The primary objective of this thesis was to determine the optimum process parameters for the leaching of magnesium carbonate. The ore used for the experiments was a cryptocrystalline magnesite ore from a 516 million tonne magnesite resource located North West of Leigh Creek in South Australia. Thiess Pty Ltd is currently designing a plant to process this ore. The first stage in the process is to leach the magnesium carbonate. Magnesite is leached using hydrochloric acid to produce a magnesium chloride brine and carbon dioxideThe literature review has indicated that the variables that have the greatest effect on the leaching rate are acid concentration, temperature and particle sizeAll of the experiments were done in a 1L laboratory batch reactor that had baffles. The vessel was placed in a water bath and the temperature controlled using a thermo-regulator. An overhead stirrer was used to keep the solids in suspension. Samples were extracted from the vessel using a syringe and plastic tube at timed intervals. The samples were then analysed for calcium and magnesium content using an Atomic Absorption Spectrometer. The change in concentration of the elements was graphed vs. time and the recoveries calculated using the re-calculated feed for each test.The results showed that the optimum parameters were:1. 1.18 mm particle size2. 32% HCl concentration3. 75°C temperatureThe particle size tests confirmed what was found in the literature review. The 0.85mm particles reacted quicker but became trapped in the CO2 (g) product layer and hence the rate of reaction was hindered. The optimum particle size was large enough to not become trapped in the foam layer above the surface whilst the increased surface area (compared to larger particles) available to react resulted in a high rate of reaction.It was also found that contacting the ore with lixiviant containing MgCl2 resulted in a reduced initial rate of reaction and therefore a reduction in the CO2 (g) evolved. A MgCl2 concentration of 46.9 g/l in the initial lixiviant reduced the recovery of magnesium by 6% however there was a significantly less amount of foam formed.It was initially though that the reaction of magnesium carbonate with HCl is reaction controlled. The reaction rates for each test were modelling using the equations given by Levenspiel (1996). It was found that the reaction rate is hindered by diffusion through a product layer. This was explained by the formation of a CO2 (g) bubble that surrounded the reacting particle. The HCl is prevented from contacting the particle and the MgCl2 is prevented from diffusing away from the particle while the CO2 (g) bubble is attached. As the bubble grows too large for the particle, it breaks and rises to the surface. Once this happens, the MgCl2 has to diffuse into the bulk solution before the HCl is able to contact the particle.The workplace risk assessment and control as well as the job safety analysis methods were used to assess and manage the risks involved with using HCl in the laboratory. It was found that the greatest risk occurred in the slurry filtration and sample analysis stage. The major hazards were HCl inhalation and contact with the eyes. To control these hazards, all of the appropriate personal protective equipment was worn, the material safety data sheet was studied and all laboratory procedures were adhered to. Finally a life cycle analysis was done for the use of HCl in the South Australia Magnesium (SAMAG) Plant.