Characteristics and sintering of vanadium-titanium magnetite concentrate

I. Overview
Vanadium-titanium magnetic iron ore is a multi-metal complex ore elements are iron, vanadium, titanium-based symbiotic magnetite. Panzhihua Mine is a vanadium-titanium magnet concentrate after magnetic separation. Because it is a grinding process, the particle size is very coarse. The content of the concentrate is less than 0.074mm, and the content is only 35% to 40%. From the chemical composition, TiO 2 is as high as 12%~13%, iron grade is only about 51.5%, Al 2 O 3 is also high, up to 4.5%. Due to the special physicochemical properties of vanadium-titanium magnetite concentrate, some vanadium-titanium magnet concentrates are sintered. Special.
Second, the characteristics of vanadium-titanium magnet concentrate
The main features of vanadium-titanium magnet concentrate obtained by a series of grinding magnetic separation are:
(1) The concentrate has a coarse particle size. Concentrates less than 0.074mm account for 30% to 40%, and the surface of the particles is flat and the edges are smooth. The difference in size is small and the sphericity is poor, resulting in poor gas permeability of the sintered layer and low sintering utilization coefficient. Effective measures to strengthen ordinary concentrate granulation, used to strengthen Panzhihua vanadium-titanium magnet concentrate granulation, the effect is poor.
(2) The grade of concentrate iron is low. The theoretical iron content of vanadium-titanium magnetite itself is low, and the gangue minerals in titanium magnetite are difficult to select. This is the reason for the low grade of vanadium-titanium sinter and the large amount of smelting slag.
(3) The magnetite concentrate has a low content of SiO 2 and a high content of TiO 2 . Due to the low content of SiO 2 in the concentrate, the amount of liquid phase generated during sintering is insufficient, and the sintered ore is difficult to be well bonded; the high content of TiO 2 not only reduces the iron content of the sintered material, but also has a high sintering temperature and, at the same time, The formation of CaO•TiO 2 is not conducive to the consolidation of sinter, resulting in vanadium-titanium sintered ore with high brittleness, poor strength and high returning ratio. This is another important reason for the low utilization coefficient of sintering of vanadium-titanium sinter.
(4) The content of Al 2 O 3 is high. This has an adverse effect on the strength of the sinter and the high and low temperature reductibility.
These characteristics are closely related to the mineral composition of the ore and the beneficiation process, which determines its sintering properties.
Third, vanadium-titanium magnet concentrate sintering
Vanadium-titanium magnet concentrate is the main iron-containing raw material for sintering. It accounts for 70%-80% of the production of Panzhihua Iron and Steel, and the remaining iron-containing raw materials are ordinary ore-rich powder. Domestic iron ore grades are lower.
(1) Characteristics of sintering production of vanadium-titanium magnet concentrate 1. Difficulties in sintering of vanadium-titanium magnet concentrate Concentration of vanadium-titanium magnet concentrate is:
(1) The sphericity is not good, the pellets have low heat strength, and the material layer has poor gas permeability. Concentrate spheroidality is related to hydrophilicity, grain size, coarse-grain fraction, particle surface roughness, porosity and other factors.
The heat of wetting of Panzhihua vanadium-titanium magnet concentrate is large, indicating that its hydrophilicity is good, but its particle size is too coarse. The concentrate content is less than 0.074mm, the concentrate content is only about 35%, and the specific surface area is only 491.1723cm 2 /g. The rate is low, and the sphericity index is the smallest without adding any binder, indicating that the sphericity is the worst.
In addition, the quasiparticle strength in the granulated mixture is extremely poor when no binder is added. The resistance losses of the sinter zone, combustion zone, pre-tropic zone and over-wet zone during sintering are 1176Pa, 3332Pa, 4312Pa, 1960Pa, and the pre-tropical zone is the thinnest, but the resistance is the largest, which indicates that when heated and squeezed, The particles are heavily pulverized, which inevitably affects the permeability of the entire layer.
