Pyrite oxidation in carbonate-buffered solution: 2. Rate control by oxide coatings

摘要: Abstract The kinetic behaviour of pyrite oxidation in the laboratory was studied over a period about 10,000 hours reactors through which carbonate-buffered solution and air (20% O2) flowed continuously. Three grain size fractions were monitored. concentration sulphate mass effluent measured periodically to calculate rates. results indicate that rates reaction decreased significantly with time. initially exhibited an inverse dependence on (within 400 h) then became more linear square at later times (after 8000 suggesting surface-layer control Surface analysis by X-ray Photoelectron Spectroscopy revealed presence ferric oxide surfaces, ion boring auger electron spectroscopy indicated layer thickness order 0.6 microns 215 micron grains. data are represented shrinking core model includes effects surface rate constant plus diffusive resistance oxygen transfer accumulating as proceeds. three sizes (representing different specific areas) consistent estimates (Ks = 3.07 × 10−6mh−1 ± 46%) diffusion coefficient for (Ds 1.08 10−12m2h−1 30%). estimated end experiment agreed well value. Oxide accumulation surfaces under neutral pH conditions significant reduction This has important implications release products, including hydrogen ions, environments where sulphide mineral wastes exposed atmosphere.