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Kholiqulov Doniyor, candidate of Technical Sciences, Almalyk branch Tashkent state technical university E-mail: [email protected] Samadov Alisher, doctor of technical sciences Almalyk branch Tashkent state technical university
Boltaev Olmos, senior teacher of chair"Metallurgy" Almalyk branch Tashkent state technical university
Akhtamov Fozil, senior teacher of chair"Metallurgy" Almalyk branch Tashkent state technical university
THE RESULTS OF LABORATORY RESEARCH PROCESSING OF ZINC CAKE ZINC PLANT JSC "ALMALYK MMC"
Abstract: In the work analyzed pyrometallurgical and hydrometallurgical methods for processing of zinc cakes. Defined methodology for conducting the calcination of the zinc filter cake in the presence of water vapor, facilitating the extraction of valuable components from the filter cake. The optimal parameters of roasting. Keywords: zinc, technology, roasting, sulfides, cake, roasting, steam, gas, composition.
The main sources of obtaining of zinc on the joint-stock company "Almalyk mining and metallurgical plant" are zinc concentrates by selective flotation concentration of polyme-tallic ores. Zinc concentrates are fired in a kiln "Fluidized Bed Roaster" for the oxidation of sulfides of metals and the resulting calcine leached with an aqueous solution of sulphyric acid to convert zinc into the solution. In the leaching of zinc calcine in a solution of partially transformed there in components -copper, cadmium, iron, arsenic etc. the work Purpose is research and development of technology for roasting zinc sludge cake in the presence of water vapor (thermoprocessing).
Nowadays, in the JSC "Almalyk MMC" for extractions of zinc cakes are waelz processing (restoration variety firing) at a temperature of1100-1300 0C laced with coke and petcoke in the amount of30-40% by weight of the processed material. At the same time, get zinc sublimates and clinker - residue from waelz. Disadvantages waelz-process are: the high consumption of expensive and scarce coke; high temperature regime of the process; the unresolved issue of extraction of other valuable components like gold, silver, lead, copper, iron, etc., to the lack of rational technology of processing of clinker. Therefore, the development of improved technology for the processing of zinc cakes, providing a high extraction of zinc and other valuable metals into marketable products is an urgent task [1].
Nowadays in the world practice are used pyrometallurgical and hydrometallurgical methods for processing of zinc cakes. Pyrometallurgical methods of processing of the cakes
are very diverse and are based mainly on the reactions of recovery of the oxide and ferrite of zinc, using a carbonaceous reducing agents at relatively high temperatures, sublimation of zinc, lead, rare metals and the oxidation of sublimates in the gas phase [2-3]. Pyrometallurgical methods include melting sludge in furnaces of various types (mine, electric) and the reduction-distillation roasting - waelz processing in tubular furnaces. Known methods for processing of zinc cakes can be divided into three groups: 1) methods of destruction of the zinc ferrites by the action of carbonaceous reducing agents (C and CO); 2) methods of decomposition of the ferrites of zinc sulfur and sulfurous anhydride and sulfuric acid; 3) the methods of direct dissolution of zinc ferrites in sulphuric acid.
In world practice, the transition from pyrometallurgical to hydrometallurgical methods of processing zinc cakes is successfully carried out. As is known, due to ferrite formation during roasting of zinc concentrates in the process of leaching of the calcine, part of the zinc remains in the cakes in the form of ferrite and other insoluble compounds. Together with zinc, lead, gold, silver, as well as up to 50-60% Cu and 30% Cd almost completely go to the leaching residue. The zinc content in the cake and its distribution between the solutions and the residue from leaching depends on the quality and nature of the raw materials. When processing high-grade zinc concentrates with a low content of iron and lead, no more than 10-12% Zn from the initial amount passes into zinc cakes. In the case of processing low-grade concentrates (with a high
iron content), the degree of zinc conversion to cakes increases to 20-25% [2-5].
In recent years, hydrometallurgical methods of processing zinc cakes, based on reactions of decomposition of zinc ferrites with sulfuric acid at atmospheric or elevated pressure, have received the greatest development. Since the use of sulfuric acid as the main reagent is technologically combined with the standard hydrometallurgical zinc production scheme, these methods seem to be the most perspective. Hydrometallurgical methods for processing cakes have been developed relatively recently and are based on reactions of dissolving ferrites and zinc sulphude with sulfuric acid at atmospheric or elevated pressure, converting zinc, copper, cadmium, rare metals and iron into solution, followed by separation of iron from the solution in the form of various compounds. The use of sulfuric acid is technologically and economically feasible, since this produces a solution of zinc sulfate, which can be introduced into the main cycle of an electrolytic zinc plant.
Currently, there are three known schemes for hydrometallurgical processing of zinc cakes [2, 5]: leaching of cake under pressure with the release of iron from solution in the form of (Fe203) - hematite -process; leaching of the cake at atmospheric pressure with the release of iron from the solution in the form of goethite (FeOOH) - goethite-process; leaching cake at atmospheric pressure with the release of iron from solution in the form of jarosite (MeFe3(SO4)2(OH)6) -a jarosite process.
