Study On The Basic Theory And Technology Of Extracting Indium In Zinc Oxide By Microwave - Ultragravity

As a scarce metal for strategic resources, indium is widely used in indium tin oxide (ITO) for LCD’s tablet computers, solder alloy, electronic metal and semiconductor devices, photovoltaic cell, high speed sensor and so on because of its excellent performance. Indium is playing irreplaceable role in high-tech industry. Zinc oxide flue dust(ZOFD) is one of the zinc metallurgical by-product through rotary kiln reduction, which contain-valuable metals, such as Zn, Pb, Sn and In, etc. and also is an important indium-bearing secondary resources. It is a kind of objective needed for-business market competition and risk-resisting ability to improve recovery rate of indium. The more important side of indium recovery is not only efficient use of these limited resources, but also elimination of secondary pollution caused by the accumulation of smelting waste residue. Thus, the procedure is meaningful to cycling economy and sustainable development of China.There was a great variation in chemical composition caused by different mineral resources, and more complicated in the mineral phases. Indium is often embedded or wrapped in anglesite, refractory spinel phase, conventional acid leaching method can’t broken the mineral structure due to it’s stable thermodynamic properties. At the same time, amounts of impurity elements exist in leaching solution, and extraction using organic phase resulted in co-extraction of Fe(Ⅲ) and As, etc, leading to a significant reduction in the quantum of indium extraction due to accumulation of Fe(Ⅲ) in the organic phase. In this paper, a new process "microwave sulphation roasting-water leaching "joint" impinging stream-rotating packed bed nonequilibrium extraction"was proposed to deal with zinc oxide dust as the research object. Microwave roasting effectively broken the indium-bearing mineral phase structure and promoted indium leaching. IS-RPB can strengthen the mixing, and greatly increase the extraction mass transfer area, leading to effectively separate target metals from impurity elements. The synergy of two intensification process has greatly increased the recovery rate of indium. The main contents and results in this study are given as follows:(1)The ZOFD mineralogy research showed that:most of zinc exists in oxide, lead is mainly present as sulfate and oxide, part of the iron and zinc formed spinel ferrite, indium mostly exist in oxide, a small number of indium packages in the spinel phase. the amount of zinc, lead and iron is more than 50% of the total composition. ZOFD particle size is fine and 90% of them is less than 75 microns accounted for the content of indium was not significantly different among particles.(2) the cylindrical cavity perturbation method was selected to determine the dielectric constant and dissipation factor of zinc oxide flue dust, sulfuric acid and mixing sample under different temperature. The results indicated that the dielectric constant of sulfuric acid, mixing sample and ZOFD kept around 34,3.1-2.3,2.9-3.2, respectively at the temperature range of ambient temperature to 250 ℃. The absorbing performance is that sulfuric acid is greater than the mixed material approximately equaling to zinc oxide dust. Under the condition of a certain power, the heating rate of sulfuric acid is the fastest, and that of mixed material increas with the raise of the ratio of acid to sample.(3) The thermodynamic analysis of microwave sulphating roasting and water leaching show that the mineral phase in ZOFD can react with sulfuric acid to generate sulfate, and the pH value of lixivium is 0.2, then hydrolysis of metal ions in the solution will not happen. Single-factor experiments of microwave roasting-water leaching was carried out. The indium leaching rate is more than 90% at optimal conditions as following:average particle size 53 μm, roasting temperature 180℃, roasting duration 60min, the ratio of acid to sample 0.5 in microwave roasting process and leaching time 30min, liquid-solid ratio of 4:1, stirring speed 300 rpm in water leaching process. Response surface methodology is used to optimize experimental parameters for high indium recovery and obtain the following results:roasting temperature 208 ℃, the ratio of acid to sample 0.51 ml/g, roasting time 93 min, indium leaching rate can be reached to 92.78%. Indium leaching rate was used as evaluation parameter to discuss leaching kinetics of roasting reaction. Shrinking core model was used to describe the kinetic parameters and to identify the rate controlling step. Indium extraction was controlled by the internal diffusion in the solid product layer, with the apparent activation energy of the roasting reaction was 12.68 kJ/mol for indium. The kinetic equations of indium for the diffusion controlled process can be described at the range of experimental temperature as follows: 1+2(1-x)-3(1-x)2/3=kdt=4.08exp(-12680/RT)t. Compared with muffle furnace roasting and hot acid leaching at the same conditions, indium leaching rate increased by 8% and 22%, respectively.(4) In this paper, a new type extractor, Impinging Stream-Higee Reactor(IS-HR) has been developed, which is adapted to separate indium from lixivium. Adjustable parameters such as super gravity factor, impinging speed, nozzle diameter power-driven device of the reactor are reasonable designed. Negative pressure produced by the eddy current damper working together with cones porous plate ensure the residence time of extraction and increase the mass transfer area. The mass transfer performance of the new extractor has also assessed, and the results showed that the stage efficiencies of this reactor is greater than 95%.(5) In order to separate In(Ⅲ) and Fe(Ⅲ) from the sulphate leaching solution, solvent extraction with Di-2-ethylhexylphosphoric acid (D2EHPA) was investigated using a IS-HR in laboratory scale. The effects of operating parameters, such as feed solution pH, flow rate ratio, the high gravity factor, the concentration of D2EHPA, initial iron concentration, stripping solution concentration were examined. The experimental results showed that the IS-RPB was effective in the separation of In(Ⅲ) and Fe(Ⅲ)under extractant concentration of 25%, flow ratio of A/O=2:1, organic phase flow rate 30 L/h, high gravity factor 83 in extraction, and 3 mol/L as the stripping solution, flow ratio of O/A=5:1, loaded organic phase 50 L/h, high gravity factor 103 in stripping process. The extraction and stripping efficiency as high as 99% could be achieved, at a separation factor in excess of 3000. Compared with other mixing devices, IS-RPB contactor has better micromixing characteristics, and organic phase emulsification and entrainment phenomenon was not found, which has a good application prospect.In conclusion, the goal of improving leaching rate of indium and highly efficient resource recycling has been realized in this study. It provides a basic theory of microwave roasting mineral, and promotes the super gravity technology penetrating to hydrometallurgy technology field. It is of great significance to accelerating indium metallurgical industrial transfer and upgrade.