Basic theory of leaching process in wet zinc smelting (1)
Dip [1~3,7,8]
A wet process is the primary leach zinc refining. In this aspect of the process To feedstock zinc and tin and other valuable metals dissolved completely as possible, so that it goes into solution, in order to achieve high metal recoveries. On the other hand, at the end of the leaching stage, some harmful impurities (such as Fe, As, Sb, Si, etc.) are separated from the zinc immersion liquid and left in the leaching slag. At the same time, it also strives to obtain leaching pulp with fast sedimentation speed, good filtration performance and easy liquid-solid separation.
In wet zinc smelting, the raw materials used for leaching mainly include: calcined materials (calcined and soot) obtained by roasting of zinc sulfide concentrate, zinc oxide concentrate, zinc sulfide concentrate and smelting plant in the production process. Crude zinc oxide powder and zinc oxide soot.
In the leaching, although the leaching of the hydrochloric acid solution is reported, it is mainly leached with a sulfuric acid solution. The leaching method differs depending on the nature of the leaching material. According to the composition and properties of the raw materials, there are: (1) conventional leaching process of calcined material; (2) hot acid leaching process of calcined material; (3) oxygen pressure leaching process of zinc sulfide concentrate; (4) oxidized ore acid leaching process ; (5) acid leaching process crude zinc oxide, and lead zinc dust. However, in the above several leaching processes, the acid leaching process of the calcined material is currently in a dominant position.
Basic theory of leaching process Leaching thermodynamics of calcined material A potential E-pH diagram and stability of metal ions in aqueous solution Stability of various metal ions in aqueous solution and potential of metal ions in solution, pH value, ion activity, Temperature and pressure are related. Hydrometallurgy widely uses the potential E-pH diagram to analyze the thermodynamic conditions of the leaching process. The potential E-pH diagram shows the relationship between the potential of the basic reaction in the aqueous solution and the pH value. From the figure, not only the equilibrium conditions of various reactions and the stable range of each component can be seen, but also the direction and limit of equilibrium movement when the conditions change. The following is a brief description of the Gibbs free energy change and equilibrium type of the heterogeneous reaction between solid and liquid phases at room temperature (25 ° C), and the drawing and application of the potential E-pH diagram.
The relevant chemical reactions of the leaching process can be represented by the following general formula.
aA+nH + +ze ==== bB+cH 2 0
According to the characteristics of the reaction, the reaction can be divided into three types: (a) (b) and (c). In the (a) reaction, only electrons migrate, and H + or OH - does not change, that is, the potential E is independent of the pH. The redox reaction, the Gibbs free energy of the reaction changes to
At this time, the change of Gibbs free energy is transformed into the most useful work done by the outside world. Because the hydrogen standard is zero, the φ electromotive force E can be used in the formula.
—△ G ө = zFE ө [next]
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