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Chromium: Chemical reactions Pilgaard Elements

Metallic chromium dissolves in dilute hydrochloric acid forming Cr(II) and hydrogen gas, H 2. In aqueous solution, Cr(II) is present as the complex ion [Cr(OH 2) 6] 2+. Similar results are seen for sulphuric acid but pure samples of chromium may be resistant to attack. Chromium metal is not dissolved by nitric acid, HNO 3 but is passivated instead.

Electrochemical Properties · Safety

Chromite an overview ScienceDirect Topics

Chromite (Cr) occurs exclusively in mafic and ultramafic igneous rocks (Papp and Lipin, 2006).Although some Cr-based minerals such as crocoite (PbCrO 4), vauquelinite (Pb 2 Cu[CrO 4][PO 4]), uvarovite (Ca 3 Cr 2 [SiO 4] 3), and merumite (4(Cr,Al) 2 O 3 ·3H 2 O) are well known, chromite (FeCr 2 O 4) is the only one that is a commercially recoverable source of Cr (Sueker, 2006; Glastonbury et

Hexavalent Chromium Solubility and Reduction in Alkaline

The soils, termed Low Hex and High Hex, contained 105 and 460 mg Cr(VI) kg −1, 1.8 and 10.4 g total Cr kg −1, and had pH values of 8.5 and 10.4, respectively. Total cumulative Cr(VI) removed by the extractions was 49 and 386 mg kg −1 by both the batch equilibrations and leaching methods in the Low and High Hex soils, respectively, and no

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Genesis of hexavalent chromium from natural sources in

Apr 17, 2007· The experimental rates of dissolved Cr(VI) formation in New Caledonia soil, a mature soil having Cr(III) within chromite and minor Cr(III)–Fe(III) (hydr)oxides,are 0.9 nM h −1 without and 1.3 nM h −1 with birnessite addition, both in close agreement with our predicted Cr(VI) formation rate of 1.3 nM h

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Chromium(III) oxide Wikipedia

Structure and properties. Cr 2 O 3 has the corundum structure, consisting of a hexagonal close packed array of oxide anions with 2 ⁄ 3 of the octahedral holes occupied by chromium. Similar to corundum, Cr 2 O 3 is a hard, brittle material (Mohs hardness 8 to 8.5). It is antiferromagnetic up to 307 K, the Néel temperature. It is not readily attacked by acids. . Occurrence. Eskolaite mineral

Chemical formula: Cr₂O₃

Speciation of dissolved chromium and the mechanisms

Cr(VI) was predominant in weakly alkaline natural waters, and the Cr(III) concentration was less than 1μgdm-3, which was considerably lower than that expected based on the solubility of Cr(OH) 3. The dissolution of chromium in natural water was described by the leaching of Cr(VI) from Cr(III)-containing minerals under oxic conditions.

Biosensor for detection of dissolved chromium in potable

Aug 15, 2017· The iron in the chromite ore forms a stable product ferric oxide (Fe 2 O 3) while aerial oxidation of chromite in molten alkali gives sodium chromate (Na 2 CrO 4). (1) 4 FeCr 2 O 4 + 8 Na 2 CO 3 + 7 O 2 → 8 Na 2 CrO 4 + 2 Fe 2 O 3 + 8 CO 3; Step-II Leaching: Molten sodium chromate reacts with sulfuric acid and water is precipitated reducing

Sciencemadness Discussion Board Dissolution of Chromium

Oct 03, 2012· " It is not readily attacked by acids or bases, although molten alkali gives chromites (salts with the Cr 2O2− 4 anion, not to be confused with the related mineral chromite). It turns brown when heated, but reverts to its dark green color when cooled. It is also hygroscopic." Between this is the picture Wiki throw for it: Also Wiki says:

Chromium Chemistry

Extraction Chromite, FeCr 2 O 4, is the most commercially useful ore, and is extensively used for extraction of chromium.Chromium is produced in two forms: (Chemistry of the Elements, Greeenwood and Earnshaw, Chapter 23). (a) Ferrochrome by the reduction of chromite with coke in

Chromium Chemistry

This is obtained by aerial oxidation of chromite in molten alkali to give sodium chromate, Na2CrO4, which is leached out with water, precipitated and then reduced to the Cr(III) oxide by carbon. The oxide can be reduced by aluminium (aluminothermic process) or silicon: Cr2O3 + 2Al → 2Cr + Al2O3 2Cr2O3 + 3Si → 4Cr + 3SiO2

Chromite an overview ScienceDirect Topics

Chromite (Cr) occurs exclusively in mafic and ultramafic igneous rocks (Papp and Lipin, 2006).Although some Cr-based minerals such as crocoite (PbCrO 4), vauquelinite (Pb 2 Cu[CrO 4][PO 4]), uvarovite (Ca 3 Cr 2 [SiO 4] 3), and merumite (4(Cr,Al) 2 O 3 ·3H 2 O) are well known, chromite (FeCr 2 O 4) is the only one that is a commercially recoverable source of Cr (Sueker, 2006; Glastonbury et