(2) The sintered ore has poor strength and low yield. Due to the high content of TiO 2 and Al 2 O 3 in Panzhijing and the low content of TFe and SiO 2 , the current fusion-type sintering method produces only 15% of the common silicate binder phase in the sintered ore. 20%, perovskite itself has low compressive strength, only 1/4 of the composite ferrite (SFCA). Moreover, the perovskite has a high melting temperature and a small surface tension, which is first precipitated during the sintering process and filled. Between the silicate, titanomagnetite and titanium hematite grains, the porosity of the sintered ore is high, and the adhesion between various minerals is weakened. Therefore, the strength of the sintered ore is poor and the yield is low. [next]
2. Characteristics of sintering production of vanadium-titanium magnet concentrate Concentrate production of vanadium-titanium magnet concentrate is characterized by low utilization coefficient and strength, high energy consumption for returning ore and process.
Before the production of Panzhihua Iron and Steel Co., Ltd., Panzhihua and Chengde vanadium-titanium-iron concentrate were used for sintering test. The results show that the coefficient is only 1.0t/(m 2 •h) without strengthening measures. The design utilization factor of Panzhihua Iron and Steel Co., Ltd. is 1.08t/ (m 2 •h), from commissioning to 1982, the coefficient has been hovering around 1.0t/(m 2 •h). Later, a series of intensified measures were adopted to gradually increase the utilization factor to 1.15h/(m 2 •h) through research and application. In 1999, it has reached 1.275t/(m 2 •h). In comparison, the utilization factor is low. This indicates that the strengthening of the vanadium-titanium magnetite concentrate is much more difficult than that of the ordinary concentrate, which is mainly due to the poor gas permeability of the mixture. The main factor affecting the gas permeability is the coarse grain size of the concentrate. Due to the coarse particle size and poor sphericity of the mixture, the permeability of the material layer is inevitably poor. Researchers have conducted a compression test on a mixture of particles larger than 3 mm. The results show that there are almost no smaller spheres larger than 3 mm formed by the concentrate itself. All the balls larger than 3mm are formed by returning ore, rich ore powder, limestone powder and coke powder particles. The mixture of more than 3 mm is washed with water, the adhered concentrate powder is washed away, and then the skeleton particles are dried and classified, and the detected skeleton particles of more than 3 mm are detected, and only 10% to 15% of the particles smaller than 3 mm are detected. It is indicated that particles smaller than 3 mm are difficult to form particles larger than 3 mm. Most of the particles larger than 3 mm in the mixture come from the return mine and the fine ore.
Due to the low strength of the sinter, the vanadium-titanium magnetite concentrate is actually sintered at a high return amount. In order to eliminate the vicious cycle of returning ore and balance the returning amount at an appropriate level, measures such as increasing the thickness of the layer as much as possible, ensuring the flattening and burning to improve the yield, controlling the range of suitable FeO content, and regularly changing the sieve plate are adopted. In the cold return mine, the part larger than 5mm is not more than 15%, the hot returning amount is not more than 10%, and the returning rate has dropped from 50% in 1990 to 30% in 1999.
The long-term production of vanadium-titanium magnet concentrate sintering shows that the mixture contains low carbon, generally 2.8% to 3.0%, but the process energy consumption is relatively high. From the analysis of process energy structure, accounting for 81.06% of solid fuel consumption, gas consumption accounted for 4.24% of coal, electricity accounting for 14.04%, others 0.66% high solids fuel consumption, mainly due to low yield, large amount of return fines, The calorie consumption is on the returning cycle; in addition, because the material layer is thin (the material layer reaches 450mm in 1999), the automatic heat storage of the material layer is not good, and the heat utilization is poor.
3. Vanadium-titanium magnet concentrate sintering process Vanadium-titanium magnetite concentrate sintering has the characteristics of "low-silicon" hard-burning, and the formation of TiO 2 (12% ~ 13%) is different from ordinary low-silicon sintering. In the operation, the suitable moisture and carbon content of the mixture are low, the ignition temperature is high, and the material layer is thin. The actual production operation can be summarized as follows: high wind, low water, low carbon and thin material layer.
