The vertical tank distillation zinc in the pyrometallurgical zinc has been eliminated, and the scale of electric furnace zinc smelting is small and no new development has been made. ISF lead smelting zinc is the most important in the world is almost the only fire zinc smelting method. A total of 15 closed blast furnaces in the world (including domestic ISP factories) are engaged in the production of zinc, accounting for 12%-13% of the total production of zinc. The technical development is mainly to increase the treatment of secondary lead-zinc materials; improve the condensation efficiency. The use of oxygen-enriched technology.
Wet zinc smelting is the most important zinc smelting method in the world today, and its output accounts for more than 85% of the world's total zinc production. The recent production capacity of new construction and expansion in the world is based on the wet zinc smelting process. The wet zinc smelting technology has developed rapidly, mainly in the direct oxygen leaching of zinc sulfide concentrate; the direct oxidization of zinc sulfide concentrate by atmospheric oxygen enrichment; the equipment is large and efficient; the leaching slag is comprehensively recovered and harmless. Processing; process automation control system and other aspects.
First, the fire method zinc
At elevated temperature, using carbon as a reducing agent zinc metal extraction from the zinc oxide material in the zinc smelting process is called fire.
1. Introduction to smelting methods
(1) Horizontal tank zinc smelting
The horizontal tank zinc smelting is the main zinc smelting method adopted in the early 20th century. A distillation furnace has about 300 tanks, the production cycle is 24h, and each tank produces 20~30kg in one cycle, and the residue contains zinc in the month of 5~10%, zinc. The recovery rate is only 80~90%.
The production process of horizontal tank zinc smelting is simple, and the capital investment is small. However, due to the small volume of the tank and low production capacity, it is difficult to achieve continuous and mechanized production. Moreover, the consumption of fuel and refractory materials is large, and the recovery rate of zinc is still very low, so it has been basically eliminated.
(2) Vertical tank zinc smelting
Vertical tank zinc smelting has continuous operation, and productivity, metal recovery rate, and mechanized Chengdu are all very high. However, there are shortcomings such as complex silicon carbide refractories. Vertical tank zinc smelting is used in industrial production in the 1930s. It has been basically eliminated, but zinc production in China still holds a certain position.
(3) Electric furnace zinc smelting
Zinc electric characteristics is a method of direct furnace material, to give the product zinc vapor and melt, ice copper, lead and molten slag and the like. Therefore, this method can treat polymetallic zinc concentrate. The recovery rate of zinc in this method is about 90%, and the power consumption is 3000~3600KW·h/t (Zn). Electric furnace zinc smelting is only suitable for areas where electricity is cheap.
(4) Blast furnace zinc smelting (ISP method)
A method developed in the United Kingdom in 1950, which differs from indirect heating by tank distillation in that the heat exchange and zinc oxide reduction processes are carried out in the same vessel. The blast furnace can handle zinc or lead mixed sulfide or zinc-lead oxidized ore, as well as lead-zinc soot. It is currently the main process for pyrometallurgical zinc smelting.
The zinc sulfide lead concentrate is sintered and sintered into a sintered ore with coke , added into a blast furnace, drummed into preheated air to burn the char, and subjected to reduction smelting in a high temperature and strong reducing atmosphere. The zinc vapor obtained by the reduction is removed from the top of the furnace, and the zinc is condensed by lead rain to obtain crude zinc, and the crude lead produced by the reduction smelting is discharged from the bottom of the furnace.
2. Introduction to smelting process
(1) Vertical tank zinc smelting
At a temperature higher than the boiling point of zinc, in a shaft type distillation tank, carbon is used as a reducing agent to reduce the pellet of the zinc oxide mineral, and the zinc vapor generated by the reaction is condensed into liquid metal zinc. China Huludao Zinc Plant is one of the only remaining vertical zinc tank smelting plants in China and the world. The production process of vertical tank zinc smelting is composed of three parts: oxidized roasting of zinc sulfide concentrate, calcination grouping and vertical tank distillation.Schematic diagram of vertical tank zinc smelting furnace
(1) Oxidative roasting of zinc sulfide concentrate
The composition of the general zinc sulfide concentrate is: Zn 46%-62%, S27%-34%, Pb<2%, Cu<1%, Fe2%-9%. The purpose of the calcination is to convert ZnS in the concentrate to ZnO, and to remove S, Pb, Cd, As, Sb, and the like. After calcination at a high temperature above 1000 ° C and an excess air ratio of less than 1.1, all of the zinc in the product calcination exists in the form of ZnO and its salts, 98% of Cd is volatilized and removed, and the Pb removal rate is 70%.
