Large quantities of waste generated in the non-ferrous metal smelting process, and more varieties. At present, the annual emission of smelting waste residue is about 50 million tons. Stacking requires land or farmland, and the composition of non-ferrous metal smelting waste is complicated. Some smelting wastes are piled up in open-air slag yards for a long time. After different ways of migration or transformation, they often cause different degrees of pollution to the surrounding environment. Moreover, many smelting wastes also contain heavy metal components that can be used. These wastes are discarded and harmful, and they are used as treasures.
Copper slag
Copper slag contains a large amount of available resources. Modern copper smelting process focuses on improving production efficiency. Copper oxygen-rich self-heating smelting has a series of advantages in smelting strength, energy consumption and environmental protection. It is a major development direction of copper smelting technology in the world today. With the increase of oxygen enrichment concentration and the increase of smelting strength, the copper content of the smelting slag will increase. The recovery of this part of copper resources is the main purpose of processing copper smelting slag at this stage. Of course, most of the precious metals in the slag are symbiotic with copper, and most of the precious metals can be recovered while recovering copper. Main mineral slag containing iron minerals (Table 1), grade iron is typically more than 40%, much greater than the average 29.1% iron ore industrial grade. Iron is mainly distributed in the olivine phase and the magnetic iron oxide mineral, and the iron concentrate can be obtained by magnetic separation. Obviously, based on the characteristics of copper slag, the basic theoretical research on the separation of valuable components is carried out, and the separation technology that can realize the re-recycling of valuable components is developed to provide technical basis for the industrialization of copper-containing slag re-resources, and to the national economy and The development of science and technology has important practical significance.
Table 1 Composition of copper slag for various smelting methods (%)
I. Process mineralogical characteristics of copper slag
With the continuous development of copper metallurgy technology, the traditional copper smelting technology includes blast furnace smelting, reverberatory furnace smelting and electric furnace smelting are gradually replaced by flash smelting. At the same time, the so-called one-step smelting is different from the above secondary smelting method. Copper smelting methods, such as Noranda, Vanukov, and Isafa, have also received increasing attention. Converter smelter, copper flash smelting slag and other relatively high (especially high slag containing arsenic and other harmful elements), the processing returns difficulties, these materials often require open process. The main components of copper slag slag are iron silicate and magnetic iron oxide. An amorphous glass body composed of fayalite (2FeO · SiO 2 ), magnetite (Fe 3 O 4 ), and some gangues (Table 2, Table 3). Mechanical entrainment and physicochemical dissolution are two forms of loss of metal in the slag. In general, the loss of copper in the slag increases as the oxygen potential of the slag, the niobium grade, and the slag Fe/SiO 2 ratio increase. The copper in the smelting slag mainly exists in the form of matte or pure copper (Cu 2 S). Almost no metal copper. More common copper sulfides are discontinuously distributed in the form of fine beads between the olivine and the glass. There is a small amount of metallic copper in the blowing slag. In the slag containing high copper, the content of Cu and S also increases. The valuable metals lost in mechanical entrainment are due to the large amount of Fe 3 O 4 formed during the smelting process, resulting in an increase in the viscosity of the slag and a decrease in the specific gravity of the slag. The dross cannot be effectively separated.
Also found: é”matte
A eutectic of a colored heavy metal sulfide and an iron sulfide, also known as a melting point. It is an important intermediate product of pyrometallurgy of sulfide concentrates of metals such as copper and nickel . The smelting process for the purpose of producing hydrazine is called smelting smelting. In the smelting smelting, the metal to be extracted is enriched in the samarium in the form of sulfide, and the precious metal and other valuable components are also enriched therein, and the gangue is melted into slag and separated from the strontium.
The scorpion obtained from several typical copper smelting is called copper bismuth (or matte) and belongs to the Cu 2 S-FeS system. Sulfonium-containing lower FeS slag smelting of copper matte obtained final beryllium commonly known as white (or white ice copper). Cu 2 S-Ni 3 S 2 -FeS system copper nickel niobium (or copper nickel matte) can be obtained by melting a nickel sulfide concentrate electric furnace or a flash furnace. Some factories add a vulcanizing agent ( gypsum , pyrite) and a reducing agent to treat the nickel oxide ore, and perform so-called reduction vulcanization to obtain an intermediate product of nickel niobium (or ice nickel) belonging to the Ni 3 S 2 -FeS system. In the reduction smelting of lead agglomerates with high copper content, in order to separate and recover the associated copper, a layer of lead ice copper composed of Cu 2 S-FeS-PbS system is often formed between the crude lead and the slag. The main components of several curved sputum are shown in the table.