The chemical composition of zinc cake,%: Zn
L ' common
-21.42; Zn t - 5.5; Zn - 13.26; C - 0.14; S - 7.55;
' water ' sour ' ' common
SSO4-6.86; Pb - 5.65; Fe - 12.21; SiO2-9.3; Al2O3-1.42; Cu -- 2.32; Cd - 0.26; CaO - 2.67; MnO - 085.
The methodology of extraction of valuable components from cakes of zinc production. The filter cake zinc production, designed for leaching, must responsible the following requirements: to have a sufficiently low content of sulfide sulfur (< 0.1-0.3%); moderate content of soluble sulphides (SSO2 < 2-4%); high content of fine fraction (-0.15 mm); moderate content of ferrite and silicate of zinc.
These requirements derive from technological problems of hydrometallurgical processing. Therefore, to achieve this, the cake is subjected to thermobarometry. Laboratory experiments on baking a cake (with weighed samples of 100-200 g) are carried out on the installation (fig. 1) consisting of steam generator cooling and trapping sublimates system, vacuum pump and electric furnace. The experimental procedure is as follows: product size -0.074 mm is dried at a temperature of 105 0C to constant weight, after which the sample is transferred to a tubular rotary kiln. When the furnace temperature reaches 250 oS in an oven fed dry steam from the steam generator. Exhaust gases pass sequentially through two absorption vessel, containing solutions of copper sulphate and hydrogen peroxide, respectively. During and after the end of the experiment of sinks sampled for analysis on the content of H2S and SO2. The content of sulfur in the absorption solutions are judged on the degree of roasting of the product. After the experiment setup is cooled, the suspension is removed and weighed, is determined by the difference of the initial and final mass, which is judged on the degree of oxidation. Processed, thus, the product is the starting material for leaching.
Figure 1. The scheme of laboratory installation:
1 - electric furnace of SUOL-O,25.1/12-M1; 2 - heater; 3 - steel tube; 4 - a porcelain boat with a weighed; 5 - appliances stove; 6 - source of water vapor; 7 - refrigerator; 8 - receiver of condensate; 9 - vessel of the absorption of hydrogen sulfide; 10 - absorption vessel, sulphur dioxide; 11 - flow meter; 12 - water-jet pump; 13 - valve for adjusting the air supply; 14 - thermocouple PPT
In order to achieve these goals, it is necessary to select the appropriate composition of the initial charge, temperature and composition of the gas phase for thermal processing. Of great importance is the instrumentation process. To address these issues, it is necessary to consider the scientific foundations of the processes of thermal processing, i. e. their chemistry, thermodynamics and kinetics [6]. At the same time, it should be noted that the processes of thermoprocess-ing of zinc cakes differ from the processes of firing or fusing cakes. The main difference is that the firing processes occur without the formation of liquid phases of complex composition. Therefore, sulfides, especially ZnS, retain their individuality. This gives grounds to consider these processes as applied to individual sulfides.
Determining the optimal parameters of thermoprocessing cake zinc production. The study studied the effect of temperature thermoprocessing on the degree of extraction
of different metals in a solution. The experiments were performed in the temperature range from 600 0C before 1000 0C. The results of the experiments shown in (Fig. 2). Pre thermoprocessing at 900-1000 oS has a positive effect on the degree of extraction of zinc in sulfuric acid solution. At temperatures above 1000 oC the extraction of Zn and Cu from thermopro-cessing product in the solution increases slightly. Therefore, it is optimal for thermoprocessing cake zinc production can be considered the temperature 950 oC.
Thermoprocessing the calcine is leached with sulfuric acid solution. The use of sulfuric acid is technologically and economically feasible, so as to give a solution of zinc sulphate, which you can enter in the main loop of the zinc plant. Conditions of experiments: thermoprocessing (flow of water vapor of 15-20 ml/min, iprocessing - 1 hour), leaching (100 g/l, W: T = = 5 : 1, tleachlng- 1 hour, t = 60 oC). The results of the study shown in (Fig. 2, 3).
Figure 2. The dependence of the degree of desulfurization metals on temperature
Temperature,
Figure 3. The dependence of the degree of extraction of metals into solution from the temperature
Thermoprocessing zinc cake at the optimum temperature in time leads to a decrease of the mass of sample of the product and increase the content of zinc and other metals in the calcine. Based on these results and on economic grounds it can be argued that the optimum temperature of thermoprocessing is 950 oS, and the time of thermoprocessing - 1 hour. The results of the study indicate the possibility of effective processing of zinc cakes with subsequent sulfuric acid leaching. The chemical composition of the product thermoprocessing cake zinc production using chemical method analysis,0^ Zn-25.2; Cu-3.02; Cd-0.31; Fe-15.3; Ss-0.2; Pb-5.98; SiO2-10.5; Al2O3-1.6. On the basis of the laboratory tests it
References:
is recommended that the technology of processing zinc cakes, providing a combined technology of extraction of valuable metals, which includes thermoprocessing (for translation of zinc in water soluble form) and sulfuric acid leaching (extraction of zinc in solution).
As a result of analysis of numerous comprehensive studies, it was possible to establish the possibility of processing zinc cakes and extraction of heavy non-ferrous metals. Recycling zinc cakes is environmentally safe and does not form toxic gases. The method of zinc cake roasting in the presence of water vapor is determined, which facilitates the extraction of valuable components from the cake.
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