The main calcination reaction is:
2ZnS+3O2=2ZnO+2SO2
2SO2+O2=2SO3
ZnO+SO3=ZnSO4
4FeS2+11O2=2Fe2O3+8SO2
Further ZnO and Fe2O3 to produce iron zinc ZnO.Fe2O3.
The large-scale boiling furnace has a circular cross section, and the lower part is provided with a high-temperature resistant bottom, and the hood is arranged at a certain distance on the bottom of the furnace. There is a calcine overflow port around 1 m above the bottom of the furnace, and a flue gas outlet at the top of the furnace. The feeding chamber is built in a partially expanded portion of the bottom of the furnace. The zinc concentrate containing about 6% water is added to the furnace from the front chamber, and when the wind cap is blown out by the wind, it is quickly mixed into the fluidized layer, heated, and a roasting reaction occurs. The pellets produced by the overflow port are sent to the pelletizing ball, and the flue gas is purified and sent to the sulfuric acid production system, and the collected soot is used for comprehensive utilization.
The main technical and economic indicators of boiling roasting are: desulfurization rate of 90%, zinc recovery rate of 99.5%, cadmium recovery rate of 85%, and soot rate of 23%.
(2) Calcination and coking
Vertical tank zinc smelting is a gas-solid reaction process. The materials to be added must have good gas permeability and heat transfer performance, as well as considerable heat strength, and the compressive strength is above 4.9 MPa. For this purpose, the zinc calcine is made into agglomerates and cokeled. First, the process of zinc calcine and reduced with coal powders, adhesives mixed, milled, compressed into briquettes, and then drying the fuel into the library mechanized drying. After drying, the agglomerate is mechanically lifted from the top of the furnace to the coke oven, and at a temperature of 800 ° C, the coke coal in the ore is cohesive to cause agglomeration, and at the same time, residual moisture in the dry agglomerate Was completely removed.
(3) Vertical tank distillation
The vertical tank body is a vertical well-shaped furnace body made of silicon carbide material with high mechanical strength, good heat transfer performance and chemical stability at high temperature. The cross section is a long and narrow rectangle with a height of 8-12 m and a heated area of ​​100-110 m2.
The size of the large-scale vertical tank in modern times is (2535mm×2mm)×290mm×12261mm, and there are gas combustion chambers on the outside of the two long-side tank walls to indirectly heat the ore in the tank. The hot mass from the coke oven is added to the top of the tank through the sealing bell, and is heated to above 1000 °C during the lowering process. The ZnO reduction reaction in the ore is intense:
ZnO+CO=CO2+Zn (1)
CO2+C=2CO (2)
The reduction reaction of ZnO is mainly a gas-solid reaction. The CO produced in the system (in the ore) with excess carbon at 1000 °C can ensure the complete completion of the reaction (1). The solid-solid reduction reaction between solid carbon and ZnO has only a minor significance.
The furnace gas produced by the reduction contains about 35% of the gas zinc, and enters the condenser with the graphite rotor through the upper extension under the tank mouth. Under the zinc rain trapped by the rotor, the zinc vapor condenses into liquid zinc, timing Liquid zinc is discharged from the condenser and cast into a zinc ingot. The gas exiting the condenser is washed and purified to remove the remaining zinc, and is a tank gas containing about 80% of CO and about 10% of H2, and all of them are returned to the vertical tank as fuel. The bottom of the vertical tank has a continuously running slag discharge machine, and the boiled zinc agglomerates are discharged through the machine. The main technical and economic indicators of vertical tank zinc smelting are as follows: zinc smelting recovery rate >94%; waste slag containing zinc <1.0%; coal consumption 2.3 t/t Zn; tank life 2 years; power consumption 550 kWt/t Zn; equipment operation The rate is over 93%.
