c Conversion method for iron removal and its application The Outokumpu conversion method was developed by Outokumpu. Feature of the process is the leaching of zinc ferrite and the iron precipitation stage to achieve a combined process. Since February 1973, it has been put into practice at the Kokkola Electric Zinc Plant.
At the same time as leaching and sinking iron, the formed shovel is called mixed type yellow shovel, and H 2 S0 4 -Fe 2 (S0 4 ) 3-(NH 4 ) 2 SO 4 -H 2 0 is shown in the above figure. -(NH 4 ) x (H 3 0) (1-x) -[Fe 3 (S0 4 ) 2 (OH) 6 ] is a stable curve for the formation of mixed yellow iron samarium. If the point representing the composition of the solution is above the curve, Fe 3+ in the solution will form a mixed type of pyrite precipitate. The rate of precipitation is determined by the distance of the Fe 3+ concentration from the corresponding equilibrium value. When the representative point is located in the liquid equilibrium curve component (stable region of solid material) or more, it is possible to leach the zinc ferrite and simultaneously Shentie of valuable metals iron zinc sulphate material will simultaneously form at atmospheric pressure Extracted, the reaction can be expressed as follows:
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Theoretically, the leaching of zinc ferrite and the precipitation of iron can be carried out under the conditions above the equilibrium line in the figure below. However, because the leaching rate of zinc ferrite will decrease when the acid content of the solution decreases, and the amount of acid in the solution increases, the amount of residual iron will increase. Therefore, in practice, it is necessary to choose to operate within the optimal acidity range. As shown in the figure, the conversion process of zinc in the Kokkola plant increased the leaching yield of zinc from 92% to 96%.
d Treatment and utilization of iron slag The yellow iron slag method usually uses calcined sand as a neutralizer in the zinc smelting plant, resulting in the loss of valuable metals. Since lead , silver , antimony, etc. can also form a yellow iron bismuth type double salt in the process of removing iron, how to recover valuable metals, sulfates, iron products and slag from the slag residue has attracted the attention of scholars all over the world.
The behavior of silver in wet zinc smelting was examined by chemical and mineral methods. Upon calcination, the silver minerals in the concentrate are converted to silver sulfate, silver oxide and metallic silver. At the time of leaching, silver is mainly dissolved in the form of silver sulfate (Ag 2 SO 4 ), and then immediately converted into an insoluble Ag 2 S precipitate and surrounded by fine or coarse sphalerite particles. In the case of hot acid leaching, an elemental group of sulphur-pyrogen sulphide is formed in which fine inclusions of Ag 2 S or Ag 2 S and silver which replaces monovalent cations in the yellow samarium are present. The dissolved silver has a strong affinity for the pyrite compound. More than 90% of soluble silver is co-precipitated with Na + , NH 4 + , Pb 2+ and the like.
In the precipitation of yellow iron sputum, silver yellow iron sputum is more stable than sodium or ammonium type yellow iron sputum. In the silver and sodium coexisting system, the silver content in the yellow iron sputum increases with the increase of the silver concentration in the solution. However, potassium-type yellow iron sputum is more stable than silver. Therefore, if K + is used as a precipitant, it is disadvantageous to trap a trace amount of silver in the solution.
China's Huidong Smelting Plant has done an industrial test to treat zinc slag by thermal acid leaching-iron slag and iron slag transformation. The produced lead-silver iron slag produced by the mineral processing contains 1.5% silver.
The Shenyang Smelter and the Liaoning Metallurgical Research Institute have studied the process of comprehensive recovery of valuable metals from the slag.
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