Crystallization of Chromite and Chromium Solubility in

Abstract. The equilibrium between chromite and melt has been determined on four basalts at temperatures of 1200–1400°C over a range of oxygen fugacity (f o2) and pressures of 1 atm and 10 kb.The Cr content of chromite-saturated melts at 1300°C and 1 atm ranges from 0·05 wt.% Cr 2 O 3 at a log f o2 = −3 to 1·4 wt.% at a log f o2 =−12·8. The Cr 2+ /Cr 3+ of melt increases with

Chromate Reduction in Highly Alkaline Groundwater by

chromite ore is roasted with an alkali carbonate and limestone to produce soluble Cr(VI), which is then extracted with water upon cooling.4,5 Large volumes of chromium ore processing residues (COPR) are produced,5 which typically contain 2−7% chromium as a mixture of Cr(III) and Cr(VI) compounds.6

Minerals Free Full-Text Advances towards a Clean

Because of the acute toxicity of Cr(VI)-bearing substances, the pollution problem caused by chromite process residue has become a worldwide concern. In the view of relevant studies, the technologies based on the alkali treatment cannot fundamentally resolve the pollution problem, because the oxidation of Cr(III) to Cr(VI) is unavoidable during chromite decomposition.

Treatment of Hexavalent Chromium in Chromite Ore

We investigated a method for delivering ferrous iron into the subsurface to enhance chemical reduction of Cr(VI) in chromite ore processing solid waste (COPSW) derived from the production of ferrochrome alloy. The COPSW is characterized by high pH (8.5−11.5) and high Cr(VI) concentrations in the solid phase (up to 550 mg kg-1) and dissolved phase (3−57 mg L-1). The dominant solid-phase

Speciation of dissolved chromium and the mechanisms

Cr(VI) was predominant in weakly alkaline natural waters, and the Cr(III) concentration was less than 1μgdm-3, which was considerably lower than that expected based on the solubility of Cr(OH) 3. The dissolution of chromium in natural water was described by the leaching of Cr(VI) from Cr(III)-containing minerals under oxic conditions.

Chromium (Cr) and water Lenntech

Chromite is the starting product for inflammable material and chemical production. Chromium may be present in domestic waste from various synthetic materials. Through waste incineration it may spread to the environment when protection is insufficient. In nuclear fission the 51 Cr isotope is released, and this can be applied for medical purposes.

Biosensor for detection of dissolved chromium in potable

Aug 15, 2017· Chromium (Cr), derived from the Greek word Chroma meaning color (Liddell et al., 1940), is the first element of atomic number 24 placed in group VI.Chromium on its various oxidation states such as Cr(0), Cr(II), Cr(III), Cr(IV), Cr(V), and Cr(VI) are useful for the manufacturing of a vast and varied group of chemicals (Richard and Bourg, 1991, Mertz, 1992, Papp and Lipin, 2001).

Chromium Chemistry

Extraction Chromite, FeCr 2 O 4, is the most commercially useful ore, and is extensively used for extraction of chromium.Chromium is produced in two forms: (Chemistry of the Elements, Greeenwood and Earnshaw, Chapter 23). (a) Ferrochrome by the reduction of chromite with coke in

Chromium Chemistry

This is obtained by aerial oxidation of chromite in molten alkali to give sodium chromate, Na2CrO4, which is leached out with water, precipitated and then reduced to the Cr(III) oxide by carbon. The oxide can be reduced by aluminium (aluminothermic process) or silicon: Cr2O3 + 2Al → 2Cr + Al2O3 2Cr2O3 + 3Si → 4Cr + 3SiO2

Chromium Info [MarZ Chemistry]

To obtain pure chromium, chromite is first treated with molten alkali and oxygen, converting all of the chromium to the alkali chromate, and the latter is dissolved in water and eventually precipitated as sodium dichromate, Na2Cr2O7.

uses for low concentration chromite

Conversion of the concentrated chromite ore into Na 2 CrO 4 . The concentrated ore is mixed with excess of Na 2 CO 3 and a small amount of lime and roasted in a reverberatory furnace at 9001000 o C in the presence of free supply of air. The concentration and reduction percentage of Cr(VI) varied with the cellulose dosage were investigated

(PDF) Advances towards a Clean Hydrometallurgical Process

Cr(VI) in alkaline solution in the pr esence of an oxidant, the green and blue regions can chromium in the chromite spinel be dissolved effectively in the form of. Cr. 3+

Long-term stability of FeSO4 and H2SO4 treated chromite

In this study, the long-term stability of Cr(VI) in the FeSO4 and H2SO4 (FeSO4-H2SO4) treated chromite ore processing residue (COPR) after 400 curing days and the stabilization mechanisms were