(A) poor weakly magnetic iron ore reducing magnetic roasting Reductive magnetization roasting is one of the effective methods for treating weakly magnetic lean iron ore. Main various coal gas, natural gas and coke, pulverized coal as reductant other industrially primarily from reduction of CO, H 2, and C. The equilibrium diagram of Fe-CO-O 2 and Fe-H 2 -O 2 in the hematite reduction roasting process is shown in Figure 5. The figure is the equilibrium curve with carbon monoxide reduction and the dashed line is the equilibrium curve with hydrogen reduction. . It can be seen from the figure that: (1) Fe 2 O 3 is easily reduced to Fe 3 O 4 at almost any temperature, but the reaction rate is low when the temperature is low; (2) If the temperature is higher than 572 ° C, if CO% ( Or when H 2 %) is high, an over-reduction reaction may be generated to form weak magnetic FeO; (3) when the temperature is lower than 572 ° C, if CO% (or H2%) is high, an over-reduction reaction may also be generated to generate gold. It is iron. Therefore, the furnace temperature and gas flow rate should be strictly controlled during the reduction roasting, and the baking time should not be too long. When the temperature is lower than 810 ° C (the intersection of curves 2 and 6), the carbon monoxide has a lower reduction ability than hydrogen. The intersection of curves 2, 3, 4, 5, 6, 7, 8 corresponds to 572 ° C. When the temperature is lower than 572 ° C, no ferrous oxide is formed regardless of the gas phase composition. When the temperature is higher than 572 ° C, the temperature is higher. Gao Yu is easy to produce ferrous oxide FeO. 3Fe 2 O 3 +CO→Fs 3 O 4 +CO 2 Where R—reducing the degree of reduction of the calcined ore; The relationship of K p -T in the range of 500 to 1000 ° C is shown in Fig. 6. Since the reactions (5) and (6) are extremely easy to carry out in the temperature reaction range, the two reactions are not shown. As can be seen from the graph, the reaction formulas (1) to (6) are much larger than the equilibrium constants of the reactions (7) to (10), so the control gas phase composition %CO 2 /%CO is greater than 2.53. When the nickel-containing laterite ore is reduced and calcined, a multi-layer baking furnace is generally used in foreign countries, and a rotary kiln can also be used. Industrial tests using boiling furnaces in China have also achieved good targets, and the calcination temperature is 710-780 ° C. The calcine after reduction should be protected by air cooling to prevent it from being reoxidized by air. Tests have shown that the effect of nitrogen-tight sealed cooling is the best, and the effect of carbon dioxide protection cooling is second. [next] Clutch Release Bearing For VOLVO Clutch Release Bearing For Volvo,Car Release Bearing,Release Bearing,Clutch Plate Release Bearing Hangzhou Kangxin Bearing , https://www.cnkxb.com
Limonite (2Fe 2 O 3 · 3H 2 O) first removes water of crystallization during calcination and is then reduced to magnetite like hematite. For siderite, it can be decomposed into magnetite by neutral magnetization roasting:
For pyrite, only oxidative magnetization roasting can be used. Under a oxidizing atmosphere, pyrite can be oxidized to pyrrhotite by short-time calcination, and further roasted to magnetite after prolonged calcination:
7FeS 2 +6O 2 →Fe 7 S 8 +6SO 2
3Fe 7 S 8 +38O 2 →7Fs 3 O 4 +24SO 2
The reduction magnetization roasting process is mainly used to treat lean hematite. Neutral magnetization roasting and oxidative magnetization roasting are mainly used to remove siderite and pyrite from other concentrates (such as phosphate concentrates, rare metal concentrates, etc.).
The degree of reduction in production is commonly used to measure the quality of magnetized roasting products. The degree of reduction is the ratio of the ratio of ferrous oxide content to total iron content in the reduced magnetized roasting ore:
FeO—reducing the content of ferrous oxide in the calcined ore, %;
TFe—reducing the content of total iron in the calcined ore, %;
The degree of reduction of magnetite is 42.8%. According to the ore properties and sintering conditions of China's Angang Sintering Plant, it is considered that when R=42～52%, the magnetism of sinter is the best and the selection index is the highest. However, it should be pointed out that the reduction index can not truly reflect the quality of the roasting ore, but this method is simple and easy to implement, and has certain practical value.
The main factors affecting the quality of the reduced calcined ore are the ore properties (mineral composition, structure, particle size composition), calcination temperature, gas phase composition and reducing agent type. It is generally believed that the ore-like structure of the ore is denser, silt-like and tuberculous, and the iron ore mainly composed of quartz is easy to be reduced. The size of the ore is small and easy to be reduced. The size range of the ore should not be too wide. It is considered that 75 to 20 mm is ideal, and the lower limit of the temperature of the reduction roasting is usually 450 ° C and the highest temperature is preferably lower than 700 to 800 ° C. The porosity is small. When the coarse ore having a large particle size or a solid reducing agent is used, the reduction temperature is generally 850 to 900 °C. If the temperature is too high, it will easily generate weak magnetic iron silicate, which will soften and fuse the charge and affect normal operation.
