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Title: Deployment of calcium polysulphide for the remediation of chromite ore processing residue
Author: Anunike, Chidinma
ISNI:       0000 0004 5371 4488
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 2015
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Chromium contamination of groundwater and soils continues to pose a major environmental concern. Soils may have become contaminated with chromium through former industrial activities geochemical enrichment. The nature of the industrial activity will determine the form and concentration of the chromium as well as the presence of co-contaminants and the pH and redox of the soil. Chemical reductants have been widely used for the transformation of hexavalent chromium in the environment. Over recent decades attention focused on the chemical reductant calcium polysulphide which has performed effectively in the treatment of groundwater and soil samples contaminated with Cr(VI). Yet a detailed understanding of calcium polysulphide (CaSx) performance has not yet been established. Hexavalent chromium concentrations in aqueous and groundwater samples were significantly reduced by calcium polysulphide and CaSx:chromate molar ratio of 1.5 was sufficient to prevent partitioning of Cr(VI) into solution and to precipitate the solution phase. Calcium polysulphide was used for the remediation of solid chromite ore processing residue (COPR) samples. Prior to the application of calcium polysulphide to COPR, each of the key steps were optimized. A range-finding experiment was conducted to understand the dosage and treatment regime at which Cr(VI) immobilization within COPR was optimal. The results indicated that unsaturated deployment of CaSx into the medium outperformed that in saturated systems. A higher polysulphide amendment dose of 5% w/v concentration enhanced the final treatment of Cr(VI) within COPR. The toxicity and carcinogenicity of Cr(VI) over Cr(III) requires a technique capable of discriminating between valencies. The EPA Method 7196A specifically quantifies the concentrations of Cr(VI) in environmental samples and was used for all analysis to differentiate between Cr(VI) and Cr(III). Cr(III) was calculated as the difference between the Cr(VI) and Cr-total concentrations. In addition to the EPA 7196A, a novel ion exchange resin (IER) procedure was developed to differentiate the two species of chromium. After optimisation, Amberlite resins IRA 400 and IR-120 were used for the specific sorption and subsequent analysis of aqueous Cr(VI) and Cr(III) solutions. For the selective removal of chromate from groundwater, waste water and soil samples, Amberlite IRA 400 achieved a consistent performance of >97% removal in a range of trials. The IERs in this work were applied as analytical tools however they could be applied as remediation tools. While aqueous treatment of chromium contaminated media using CaSx was very successful, COPR treatment proved to be difficult due to the complex nature of the system. An understanding of stoichiometric responses to CaSX has been established, but the nuances of soil physicochemical interactions require more thorough investigation.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Soil pollution ; Groundwater ; Soils ; Soil remediation