With the sustained and rapid development of China's social economy, the contradiction between supply and demand of mineral resources and mineral products has become increasingly prominent, and resource bottleneck constraints have become prominent. At present, the level of China's development and utilization of mineral resources is not high enough level of intensive use, and efficient utilization of technology over lean iron ore and table outside the mine behind a total, most have not been associated mineral resources, rational utilization of tailings and waste rock comprehensive Limited utilization. Relying on scientific and technological progress, strengthening the comprehensive utilization of mineral resources and promoting the development of mining circular economy are the most effective measures to alleviate the bottleneck of mineral resources and ensure the security of national resources. It is of irreplaceable significance for the sustainable development of China's economy and society.

I. Status and problems of the utilization of ultra-poor iron ore resources

At present, more than 90% of China's iron ore is poor ore, with an average grade of only about 30%. According to statistics, China has retained proven reserves of iron ore of 60 billion tons, of which the surface off-mine and super-poor mines are as high as 24 billion tons. Among the ultra-poor iron ore, magnetite ore accounts for 47%, vanadium- titanium magnetite ore accounts for 22%, hematite ore accounts for 21%, siderite ore accounts for 3.8%, limonite ore accounts for 2.7%, and symbiosis Mineral ore accounts for 3.5%. Due to the technical level and economic benefits at that time, on the one hand, in the existing mining process, most of the existing ultra-poor off-balance mines that were stripped out were piled up and unused; on the other hand, there are still a large number of The ultra-poor iron ore has not yet been developed and utilized. For example, heavy steel Taihe vanadium-titanium magnetite, low-grade vanadium-titanium magnetite resources have 107.177 million tons, grade 17.59%. The ultra-poor magnetite and ilmenite resources in the Ankang area of ​​Shaanxi are as high as 350 million tons, and the iron ore grade is mostly between 15% and 25%. In addition, according to incomplete statistics, there are still billions of tons of ultra-poor iron ore or off-balance ore that have not been exploited in the country. The use of low-grade iron ore has the following technical problems.

(A) low-grade iron ore grade is very low, near-mine ore was graded relationship with the surrounding rock, ore and rock ill-defined, with the current mature chunk of dry magnetic separation tailing or chunks of jigging technology, the beneficiation stone-grade general increase of only a few percentage points, while tailing a very small, iron metal is also a great loss.

(2) During the mining process, the ore loss rate and the waste rock mixing rate are difficult to control, which makes the grade of the selected ore difficult to control. In addition, the amount of off-balance sheet mineral resources is large. If the mining enterprises are in the process of mining, if the off-balance sheet mine is abandoned, it needs to occupy the dumping site and affect the environmental protection; if the surface ore is recovered, the ore grade will be reduced, which will greatly affect the grade of the ore concentrate. And metal recovery rate.

(3) The ore grade of ore is low, relatively difficult to choose and difficult to choose, and the ratio is large. If it is treated by conventional mineral processing technology , it will result in high cost of concentrate, poor economic benefit or loss of mine.

Due to the limitation of the sorting principle of dry magnetic separation equipment , the dry magnetic separation tailing effect of the ore is very poor under the finer particle size, and there is no mature high-efficiency wet magnetic separation equipment suitable for the tailing of finely divided products.

(4) If low-grade iron ore is selected after grinding, a large amount of fine tailings will be produced, which will increase the tailings treatment cost and cause environmental pollution. Therefore, the comprehensive utilization of tailings and reasonable stockpiling must be considered.

At present, foreign industrialized countries have hardly exploited ultra-poor and off-balance iron ore resources. Only a few countries have developed and utilized ultra-poor and off-balance iron ore resources. Domestic mining companies that use ultra-poor and off-balance iron ore are also rare, mostly in the stage of technical research and economic evaluation. For the difficult to choose ultra-poor, off-balance iron oxide ore, due to the high cost of mineral processing and technical difficulties, it has not been developed and utilized in China.

