| Zinc productions of China increased significantly, which resulted in a growing shortage of zinc resources and decline of zinc ore grades. Therefore, in order to improve zinc resource utilization, it is an inevitable trend to produce high value-added zinc products with low-cost and high-efficient. As a new type of inorganic functional material, nano-ZnO is widely used, due to the special nature which macroscopic objects are not got. However, the preparation of nano-ZnO mostly used zinc or zinc salt as row material. The complex and high cost process is not suitable for industrial production. In this paper, nano-ZnO is prepared by low-temperature aqueous solution, after leaching zinc from zinc oxidation slag dust. This method has practical significance in solving problems of environmental pollution and resource reutilization with the simple and pollution-free process. The main conclusions of this thesis are as follows:(1)Sulfuric acid is selected as the leaching agent to extract Zn from zinc oxidation slag dust. The effect of initial sulfuric acid concentration, liquid-to-solid ratio, leaching time and temperature on the leaching rate of zinc and iron are investigated. The optimum leaching conditions are as follows: initial sulfuric acid concentration of 1.5 mol/L, liquid-solid ratio of 6∶1, leaching temperature of 80 ℃ and leaching time of 2 h; The leaching rate of Zn and Fe are 87.1% and 24.69% under these conditions. The composition of leachate: Zn of 59.41 g·L-1, Fe of 2.57 g·L-1, Pb of 0.0093 g·L-1, Cu of 0.08 g·L-1, Cd of 0.12 g·L-1.(2)Two steps are used to purify the leachate.(a) Oxidizing method of iron-removal using H2O2. The effect of pH, the dosage of H2O2, reaction temperature and reaction time on iron-removal is discussed in detail. The optimum conditions are determined as follows: p H=5, the dosage of H2O2 above the theory counting 1.4 times, reaction temperature of 90 ℃ and reaction time of 1 h. Under these conditions, the content of iron ion in the purifying liquid is 0.502 mg·L-1 and iron removal rate reaches 97.48 %.(b) Removing copper, cadmium and other impurities by the method of zinc powder replacement. The effect of zinc powder dosage, reaction temperature and reaction time on copper and cadmium removal are investigated. The optimum conditions are as follows: the dosage of zinc powder above the theory counting 7 times, reaction temperature of 50 ℃ and reaction time of 60 min. Under these conditions, the contents of copper and cadmium ion in the purifying liquid are 0.035 mg·L-1 and 0.054mg·L-1, which achieve the requirements of purification. The refined ZnSO4 solution can be used in preparing nano-Zn O.(3)ZnSO4 and NaOH solutions are used to prepare nano-ZnO by low-temperature aqueous solution. The effect of n(Zn2+)/n(OH-), reaction temperature and initial concentration of Zn2+ on the crystal structure and morphology of the products are investigated. The optimum preparation conditions are as follows: initial concentration of Zn2+ 0.1mol/L, n(Zn2+)/n(OH-)=1∶5, stirring reaction for 1 h at the temperature of 62℃, nano-ZnO of hexagonal wurtzite structure with cone-shaped and average particle size of 100 nm is prepared. The results show that the cone-shaped nano-ZnO is formed by the growth units of ZnO22- and the process of “crystal-dissolution-recrystallization” from Zn(OH)2 to ZnO.(4)The ultraviolet-visible light absorption properties of cone-shaped nano-ZnO are investigated. It has strong absorption at ultraviolet region of 280 ~ 400 nm and good transmittance at visible region. Compared to commercial ZnO, nano-Zn O has significant property of shielding ultraviolet and permeating visible light. |
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