First, the status of lead smelting

In the past ten years, China's lead smelting industry has developed rapidly. In 2005, the country produced 2.378 million tons of refined lead, an increase of 1,671,800 tons compared with 706,200 tons in 1996. In the same period, the annual production of lead in the world, from 5.785 million tons in 1996 to 7.6688 million tons in 2005, only increased by 1.683 million tons. It can be seen that during this period, more than 99% of the world's lead production increased by China. China's lead output has increased by an average of 14.9% in the past 10 years, and its growth rate is the highest in the world.

According to statistics, more than 400 lead smelters have been built nationwide, including 3 smelters with a refined lead production of over 100,000 tons in 2005, and 8 with an annual output of 50,000-100,000 tons, and more than 30,000 t/a. 18, its total output is about 1.33 million tons, accounting for 56% of the country's total refined lead production. See Table 1.

China's traditional lead smelting process produced accounted for 85% of total production of lead, Zhuzhou Smelter addition, Henan Yuguang, Jinli, northern Henan, Wan Yang, Jiaozuo Oriental, Neimeng Lin Dong, smelters using sintering machine, the rest Sintering is performed using a sintering pot or a sintering plate.

A sintering - blast furnace smelting of lead zinc ISP process, in the country have four, five production lines, wherein two Shaoguan smelter, silver white, Huludao Zinc, Huang Qinghai have a county.

Sintering machine-blast furnace lead-smelting process is relatively mature, but low-concentration sulfur dioxide flue gas recovery is difficult. Zhuzhou Smelter introduces Topsoe acid-making technology, Henan Yuguang Gold-lead Group, Yubei Metal Smelter and Jiyuan Wanyang Smelting The Group and others all adopt unsteady acid production technology. However, due to process conditions and equipment limitations, SO ₂ unorganized emissions and lead dust pollution have not been effectively controlled. As for the sintering pot-blast furnace lead-smelting process that is still in production (the production is banned from the country in 2000), SO ₂ and lead dust pollution is particularly serious.

Table 1 List of enterprises with an annual output of more than 30,000 tons of refined lead in China in 2005

In recent years, as the country's environmental protection requirements have become stricter, new lead-smelting methods have been gradually promoted and applied in China, such as the introduction of the Isafa (ISA) introduced by Qujing in Yunnan and the Kaldo method introduced by the Northwest Mining Company. The lead process has been put into production.

In particular, China's self-developed oxygen bottom-blowing blast furnace reduction process for lead smelting is very fast. In addition to Henan Yuguang Gold and Lead Group, Anhui Chizhou, Hunan Shuikoushan and other four devices have been successfully put into operation, Henan Lingbao Lingye shares The company has ignited the oven in August this year, and Yunnan Xiangyun Feilong Industrial Co., Ltd. has started production on September 20.

At present, the new lead system has been built or modified by this process, and there are three companies that have entered the construction drawing design stage: Chifeng Xingye, Baiyinnuoer Lead-Zinc Mine and Jiyuan Jinli. There are 4 companies in Ganzhou, Goyang, Guixi and Shadian.

The oxygen bottom blowing-blast furnace reduction lead-smelting process (SKS) is a successful molten pool smelting technology in China after nearly 20 years of experimental research. It has a good investment, good environmental protection, high recovery rate of sulfur and associated metals, and is suitable for handling high arsenic materials. It has strong competitiveness for the transformation of existing lead plants and is one of the key environmental protection projects promoted by the state. After the above 13 projects are completed and put into production, more than half of China's mineral refined lead will be produced by this process. Coupled with the introduction of several technologies, the environmental status of lead smelting in China will be fundamentally improved. The overall level will be in the world's leading position.

At present, in the research of lead smelting, Central South University has made some progress in the direct smelting technology of oxygen side blowing pool smelting in Xinxiang, Henan. Henan Yuguang Gold and Lead Group has carried out direct reduction test of liquid high lead slag, and encountered some engineering problems, but it has proved that the process mechanism is feasible.

In terms of lead refining, China and Japan basically adopt electrolytic refining process. The quality of their products is stable, the output of intermediate materials is small, and the associated elements are easy to recycle. It is especially suitable for the treatment of sorghum and lead. The fire method refining commonly used in Russia, Europe and the United States has the advantages of low investment, low lead accumulation in the middle, and fast capital turnover.