2. Analysis of ore properties and characteristics of existing iron ore resources in Chongqing Iron and Steel Co., Ltd.

Chongqing Iron and Steel is located in Chongqing in the southwestern region. The iron ore resources in Chongqing and its surrounding provinces and cities are very poor. The nature of the ore is not difficult to choose, and it is a super-poor magnetite resource with very low grade. The domestic iron ore base currently owned by Chongqing Iron & Steel Co., Ltd. is roughly divided into four parts: one is Xichang Taihe vanadium-titanium magnetite in Sichuan; the other is Xiaoyanghe magnetite mine in Xunyang, Shaanxi; the third is Wushan Peach Blossom Hematite; the fourth is Lijiang Chi-Roserite ore. The ultra-poor iron ore resources are mainly concentrated in the Xichang Taihe vanadium-titanium magnetite mining area in Sichuan and the Xiaojinhe magnetite mining area in Xunyang, Shaanxi. The ore situation and ore properties and characteristics of the heavy steel ultra-poor iron ore resources are as follows:

(1) Taihe vanadium-titanium magnetite

Taihe vanadium iron ore is one of the four major vanadium-titanium magnetite deposits in the Panxi area. The proven industrial reserves are 235 million tons and the prospective reserves are 350 million tons. Taihe Iron Mine began construction in 1971 with the approval of the former Ministry of Metallurgy. During this period, it experienced slow construction, expansion and reconstruction, and officially started production in 1988. At present, the construction of the 6.3 million t/a mining and expansion project of the ore has begun.

The ore mineral composition consists of oxidized minerals, silicate minerals and sulfide minerals.

Mineral oxide: titanium magnetite, ilmenite, followed by a lesser amount of magnesium aluminum spinel, and magnetite.

Titanium magnetite is the most important iron-bearing mineral in ore and contains a certain amount of titanium. Generally, it is semi-self-shaped, and its shape is distributed between other mineral particles, and the particle size is above 0.1-4. Its output can be divided into two types: early magma magnetite and magma late magnetite. Titanium magnetite is a solid solution continuous crystal composed of magnetite, stellite ilmenite, ilmenite, magnesium aluminate spinel and vanadium maghemite.

Ilmenite: It is self-shaped and his shape is distributed between the titanium magnetite and the citrate mineral particles. It often forms a granular crystal structure with the former, and sometimes contains each other. The particle size is 0.1 to 3.Omm.

Sulfide minerals: Sulfurs are commonly found in various ores, but they are not uniform, and the general content is 0.5% to 1%. Sulfides mainly pyrite and pyrrhotite, followed by a yellow copper ore, cobalt ore sulfur, nickel pyrite, marcasite; purple sulfur small amounts of iron nickel, cobalt-containing pyrite, needle Nickel and trace luminance diamond mines, sulfur, cobalt, nickel party, party chalcopyrite, vallerite, blue copper, sphalerite like. The pyrite particle size is 0.01 to 1.2 mm, and the pyrrhotite particle size is 0.01 to 0.7 mm.

3. Technical status and development trend of domestic use of ultra-poor iron ore

One of the ways to use resources efficiently is to reduce the ore grade and to recycle some of the non-economic reserves. One of the prerequisites for achieving this goal is how to achieve pre-selection and tailing, so that while reducing the ore grade and expanding the reserves of resources, the grade of the beneficiation is not reduced, and the production of ore dressing is not improved. Therefore, whether it is super-poor magnetite or ultra-poor iron oxide ore, it is necessary to use high-efficiency crushing and sorting equipment before the grinding, to seek better tailing effect, greatly improve the grade of human grinding ore, and adopt more thoroughly. The “multi-breaking and less grinding” method enhances the economic efficiency of ore dressing of ultra-poor iron ore.

