Wet copper smelting, also known as bile copper process, mainly includes two aspects. First, copper leaching, that is, iron is put into the solution of bile alum (commonly known as bile water), so that copper ions in bile alum are replaced by metals and precipitated into elemental copper; The second is collection, that is, the replaced copper powder is collected and then melted and cast. Although the methods used in different places are different, there are three main methods to sum up: the first method is to use the nearby terrain to dig trenches, use mats to lay the bottom, mash pig iron and discharge it into trenches, introduce bile water into trenches for soaking, use the color difference between copper salt solution and iron salt solution to soak until the color changes, then release the soaked water, take out mats, collect copper deposited on mats, and introduce new bile. As long as iron does not react completely, it can be produced repeatedly. The second method is to set a gallbladder water tank in the gallbladder water area, forge iron into thin slices and put them in the tank, soak the iron sheet with gallbladder water until the surface of the iron sheet is covered with a layer of red copper powder, take out the iron sheet and scrape the copper powder on the iron sheet. The second method is more troublesome than the first method, that is, forging the iron sheet into thin sheets. When iron is forged into thin slices, the surface area of iron with the same mass increases, which increases the contact opportunity between iron and bile water, shortens the replacement time and improves the yield of copper. The third method is decoction, in which bile water is introduced into an iron container for decoction. The tool for containing gallbladder water here is both a container and one of the reactants. Copper can be obtained by boiling in an iron container for a certain period of time. The advantage of this method is that bile water turns from dilute to thick during the heating and decocting process, which can accelerate the replacement reaction of iron and copper ions, but it needs fuel and special personnel to operate, which has a large workload and little benefit. Therefore, the first two methods were adopted in the production of bile copper in Song Dynasty. The Song Dynasty also had a clear understanding of the control of copper leaching time by bile copper method, knowing that the thicker the bile water, the shorter the copper leaching time; The gallbladder water is thin and the copper immersion time is long. It can be said that by the Song Dynasty, a set of relatively perfect technologies had been developed, from the way of copper impregnation and the method of copper extraction to the control of copper impregnation time.
The main raw material of pyrometallurgical copper smelting is copper sulfide concentrate, which generally includes roasting, smelting, blowing and refining.
Roasting is divided into semi-oxidation roasting and total oxidation roasting ("dead roasting"), which respectively remove part or all of sulfur in the concentrate and remove some volatile impurities such as arsenic and antimony. This process is an exothermic reaction and usually does not require additional fuel. Semi-oxidation roasting is generally used in matte smelting to maintain the amount of sulfur needed to form matte; The reduction smelting adopts total oxidation roasting; In addition, roasting in hydrometallurgy of copper sulfide concentrate is to convert copper into soluble sulfate, which is called sulfation roasting.
Smelting is mainly matte smelting, aiming at oxidizing some iron in copper concentrate or roasted ore, and removing it together with gangue, flux and other slags to produce matte with high copper content (XCU2SYFs). The total amount of copper, iron and sulfur in matte often accounts for 80% ~ 90%, and almost all the precious metals contained in matte enter.
The copper content of matte depends on the concentrate grade and the desulfurization rate during roasting and smelting. The grade of matte in the world generally contains 40% ~ 55% copper. The production of high-grade matte can make more use of the reaction heat of sulfide and shorten the blowing time of the next process. The copper content of smelting slag is related to the grade of matte, and the copper content of slag is generally 0.4% ~ 0.5%. The main reactions in the smelting process are as follows:
2 cufe 2→Cu2S+2 FeS+S
Cu2O+FeS→Cu2S+FeO
2FeS+3O2+SiO2→2FeO SiO2+2SO2
2FeO+SiO2→2FeO SiO2
Traditional matte smelting equipment includes blast furnace, reverberatory furnace and electric furnace. Most of the newly built modern large-scale copper smelters use flash furnaces.
Blast furnace smelting blast furnace is a shaft furnace, which has long been used by small countries to directly smelt copper. The traditional method is sintering block blast furnace smelting. The copper sulfide concentrate is first sintered and roasted to remove part of sulfur, and made into sintered blocks, which are layered into the furnace together with flux and coke. According to the batch, matte and waste residue are produced by smelting. This method has low SO2 content in flue gas, and it is not easy to recover sulfur economically. In order to eliminate the harm of smoke and recover the sulfur in the concentrate, the blast furnace smelting method of concentrate was developed in 1950s, that is, copper sulfide concentrate was mixed and kneaded into paste, and then some lumps, fluxes and coke were added into the furnace from the central charging port of the top of the furnace in batches to form a material seal, so as to reduce air leakage and increase SO2 concentration. The kneaded material is dried and roasted by hot flue gas in the furnace to form a sintered material column, and the block material also surrounds the sintered material column in a column shape to maintain air permeability and make the smelting operation normal. This method is used in Shenyang Smelter and Fuchunjiang Smelter in China.
