In order to understand the formative processes and textural change of anglesite from galena under natural sulfuric acid condition, chemical reaction of galena with sulfuric acid was experimentally examined. In the experiment, galena was sealed in the polypropylene bottle with sulfuric acid solution, and left for fixed duration in time. Three series of experiments, i.e., long term, rate analysis and solid textural analysis experiments, were carried out with changing temperature (30 to 170 °C), concentration of sulfuric acid (0.01 to 1 mol/l), duration (1 to 56 days) and state of galena (powder, grains or plastic crystals). The run products were filtered by 0.20 μm membrane filters, and the filtrated solution and residual solid were analyzed.
In the residual solid for all runs, the one and only identified reaction product is anglesite. In the long term experiment using powdered galena for 56 days, the amount of anglesite production increases with the increases of sulfuric acid concentration and temperature, which is well correlated with the equilibrium calculation results with considering oxygen contents in the bottle. The rate analysis experiment using powdered galena indicates that the amount of anglesite production increases with reaction time. Dissolution rate of galena for 1 day increases with the decrease of sulfuric acid concentration and the increase of temperature, in the range of 8.29×10
-9 mol・m
-2・s-
1 for the conditions of initial sulfuric acid 1 mol/l-110°C and 1.83×10
-8 mol・m
-2・s
-1 for 0.1mol/l-170°C. In the solid textural analysis experiment using grains or plastic crystals of galena, two types of anglesite occurrence are found, i.e., coarse euhedral crystals growing outside on galena surface and aggregates of fine grains which replace the initial galena crystal from surface. This differences would be explained by the degree of saturation for lead and sulfate ions under the microenvironment at the site of their formation. The random orientations of coarse euhedral crystals of anglesite on galena may be due to nonepitaxial growth. The increase of size of coarse euhedral crystals with time can well be explained by the Ostwald ripening.
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