| In China,tin plating is an essential foundation industry in the national economy.At the same time,environmental issues have become more prominent,along with a range of issues including the depletion of tin mineral resources and the lack of regenerated tin development and utilization.The recovery of tin from tin slag is a significant measures to alleviate the shortage of tin resource,and have far-reaching effects on improving the environment and deepening the development and utilization of regenerated tin.The paper take plating tin slag as processing object,put forward alkaline leaching and zinc powder cementation,selecting suitable activator to realize the efficient cementation of zinc powder.The microstructure,phase composition,element valence and distribution of tin products were characterized by X-ray diffraction and electron microprobe as well as X-ray photoelectron spectroscopy.This paper is based on it to study the mechanism of zinc cementation.(1)The alkaline leaching was conducted for tin plating slag and optimized,the optimal leaching conditions are as follow:200g/L sodium hydroxide concentration,liquid-solid ratio is 8,4 hours of leaching time,90℃ of leaching temperature,agitation speed is 40r/s,and the highest leaching rate can be reaching 97.12%.The kinetic analysis of alkaline leaching indicates that the intra-particle diffusion limitation is main control step.The apparent activation energy of alkaline leaching is 9.725kJ/mol,which obeys shrink core model.(2)The thermodynamic analysis shows that adding zinc powder in alkaline solution can enhance the cementation ability of zinc and in favor of zinc electrolysis to recover ultrafine flake zinc powders which has more advantages in cementation reaction.Molar ratio of zinc to tin is 4 and 90℃ for reaction temperature can obtain better result.The activator selection shows that CuO,SbCl3,activated carbon have preferable effect,among them,CuO achieves maximum impact.The best dosage of CuO is one percent of zinc powder moles,under this condition,the rate of displacement can reach 99.75% and the concentration of residual tin in the solution is lower than 100mg/L.The purity of tin can reach higher when the molar ratio of zinc to tin is 2.On the basis,the two sections of adding zinc powder could make the tin purity increase to 91.34%,the four sections,the purity can be up to 95.31%.Without CuO,the activation energy of ultrafine flake zinc cementation is 44.852kJ/mol,the energy was reduced to 27.615kJ/mol after adding 1% CuO.The effect of CuO on the dissolution of zinc which in the tin solution was decreased when a small amounts of tin exist.(3)The result of ICP-OES analysis that almost all activator of Cu element in the activator entered into the tin product.XRD spectrum shows that the addition of activator brought other substance does not belong to tin,zinc and their oxides.Electron probe showed that zinc is closely combined with copper,the combinations are wrapped by tin gradually and come into with the increase of reaction time.Excess of CuO can lead to incomplete combination,excessive copper scattered around the tin,which reducing the purity of tin product and efficiency of zinc cementation.By means of XPS,the combinations of zinc and copper are supposed to be a certain kind of alloy,which can be viewed as zinc-copper micro battery and promote the deposition of tin in the surface.Because of the existence of the micro battery,the electrode potential is more negative than the zinc powder,the electric potential difference between zinc and tin is further widened in the process of displacement.(4)The paper preliminary explored the feasibility of preparation including sodium fluoride and iron oxide by electroplating sludge,the morphology of byproducts was characterized and the recovery rate was determination.There were few distinctions between simulated and actual leaching liquor,however,the displacement efficiency and purity of products have reduced in different degrees,which indicated that the impurity ions have effect on the zinc cementation.The electrolytic products,whether simulated or actual liquor,all belong to flake zinc.The main difference is that the particle size of zinc powder recycled by actual liquor,electrodeposition is smaller than that of simulated liquor,which may be because the very low content of impurity ions have refined the zinc powder an important role in refining zinc powder.Finally,the paper put forward the whole process about alkaline to handle the tin sludge.This process can effectively recycle tin,fluoride and iron,and the preparation of metal tin,sodium fluoride and iron oxide products,which is useful to obtain better economic benefits.Furthermore,there is no waste water discharge,no secondary pollutants in this process.The process also has good environmental benefits. |
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