(1) Dry pre-selection and throwing tail technology

For the lean magnetite with lower grade, most of the magnetite ore dressing plants at home and abroad adopt the method of coarse-grained dry magnetic separation and tailing, and abandon a large amount of tailings before the ore is put into the mill to increase the treatment capacity. Improve the quality of selected products and reduce production costs. However, for ultra-poor magnetite ore with a grade below 20.00%, due to the extremely low grade (the boundary grade is generally artificially defined), the grade difference between the ore and the surrounding rock is very small, the dry magnetic separator The distribution effect is not ideal. In addition, research and production practices have shown that, due to the limitations of raw magnetic separation equipment, even if the ultra-poor magnetite ore selected in the future is dry magnetically selected and tailed at a finer particle size, it cannot be completely Solve the problem of low grade, high tailings, high cost, low economic efficiency, and large loss of magnetic iron in tailings. Therefore, the use of ultra-fine crushing and wet magnetic separation tailing technology before the grinding is the development direction of the pre-selected throwing waste technology for ultra-poor magnetite ore in the future.

At present, Taihe Iron Mine and Xiaojinhe Magnetite use dry pre-selection tailing technology for the recovery and utilization of ultra-poor iron ore. The Maanshan Mine Research Institute of Sinosteel conducted a pre-selected tail-slip test on the off-balance ore and low-grade ore of Taihe Iron Mine, and classified four types of ore samples (primary, Fe ₃ , Fe ₄ and weathered). Dry pre-selection and throwing waste tests with different schemes and different conditions. In addition to the deep oxidation of the ore and the high pulverization rate of the ore (5mm yield is 53.34%), the other three types of ore samples have been discarded by dry pre-selection, and all have achieved ideal technical indicators. The primary ore can be thrown out of a pre-selected waste, which can produce 34.49% of waste rock. The grade of coarse concentrate is 22.68%, which is 3.5 percentage points higher than that of the ore. The Fe ₃ ore can be thrown out by the second section. The rate is 16.10% of waste rock, the grade of coarse concentrate is 22.74%, which is 1.52 percentage points higher than that of the ore. The Fe ₄ ore sample can be thrown out of waste by the second stage, which can throw a waste stone with a yield of 18.27%. It was 20.38%, which was 1.73 percentage points higher than that of the mine.

The Sino-Steel Group Maanshan Mine Research Institute conducted a dry pre-selection tailing test on the Xiaojinhe super-poor magnetite. When the original ore was selected to have a particle size of -15 mm, the CTL0806 powder ore dry magnetic separator was used for sorting. The magnetic field strength is 279 kA/m. The test conditions and test results are shown in Table 1. It can be seen that the sorting effect of the fine ore dry sorting machine is better than that of the magnetic pulley. The yield of dry-selected tailings is greatly increased, the grade of iron and magnetic iron is significantly reduced, and the whole iron grade and magnetic iron grade of dry-selected concentrate are also Greatly improved.

In short, the use of dry pre-selection tailing technology to recover the ultra-poor iron ore resources of Taihe Iron Mine and Xiaojinhe Magnetite has a general effect. In order to efficiently recycle resources, further research is needed to study better processes and recycling technologies. The results of dry sorting of fine ore are shown in Table 1.

Table 1 Test results of powder ore dry magnetic separator

(2) Grinding and sorting process

Because the grade of ultra-poor and off-balance iron ore is extremely low, the iron mineral inlay has a very fine grain size. In order to achieve energy saving and high quality of concentrate, the grinding and sorting process generally adopts multi-stage grinding. The principle process of phase selection. The selection process of magnetite is mainly based on weak magnetic separation and fine screening. If it is necessary to further improve the quality of magnetic separation concentrate, a weak magnetic separation and reverse flotation combined process can be used. In terms of flotation reagents, although significant progress has been made in the reverse flotation reagents for Anshan-type quartz -type iron ore, there are still few or blank high-efficiency reverse flotation reagents suitable for other types of iron ore. In order to throw out a large number of tailings at the same time, and at the same time ensure as much as possible without losing useful iron minerals, the relevant iron ore beneficiation plant basically carries out optimization research from grinding and sorting technology. Foreign countries tend to grind a ball mill grinding program. The relevant iron ore dressing plants that have been produced in China basically adopt the ball mill-ball mill grinding scheme, that is, the ball mill is used as the grinding equipment for rough grinding and magnetic separation tailing, and the grinding cost is higher than that of the rod mill. Although the use of grinding and wet magnetic separation technology can achieve the purpose of discarding a large number of coarse tailings in advance, it cannot completely solve the fundamental problem of high energy consumption and high cost of mineral processing.

