The adsorption behaviour of dissolved zinc and cadmium present in River Tawe freshwater in the presence of added clay mineral and naturally occurring suspended seawater particles was monitored using differential pulse polarography and differential pulse anodic stripping voltammetry. Zinc and cadmium were both found to be rapidly adsorbed on to suspended particles added to membrane filtered freshwater. Duplication of these experiments using Swansea Bay seawater and sodium chloride solution (3.2% w spiked with ionic zinc and cadmium) revealed an overall reduction in the extent of zinc adsorption and no cadmium adsorption, in comparison with the freshwater experiments. Mixing experiments where freshwater possessing a high trace metal content and low suspended load (natural particles or the clay mineral illite) demonstrated non-conservative behaviour with addition for cadmium over the time scale of an 8-10 hour mixing experiment. The scatter of data produced by the mixing experiments, with respect to zinc, is quite large and offers only a qualitative rather than a quantitative measure of non-conservatism with zinc removal. The additions of calcium and magnesium ions (to freshwater suspensions containing adsorbed zinc, in quantities to produce concentrations of these ions equivalent to those found in seawater), did not initiate any desorption of zinc within 3-4 hours. The reaction is thought to proceed via a mechanism possessing an irreversible step whereby the adsorption of zinc becomes specific rather than simply electrostatic. Some adsorbed cadmium (12-40%) is released into solution when particulate bearing freshwater is rendered saline. The formation of a monochlorocadmium complex in seawater may contribute to drive the equilibrium of cadmium away from the adsorbed state. The standard addition of lead to water samples was found useful for the estimation of the complexing capacity of freshwater and seawater (with respect to non-labile complex dissociation). L3 camination of lead at naturally occurring concentrations was hampered by contamination and sample interactions with borosilicate glassware.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:636167 |
| Date | January 1981 |
| Creators | Bryant, R. |
| Publisher | Swansea University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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