Identification of Two Iron− Chromate Precipitates in a Cr(VI)-Contaminated Soil

Abstract

Two iron−chromate precipitates, KFe3(CrO4)2(OH)6 (the chromate analog of the sulfate mineral jarosite) and KFe(CrO4)2·2H2O, were discovered in a soil contaminated by chrome plating solutions. The precipitates were identified by electron microscopy and powder X-ray diffraction. KFe3(CrO4)2(OH)6 was found as small crystals interspersed within the bulk soil. KFe(CrO4)2·2H2O forms crusts in cracks and fractures of the soil. Powder X-ray diffraction of the whole soil indicates that most of the Cr(VI) in the soil is present as KFe3(CrO4)2(OH)6 and that the overall amount of KFe(CrO4)2·2H2O in the soil is relatively small. The reaction for the transformation between these two phases indicates that KFe(CrO4)2·2H2O is likely to form in more acidic , K+- and HCrO4 --rich environments than KFe3(CrO4)2(OH)6. Although both of these chromate phases have been synthesized and described, to our knowledge, this study is the first report of their occurrence in the environment.

Effects of pH and dissolved oxygen on Cr(VI) removal in Fe(0)/H2O systems

“…Chromium (Cr) is widely used in many industrial processes and products, including in metallurgy (as a corrosion inhibitor), paint pigments, antifouling agents, fungicides, leather tanning, and electroplating, and is released as industrial waste into aquatic environments [1][2][3][4][5]. In aquatic environments, Cr is present in several oxidation states, although only hexavalent [Cr(VI)] and trivalent [Cr(III)] chromium are biologically important [6].…”

“…Oxidation of the Fe(0) surface is a spontaneous corrosion reaction forming Fe(II) and Fe(III) ions, and Fe(0) can act as an electron donor, causing the reduction of dissolved ions. The Fe(II) formed at the corroding Fe(0) surface reacts with OH − to form ferrous hydroxide [Fe(OH) 2 ] that can be further oxidized to green rust I and II, magnetite, lepidocrocite, ferrihydrite, and goethite [17][18][19]. However, contaminant removal in Fe(0)/H 2 O system is not only one mechanism for reduction (chemical process), but also adsorption of iron corrosion products (physical process).…”

Concentration fluctuation and dead zone phenomena caused by ion-induced trapping effect in electrokinetic remediation of chromium-contaminated soil

“…The red band between Zone 1 and Zone 2 moved slower than red band between Zone 3 and Zone 4 because of higher concentration of KCl in Zone 1, resulting in that two red bands came closer gradually (Photo C) and finally merged in 233 minutes (Photo D). The black substance in Photo D is perhaps a mixture of Fe 2+ , Fe 3+ , Cr 3+ , HCrO 4 -.Fe 2 (CrO 4 ) 3 or KFe(CrO 4 ) 2 ·2H 2 O [20]. This is another type of "dead zone" caused by chemical reaction which will not be discussed in this paper.…”

A Comparison of Iron and Aluminium Electrodes in Hydrogen Peroxide-Assisted Electrocoagulation of Organic Pollutants

“…Using SEM, the structural features of the sludge can be evaluated and the elemental composition can be determined with EDS (Baron et al, 1996;Mahmood et al, 1998). The microphotograph in Fig.…”