(1) Gale. The sintering process must have sufficient air flow through the layer to meet the needs of fuel combustion and physicochemical reactions. The vanadium-titanium magnetite concentrate contains high FeO (30% to 31%), while the FeO in the sintered ore is low. Therefore, in the sintering process, the titanium magnetite is oxidized to form titanium hematite, which requires more oxygen. According to theoretical calculations, sintering of per ton of vanadium-titanium magnet concentrate consumes 39 m 3 of air more than ordinary concentrate. Considering the air excess coefficient and the air leakage rate, the unit consumption air volume is 150 m 3 . Therefore, according to the practice of vanadium-titanium magnet concentrate sintering, the design must take into consideration the high air consumption.
(2) Low water. Vanadium-titanium magnet concentrates are suitable for lower moisture than ordinary concentrates. Mainly due to the fact that the titanium-containing minerals are mainly composed of titanium magnetite, the structure is dense, the hydrophilicity is poor and the wet capacity is small. According to the results of the Xichang sintering test, the suitable moisture content of the mixture is 5.6%-6.5% under the condition of no preheating, and 7.0%-8.0% under the condition of steam preheating. The suitable moisture controlled by the actual production of Panzhihua Iron and Steel is 7.0. %about. According to the characteristics of strong vanadium-titanium magnetite sintering, the water is added to the water once to 7.0%, and a small amount of secondary water is added to maintain a stable gas permeability.
(3) Low carbon. The vanadium-titanium magnet concentrate has a lower carbon content than ordinary concentrate. The main reason is that the amount of liquid phase generated during sintering is small, the iron concentrate contains high FeO, and the oxidation exotherm is more when sintering, the water evaporation of the mixture and the heat consumption of vaporization are less, so the fixed carbon content of the mixture is low, generally about 2.8%. .
(4) The material layer is thin. The vanadium-titanium magnetite concentrate has a poor sphericity and a thinner layer during sintering. Despite the research and the adoption of a series of measures to increase the thickness of the layer, the layer was increased from 240mm in the 1980s to 450mm in recent years, but it is still lower than the thickness of 500-550mm in domestic mines.
4. Strengthening of sintering of vanadium-titanium magnetite concentrate In order to strengthen the sintering of vanadium-titanium magnetite concentrate, effective measures for sintering ordinary concentrate have been taken, but the sintering utilization coefficient is only increased to 1.275t/(m 2 •h). It shows that the strengthening of the vanadium-titanium magnet concentrate sintering is difficult. The strengthening measures are as follows:
(1) Application of the loose feeder. In 1982, a double-layer submerged pipe loosener was installed, which was later modified into a three-layer submerged pipe loosener, and then changed into a flat steel type loosener, which increased the material layer by 40-60 mm and increased the yield by 2%. Solid fuel savings of 1.2kg / t.
(2) Strengthening sintering with quicklime. Ordinary concentrates are sinter-sintered with slaked lime and quicklime. Since the early 1960s, they have been effective and have been popularized so far. Researchers have conducted intensive sintering experiments on vanadium-titanium magnetite concentrates in related factories in Chengde, Beijing, Xichang, etc. The results show that the use of quicklime or slaked lime accounts for 40% of the melt dose, and the yield increase effect is 10%-18%. In the industrial test of slaked lime in 130m 2 sintering machine, the dosage is 50% of the total melting amount, the material layer is increased by 30~40mm, the output is increased by 13%~17%, the sinter drum index is increased by 2%, solid Fuel consumption is reduced by 10%. In 1998, quicklime was put into use, with a ratio of 4.5% to 5.0%, an increase of 6% to 8%, and a reduction in solid fuel consumption of 5 kg/(t mine). Quicklime mainly plays the following roles:
1) Improved the original gas permeability of the sintered mixture. The hydrated colloidal colloidal particles after lime digestion are extremely fine, the average specific surface area is up to 30m 2 /g, the dispersion is high, and the cohesive force is strong, which greatly improves the spheroidization and granulation of the concentrate, and the particle size of the mixture is less than 3mm. Dropped by about 10%, so that the vertical sintering speed increased from 19.58mm / min to 20.3mm / min.