It is worth noting that the 100,000 t/a electric lead project completed and put into operation by Yunnan Metallurgical Group Corporation in 2005 in Qujing, Yunnan, has adopted internationally popular lead pans, large electrolytic cells, large plates, low current density, long cycle, etc. Advanced production technology and equipment, and imported advanced lead anode vertical casting production line, lead cathode automatic rowing unit, lead cathode manufacturing machine and initial plate DM casting machine. The completion and commissioning of the project has further narrowed the gap between China's lead refining industry in terms of technical equipment, process control and other world advanced levels, and played an important role in China's lead refining production.

Second, the direction of lead smelting technology development

(A) Based on China has introduced a QSL, ISA, Kaldo process, newly clouds Tin Group has introduced other foreign Ausmelt lead smelting process, where high hot lead slag powder coal direct reduction process due to lead, lead oxide, Lead sulfide has a low boiling point, and both have a high smoke rate and a large amount of return. The same problem exists in the oxygen side blowing smelting process studied by Central South University. In order to reduce the soot rate in the lead reduction stage, China's self-developed bottom-blown smelting and imported ISA methods use liquid high-lead slag ingots, blast furnace reduction smelting, effectively reducing the smelting rate of reduction smelting, and lead, silver, sulfur recovery The rate is high, the operation is stable, and it is easy to master, so the bottom blowing smelting is quickly promoted. However, the high-lead slag ingot is reduced by the blast furnace, and the latent heat of the liquid slag is wasted. As the price of coke increases, the cost of lead smelting increases. Therefore, the development of liquid high-lead slag electrothermal coke direct reduction technology can replace the blast furnace and make full use of high lead. The latent heat of the slag reduces the coke consumption and the amount of flue gas to the theoretical value, thereby greatly reducing the soot rate and reducing the smelting cost. This should be an important research and development topic and development direction of lead smelting technology in China in the future.

(2) Lead smelting technology Compared with foreign countries, most of China's lead smelting plants are small in scale, low in equipment level, low in labor productivity, and poor in comprehensive utilization. The future development direction should increase concentration, expand enterprise scale and improve equipment. Level and build a lead-zinc joint venture to leverage the complementary advantages of lead and zinc smelting, take the road of circular economy, and improve the comprehensive utilization of resources.

Third, the status quo of zinc smelting in China

In the past 15 years, China's zinc production has grown rapidly, from 1,076,700 tons in 1995 to 1.957 million tons in 2000, reaching 2.71 million tons in 2005. From 1995 to 2005, the average annual increase was 9.7%; from 2000 to 2005, the average annual increase was 6.7%. As the zinc production base increases, the annual growth rate has been decreasing year by year. However, since 2002, China's zinc production and consumption rank first in the world, and it is a real zinc production and consumption country.

China's zinc smelting process is mainly based on wet smelting, followed by fire smelting. The standard process of the wet smelting process is zinc concentrate roasting → leaching → clean liquid → electrowinning → electric zinc product. Among them, due to different conditions of leaching operations, it is divided into low temperature conventional leaching and high temperature high acid leaching. The conventional leaching process uses a rotary kiln to volatilize residual zinc in a typical leaching slag. The high-temperature and high-acid leaching slag is directly sent to the slag yard for storage. The leaching solution for iron removal has four different processes in China, such as the yellow potash method used in the silver-zinc smelting plant, and the Chifeng Cobo-red zinc plant. Ammonia slag iron slag method, because of low zinc content in iron slag, also known as low pollution huangkang shovel method, Xiangyun Feilong Industrial Co., Ltd., etc. using the goethite method, Wenzhou smelting plant, etc. Secondary needle iron ore method. Based on these differences, the wet zinc smelting process is diverse.

The modern smelting plant of the wet zinc smelting single series 100,000 t/a electric zinc has been completed and put into operation in Baiyin, Zhuye, Qujing, Jiyuan and Bayannaoer, and there are still two under construction. Its equipment and self-control level have reached the world's advanced level. In terms of process operation, labor productivity and depth of liquid purification still have a large gap compared with developed countries.

Fire method zinc smelting:

There are three existing zinc smelting processes in China, namely, vertical tank zinc smelting, ISP blast furnace zinc smelting, and electric furnace zinc smelting. A few years ago, in the remote areas, the original manger furnace, saddle furnace, square furnace or slightly flattened flat furnace was used for zinc smelting. Due to its high energy consumption, low recovery rate, waste of resources and environmental pollution, it has been banned by the state. Production and construction have been basically shut down or rebuilt.