(2) Zinc smelting in a closed blast furnace
The method is to reduce zinc and lead from a lead-zinc concentrate agglomerate in a blast furnace with a closed furnace top, and the zinc vapor is condensed into zinc in the lead rain condensation, and the lead and the slag enter the hearth. The hot front bed separates the slag from the lead. This method is successfully researched by Imperial Smelting Corp. (ISP). It is highly adaptable to raw materials. It can process both primary lead-zinc concentrate and secondary lead-zinc materials. The vertical tank zinc smelting method is low.Schematic diagram of zinc smelting in a closed blast furnace
Fuel combustion and metal oxide reduction are the basic reactions in a closed blast furnace. The coke added to the furnace is combusted at a high temperature with oxygen blasted into the air at the tuyere to generate the heat required for the zinc smelting process. The main smelting reaction is:
C+O2=CO2
CO2+C=2CO
ZnO+CO=Zn+CO2
CdO+CO2=Cd+CO2
PbO+CO=Pb+CO2
The technical characteristics of ISP are: 1 use sealed high temperature furnace top (1000-1100 °C) to prevent zinc vapor from cooling and oxidation before entering the lead rain condenser; 2 use high density, low melting point, low vapor pressure lead for condensation and zinc absorption. The vapor medium is beneficial to the rapid condensation of zinc vapor, preventing oxidation and separation of lead and zinc; 3 using high calcium slag system (CaO/SiO2=1.0-1.5), high slag melting point (125 °C), low density, to reduce slag The separation of zinc and slag from lead creates favorable conditions.
The lead-zinc process of closed blast furnace mainly includes three parts: sintering and roasting of lead-zinc material, reduction and volatility of closed blast furnace and condensation of lead-rain condenser.
(1) Sintering roasting
The lead-zinc concentrate contains Pb+Zn in the range of 45%-60%. After mixing with other zinc-containing materials, it is desulfurized and sintered into a block on a sintering machine. The sintered block should have a certain thermal strength to ensure the gas permeability in the furnace. The composition of the agglomerate is (%): Zn41.4, Pb 19.2, FeO 12, CaO 5.7, SiO2 3.8, S 0.8.
(2) Closed blast furnace to reduce volatile smelting
The area of ​​the early furnace tuyere is 5.1-6.4m2, and the largest is currently 27.2m2. Most plants use 10m2 and 17.2m2. The height of the material column in the furnace is 6m, the furnace height is 10.66m, and the inner diameter of the tuyere is 159mm, a total of 16. Bunk sealing bell top feeder, high aluminum lightweight masonry bricks in the furnace body portion, a lower magnesia brick of high alumina bricks, hearth, three cups of water cooling the outer wall of the steel sheet. During smelting, the agglomerate, the lime flux and the preheated coke are fed into the furnace from the top of the furnace in batches. The lead and zinc in the agglomerate are reduced, and the zinc vapor enters the condenser along with the CO2 and CO flue gas, and the smelting product is crude lead. The copper slag and the slag are separated into the electric heating front bed through the hearth, and the slag flue gas is treated to recover the zinc, and then discarded, and the bismuth and the crude lead are further processed.
(3) Zinc vapor condensation
The condensing equipment is a lead rain splash condenser. The condenser has a shape of 7-8m in length, 3m in height and 5-6m in width. It has 8 rotors inside and is immersed in the lead pool in the condensation. The lead rain raised by the rotor rapidly cools the zinc-containing steam furnace gas to below 600 °C, so that the zinc is condensed into zinc liquid and dissolved into the lead pool. The lead liquid is continuously circulated by the pump, and the lead liquid flowing out of the condenser is cooled in the water cooling flow tank. At 450 ° C, then enter the separation tank, the liquid zinc density is small in the upper layer of lead liquid, control a certain depth to make it continuously flow, cast into zinc ingot.
The main technical and economic indicators of blast furnace lead and zinc are: hot air temperature 950-1150 ° C, condensation efficiency 90%-92%, ash slag containing Pb 0.15%, Zn 1.35%, crude zinc containing more than 98% zinc, lead 1.2% -1.5%, crude lead contains more than 98% lead, zinc content 0.1%, smelting recovery rate Pb>93%, Zn>94%, and S utilization rate of raw materials is 90%-92%.
