Study On Recovery Of Zinc And Other Valuable Metals From Roasting Dust Of Zinc Pyrometallurgy

During the high-temperature oxide roasting of zinc concentrate in zinc pyrometallurgy, a large quantity of roasting dust will be produced, which account for 20% of the total input. Because of its complex components, it is difficult to be recycled. At present, the recovery method in industrial, such as roasting kiln, causes serious environmental pollution, and it is also complicated and cost high. Therefore, in my thesis, I focus on "Study on the recovery of Zinc and other valuable metals from roasting dust of Zinc pyrometallurgy". A new process for deal with roasting dust with hot acid leaching is put forward, which can recycle zinc and other valuable metals. The process realizes the clean production with completely hydrometallurgy, the conditions and reaction mechanism of the process is investigated systematically.Pre-Experiments of roasting dust with method of flotation, bio-leaching and hot acid leaching showed that:the flotation process made the valuable metal more deconcentration and can not be recycled; bio-leaching has the shortcomings with a long time and low leaching ratio, and dissolved cadmium has bad effects on the growth of bacteria. As a result, the pre-experiments illustrate that both flotation and bio-leaching methods are not suitable to deal with roasting dust.The operation condition, reaction mechanism and kinetics of neutral leaching roasting dust are investigated. The optimal operating conditions are determined as follows:reaction temperature 65℃, acid concentration 90g/L, solid-liquid ratio 5:1 and reaction time 60min, in accordance with these conditions, zinc leaching ratio is 71.29%, slag ratio is 54.84%, and the content of zinc in slag is 23.12%. The kinetics show that the apparent activation energy for the process is E=11.92kJ/mol, the process is under the control of diffusion.The operation condition, reaction mechanism and kinetics of hot acid leaching slag are studied. The optimal operating conditions for the process are obtained as follows:reaction temperature 95℃acid concentration only 200g/L, solid-liquid ratio 5:1, reaction time 180min. The MnO2 addition is 0.6 times of the theoretical capacity. In accordance with these operation conditions, zinc leaching ratio is 93.37%, slag ratio 8.38%. The kinetics shown that the process can be expressed with shrinking core model. The apparent activation energy for the process is 48.09kJ/mol, it is under the control of chemical reaction, the reaction order of [H+] and [Fe3+] is 0.4,0.2 respectively, the reaction kinetics equation is: 1-(1-α)1/3=4.90 [H+]0.4 [Fe3+]0.2d0-exp(-48090/RT)t+AThe process of removing iron from hot-acid leaching solution with the method of goethite is researched, and the operation condition is optimized as follows:the end of pH=3.0, temperature 60℃, reaction time 80min, air flow velocity 20L/min, the results shows that the ratio of removing iron is over 99.5% and iron in liquid is less than 0.1g/L.The processes for recycling indium, cadmium, lead, and silver form roasting dust are studied respectively. Indium recovery process includes:indium enrichment from hot acid leaching solution, acid leaching indium slag, extraction and anti-extraction, and extracting sponge indium with the replacement of aluminum plate. After that, sponge indium can be obtained at the purity of 97.75%, and its recovery ratio is 92.66%. Cadmium recovery process includes:the cleaning of neutron leaching solution, the acid leaching of copper and cadmium slag, the copper removal of acid leaching solution, the extraction of sponge cadmium with the replacement of zinc powder, and the casting of sponge cadmium etc. The pig cadmium can be obtained at the purity of 98.45%, and its recovery ratio is 90.73%. The lead and silver can be recycled by the folation process of sulphur and the alkali smelting technology, and pig lead can be obtained in which contain lead 98.29% and silver 0.169%. The recovery ratio are 90.09% for lead and 94.14% for sliver.Based on the experimental results, the expanding test is done in Liaoning Huludao Zinc Smelter. The experiment result, total zinc leaching ratio 97.45%, is verified at the expanding test in factory.According to the amount of 63,000 tons roasting dust per year produced by Liaoning Huludao Zinc Smelter, the whole industry process for dealing with roasting dust is designed. According this process, it is known that 26,300ton zinc per year will be recycled from neutron leaching solution, which occupies 93.93% of total zinc amount in roasting dust. Cadmium can be recycled 394.9 tons, pig lead 2330 tons (in which lead 2290t, sliver 3.86t), and sponge indium 2.56 t. The loss of metal in roasting dust as follows:zinc loss 1.50% since its residue in leaching slag, loss 4.49% in the slag of removing ferrous, and 0.08% in other slag. Lead loss 3.90% in ferrous slag, loss 3.61% in smelting slag,2.40%in other. Cadmium loss 0.11% in leaching slag,2.89% in ferrous slag, and 0.53% in other slag like cupper cadmium and cadmium slag. Indium loss 0.89% in leaching slag,4.17% in ferrous slag, and 2.28% in other slag. Sliver loss 1.74% in smelting slag,2.63% in dust of smelting,1.49% in other. To sum up, base on the characteristic of zinc roasting dust, a new process of treating roasting dust with hot acid is put forward, the operation condition, reaction mechanism, and kinetic of the process are studied systematically, and the process is verified with expanding test in industry. It is very important to dealing with zinc roasting dust, and recycle all metals, this not only can meet the industrial production, but also protect environmental, and make the resource to be utilized in the comprehensive way.