Analysis of current situation of domestic vanadium extraction process and facing problems

Stone coal vanadium, generally refers to the vanadium-containing carbonaceous shale, coal gangue vanadium-containing raw materials like industrial process to extract vanadium compound.

China's stone coal vanadium extraction industry started in the late 1970s, and has since experienced two major development periods, namely the initial development period in the 1980s and the large development period from 2004 to the present. After 30 years of development, the stone coal extraction vanadium industry has already played an important role in the vanadium industry, and the output is estimated to have reached about 40% of the total vanadium production. In the industrial industry, vanadium extraction from stone coal is a younger industry. In terms of process and equipment, it is still in a relatively backward situation, and there is still a large space for technical and economic improvement.

I. Current status of vanadium extraction from stone coal

After 30 years of development, the vanadium extraction process of stone coal has developed into two major process routes, namely, the vanadium extraction process by hot method roasting and the vanadium extraction process by wet acid leaching. The method for extracting vanadium by fire method by fire method refers to a process in which ore is subjected to high temperature oxidation roasting, low-temperature vanadium is oxidized and converted into pentavalent vanadium, and then wet leaching is carried out to obtain a vanadium-containing liquid to realize vanadium extraction by ore; wet acid leaching The vanadium extraction process refers to the direct acid leaching of vanadium-bearing ore, including the process of dissolving vanadium in the mineral to obtain a vanadium-containing liquid under high concentration of acidic conditions, even in the presence of heat and pressure, and oxidant.

(1) Vanadium extraction process by fire method

The vanadium extraction process by fire method is divided into vanadium extraction process by vanadium extraction process, vanadium extraction process by blank roasting, vanadium extraction process by calcification roasting, etc. according to the difference of additives in the roasting process or the difference of roasting mechanism.

1. Adding salt roasting and vanadium extraction process

In 1976, in cooperation with the Institute of Metallurgy Hunan Yueyang commune opened a new experimental study of extracting vanadium from stone coal and plant production. The roasting equipment was selected from the flat kiln of the Anhua Vanadium Plant and improved. By 1979, the traditional process of stone coal with salt, sodium oxide, roasting, water immersion, hydrolyzation, coarse vanadium, crude vanadium, alkali refining, and refined vanadium has been formed. This process is also the industry's traditional "sodium roasting". , two-step method of vanadium precipitation or "addition of salt to roasting and vanadium extraction process".

The advantages of the process: mature technology, simple equipment, and low investment.

The defects of the process: the roasting exhaust gas is seriously polluted, or the exhaust gas treatment cost is high and the technical difficulty is large. According to the calculation and actual measurement, if 8% salt (sodium chloride) is added during the roasting process of vanadium-bearing coal, the total concentration of hydrogen chloride and chlorine in the flue gas will reach 10000mg/Nm ³ , according to the comprehensive emission standard of atmospheric pollutants. GB16297-1996, the maximum allowable concentration of hydrogen chloride is 150mg/Nm ³ , and the chlorine gas is 85mg/Nm ³ . If the flue gas is not treated, the two pollutants in the flue gas exceed 80 times. The flue gas is treated, and the current industrial approach is lime milk absorption or caustic absorption. The lime milk absorption method belongs to the gas-liquid solid reaction, which requires high absorption equipment, and the corresponding flue gas treatment equipment has large investment; the caustic soda absorption method has good effect and the equipment investment is low, but the treatment cost is high, according to general industrial conditions, such as ore inclusion. The calculation of vanadium grade is 1%. For every ton of vanadium pentoxide produced, it takes more than five tons of sodium hydroxide and the absorbent consumes more than 15,000 yuan. However, more technical and economic problems are followed, and smoke pollutants are absorbed. After that, it will be transformed into wastewater pollution. According to the current general technical measures in the industry, the part of the flue gas treatment wastewater is incorporated into the process. According to the process calculation and industrial measurement, the part of the wastewater is incorporated into the process and will be made once. The chloride ion content in the process water is as high as 16g/L or more, which seriously affects the enrichment of vanadium ions in the ion exchange process, and more importantly affects the cycle utilization rate of the process water. Therefore, the process water cycle utilization rate of the process is very low, according to industrial research. Data, the water circulation utilization rate of the process is less than 40%, and each ton of vanadium pentoxide product is produced, and the process wastewater discharged is up to 300m ³ or more. The soil salinization around the company has also caused a series of vanadium-related environmental incidents over the years!

