [16][17][18][19]. Nanoscale Fe 0 has been suggested as an alternative means of exploiting the reactivity of Fe 0 because it possesses a larger specific surface area and higher surface reactivity than granular Fe 0 [20][21][22].…”