2) Improved thermal stability of the quasiparticles. Due to the water absorption and water retention of the finely dispersed hydrated colloidal particles and the heat shrinkage, the formation of the overwetting layer is alleviated during the sintering process, thereby reducing the breakage of the quasiparticles in the overwetting layer. When the quicklime is used, the super wet layer is less than 0.8 mm. The particles are only 37.29%, and when using limestone, they reach 71.89%. In addition, when the quasi-particles are heated, the colloidal particles in the quasi-particles are close to each other, and the strength is not as low as that of the ordinary quasi-particles. Increased.
3) Improved sintering reaction conditions of the material. When using quicklime, CaO directly contacts with various other minerals, promotes solid-liquid reaction, reduces free CaO, and is beneficial to the crystallization of various minerals, thereby improving the quality of the sintered ore. [next]
(3) High negative pressure sintering. In order to study the high negative pressure strengthening effect of vanadium-titanium magnetite concentrate sintering, in 1986, the negative pressure of the smoking machine was increased from 11760Pa to (14210±490)Pa, the thickness of the corresponding material layer was increased from 281mm to 307mm, and the machine speed increased by 54mm/min. The main pressure of the main pipe increased by 666Pa. The actual output increased by 6.09t, the drum index increased by 2.9%, and the solid fuel consumption (standard coal) decreased by 0.38kg/t. The whole plant has promoted high vacuum sintering.
(4) The use of coal char is divided. The solid fuel for sintering in Panzhihua Iron and Steel Co., Ltd. is coke breeze and anthracite powder. When mixed and mixed, it is difficult to achieve the proper particle size due to the large difference in crushing performance between the two. In order to prevent the excessive pulverization of the anthracite or the excessively large particle size of the coke powder and the difference in the combustibility of the pulverized coal and the coke powder and the difficulty in stabilizing the ratio between the two, the fluctuation of the sintering process and the utilization of heat are not exerted. For this reason, coal and coke are broken and used. Practice shows that the separation and utilization are beneficial to the sintering process, the energy saving effect is remarkable, and the solid fuel consumption (standard coal) drops by 5.4kg/t.
(5) Application of secondary fuel addition technology. Domestic and foreign studies have proved that the secondary fuel addition process can improve fuel combustion conditions and has obvious energy-increasing effects. The use of this technology in the sintering of vanadium-titanium magnet concentrate has also achieved the effect of increasing production and reducing consumption. Panzhihua Iron and Steel Co., Ltd. carried out industrial tests in 1995. In 1997, it was officially promoted and applied on two sintering machines. The fuel addition ratio was 50:50, which achieved a good effect of increasing production by 6.17% and reducing consumption (standard coal) by 1.04kg/t. And the coke powder addition effect is better than anthracite.
(6) Further increase the temperature of the mixture. Vanadium-titanium magnet concentrate sintering due to poor gas permeability of the material layer and slow vertical sintering speed, in order to further improve the gas permeability, the steam preheating mixture method in the ore tank is adopted to make the temperature of the mixture reach above 70 °C, which reduces the damage of the over-wet layer. The permeability of the material layer is further improved.
(7) Sintered sprayed halides. Vanadium-titanium sinter contains TiO 2 (up to 8.9%-9.0%) and Al 2 O 3 , and the low-temperature reduction pulverization rate is as high as 52.75%, which seriously affects the permeability of the blast furnace column. In view of this, Panzhihua started sintering the finished product in 1995. The mine is sprayed with a halide solution to reduce the low-temperature reduction pulverization rate of the sinter to less than 20%. The blast furnace uses spray-salted sinter to increase the yield by 4% to 8%, and the focal coke is 1.3 to 2.4 kg/t. The amount of gas ash blown out is significantly reduced.