Simply put, the flue gas pollution during the process of adding vanadium and roasting vanadium is converted into wastewater pollution, resulting in high waste gas treatment cost, low wastewater recycling rate, large wastewater discharge, and serious environmental pollution.

At present, there are provinces in China that have stone and vanadium extraction industries. Most of the newly-built enterprises adopt industrial policies that prohibit the use of salt-adding (including low-salt) roasting and vanadium extraction technologies, such as Henan, Hubei, Chongqing, Shaanxi, Xinjiang, and Guizhou. Although some provinces do not have such regulations, as companies, as investors, they should be clear about the pros and cons.

2. Calcination roasting and vanadium extraction process

Calcium roasting process refers to the addition of lime or limestone to vanadium-containing minerals. At high temperatures, low-valent vanadium is oxidized to high-valence vanadium and forms calcium metavanadate compounds. Calcium metavanadate compounds are easily dissolved in weakly acidic environments. Liquid to achieve separation and extraction of vanadium from minerals.

The technical route of calcification roasting and vanadium extraction first appeared in the literature of the Soviet Union in the 1950s, but it was not industrialized. In the mid-to-late 1990s, a domestic research institute had conducted industrial tests in enterprises, but it did not achieve industrialization. The research team led by me led the research and development of this technology in the late 1990s, and entered the enterprise for industrialization stage test several times. In 2006, an enterprise in Henan realized the industrial scale production of 200 tons of ore per day. The process has the following advantages and disadvantages:

(1) Replacement of salt with calcium salt (lime, limestone) completely eliminates the problem of exhaust gas pollution of toxic and harmful gases such as HCl and Cl ₂ in the sodium roasting process. The calcium salt added during the calcination process (about 5%) basically reacts with the sulfuric acid in the leaching process to form a small amount of calcium sulfate precipitate. The advantage of the process is that the water-soluble ion content in the process water is low, which is beneficial to the recycling of the process water, according to Design calculation and industrial measurement, the process water recycling rate can reach more than 90%, with 90% cycle utilization of process water for long-term operation, the chloride ion concentration in the system can be controlled below 5g / L, does not affect the vanadium exchange process Enrichment of ions and ion balance of the system. For each ton of vanadium pentoxide produced, the process wastewater discharged or treated is only about 60 m ³ , which is one-fifth of the vanadium extraction process;

(2) The roasting material is low acid leaching (acid concentration 1-2%, sulfuric acid), low sulfuric acid consumption, acid consumption per 100 tons of ore is only about 4 tons, low production cost, less liquid impurities, and is beneficial to process water circulation use;

(3) The equipment investment is higher than that of the salt roasting process. The salt-baking process can be carried out by means of water immersion to obtain vanadium-containing liquid. SMEs generally use the direct ball immersion method, and the equipment investment is low. It is not necessary to consider the anti-corrosion problem, but some enterprises also adopt acid leaching method in order to improve the vanadium recovery rate. The calcification roasting process must adopt the method of acid leaching. The calcined material needs to be pulverized again, and then mechanically stirred and leached, and then the belt slag filter is used for slag separation. The process needs to consider equipment corrosion protection.

3. Other vanadium extraction process by fire method

Including blank calcination and vanadium extraction process, composite additive roasting and vanadium extraction process.

The blank roasting and vanadium extraction process is also called vanadium-free roasting and vanadium extraction process, and no additives are added during the roasting process. In the early 1990s, the Hunan Coal Research Institute and related enterprises researched and developed the technology. Currently, the technology is only used by individual enterprises in Huaihua City, Hunan Province. The total yield of vanadium in the ore is between 38% and 45%. Improved, the overall yield can be further improved. This process has a strong selectivity for ore, so this technology does not have the promotion value in the industry.

