Marmatite Enriched Atmospheric Direct Leaching Kinetics

On the basis of the review of the development of direct leaching techniques as well as theleaching kinetics of marmatite, the slow leaching rate in atmospheric direct leaching (ADL) ofmarmatite is focused, so that the leaching kinetics of zinc, iron and the oxidation formationkinetics of elemental sulfur are studied in this dissertation. The leaching conditions under thebottom of ADL tank are simulated by autoclave. The main subjects in this dissertation are asfollows:The mineral presence as well as the existence of zinc and iron in marmatite concentrate isanalyzed by ICP, X-ray diffraction (XRD), scanning electron microscope (SEM) and energyspectrum (EDX).The effects of oxygen-blowing, stirring speed and the initial concentration of sulphuric acidon the leaching of marmatite are discussed firstly.Orthogonal experimental designing method is employed to evaluate the effects oftemperature, slurry pressure and particle size of concentrate on the extraction as well as theleaching rate of zinc and iron. The effects of such three factors on the oxidation formation ofelemental sulfur are further discussed. It is indicated that temperature has great influence on theextraction as well as the leaching rate of zinc and iron and its contribution rate is higher than thatof slurry pressure or particle size of concentrate on the basis of range analysis and varianceanalysis. It is also clarified that temperature effects the oxidation formation of elemental sulfurgreatly.The controlling step in the leaching of zinc and iron as well as in the oxidation formation ofelemental sulfur is discussed on the basis of kinetic fitting under the following conditions: thetemperature of343to383K, the slurry pressure of0.3to0.7MPa, the particle size of (-74μm,+63μm),(-63μm,+40μm),100%-40μm. The results show that the leaching of zinc iscontrolled by interface chemical reaction while that of iron is for mixed controlling of bothinterface chemical reaction and diffusion. The apparent activation energy of zinc and iron iscalculated as73.30kJ/mol and37.66kJ/mol respectively. The kinetic equations are establishedfor zinc and iron, which follow shrinking core model. The significance of kinetic equations forboth zinc and iron is further tested.The oxidation formation of elemental sulfur is determined as zero order reaction. Theactivation energy is further calculated as47.58kJ/mol, which shows the oxidation formation ofelemental sulfur is controlled by chemical reaction in the ADL process of marmatite.