(3) Electric furnace zinc smelting
In the 1930s, electric furnace zinc smelting technology appeared abroad. In the 1980s, China began to use electric furnace zinc smelting technology. Up to now, more than 10 small-scale pyrometallurgical zinc plants have been promoted and applied, with a production scale of 500-2500 t/a.
The electric furnace zinc is based on electric energy as a heat source. In the presence of a reducing agent such as coke or coal, the furnace charge is directly heated to continuously reduce the ZnO component into zinc vapor and condense into metal zinc. The process can treat high-copper high-iron zinc ore, but requires that the raw material contains S not more than 1%, and the pre-removal treatment is required for the carbonate-zinc ore containing S high.
The shape of the electric furnace is circular or rectangular, horizontal, and the power is 500kW, 1250kW, 200kW and 2250kW. The hearth area is 4-8 m2 and the electrode diameter is 200-350 mm. The main indicators are: melting temperature 1250-1350 ° C, electric energy consumption 4600 kWh / t Zn, residue zinc containing 3% -5%, crude zinc grade 98.7%, direct yield 80%, total recovery rate of 95%.
Second, wet zinc smelting
Zinc-zinc wet-zinc is obtained by diluting zinc roasting ore with dilute sulfuric acid (ie, waste electrolyte) to obtain zinc sulfate solution. After purification, zinc is extracted from the solution by electrowinning. At present, wet zinc smelting has the advantages of large production scale, low energy consumption, good working conditions, easy mechanization and automation, and the industry is dominant.
Nearly 80-85% of the world's zinc is produced by wet smelting, and most of them use acid leaching to electrolyze. In the conventional process, different wet smelting processes are derived due to different treatment methods for leaching.Schematic diagram of zinc smelting
(1) Zinc concentrate roasting
The use of air or oxygen enrichment to oxidize ZnS in zinc concentrate to ZnO and ZnSO4 at high temperatures while removing impurities such as As, Sb, and Cd. The roasting product is calcined, sent to leaching zinc, flue gas or sulfuric acid or concentrate ore roasting to produce liquid S02-wet zinc smelting is different from pyrometallurgical roasting. It is required to retain 1%-2% sulfur in wet zinc smelting calcine. It exists in the form of SO42- to supplement the insufficient sulfuric acid when the zinc calcine is leached. The calcination of pyrometallized concentrate concentrates all ZnS to ZnO to improve the recovery rate of smelting.
(2) Zinc roasting leaching and leachate purification
The blasting of the calcined zinc consists of two stages: neutral leaching and acid leaching. A neutral leaching uses waste electrolyte, and the second stage uses sulfuric acid as the leaching solution, acidity of 30-60 g/L H2SO4, and leaching temperature of 65-70 °C. The leachate contains Zn > 120 g / L. Factors affecting leaching include leaching temperature, stirring speed, acid concentration, and zinc baking particle size. The ZnO leaching reaction is:
ZnO+H2SO4=ZnSO4+H2O
In order to increase the zinc leaching rate in the zinc baking sand, air agitation is used to enhance the leaching process. Insoluble ZnO.Fe2O3, ZnO.Al2O3 and ZnS are dissolved.
(3) Zinc electrolytic deposition
The purified zinc sulphate solution is added to the additive and continuously fed into the electrolytic cell through the high-position tank, and the tank is covered with an insoluble lead-calcium alloy anode and an aluminum cathode. When a direct current voltage is applied to both electrodes, zinc ions in the electrolyte are continuously deposited on the lead cathode. The waste electrolyte finally produced by electrolysis is partially sent out as a calcining leaching agent, and partially formulated into an electrolyte to be returned. The precipitated zinc-aluminum cathode is taken out at regular intervals (24-48 h), and after washing, the zinc sheet is peeled off, and then melted into a zinc ingot, and the cathode is returned to use after being cleaned. The basic reaction of zinc electrolytic deposition is:
On the cathode: Zn2++SO42-+2e=Zn+SO42-
On the anode: 2H+2OH--2e = 1/2O2+2H++H20
Total reaction formula: ZnSO4+H2O=Zn+H2SO4+1/2O2
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