(3) Coarse grain wet magnetic separation technology

At present, the conventional crushing system of the domestic concentrator has been able to reduce the particle size of a section of ore milled to below -12 mm, or even -8 mm. According to preliminary statistics, when the particle size of magnetite ore is broken to about l0mm, 10% to 30% of the gangue minerals have been dissociated, which can be discarded as qualified tailings. If this part of the gangue mineral can be removed in time and effectively, it can not only improve the grinding grade of the ball mill, increase the processing capacity of the mill, but also achieve the purpose of energy saving, consumption reduction and efficiency improvement, and the part of the coarse veins that are thrown away. Stone does not have to enter the tailings pond, which can greatly extend the service life of the tailings pond. At the same time, grinding equipment is also developing in the direction of large-scale. These favorable conditions lay the foundation for the research, popularization and application of coarse-grain wet magnetic separation technology. The Maanshan Mine Research Institute has developed a patented high-efficiency coarse-grained wet magnetic separator (for pre-grinding). The main technical performance indicators of the equipment: 1 processing material particle size 0 ~ 20mm; 2 equipment processing capacity 80 ~ 200t / h; 3 tailing yield > 15%; 4 magnetic iron loss rate ≤ 1%; cylinder surface magnetic induction 300 ~500MT; 5 cylinder, tank use period ≥ la.

The key technology that has not been prepared is a breakthrough in the conventional wet magnetic separator, which has poor coarse magnetic separation effect, easy wear of the cylinder, blockage of the tank and low concentration of concentrate. The above problems of the conventional wet magnetic separator are solved by the improvement of the magnetic structure, the formation of the composite cylinder by the barrel and the wear-resistant material, the design of the novel sorting tank structure, and the forced flushing water discharge facility.

(4) High-efficiency rolling superfine crushing technology

Since the energy consumption of grinding accounts for more than 80% of the entire grinding operation, the “multi-grinding and grinding less” technology has always been one of the most concerned focuses at home and abroad. Rolling technology is currently recognized as the most advanced high-tech crushing technology. . High-efficiency rolling technology is a high-tech crushing technology developed by Germany in 1984. It has been successfully applied to many factories in the world, mainly cement and limestone plants. In recent years, foreign roller presses have been used in iron ore beneficiation plants, but they are still in the process of research and development or introduction and digestion in China. The device has the characteristics of low energy consumption per unit crushing, fine and uniform granularity of the crushed product, small floor space, high equipment operation rate and long working life of the wear parts. Therefore, the high-efficiency rolling technology is the development trend of the “multi-breaking and less grinding” technology in the future, and is the key technology for the efficient and comprehensive utilization of ultra-poor and off-balance iron ore.

The Maanshan Mine Research Institute of Sinosteel and the Hegang Taihe Iron Mine have carried out experimental research on high-efficiency rolling and ultra-fine crushing technology for Taihe iron ore surface ore and low-grade refractory ore. The test is currently underway. The results of the phase test show that the unit energy consumption is 1.4~1.6kW/t when the fine crushed product is closed by the roller press, achieving the effect of high efficiency and energy saving. According to the roll surface wear test results, the working life of the roll surface can reach 10000h. After the low-grade vanadium-titanium ore is fully dispersed by the ultra-high pressure roller compactor, the wet-process magnetic separation tail can increase the grade of the ore milled from about 18.00% to 38.64%, and the yield in advance is 45.80%. 7.31% of coarse tailings, the effect of early tailing is very significant. For tailings of about 3 to Omm, some coarse particles can be separated by classification method, which can be used for construction sand or storage, which can greatly reduce the tailings transportation volume, and the economic benefits and environmental benefits are obvious.