The composite additive roasting and vanadium extraction process is a modification of the vanadium extraction process and the calcification roasting vanadium extraction process, and does not belong to a single column of vanadium extraction process. Small experiments by the process, depending on the characteristics of the ore around, adding different firing process to determine the composition ratio of additives, such as sodium chloride, sodium carbonate, lime, ammonium chloride, manganese ore and so soft.

(2) Process for extracting vanadium by wet acid leaching

The wet acid leaching vanadium extraction technology refers to the leaching of vanadium in the ore by using a higher concentration of acid without roasting the ore. The acid is usually sulfuric acid. Some technical units are mixed with hydrochloric acid, and even the price is high, dangerous, and corrosive. Hydrofluoric acid (fluorinated salt) is very strong, and some oxidants are often added. The leaching process is usually carried out under heat and pressure, and if it is not pressurized, the cost is to increase the amount of the oxidizing agent or to use a more oxidizing oxidizing agent. The advantage of this process is that there is no smoke pollution problem in the roasting process. The disadvantage is that the investment is large and the production cost is high. Because the production process is very corrosive and requires high equipment, the investment is very large, and another major disadvantage of the process is that The amount of waste water is large, because the amount of acid used is large, and some heavy metals in the ore are dissolved in a large amount, and the composition of the wastewater is complicated. The technology also has certain selectivity for ore. In some enterprises, a wet process has been established. After the production, it has to increase the pre-baking in the pre-process. Even the technical unit has proposed the ore pre-baking-wet method. The process of extracting vanadium is contrary to the original intention of the vanadium extraction technology.

Second, the problem of stone extraction from vanadium

The extraction of vanadium from stone coal is a relatively young industry. It is still in a relatively backward situation in terms of process and equipment, and there is still a large space for technical and economic improvement.

(1) Selection of vanadium extraction process for stone coal

The choice of vanadium extraction process has always been a real problem in the industry. Scientifically speaking, in the face of complex and variable vanadium-containing raw materials, there is never a vanadium extraction process that is feasible in all directions. According to the different characteristics of stone coal, the appropriate vanadium extraction process should be selected through the system of metallurgical testing. . In addition, when determining the vanadium extraction process, the following factors need to be considered:

1. The industrial policy of the company's location for the extraction of vanadium from stone coal. In the provinces and cities where there are stone coal extraction vanadium industries, most of them have formulated similar industrial policies for the extraction of vanadium from stone coal. It is generally not allowed to use the sodium method to roast the vanadium extraction process for new enterprises, and even the flat kiln roasting equipment is not allowed. Some of these policies or regulations are disclosed in the industry in the form of clear documents, and some are in the form of inspection reports and development plans of relevant government departments as the guiding basis for project approval;

2. Environmental characteristics and environmental capacity of the project location. For areas that are particularly sensitive to water pollution, the vanadium extraction process by wet method and the vanadium extraction process by sodium method are used. Because the amount of wastewater is particularly large, it can be matched with the corresponding wastewater treatment equipment, but it must be especially cautious; areas that are particularly sensitive to air pollution. The use of fire roasting to extract vanadium should be particularly cautious;

3. Process reliability and maturity. The market for stone and vanadium extraction technology is quite chaotic, and various technologies are unconventional. Some enterprises have invested tens of millions of yuan but cannot produce products, or the technical and economic indicators are low. Whether a technology is mature and reliable, as a company should focus on whether the technology has been successfully applied in industrial practice, and the economics of a technology should be determined by the relevant technical parties to take the complete unit consumption table as the basis for judgment;

4. The price of sulfuric acid in the project site. In the process of extracting vanadium from stone coal, the raw material with higher dosage and lower value is sulfuric acid. The price of sulfuric acid varies greatly from region to region. If a sulfuric acid needs to be purchased long distance and the price is obviously high, a wet acid leaching is constructed. Vanadium plant, which will be uncompetitive in the industry;

(2) The technical level of the industry is not high, and the self-discipline is insufficient. The illegal small vanadium plant is banned, and the negative impact of society is large.

