April 29, 2021
Refractories for zinc smelting
There are two kinds of zinc smelting: pyrometallurgical smelting and hydrometallurgical smelting. The pyrometallurgical smelting mainly includes vertical pot zinc distillation furnace, tower distillation furnace, closed blast furnace and electrothermal zinc smelting, etc. Hydrometallurgical zinc smelting has the traditional two-end leaching method, that is, the leaching slag is treated by volatile kiln and hot acid leaching process, that is, the slag is treated by jarosite method, goethite method, hematite method, and the whole wet process pressure leaching process, zinc smelting with lead-zinc closed blast furnace, etc.
Distillation zinc smelting in China accounts for about 30% of the crude zinc smelting, and the refined zinc produced by tower zinc rectifying furnace accounts for 50% of the refined zinc products.
Vertical zinc smelting process is one of the main processes of pyrometallurgical zinc smelting. Although there are few factories using this process abroad, a considerable amount of crude zinc is produced by this vertical zinc smelting process in China, and all the crude zinc produced by pyrometallurgical zinc is refined in the rectification furnace.
The vertical pot zinc smelting distillation furnace is an equipment of fire zinc smelting heated by flame. It is composed of the tank body (tank body, upper extension, lower extension), combustion chamber, heat exchange chamber and condenser and other parts. The total height of large double pot furnace body can reach 20m. The principle is as follows: sintering agglomerates containing coke powder are added from the top of the furnace, the agglomerates run downward, and are briefly heated by the combustion chamber outside the tank. The ZnO in the agglomerates is reduced to gaseous Zn at 1200~1300℃, and the furnace gas containing Zn vapor enters the condensing tube from the upper extension of the furnace (600℃), condenses into liquid zinc, and the residual slag is discharged from the lower part.
The vertical tank is heated indirectly, and the tank is in reducing atmosphere. In addition, when the coke agglomerate moves in the tank, the inner wall of the tank body bears the friction of the agglomerate with high temperature and hardness, so the silicon carbide material with high thermal conductivity, high strength, strong corrosion resistance and high wear resistance is selected. At the same time, in order to ensure that the tank has a strong reducing atmosphere, the silicon carbide masonry must be carefully processed and constructed. In order to ensure good air tightness and thermal stability, sand sealing groove is generally used at the joint of cans (i.e. the two ends of the tank) and cans (i.e. the side walls of the tank). The condenser is also made of silicon carbide because of its good thermal conductivity. The combustion chamber is arranged on both sides of the tank, through heating the outer wall of the tank indirectly heating the ore in the tank, basically the same high as the tank, but the width is not large, is thin and high type, the temperature is 1300~1350℃, so the high temperature strength of refractory materials is high, currently with high quality high aluminum brick masonry. The temperature of the heat exchange chamber and condenser is not high, and clay brick masonry is generally used.
Tower type zinc rectifying furnace is the most important equipment for refining zinc by fire process. It includes melting furnace, liquating furnace (including fractionation chamber), lead tower condenser, high cadmium zinc condenser, fine zinc storage tank and so on. In fact, it is the general name of multiple equipment, with complex structure. Lead tower and cadmium tower are the main equipment of the tower type zinc rectification furnace group. Their furnace type is similar, and in the middle is a group of dozens of trays stacked. Usually zinc rectification furnace is mainly composed of two lead tower and a cadmium tower.
Distillation process is the use of zinc and other impurities boiling point is different and zinc boiling point is low (zinc 916℃, lead 1750℃, cadmium 765℃), the use of continuous fractionation principle will impurity metal (mainly lead, iron, cadmium, etc.) separation, in order to obtain fine zinc or 1~3 grade zinc.
The distillation process is divided into two stages: the first stage is the separation of lead, iron, copper, tin, smoke and other high boiling point metals in the lead tower, and the production of lead (smoke), iron zinc alloy and cadmium free zinc in the furnace; The second stage is carried out in the cadmium tower. Cadmium-containing zinc produced in the condenser of the lead tower flows into the cadmium tower, and refined zinc is produced in the lower part of the tower after fractionation, while cadmium is enriched in the high cadmium zinc in the condenser.
When method zinc, such as reduction, distillation and distillation process, because of the zinc vapor easy oxidation by oxygen, carbon dioxide and water vapor, so the zinc smelting reduction and distillation equipment generally adopt the method of closed or flame heating insulation for smelting, distillation airtight, not deformation, muffle layers should choose high thermal conductivity, high strength, and not with burden or zinc vapor reaction materials.
In addition, the zinc vapor must be condensed and collected, generally equipped with condensing equipment, in order to splash the condensed zinc vapor into liquid zinc, the rotor used in the condenser rotates at a speed of 750~1000r/min, the material used in the rotor requires high thermal shock resistance and high temperature mechanical strength, and does not react with liquid zinc and zinc vapor. The tray in the tower zinc rectification furnace, because it is directly in contact with the metal vapor and melt, the material is required to have a good ability to resist the corrosion of metal vapor and melt, and has a high thermal conductivity and high strength, so the furnace lining with silicon carbide refractory is the best.
Silicon carbide refractories with good chemical stability, high temperature strength, high thermal conductivity, good thermal shock resistance, abrasion resistance, resistance to erosion, was wet with metallic melts metal vapor erosion resistance, etc, the most suitable for zinc vertical distillation furnace wall, zinc distillation furnace tray, condenser and the rotor, in areas such as the key parts in the kiln with silicon carbide refractories, in addition, other parts also use sticky soil, high aluminum, magnesia and monolithic refractories.