If Taihe Iron Mine uses high-efficiency rolling ultra-fine crushing technology to achieve semi-industrial or industrial test success, Taihe Iron Mine's 3 million t/a mining and expansion technology transformation project will reduce the land pressure required for its project and facilitate drainage Stability of the soil field; increased total ore, extended mine service life; reduced waste discharge, environmental protection; improved resource utilization; local labor employment; a above. Low-grade vanadium-titanium magnetite in Panxi area accounts for about 3 billion tons, and ultra-poor magnetite and ilmenite in Ankang area also have 300-500 million tons. If pre-selected tail-selling technology can be promoted, economic and social benefits are immeasurable. .

Fourth, recommendations and countermeasures

(1) In order to ensure the utilization of resources, economic benefits and environmental benefits for the ultra-poor iron ore resources of different properties of heavy steel, joint research with domestic institutions and scientific research institutions. Before the development and utilization, it is necessary to carry out reasonable process optimization research, and carry out comprehensive technical and economic analysis to determine a reasonable selection grade and product plan.

(II) Through the introduction, digestion and absorption and technological innovation, strengthen the research and development and popularization of rolling ultra-fine crushing technology and coarse-grain wet magnetic separation technology, in order to truly realize the concept of efficient utilization of ultra-poor iron ore resources and energy conservation and emission reduction.

(3) In order to make rational use of weak magnetic iron ore resources such as ultra-low hematite, large-scale high-efficiency coarse-wet strong magnetic separation equipment should be developed to fill the blank of wet magnetic separation and tailing technology of weak magnetic iron ore in China. At the same time, it solves the problem of comprehensive utilization of low-grade ore of heavy steel peach flower hematite and Chajiang-style Chiyiling iron ore.

(IV) In order to reduce the storage of coarse tailings and the discharge of fine tailings and reduce the impact of tailings on the environment, the research and application of new technologies for comprehensive utilization of tailings should be strengthened.

Tungsten Carbide Roller

Tungsten carbide roller has characteristics of good wear resistance, high temperature red hardness, thermal fatigue resistance and thermal conductivity and high strength , have been widely used in high-speed wire rod, bar, rebar, seamless steel tubes, etc. Domestic production of tungsten carbide roller materials mostly WC- Co, WC- Co- Ni- Cr two series, and the content of Co, Co- Ni - Cr is in the range of 6wt% ~ 30wt%. From the use of perspective, tungsten carbide rollers has good mechanical properties, its flexural strength up to 2200 MPa or more, shock toughness up (4 ~ 6) × 10^6 J/ m^2, Rockwell hardness (HRA) is up to 78 to 90, widely in the high-speed wire rod rolling process, which is much higher than single-slot chilled cast steel or high speed steel rolls.Tungsten carbide is made of Tungsten Carbide Powder and binder phase (such as drilling, nickel, etc.), and then pressing and sintering, regardless of the conditions under cold rolled or hot rolled has excellent wear resistance, tungsten carbide rollers has been widely used in pre-finishing mill and finishing of high-speed wire rod currently. On the performance of tungsten carbide roller in hot-rolling wire rod , the material must meet the following requirements:
1. Sufficient anti-fracture strength;
2. Good abrasion resistance;
3. The smooth surface finish;
4. Excellent corrosion resistance, thermal fatigue, thermal cracking performance.
Tungsten carbide roller rings can working in bad conditions , small profile rolling (especially rebar rolling) process conditions is harsher than the high-speed wire rod, and therefore corresponds to the profile rolling ,tungsten carbide rollers recommend using high binder phase carbide.