Aspects of the interaction of trace metal ions with calcium carbonate
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
The interaction of high-Mg calcite and aragonite with a number of different trace metals was studied, in particular with Cu2+, Ni2+ and Co2+. Laboratory experiments into the initial sorption of these three metal ions onto the surfaces of artificial aragonite and high-Mg calcite were performed for a pH range of 6.8-8.2, in buffered solutions saturated with respect to calcite. Below a pH of 8-8.2, substantial dissolution of the unstable polymorph occurred, with little uptake of Co2+ or Ni2+. At a pH of 8.2, uptake was rapid, reaching a plateau in less than 5 min for all three metals. A higher proportion of the available Cu2+ was taken up than of the available Co2+ or Ni2+. Two environmental situations were also investigated. Firstly, samples of water, rock and aragonitic speleothems from Bohemia Cave, Mt. Owen, central Nelson, were examined for major and trace element concentrations. Water samples from the area were found to have very low trace metal ion concentrations, and little consistent relationship between the level of interaction with the environment and the trace metal concentration was seen. Concentration factors of trace metals into the speleothems were much larger than concentration factors of minor or major elements. Metal concentrations in the speleothems were lower than in the surrounding rocks, due to the slow deposition rate of the aragonite crystals, and the exclusion of small cations from the lattice of aragonite. Speleothem samples were analysed by electron microscopy, and structures are described. Secondly, uptake of sub-lethal concentrations of Cu2+, Ni2+ and Co2+ by Corallina officinalis (Corallinales, Rhodophyta) was studied, from a chemically-defined artificial seawater medium. Cu2+ was found to be toxic at even low levels of contamination. All three metal ions were taken up by the live seaweed, in proportion to the metal concentration of the medium. Partitioning of the metal ions was examined, between the inorganic phase of high-Mg calcite, deposited in the plant's cell walls, and the organic material of the plant. Killed seaweed were also "cultured", and found to contain considerably less metal ion than live seaweed. The presence of an increasing excess of Ni2+ had a negative effect on the uptake of Cu2+, but no interaction was seen between Co2+ and the other metal ions. Concentration factors were greatest for Co2+, followed by Cu2+ and Ni2+. C. officinalis has potential as a bio-monitor of pollution levels in seawater, but its usefulness requires further assessment.