Reverberatory furnace smelting is suitable for treating flotation concentrate. The reverberatory furnace smelting process has a low desulfurization rate of only 20% ~ 30%, which is suitable for treating high copper grade concentrate. If the raw material contains low copper and high sulfur, it should be roasted before smelting. Reverberatory furnace has been the main equipment for copper smelting for a long time because of its large production scale and strong adaptability to raw materials and fuels. By the early 1980s, the production capacity of reverberatory furnace still ranked first in copper smelting equipment in the world. However, the reverberatory furnace has a large amount of flue gas, and the SO2 content is only about 1%, so it is difficult to recover. The thermal efficiency of reverberatory furnace is only 25% ~ 30%, and the reaction heat in smelting process is less utilized, and the required heat is mainly supplied by additional fuel. Since 1970s, countries all over the world have been studying how to improve reverberatory furnace smelting, and some have used oxygen injection device to inject concentrate into the furnace to strengthen sealing, so as to increase SO2 concentration. The first smelter of China Baiyin Company added copper concentrate into reverberatory furnace for smelting, which improved the smelting intensity and the flue gas could be used to produce sulfuric acid.
The reverberatory furnace is rectangular and made of high quality refractory. The burner is arranged at the furnace head, the flue gas is discharged from the furnace tail, the burden is added from the furnace top or the upper part of the side wall, the matte is discharged from the matte hole at the bottom of the side wall, and the slag is discharged from the slag hole below the side wall or the end wall. Furnace head temperature 1500℃ ~ 1550℃, furnace tail temperature 1250℃ ~ 1300℃, and flue gas emission is about 1200℃. When smelting roasted ore, the fuel rate is 10% ~ 15%, and the bed energy rate is 3 ~ 6t/(m2 day). Copper concentrate is directly put into the furnace, with fuel rate 16% ~ 25% and bed energy rate of 2 ~ 4t/(m2 day), which is called green concentrate smelting. China Daye Smelter uses 270m2 reverberatory furnace to smelt green concentrate.
Electric arc furnace (EAF) is used for copper smelting, which has wide adaptability to materials and is generally used in areas with low electricity price and for treating concentrates with more refractory gangue. The amount of flue gas in electric furnace smelting is small. If properly controlled, the concentration of SO2 in flue gas can reach about 5%, which is beneficial to sulfur recovery.
Copper smelting furnaces are mostly rectangular, and a few are round. Large electric furnaces are generally 30 m ~ 35 m long, 8 m ~ 10 m wide and 4 m ~ 5 m high. Six self-baking electrodes with the diameter of 1.2 m ~ 1.8 m are used, and three single-phase transformers are used for power supply. The apparent power of electric furnace is 3000～50000 KVA, the area power of each furnace bed is about 100kw/m2, the bed energy ratio is 3 ~ 6t/(m2 day), the charge power consumption is 400 ~ 500kw h/t, and the electrode paste consumption is about 2 ~ 3kg/t ... China Yunnan Smelter adopts 30000.
Flash smelting is to dry the mixture of copper sulfide concentrate and flux until the water content is below 0.3%, mix it with hot air (or oxygen or oxygen-enriched air), and spray it into the furnace for rapid oxidation and melting to generate matte and slag. Its advantages are high smelting intensity and full use of the heat of sulfide oxidation reaction. Reduce energy consumption in smelting process. The concentration of SO2 in flue gas can exceed 8%. Flash smelting can adjust the grade of matte in a wide range, which is generally controlled at about 50%, which is beneficial to the next blowing. However, the slag contains high copper and needs further treatment.
There are two types of flash furnaces: Otto Kemp type and International Nickel Company type. At the end of 1970s, dozens of factories in the world adopted Otto Kemp flash furnace, and Guixi Smelter in China also adopted this type of furnace.
Copper blowing takes advantage of the fact that ferrous sulfide is easier to oxidize than cuprous sulfide. In a horizontal converter, air is blown into the molten matte to oxidize ferrous sulfide into ferrous oxide, and the ferrous oxide is scraped off with the added timely flux, while other impurities are partially removed. Then continue to blow air to oxidize the sulfur in cuprous sulfide into flue gas to obtain crude copper with 98% ~ 99% copper, and precious metals also enter the crude copper.