The last production line was closed in 1980 in the vertical tank zinc smelting. China's vertical tank zinc smelting is typical of Huludao zinc plant. After years of efforts, the plant has developed high-temperature boiling roasting, self-heating coke oven, large distillation furnace, rectification furnace, double-layer gas generator, and slag vortex melting. New technologies such as furnaces have raised the vertical tank zinc smelting to a new level, and have built 200,000 t/a vertical tank zinc smelting capacity. However, due to the difficulty in large-scale single-series production capacity, coupled with the difficulty in energy consumption and environmental protection, it has not been widely promoted and applied.

The ISP blast furnace zinc smelting is also called the empire smelting method. The upper part of the furnace produces zinc and the lower part produces lead. China has built 5 sets of equipment, and the total amount of zinc produced last year was 20 to 210,000 tons. This process has unique advantages for the treatment of mixed concentrates where lead and zinc are difficult to sort. It developed rapidly in the 60s and 70s. With the improvement of the separation technology of lead-zinc mixed ore, and the environmental problems such as the flue gas of the lead-zinc concentrate sintering process and the dust pollution of the powder-returned powder, it is difficult to solve the environmental problems, and the ISP process is already setting sun. 19 sets of ISP devices, in developed countries, many have been closed due to environmental reasons, in 2004, Australia's Kirk, Creek's ISP factory has also been closed.

Zinc smelting in electric furnaces, due to relatively low investment, is short process, easy to operate, and has no outstanding problems in environmental protection. Therefore, in the remote provinces such as Yunnan, Guizhou, Sichuan, Shaanxi, Gansu, Ningxia and Qinghai, there are zinc resources and sufficient electricity. The place has been developing continuously for more than a decade. At present, 35 factories in the country have completed the commissioning of 58 electric furnaces. The total installed capacity of electric furnaces is 112k·kW, and the annual output of zinc is 15 to 160,000 tons. There are currently 8 manufacturers, nearly 40 electric furnaces under construction, with a total power of nearly 120 K·KW. Among them, there are Yunnan Wenshan Electric Furnace Smelting Plant, which plans to build six 4000kVA electric furnaces, Guizhou Hezhang to build 10 sets of 2000kVA electric furnaces, and Liupanshui to build 14 sets of 3500kVA electric furnaces. The power consumption of the electric furnace that has been put into operation is between 1000 and 6300 kVA, and the power consumption of the product fluctuates between 3500 and 4300 kW·H/t of coarse zinc depending on the grade of the concentrate.

In addition, Liuzhou Zinc Products Factory and Shuikoushan Nonferrous Metals Co., Ltd. and other manufacturers will use zinc calcination to reduce the volatilization and directly produce the commercial zinc oxide. The annual output of zinc oxide fluctuates between 300,000 and 400,000 tons. . This should also be attributed to the range of pyrometallurgical zinc. China's zinc production in the past decade is listed in Table 2:

Table 2 China's zinc production unit: 10,000 t

Table 2 except for electric zinc, all of which are pyrometallurgical products. In 2004, the electric zinc was 1.951 million tons, accounting for 71.8% of the total zinc production in the year, and the ISP blast furnace produced 210,000 tons of zinc, accounting for 7.7%. Zinc is 160,000 tons, accounting for 5.9%, and the rest is about 35 to 360,000 tons of zinc in vertical tanks, accounting for 13%. From Table 2, in 1995, the output of electric zinc only accounted for 41% of the total output of the year, and by 2004 it has increased to nearly 72%, indicating that the development speed of wet zinc smelting is much greater than that of pyrometallurgical zinc.

In 2005, China's enterprises with an annual output of more than 30,000 tons of zinc are listed in Table 3:

Table 3 Enterprises with an annual output of 30,000 tons of zinc in China in 2005

Source: National Bureau of Statistics, China Nonferrous Metals Industry Association

Technical progress of zinc smelting in recent years

In the 1990s, with the construction of a single series 100,000 t/a electric zinc smelter, 109m ² large boiling furnace roaster, waste heat boiler, calcine boiling cooler, high efficiency cooling cylinder, 150m ³ high efficiency and energy saving were adopted and developed. stirring tank, a large plastic cell, mechanized stripping machine zinc, molten zinc 40T large low-frequency induction furnace, automatic pouring - stacking - balers and other advanced equipment and antimony salts depth of three sections net fluid technology, resulting in a wet mill of The level of zinc technology has entered the world's advanced ranks.