(8) Oxygen-enriched ignition. Increasing the oxygen concentration of the ignition combustion air improves the combustion efficiency of the ignition gas and strengthens the sintering process. After the vanadium-titanium ore is sintered by oxygen-enriched ignition (enriched oxygen level is 24.4%), the yield and utilization coefficient increase.
(9) Hot air sintering. The vanadium-titanium ore is hot air-sintered with a hot air temperature of 140 ° C, the hot air area is 1/4 of the sintered area, the surface sinter strength is increased, and the yield is increased by about 1%.
(10) Reduce the gap in the transportation process of finished products. Due to the presence of the mineral structure TiO 2 •CaO, the vanadium-titanium sinter causes the sinter mineral to be brittle and is not resistant to hitting. Because Panzhihua Iron and Steel Co., Ltd. is located in the mountainous area, the sintering machine and blast furnace are not arranged on one plane. The transportation distance is long and the drop is large. For example, the difference between the No. 6 sintering machine and the No. 4 blast furnace is as high as 60m, so the finished ore is transported. After multiple transfers and beats, the average particle size is greatly reduced. Especially for vanadium-titanium sinter, the drop difference means reducing the sinter beating, which means that the sinter yield is increased and the output is increased. In the past 10 years, many methods have been used to improve the process, reduce the drop of sinter in the transportation process, reduce the drop of more than 20 meters, and increase the particle size of sinter by more than 5%.
(11) Add steel slag powder technology. The steel slag composition of Panzhihua Iron and Steel Co., Ltd. is characterized by: 1.5% V 2 O 5 , and its mineral composition mainly includes: 1) tricalcium silicate, accounting for about 50% of the volume; 2) vanadium calcium titanium oxide [Ca(TiV) 2 O 7 ], about 30% of the volume; 3) Magnesium iron ore, accounting for 15% of the volume. Panzhihua Iron and Steel Sintering and Steel Slag Powder Technology was put into industrial application in 1988. When 80kg of steel slag powder is added per ton of sinter, it has an effect of increasing production by 2.97% and improving the storage performance of sinter. The granulated content of less than 5mm after 7 days of storage without slag is increased by 4.5%, and only after adding steel slag The increase of 1.74%. When each sintering machine is equipped with 3% steel slag powder, the consumption of limestone powder decreases, the energy consumption of the process decreases by 1.55kg/t, and the drum index increases by 0.93%. The main reasons for achieving the above effects are: 1) Steel slag The powder is coarser, the slag powder larger than 3mm accounts for about 30%, and the average particle size is 2.14mm. After being added into the sintering mixture, the particle size composition of the mixture is improved, and the particle size content of more than 3mm is increased by about 5%, thereby improving Breathability of the material layer; 2) Most of the steel slag powder is low-melting silicate mineral. After replacing part of the limestone powder into the sintering mixture, the melting point of the mixture can be reduced, and the decomposition process of the replaced limestone powder and the required The heat can improve the conditions of the solid and liquid phase reactions, accelerate the sintering speed, and increase the sintering strength. In addition, after adding steel slag, the amount of free CaO in the sinter is reduced, so that the storage performance can be improved.
(12) Thick material layer technology. Increasing the thickness of the layer can play the role of automatic heat storage of the thick layer, prolong the high temperature retention time of the layer, and ensure the formation of various slag phases and the development of various crystal phases. In addition, the carbon content can be reduced, the oxygen level of the layer atmosphere can be increased, thereby inhibiting the growth of the perovskite and developing a high-quality ferrite binder phase. Therefore, sintering thick layers is an important way to improve the quality of sintered ore.
Since the production of Panzhihua Iron and Steel Co., Ltd., various measures have been taken to improve the gas permeability of the mixture, and the thickness of the material layer has been continuously increased from about 200 mm at the initial stage of production to about 440 mm in 1999.

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