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The adsorption of Ni, Cu, Zn, Cd and Pb by δ-MnO₂ and its inclusion in an equilibrium model of metal partitioning in soils
Chemical equilibrium modelling provides a mechanistic tool for the prediction of metal partitioning in soils, which is important in predicting the fate and effects of metals in soil systems. In order to set up an equilibrium model of metal partitioning in soil systems, thermodynamic data for all pro...
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| Format: | Thesis |
| Language: | English |
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Department of Chemistry
2016
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| _version_ | 1867613199044444160 |
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| access_status_str | Open Access |
| author | Pretorius, Patrius Julius |
| author2 | Linder, Peter W |
| author_browse | Linder, Peter W Pretorius, Patrius Julius |
| author_facet | Linder, Peter W Pretorius, Patrius Julius |
| author_sort | Pretorius, Patrius Julius |
| collection | Thesis |
| description | Chemical equilibrium modelling provides a mechanistic tool for the prediction of metal partitioning in soils, which is important in predicting the fate and effects of metals in soil systems. In order to set up an equilibrium model of metal partitioning in soil systems, thermodynamic data for all processes influencing metal fate in soil systems are needed. In this work, the adsorption of the metals nickel, copper, zinc, cadmium and lead by δ-MnO₂ is investigated. This was done in order to provide thermodynamic data for an important adsorption phase in soils systems. Before this work, consistent adsorption data for only one adsorption phase, hydrous ferric oxide, were available. This precluded the inclusion of manganese dioxide in equilibrium models of metal fate in soil systems. Surface complexation properties of a synthetic manganese dioxide were investigated using glass electrode potentiometry. Experimental data were interpreted according to the surface complexation model in conjunction with the diffuse double layer model of the solid/solution interface. Adsorption constants were derived using the non-linear optimization program FITEQL. The surface complexation parameters determined in this fashion were validated against results obtained from the open literature. Following this, the surface complexation parameters were included in a chemical equilibrium model of soil systems. This model was used to predict the partitioning of nickel, copper, zinc, lead and cadmium in a number of soil samples collected in The Netherlands. Contrary to results presented by other workers, it was found that a non-homogeneous surface site model was needed to explain the potentiometric data obtained for proton and metal adsorption by manganese dioxide. Best fits of alkalimetric titration data were obtained with a two-site, three surface-species model of the δ-MnO₂ surface. Site concentrations of 2.231x10⁻³ mol.g⁻¹ and 7.656x10⁻⁴ mol.g⁻¹ were obtained. Corresponding equilibrium constants for the formation of the postulated surface species are -1.27 (=XO⁻), -5.99 (=YO⁻) and 3.52 (= YOH2₂⁺). This model was successful in a qualitative manner in describing adsorption results obtained from the open literature. The prediction of metal partitioning in soil systems showed that although the inclusion of manganese dioxide in the modelled to some improvement in the agreement between observed and predicted results, other factors are present which influence metal partitioning in soils. The discrepancy between observed and predicted results furthermore showed that the processes accounted for in the equilibrium model are incomplete. |
| format | Thesis |
| id | oai:open.uct.ac.za:11427/18487 |
| institution | University of Cape Town (South Africa) |
| language | eng |
| last_indexed | 2026-06-10T12:32:20.328Z |
| license_str | Not specified — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UCTD — University of Cape Town Open Access Repository |
| publishDate | 2016 |
| publishDateRange | 2016 |
| publishDateSort | 2016 |
| publisher | Department of Chemistry |
| publisherStr | Department of Chemistry |
| record_format | dspace |
| source_str | UCTD — University of Cape Town Open Access Repository |