The latest developments are:

1) Yunnan Metallurgical Group and Kunming University of Science and Technology jointly developed a new process for autocatalytic pressure leaching of high-iron zinc concentrate iron to treat concentrate containing Zn 42.17%, Fe 14.38% and S 29.28%. The industrial continuous test indicators reached: The zinc leaching rate is 98.05%, the iron leaching rate is only 29.22%, and the elemental sulfur conversion rate is 92.2%. The technology has completed the production line of 10,000 t / a electric zinc, and entered the stage of industrialization. The process has a short process, and combines the conventional wet zinc smelting roasting, waste heat boiler, dust collection, acid production, leaching, slag treatment and the like into one or two stages of pressure leaching, and the flow is simple. In addition, the process directly produces elemental sulfur, avoids exhaust gas emissions from roasting flue gas after acid production, and environmental pollution caused by residual SO ₂ and acid mist. It is a clean process, especially for plants built in areas where sulfuric acid is not sold. Superiority.

2) The treatment of high-silicon zinc oxide ore has made breakthroughs in recent years. Yunnan Xiangyun Feilong Industrial Co., Ltd. will leaching the high-silicon zinc oxide ore and sulphide ore in the middle temperature of acid leaching, mixing according to the appropriate ratio, and then passing the high temperature. It has obtained national patents for high acid leaching, iron smelting by goethite method, desiliconization, liquid purification and electrolysis. The plant has been produced for many years using the above process, and the total recovery of zinc is 94% ±. In 2005, the output of electric zinc in the plant has exceeded 50,000 t/a, which proves that the process is mature and reliable, which has opened up a new way for the economical and efficient utilization of high-silicon zinc oxide ore that is difficult to handle in China.

3) As the price of indium exceeded 10 million yuan / t, the output value of one kilogram of indium is equivalent to one ton of zinc, zinc effective recovery of associated metals indium zinc smelting aroused great attention of peers, we have introduced the results of two studies industrial design . First, in the process of smelting high temperature and high acid jarosite by wet method, the medium leaching slag is not directly sent to high acid leaching, and the pre-neutralization, pre-neutralization supernatant sedimentation and pre-neutralization are carried out with soot and high acid leaching solution. The underflow is then sent to a high acid leaching. The supernatant of the sedimentation is returned to the neutral leaching, and the iron slag is enriched with most of the indium, which is used as a raw material for indium extraction. The improved leaching process, the total recovery of indium is more than 70%, and the indium zinc smelting plant with 50t/a indium and 50,000t/a zinc is being built in China.

4) Another research result belongs to the pyrometallurgical zinc smelting process, that is, the indium-zinc concentrate desulfurization roasting, the calcine feeding furnace is reduced and volatilized, the volatile matter is condensed by zinc rain to obtain crude zinc, the crude zinc rectification is refined to obtain refined zinc, and the indium remains. In the rectified residue hard zinc, hard zinc is vacuum smelted to recover indium. The indium of the process has a volatilization rate of >90% in the electric furnace and a total recovery rate of indium of 80%. A demonstration plant with an annual output of 30,000 t/a of zinc and 20 t/a of indium is being built in China.

Fourth, development discussion

China is a big country in the production and consumption of zinc smelting, but it is not a strong country. Like other non-ferrous metals, there are some common problems. If no effective countermeasures are taken, development is unsustainable.

1) With the rapid growth of domestic zinc consumption, it is necessary to pay attention to the development and utilization of foreign zinc resources.

China was originally a large country of zinc resources. In the last century, there were a large number of zinc concentrates, zinc and alloys exported. As can be seen from Table 4, since 2001, the import volume of zinc concentrate has exceeded the export volume. Since 2003, the foreign trade volume of zinc has turned from a surplus to a deficit. Since 2004, imports of zinc and zinc alloys have exceeded exports. At the end of 2005, the comprehensive smelting capacity including zinc products reached 4 million t/a±, while the zinc production in that year only maintained at the level of 2004, and decreased slightly (see Table 2), mainly restricted by imported concentrates. .

Table 4 Apparent consumption and foreign trade status of zinc in China

The enthusiasm for the construction of domestic zinc smelters has not been reduced. This year, more than 200,000 t/a of smelting capacity was put into operation. The domestic zinc mining capacity has increased, and it has not kept up with the growth of smelting capacity. The quantity of imported concentrates has also been restricted by the international market. Insufficient supply of raw materials has become a bottleneck for the growth of zinc smelting capacity in China. To change this situation, relevant departments and enterprises must focus on the development of foreign zinc mining resources. According to the statistics of 2005, the domestic zinc resource reserves are only 20.95 million tons, and the basic reserves are only 32.5 million tons. According to the current production and development speed, domestic zinc resources can only be maintained for 7-8 years. If you don't pay attention to it now, there will be a strategic resource crisis of zinc soon.