Since the emergence of the vanadium-bearing vanadium industry in the 1970s, environmental pollution incidents have accompanied the development of the industry. In the 1980s, it was the first major development period of the stone and vanadium extraction industry. All enterprises used the sodium method to roast the vanadium extraction process. After a series of environmental pollution incidents, a large number of township and village enterprises vanadium plants were closed, such as Hunan Province issued at that time. The elimination of the closure of the eight small enterprises behind the elimination. After 2004, the stone and stone extraction industry has once again achieved great development, but at the same time, environmental pollution incidents in various places have emerged in an endless stream, resulting in some places "talking about vanadium change." The negative social impact of the industry in the society is rooted in the substantial social harm caused by the illegal refining of vanadium, as well as some environmental incidents caused by the neglect of environmental protection by some legal refining vanadium plants. This negative impact is huge. It requires years of hard work in the stone and vanadium extraction industry to reverse the social image of the industry.

(3) The vanadium extraction process is basically mature, and the equipment support is relatively lagging

After 30 years of industrial practice and the efforts of R&D units, the process of extracting vanadium from stone coal is basically mature, but the equipment associated with this, especially large equipment and key equipment, is relatively backward, which has become a bottleneck for the development of the industry.

For example, roasting equipment, flat kiln is not a long-term plan, facing the ban, in the past two years, the rotary kiln was trial run in several factories, but none of them succeeded. The boiling furnace roasting failed to break through the large-scale, but the step-type roasting kiln was more Good progress has achieved industrialized daily roasting of 200 tons of mines, but there are also some shortcomings. The goal of the roasting equipment is to process 600 tons of ore per day for single-seat equipment, mechanized, in line with national environmental protection and sanitary standards;

In addition, the filtration and washing of the slurry has become a bottleneck in the industry. At present, the belt vacuum filter has run more than 20 sets in the industry and achieved good results, but still faces some technical problems. The outstanding performance is that the filtration capacity per unit area is low, resulting in a large filter area and length. In addition, the washing effect is not ideal, which requires the joint efforts of the process and equipment manufacturers.

In addition, in the face of the diversity of stone coal characteristics, the uncertainty of ball mill equipment selection, as well as stone coal pre-carbon removal equipment, are factors that restrict the development of the industry.

(4) Comprehensive utilization of vanadium-bearing coal resources

Stone coal is a kind of inferior anthracite with less carbon and low calorific value, and a low-grade polymetallic symbiotic ore. If only the vanadium is extracted and the comprehensive utilization of resources cannot be achieved, it will restrict the sustainable development of the industry in the long run. At present, it is more feasible to use the heat comprehensively. In a qualified enterprise or industrial park, the heat can be used to generate steam for other production facilities or to other enterprises, so that the device is simple and the investment is low; if it is used for power generation, investment Larger, and some stone coal heat is low may not be suitable for power generation. Another important issue in the comprehensive utilization of resources is the use of slag, which produces about 200 tons of slag per ton of vanadium pentoxide produced. There are many constraints on the comprehensive utilization of stone coal resources, but for long-term development, enterprises still need to carry out some forward-looking research and development work.

Third, stone coal extraction process

Although the vanadium extraction process of stone coal has developed into two major process routes, namely, the vanadium extraction process by fire roasting and the vanadium extraction process by wet acid leaching, each process has its advantages and disadvantages. I believe that the development direction of vanadium extraction process is the combination of these two technologies. In fact, some enterprises and research institutes have carried out relevant explorations in practice.

In terms of mineral properties, the ore can be oxidized and calcined in advance, which can damage the structure of the mineral to a certain extent, and facilitate the extraction of vanadium. At the same time, from the perspective of comprehensive utilization of resources, the ore roasting or combustion process can recover the thermal energy. Therefore, the pre-step of the vanadium extraction process should give priority to the roasting process; from the improvement of the total recovery of vanadium in the ore and the technical and economic level of the plant, the vanadium extraction process by fire roasting should be actively used for wet acid extraction. The technical experience of enhanced leaching of vanadium process, because the ore has been calcined at high temperature, the acid dosage can be significantly reduced when leaching, which is beneficial to reduce production costs, improve the recycling rate of process wastewater, and reduce the discharge or treatment volume of wastewater in the production process.

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