| spelling | oai:open.uct.ac.za:11427/18487 The adsorption of Ni, Cu, Zn, Cd and Pb by δ-MnO₂ and its inclusion in an equilibrium model of metal partitioning in soils Pretorius, Patrius Julius Linder, Peter W Chemistry Chemical equilibrium modelling provides a mechanistic tool for the prediction of metal partitioning in soils, which is important in predicting the fate and effects of metals in soil systems. In order to set up an equilibrium model of metal partitioning in soil systems, thermodynamic data for all processes influencing metal fate in soil systems are needed. In this work, the adsorption of the metals nickel, copper, zinc, cadmium and lead by δ-MnO₂ is investigated. This was done in order to provide thermodynamic data for an important adsorption phase in soils systems. Before this work, consistent adsorption data for only one adsorption phase, hydrous ferric oxide, were available. This precluded the inclusion of manganese dioxide in equilibrium models of metal fate in soil systems. Surface complexation properties of a synthetic manganese dioxide were investigated using glass electrode potentiometry. Experimental data were interpreted according to the surface complexation model in conjunction with the diffuse double layer model of the solid/solution interface. Adsorption constants were derived using the non-linear optimization program FITEQL. The surface complexation parameters determined in this fashion were validated against results obtained from the open literature. Following this, the surface complexation parameters were included in a chemical equilibrium model of soil systems. This model was used to predict the partitioning of nickel, copper, zinc, lead and cadmium in a number of soil samples collected in The Netherlands. Contrary to results presented by other workers, it was found that a non-homogeneous surface site model was needed to explain the potentiometric data obtained for proton and metal adsorption by manganese dioxide. Best fits of alkalimetric titration data were obtained with a two-site, three surface-species model of the δ-MnO₂ surface. Site concentrations of 2.231x10⁻³ mol.g⁻¹ and 7.656x10⁻⁴ mol.g⁻¹ were obtained. Corresponding equilibrium constants for the formation of the postulated surface species are -1.27 (=XO⁻), -5.99 (=YO⁻) and 3.52 (= YOH2₂⁺). This model was successful in a qualitative manner in describing adsorption results obtained from the open literature. The prediction of metal partitioning in soil systems showed that although the inclusion of manganese dioxide in the modelled to some improvement in the agreement between observed and predicted results, other factors are present which influence metal partitioning in soils. The discrepancy between observed and predicted results furthermore showed that the processes accounted for in the equilibrium model are incomplete. 2016-04-01T06:56:10Z 2016-04-01T06:56:10Z 1997 Doctoral Thesis Doctoral PhD http://hdl.handle.net/11427/18487 eng application/pdf Department of Chemistry Faculty of Science University of Cape Town |
| spellingShingle | Chemistry Pretorius, Patrius Julius The adsorption of Ni, Cu, Zn, Cd and Pb by δ-MnO₂ and its inclusion in an equilibrium model of metal partitioning in soils |
| thesis_degree_str | Doctoral |
| title | The adsorption of Ni, Cu, Zn, Cd and Pb by δ-MnO₂ and its inclusion in an equilibrium model of metal partitioning in soils |
| title_full | The adsorption of Ni, Cu, Zn, Cd and Pb by δ-MnO₂ and its inclusion in an equilibrium model of metal partitioning in soils |
| title_fullStr | The adsorption of Ni, Cu, Zn, Cd and Pb by δ-MnO₂ and its inclusion in an equilibrium model of metal partitioning in soils |
| title_full_unstemmed | The adsorption of Ni, Cu, Zn, Cd and Pb by δ-MnO₂ and its inclusion in an equilibrium model of metal partitioning in soils |
| title_short | The adsorption of Ni, Cu, Zn, Cd and Pb by δ-MnO₂ and its inclusion in an equilibrium model of metal partitioning in soils |
| title_sort | adsorption of ni cu zn cd and pb by δ mno₂ and its inclusion in an equilibrium model of metal partitioning in soils |
| topic | Chemistry |
| url | http://hdl.handle.net/11427/18487 |
| work_keys_str_mv | AT pretoriuspatriusjulius theadsorptionofnicuzncdandpbbydmno2anditsinclusioninanequilibriummodelofmetalpartitioninginsoils AT pretoriuspatriusjulius adsorptionofnicuzncdandpbbydmno2anditsinclusioninanequilibriummodelofmetalpartitioninginsoils |