A blowing cycle is divided into two stages: in the first stage, FeS is oxidized to FeO, and Bai Bing copper (Cu2S) is obtained by slag removal. The melting temperature is1150℃ ~1250℃. The main reaction is:
2FeS+3O2→2FeO+2SO2
2FeO+SiO2→2FeO SiO2
In the second stage, Bai Bing copper is blown into crude copper at the melting temperature of 1200℃ ~ 1280℃ according to the following reactions:
2Cu2S+3O2→2Cu2O+2SO2
Cu2S+2Cu2O→6Cu+SO2
Cuprous blowing is an exothermic reaction and can be carried out by self-heating. Usually, some cold materials must be added to absorb its excess heat. After blowing, the copper content of slag is high, generally 2% ~ 5%, and it is returned to smelting furnace or treated by beneficiation and electric furnace dilution. The concentration of SO2 in the blowing flue gas is high, generally 8% ~ 12%, which can be used to make acid. Generally, horizontal converter blowing and intermittent operation are adopted. Air with gauge pressure of about 1kgf/cm2 is blown into the melt through the exhaust holes arranged along the length direction of the converter, and feeding, slag discharge, copper tapping and smoke exhaust all pass through the furnace mouth on the furnace body.
Crude copper refining includes pyrometallurgical refining and electrolytic refining. Pyrolysis refining is to remove some impurities by oxidation slagging or volatilization, taking advantage of the fact that impurities have greater affinity for oxygen than copper and their oxides are insoluble in copper liquid. The process is as follows: adding liquid copper into a refining furnace to raise the temperature or adding solid copper to melt, and then blowing copper liquid for oxidation to volatilize impurities into slag; After slag removal, copper oxide in slag is reduced by inserting green wood or injecting heavy oil, petroleum gas or ammonia water into copper liquid. In the reduction process, the surface of copper liquid is covered with charcoal or coke to prevent reoxidation. After refining, it can be cast into copper anode or copper ingot for electrolytic refining. Refined slag contains high copper and can be returned to converter for treatment. The refining operation is carried out in a reverberatory furnace or a rotary refining furnace.
The products refined by pyrometallurgy are called pyrometallurgy copper, which generally contains more than 99.5% copper. Pyrotechnic copper often contains precious metals such as gold and silver and a small amount of impurities, so it usually needs electrolytic refining. If the content of gold, silver and harmful impurities is low, it can be directly cast into commercial copper ingots.
Electrolytic refining is carried out in acidic solution containing copper sulfate, with pyrometallurgical copper as anode and electrolytic copper sheet as cathode. Electrolytic copper containing more than 99.95% copper is produced, and anode mud is rich in gold, silver, selenium and tellurium. Electrolyte generally contains 40 ~ 50g/L copper, the temperature is 58℃ ~ 62℃, the cell voltage is 0.2~0.3V, the current density is 200 ~ 300a/m2, the current efficiency is 95% ~ 97%, the residual electrode rate is about 15% ~ 20%, and the DC consumption per ton of copper is 220~300kwh. The current density of copper electrolysis workshop in China Shanghai Smelter is 330A/m2.
In the process of electrolysis, most iron, nickel, zinc and some arsenic and antimony enter the solution, which makes the impurities in the electrolyte gradually accumulate, the copper content also increases and the sulfuric acid concentration gradually decreases. Therefore, it is necessary to regularly extract part of the solution for purification and add a certain amount of sulfuric acid. The process of liquid purification is: copper sulfate is directly concentrated, crystallized and precipitated; Copper is removed from the crystallization mother liquor by electricity to precipitate black copper, and arsenic and antimony are removed at the same time; Evaporating, concentrating or cooling and crystallizing the solution after electric copper removal to obtain crude nickel sulfate; The mother liquor is used as a part of sulfuric acid replenishment and returned to the electrolyte. In addition, copper can also be added to the extracted electrolyte, and the copper can be dissolved by blast oxidation to produce more copper sulfate. Attention should be paid to prevent the precipitation of highly toxic hydrogen arsenide during copper electrodialysis.
Other methods of pyrometallurgical copper smelting that have been applied to industrial production include:
Mitsubishi method injects copper sulfide concentrate and flux into the melt of smelting furnace, which is smelted into matte and slag, and then flows to dilution furnace to produce waste residue, and matte flows to blowing furnace to produce crude copper. This method was put into production in 1974.
The concentrate and flux granulated by Noranda method are added into a cylindrical rotary furnace and smelted into high-grade matte. The produced slag contains high copper, and the copper concentrate must be selected by flotation and returned to the furnace for treatment. This method was put into production in 1973.
High-grade copper concentrate was treated by oxygen top-blown converter process. The copper concentrate is granulated or briquetted and added to the furnace. Oxygen is blown in from the top spray gun, and fuel is injected from the top, producing crude copper and slag. China used this method to treat copper concentrate obtained by high matte nickel flotation.
Segregation method is used to treat refractory bonded copper oxide ore. The ore containing copper 1% ~ 5% is ground, heated to 750℃ ~ 800℃, and then mixed with 2% ~ 5% coal powder and 0.2% ~ 0.5% salt. Copper gas (Cu3Cl3) in ore is reduced to metallic copper by hydrogen and attached to the surface of carbon particles, and about 50% copper is obtained by flotation. This method consumes high energy and is rarely used.