Analytical and biogeochemical studies of tungsten : a thesis presented in parial fulfillment of the requirements for the degree of Master of Science in Chemistry at Massey University

Abstract

Section I: Studies were carried out to determine the optimum conditions for the determination of tungsten with a large quartz emission spectrograph. By making use of silver chloride as a carrier, large electrodes and the 2947 A analysis line, soils and rocks containing as low as 10 ppm tungsten could be analysed with reasonable reproducibility. Reliable results were not achieved for plant samples however, and the productivity of the method was very low. In view of these shortcomings, the use of the dithiol colorimetric reagent for the analysis of tungsten was investigated, and a reliable procedure with a detection limit of 0.1 ppm and very high productivity was developed for the analysis of soils, rocks and vegetation. Section II: Pot trials were carried out to investigate the uptake of tungsten by young plants of Nothofagus menziesii (silver beech). It was found that, although most of the tungsten taken up from the soil remained in the roots, the concentrations of this element in the leaves, stems and roots of the plants were all related to the tungsten concentration in the soil. Section III: Biogeochemical and geochemical investigations were carried out in an area of tungsten mineralisation at Barrytown, Westland. The results of preliminary investigations showed that the levels of manganese, tin and load in the soil were associated with the tungsten level, and may therefore be of possible use as pathfinders for tungsten. An investigation was carried out to determine whether the concentration of tungsten in plants could be used to predict the concentrations of this element in the soil. It was found that while shallow-rooting species such as tree-ferns could be successfully used to detect soil anomalies, the relationship between the levels of tungsten in soils and tree species was rather less distinct. Detailed study of trunk and soil samples indicated that this was caused largely by variation in soil properties, particularly pH, which was found to affect the solubility of tungsten. Despite the unsuitability of trees for indicating concentrations of tungsten in the soil, it was found that tree-trunk analysis could be successfully used to locate tungsten-bearing veins, without restriction in the number and types of species used.