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exchange of phosphate adsorbed on the surface of gibbsite. T h e equation iswhere A and B a r e parameters; 0 = bF/[b+a(I -m]; a and b are the molar concentrations of the phosphate on the crystal surface and in solution respectively and F is the fraction exchange of the radio-isotope at time t. First-order rate constants were obtained from the equation. T h e reference state for the first-order rate constants, and the distribution of activation energies, for exchange can be related to the Elovich equation parameters. T h e kinetic results are consistent with SS1 dissociation or SK2 bimolecular solvolysis for the phosphate ligand. T h e eschange reaction is subject to an acid-base catalysis the exact nature of which could not be determined from the available data.An Elovich-type equation has been used to describe the kinetics of isotopic

with further research based on gaps in the current knowledge of the thermodynamics and kinetics of these systems, will support the development of computer models to predict the chemical speciation and deportment of these elements through the various stages of the gold cyanidation process. The review covers lead, cadmium, mercury, arsenic, antimony, bismuth, selenium, and tellurium. Presented in this paper is the first part of this review which is a collation of the relevant information on trace element mineralogy, aqueous solution chemistry and toxicity.Although there is much information available about the aqueous solution chemistry of the trace elements, their chemistry in cyanide leach solutions remains largely unexplored. Chemical speciation modelling can assist in understanding the chemistry of the trace elements in gold cyanidation solutions, however, many significant differences exist between the predicted speciation of these trace elements for different types of modelling software. This is due to differences in the thermodynamic data used, the paucity of data that exists under appropriate non-ideal conditions, and the methods used by the software packages to estimate thermodynamic parameters under these conditions.The trace elements reviewed, particularly the species that exist in aqueous solutions, generally have significant toxicities to humans, and more so to plants and animals.Cadmium, mercury and arsenic are classified as human carcinogens whereas selenium is an essential trace element for human health, but is toxic in excess. This review