title: Heating temperature dependence of Cr(III) oxidation in the presence of alkali and alkaline earth salts and subsequent Cr(VI) leaching behavior.
abstract: In this paper, the temperature dependence of Cr(III) oxidation in high temperature processes and the subsequent Cr(VI) leaching was studied using synthetic mixtures. It was experimentally shown that in the presence of alkali and alkaline earth salts, oxidation of Cr(III) takes place, consistent with thermodynamic calculations. Heating of synthetic mixtures of Cr2O3 and Na, K, or Ca salts led to elevated leaching of Cr(VI); in the presence of Na, more than 80% of the initial Cr(III) amount was converted to Cr(VI) at 600-800 °C. Kinetic experiments allowed explanation of the increase in Cr(VI) leaching for increasing temperatures up to 600-800 °C. After reaching a maximum in Cr(VI) leaching at temperatures around 600-800 °C, the leaching decreased again, which could be explained by the formation of a glassy phase that prevents leaching of the formed Cr(VI). By way of illustration, Cr(VI) formation and leaching was evaluated for a case study, the fabrication of ceramic material from contaminated sludge. Based on the proposed reaction mechanisms, countermeasures to prevent Cr oxidation (addition of NH4H2PO4, heating under inert atmosphere) were proposed and successfully tested for synthetic mixtures and for the case study.
authors: ProcESS, Process Engineering for Sustainable Systems, Department of Chemical Engineering, KU Leuven, W. De Croylaan 46, B-3001 Leuven, Belgium. bram.verbinnen@cit.kuleuven.be
authors: Bram
authors: B
authors: Verbinnen
authors: Pieter
authors: P
authors: Billen
authors: Michiel
authors: M
authors: Van Coninckxloo
authors: Carlo
authors: C
authors: Vandecasteele
mesh_terms: D000468:Alkalies / Q000737:chemistry; D017610:Calcium Compounds / Q000737:chemistry; D002857:Chromium / Q000737:chemistry*; D017608:Chromium Compounds / Q000737:chemistry; D006358:Hot Temperature; D007700:Kinetics; D010084:Oxidation-Reduction; D010087:Oxides / Q000737:chemistry; D012722:Sewage / Q000737:chemistry; D012972:Sodium Hydroxide / Q000737:chemistry; D013816:Thermodynamics; D014874:Water Pollutants, Chemical / Q000737:chemistry*; D014961:X-Ray Diffraction
chemical_list: D000468:Alkalies; D017610:Calcium Compounds; D017608:Chromium Compounds; D010087:Oxides; D012722:Sewage; D014874:Water Pollutants, Chemical; D002857:Chromium; C074702:chromium hexavalent ion; D012972:Sodium Hydroxide; C016538:lime; C023600:chromic oxide