2) Paying attention to the recycling of renewable resources is an effective way to solve the shortage of zinc resources in China.

In China, the recycling and utilization of waste metal such as copper , lead, aluminum and tin has been paid attention to by the relevant departments and enterprises. Only the recycling and utilization of zinc secondary resources is still insufficient, and it is in a state of self-flow. Form an industry. According to the "Collection of Nonferrous Metal Materials", the output of recycled zinc in China in the past five years is listed in Table 5.

Table 5 Regenerated zinc production and proportion in China from 2000 to 2005

Due to the difficulty of statistics, the statistics in Table 5 are not necessarily accurate, but it can be seen that the utilization of renewable resources is quite low.

From 2004 to 2005, the apparent consumption of zinc in China has reached 3 million tons per year. The proportion of its consumer industry is listed in Table 6. Among them, the amount of zinc used in the galvanizing and dry battery industry has exceeded 50%, and the waste metal has not been effectively recovered.

Table 6 % of zinc used in various consumer industries

The secondary resource recovery rate of zinc in developed countries has reached 30% of zinc production. There are more than 80 home appliance steelmaking plants in the United States, which concentrate on disposing of galvanized steel and produce soot containing Zn, Pb and Cd. After being separated into a concentrated enrichment, as a raw material for the production of these metals, it effectively improves zinc and so on. The recovery ratio of secondary metals. There are currently about 50 regenerative zinc recycling plants in the world, which account for 10% of the world's total zinc production. Zinc recycling from dry batteries is still in the research stage in China. It is reported that both Japan and South Korea have built a dry battery recycling plant with an annual output of more than 5,000 tons of zinc.

The recycling of secondary zinc resources must be highly valued by relevant state departments. The first is that the waste materials of the galvanized steel with the largest amount of zinc need to be collected centrally and concentrated in a special steelmaking plant that can effectively recover zinc. Second, we must speed up the pace of research and break through the cost-effective recycling process of waste batteries. Other than zinc oxide coatings are difficult to recycle, zinc materials, die-casting alloys, copper-zinc alloys, etc., can be easily recovered as long as they are collected. If the secondary metal recovery rate of zinc reaches 30% of consumption, it means that China can recover 900,000 tons of zinc per year, which will greatly alleviate the pressure of zinc resources.

3) Expanding the scale of the enterprise to improve the overall level of comprehensive utilization of resources

China's zinc smelting enterprises have hundreds of statistics in the past few years, and there are nearly 40 single-supply zinc-smelting plants. The average zinc production of enterprises is less than 10,000 tons. There are five countries with an annual output of more than 100,000 tons of zinc, the largest in Zhuye, with an annual output of 30 to 330,000 tons of zinc. Large factories, such as Zhuye, have a relatively high level of comprehensive utilization of resources. It is difficult for small zinc plants to fully and efficiently recover associated metals in zinc resources in a cost-effective manner, and there is a problem of wasting resources. Foreign zinc companies are relatively large in scale. The world's top ten lead and zinc companies control 48.7% of the world's total lead concentrate production and 43% of total zinc concentrate production. The company's zinc production capacity is 640,000 t / a; the company's zinc production reached 650,000 t / a; the company's lead and zinc production capacity reached 900,000 t / a, is the world's largest refined zinc production company. These companies, the comprehensive utilization of zinc resources are higher than the current level of China. The development direction of zinc smelting in China should also moderately reduce the number of zinc enterprises, expand the scale of enterprises, increase labor productivity, and improve the comprehensive utilization level of resources, in order to be in a favorable position in international competition and become a strong country of zinc production.

4) From a technical point of view, the promotion of atmospheric pressure oxygen immersion process is worthy of attention. Atmospheric pressure oxygen immersion has the characteristics of pressurized oxygen, which can produce elemental sulfur. The leaching rate of zinc is as high as 98%, and overcomes the influence of monomeric sulfur on pressurized oxygen leaching, which is easy to produce material bond in the kettle and slurry pipeline. Disadvantages, the investment is also lower than the same scale pressurized oxygen immersion technology, known as the third generation of new zinc smelting technology. Or it can become the preferred technology for the promotion and application of zinc smelting in China in the future.

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