Second, the copper law slag depletion
Returning to remelting and reducing ostomy is the main method of depletion of copper slag. The slag return remelting is the traditional method of recovering copper, and the resulting bronze copper return to the main process. For the recovery of cobalt and nickel in the slag, a separate reduction of the osmium outside the main process is taken. There are many methods for slag depletion. Which method to choose depends on the site conditions, such as funds, sites, by-products, and impurities. Clearly, the smelting process is a major factor in determining the slag depletion process technology because the slag characteristics depend on the smelting technique.
As technology advances, some new ways of depletion continue to emerge.
(1) Reverberatory furnace depleted copper slag
The reverberatory furnace is a slag depletion method that has been used for a long time in the past, and the furnace top uses a reflective cylindrical reactor of an oxygen/fuel nozzle to deplete the slag. A slag having a high copper and magnetic iron oxide mineral is charged into the reactor in batches. The first step is to spray coal , oil or natural gas into the molten pool through the tuyere to reduce the magnetic iron oxide mineral, so that the magnetic iron oxide mineral content in the slag is reduced to 10%. This step is similar to the reduction phase of pyrometallurgical copper, reducing the viscosity of the slag. In the second step, the blowing is stopped to separate the ice copper and the slag in the molten slag. This method is still used in the Japanese small name smelting plant and the Calettos copper smelting plant in Chile.
(2) Electric furnace method
Depletion of the electric furnace can increase the melt temperature and reduce the copper content in the slag to a very low level, which is beneficial for reducing copper oxide in the molten slag and recovering fine particles of copper particles in the slag. The depletion of the electric furnace can not only handle the slag of various components, but also can handle various kinds of return materials. The flow of electrical energy in the melt between the electrodes produces agitation, causing the copper particles in the slag to aggregate and grow.
(3) Vacuum depletion method
Du Qingzhi and other developed slag vacuum depletion technology, the copper content of the slag layer of Nolanda Oxygen-rich molten pool slag 1/2-2/3 was reduced from 5% to less than 0.5%. The advantages of vacuum depletion are: rapidly eliminating or reducing the content of Fe 0 , reducing the melting point, viscosity and density of the slag, increasing the interfacial tension between the slag and promoting the separation of slag-clam. The vacuum is beneficial to quickly remove the SO: bubbles in the slag. Due to the rapid growth and floating of the bubbles, the slag plays a strong stirring role, increasing the probability of colliding and colliding. The main problem is that the cost is high and the operation is complicated.
(4) slag barrel method
The slag bucket is used as an additional sedimentation tank, which is the most convenient way to reduce the copper content of the waste residue. The key to this method is to use a large slag bucket to keep the temperature of the slag in the bucket and recycle some of the slag or slag enriched at the bottom of the bucket for further treatment. The slag barrel method mainly utilizes the latent heat of the slag to achieve the sedimentation of the copper droplets and the coarsening of the crystal.
(5) molten salt extraction
The molten salt extraction method is based on the difference in the partition coefficient of copper in the slag and the copper bismuth. The liquid copper ruthenium is used as the extraction phase to make full contact with the copper-containing slag, thereby effectively extracting the copper dissolved and contained in the slag. S. Vaisburd et al. conducted an in-depth study of this method and used it to treat the slag produced by the Vanukov method of Kazakhstan.
In addition, fire depletion research also has DC electrode reduction, electrophoresis enrichment and other methods.
Third, slag beneficiation method
The enrichment is separated by magnetic separation and flotation according to the difference in hydrophilic, oleophilic and magnetic properties of the surface of the valuable metal. The viscosity of the slag is large, which hinders the migration and aggregation of the copper phase grains, the fine grains, the copper sulfide content in the copper phase decreases, and the copper flotation is difficult. The greater the proportion of weakly magnetic fayalite, the more difficult it is to reduce silicon in the concentrate during magnetic separation. The size of the grains, the degree of self-shape, the relationship between the slag and the distribution of the main elements in each phase are closely related to the cooling method of the slag. During the slow cooling process, the primary crystallites of the slag melt can be grown by dissolving a precipitate to form a well-crystallized self-shaped or semi-automorphic crystal, which aggregates and grows into a relatively concentrated independent phase.