Mixed gas is commonly used as a reducing agent in production. It not only obtains better sorting index, but also benefits the gas balance of the entire metallurgical enterprise and reduces capital investment. [next]
(B) reducing the calcined nickel-containing laterite ore containing nickel laterite nickel oxide ore is the largest resource, but the low-grade nickel, nickel was present disseminated, not currently enriched by physical beneficiation methods. In the industry, nickel can be recovered by direct acid leaching or reduction roasting and low pressure ammonia leaching. Direct acid leaching requires high temperature and high pressure equipment and is not widely used. Reduction calcination-low-pressure ammonia leaching is a method in which nickel oxide is previously reduced to a metal nickel, cobalt or nickel-cobalt-iron alloy which is easily soluble in a NH 3 -CO 2 -H 2 O-based solution by calcination, and then subjected to low-pressure ammonia leaching. This process appeared in 1924 and was used in industrial production in 1944.
A common gas reducing agent (a mixed gas of CO-CO 2 and H 2 -H 2 O) is subjected to selective reduction roasting, and the main reaction is as follows:
NiO+H 2 =NI+H 2 O (1)
NiO+CO=Ni+CO 2 (2)
CoO+H 2 =Co+H 2 O (3)
CoO+CO=CO+CO 2 (4)
3Fe 2 O 3 +H 2 =2Fe 3 O 4 +H 2 O (5)
3Fe 2 O 3 +CO=2Fe 3 O 4 +CO 2 (6)
Fe 3 O 4 +H 2 =3FeO+H 2 O (7)
Fe 3 O 4 +CO=3FeO+CO 2 (8)
FeO+H 2 =Fe+H 2 O (9)
FeO+CO=Fe+CO 2 (10)
H 2 O+CO=H 2 +CO 2
2CO=CO 2 +C
The equilibrium constants of the reactions (1) to (10) are: At 2.45, the nickel-cobalt oxide is preferentially reduced to metallic nickel-cobalt, and most of the iron oxide is reduced to magnetite without generating metallic iron. Since the bonding state of metal oxides in the ore is complicated and the reaction speed is increased, the above ratio used in production should be correspondingly smaller. When %CO 2 :%CO=1:1, a small amount of ferrous oxide is inevitably formed. Metal iron.
Reduction roasting can also be used for the decontamination and selection of refractory coarse concentrates. For example, the reduction roasting of tin concentrate can eliminate the side reactions of non-volatile arsenic pentoxide , arsenate and heavy metal sulphate, which can transform iron. It is an easily immersed ferrous oxide. Foreign tin concentrates often use multi-hearth furnaces and rotary kiln. The maximum temperature for roasting in multi-hearth furnaces (4-9 layers) is 450-850 °C. For example, the removal rate of Bolivian Wento plant, %: S100, As85, Sb20-30. The rotary kiln is mainly used in Malaysia, Japan and other countries. The temperature of the kiln head is 950 °C, the tail of the kiln is 400 °C, the removal rate of sulfur and arsenic is 95 °C. A domestic factory is roasting in a boiling furnace. The boiling layer temperature is 800-900 ° C, the boiling layer height is 750 mm, pulverized coal. The addition amount is 6-10%, the impurity removal rate is %; S85-98, As75-90.
Available reduction strengthened copper oxide ore flotation baking method, such as a 0.83% copper, 0.15% of sulfur oxide copper ore, predominantly limonite iron, a small amount was pyrite form, predominantly copper malachite, There are forms such as azurite. The ore is crushed and mixed with 1 to 3% sodium sulfate, and calcined in a boiling furnace at 850 ° C. The gas phase composition is %: CO 2 6.4 to 7.0, CO 9.4 to 46, O 2 0.1 to 0.2, H 2 9.7. The iron in the sand is almost entirely magnetite. The copper is mainly composed of metallic copper particles with a particle size of 0.01-0.3 mm. After grinding, the copper can be recovered by a combined process of flotation or flotation and re-election.
Reductive roasting process also commonly used in the selection of niobium iron, coarse iron ore and titanium zircon concentrate, weak magnetic iron oxide is converted to magnetite, calcine by magnetic separation, electrostatic separation to obtain qualified concentrate.
In addition, the vulcanizing agent may be added to the charge for reduction-vulcanization roasting, such as some low-grade nickel-cobalt ore. After reduction and vulcanization, the nickel-cobalt in the calcine can be recovered by flotation of natural sulfide minerals. Pyrite can be used as pyrite, elemental sulfur, sodium sulfate, high sulfur coal or coke , gypsum , sulfur-containing gas, and the like. For example, a nickel oxide ore containing about 1% nickel is added with about 10 to 15% of pyrite, and is subjected to reduction-vulcanization roasting under a reducing atmosphere at 1100 ° C. The vulcanization rate of nickel is 90-92% flotation recovery. The rate is 84-89%, and the grade of nickel in the concentrate can reach 2.2-2.6%.