(1) Flotation method
The recovery of copper from oxygen-rich smelting slag (such as flash slag) and converter slag has been widely used in the copper smelting industry. In addition to the high copper yield and low energy consumption (lower than the electric furnace), the flotation method can remove Fe0 and some impurities from the process in comparison with the slag return smelting, and the amount of quartz used in the blowing process will be greatly reduced. The recovery rate of copper flotation is generally above 90%, the concentrate obtained is more than 20%, and the tailings contain copper in the range of 0.3% to 0.5%.
(2) Magnetic separation method
The strong magnetic components in the slag are iron (alloy) and magnetite. Cobalt and nickel are relatively concentrated in ferromagnetic minerals, and copper is in a non-magnetic phase, so that slag with good fine crystallization can be used as a means of pre-enrichment. Due to the complex distribution of useful metal minerals in the slag, there is often a continuous generation, and the weak magnetic fayalite accounts for a large proportion in the slag, so the magnetic separation effect is not satisfactory. At present, many copper smelters in the world use the beneficiation method to recover the copper metal in the converter slag, which also produces a large number of beneficiation tailings. The ore dressing workshop of Guixi Smelter uses the converter slag as raw material for sorting operation to recover the copper metal. The content of SiO in the slag tailings exceeds the standard, which fully meets the requirements of iron concentrate.
Fourth, wet leaching
The wet process can overcome the high energy consumption of the depletion process of the fire process and the disadvantage of producing exhaust gas pollution, and the good selectivity of the separation is more suitable for treating the low-grade copper slag.
(1) Direct leaching by wet method
The minerals (sulfides, metals and combined oxides) of Cu, Ni, Co, zn and other metals in the copper slag can be dissolved in the medium (dilute sulfuric acid) by oxygen oxidation under pressure, and the leaching process The reaction can be briefly described as follows:
In addition, it has been reported in the literature that HCI and HNO, and KCN are directly subjected to wet leaching. However, since these reagents are expensive, corrosive, and toxic, the industrial use of copper slag for metal extraction is unknown. After the leachate is filtered, the filtrate is treated with an extract containing the extractant. At present, the industrial application is better by the LIX series produced by Henkel and the Acorge M series extractant produced by Avecia of the United Kingdom.
(2) Indirect leaching
Proper pretreatment can modify the valuable metal phase in the copper slag to make it easier to recover and separate. Chlorination roasting and sulphation roasting are typical examples. The calcined product is directly immersed in water. The metal yield mainly depends on the pretreatment effect. The leaching rate of nickel-cobalt can be increased to 95 by leaching the calcined slag and converter slag by reduction with acid FeCI. % and 80%.
(3) Bacterial leaching
Bacterial leaching is rapidly developed due to its ability to soak copper sulfide and has a number of advantages. However, the biggest disadvantage of bacterial leaching is the slow reaction rate and long leaching period. Recent studies have involved the addition of certain metals (such as Co, Ag) to accelerate the rate of bacterial oxidation, the mechanism is that the above metal cations replace the metal ions such as Cu 2+ and Fe 3+ in the mineralized surface of the mineral surface. The conductivity of the sulfide ore is increased, so the rate of electrochemical oxidation of the sulfide ore is accelerated.
5. For the cement industry construction industry
After water quenching, the copper slag is a black, dense, hard, wear-resistant glass phase. The density is 3.3-4.5g/cm 3 , the porosity is about 50%, and the fineness modulus is 3.37-4.52, which is a coarse sand type slag. Table 4 shows the application of copper slag in the cement industry and construction industry.
Sixth, copper slag comprehensive utilization prospects and existing problems
The comprehensive utilization of copper slag can be roughly divided into two categories: one is to utilize the physical properties of copper slag, and the other is to use some components of copper slag. With the improvement of environmental protection requirements and the depletion of mineral resources, copper slag has a good comprehensive utilization prospect. The ore dressing and depletion, flotation process has no mining cost, and can fully recover copper and its precious metals such as Au and Ag. The tailings contain about 40% iron, and iron concentrate can be obtained by magnetic separation and enrichment.
The problem of the comprehensive utilization of copper slag slag is mainly that the theoretical research work of slag is not deep enough, especially the research on thermodynamics and kinetics is still rare. At present, although the comprehensive utilization of copper slag slag has been extensively studied, there are not many methods for forming industrial production scale. Comprehensive utilization of copper slag is very important for economic, social and environmental benefits.
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