The use of molybdenum oxide molybdenum iron instead of direct steel alloying, has been widely applied in foreign countries, the United States in 1974 in terms of molybdenum oxide and molybdenum steel industry iron consumption accounted for 73.3% of molybdenum oxide, molybdenum iron accounted for 25.2%, other 1.5 %. Japan uses molybdenum oxide directly into electric furnace steelmaking, with molybdenum oxide accounting for 83% and ferromolybdenum for a small proportion. In the United States in 1984, the ratio of molybdenum oxide to ferromolybdenum was 6.3.1. China's use of molybdenum oxide steel is also constantly improving. Nowadays, major large-scale special steel enterprises such as Dalian Steel Plant and Chongqing Special Steel have made extensive use of molybdenum oxide for direct steelmaking. The use of molybdenum oxide for steelmaking is superior to the use of ferromolybdenum steel.
Molybdenum oxide is calcined from molybdenum concentrate (MoS 2 ) to form molybdenum trioxide, which is used as an additive in steel making. Because molybdenum trioxide is used as an additive for steel making, molybdenum has a low recovery rate, poor gas permeability, and high deoxidation consumption. A researcher at a research institute of a group company experimentally studied a molybdenum oxide steelmaking additive different in structure and composition from molybdenum trioxide, called a molybdenum oxide agglomerate. The strength of the molybdenum oxide agglomerate is stronger than that of the molybdenum trioxide compact. It also contains molybdenum dioxide. Therefore, the use of a molybdenum oxide agglomerate block overcomes some of the drawbacks of using molybdenum trioxide compact.
Molybdenum oxide agglomerate test method and conditions
First, the test process
1. Raw materials used: molybdenum concentrate 44.49%
2. Main equipment for testing: reverberatory furnace, thermocouple, millivoltmeter, absorption tower, fan, etc.
3. Operation rules: After the molybdenum concentrate is added to the reverberatory furnace, the molybdenum concentrate is oxidized as the temperature rises. When the oxide layer reaches 15 mm to 20 mm thick, the oxide layer is moved to 700-800 ° C in front of the furnace. The temperature zones of the parts are piled up for sintering, sintered into pieces and then discharged.
The SO 2 gas in the exhaust gas is removed by absorption with lime milk.
4, the reaction principle:
Reaction equation
MoS 2 +3 
O 2 =MoO 3 +2SO 2 ↑
MoS 2 +6MoO 3 =7MoO 2 +2SO 2 ↑
Since the calcined material is calcined without agitation static during the calcination process, it can be understood from the above reaction equation that the composition of the agglomerate is mainly composed of two molybdenum oxides of MoO 3 and MoO 2 . Since the sintering is also carried out under static conditions, when the temperature reaches the melting temperature of the molybdenum oxide, some of the sinter of the deposited surface is volatilized by molybdenum trioxide, but due to overheating, a surface is formed as a bond, so the inside of the deposit There is no volatilization of molybdenum trioxide.
Second, the choice of process conditions
Roasting time (t) | 400 ° C oxide layer thickness (mm) | 600 ° C oxide layer thickness (mm) |
0.5 | - | 0.5 |
2.0 | 1 | 5 |
4.0 | 4 | 18 |
6.0 | 5 | 20 |
7.0 | 6 | 20 |
From the above test conditions: the calcination conditions should be controlled at about 600 ° C, the calcination time should be 4 hours, and the oxidation rate is faster.
Test result of relationship between baking time, temperature and recovery rate
Calcination time calcination temperature molybdenum recovery
2 hours 790°C～900°C >87%
3 hours 790°C～900°C 85%
Analysis of results: The calcination temperature should be 790 ~ 900 °C. The sintering time should be controlled within 2 hours, the molybdenum recovery rate is high, and the molybdenum recovery rate has some specific operational factors.
Sintering block chemical composition
batch number | Mo% before sintering | Post-sinter analysis results | |||
Mo% | S% | MoO 3 % | MoO 2 % | ||
4 | 43.65 | 48.26 | 1.2 | 62.76 | 11.12 |
7 | 43.65 | 50.86 | <0.01 | 66.36 | 9.15 |
8 | 43.65 | 50.67 | <0.01 | 52.39 | 22.00 |
11 | - | 48.12 | <0.01 | ||
13 | 43.98 | 49.46 | 0.065 | ||
17 | 44.49 | 49.51 | 0.089 | ||
Sintered molybdenum recovery
batch number | Before sintering | After sintering | Recovery rate% | |||
Weight kg | Mo% | H 2 O | Weight kg | Mo% | ||
13 | 95.5 | 43.98 | 3 | 71 | 49.46 | 85.9 |
17 | 97.5 | 44.49 | 3 | 83.5 | 49.51 | 98.2 |
Grand total | 91.62 | |||||
The cumulative recovery rate of the sample is 91.62%. The operation strictly controls the temperature and sintering time. The calcined material can not stay in the furnace for too long, reduce the mechanical loss, and increase the molybdenum trioxide recovery facility in the exhaust gas. The recovery rate can reach over 95%. .
The molybdenum oxide agglomerate meets the technical requirements of the steelmaking plant for molybdenum oxide additives. The technical requirements for the molybdenum oxide additive in Chongqing Steel Plant are: Mo48% or more, S<0.15%, Cu<1%, P<0.04%, Sn<0.07%, Sb<0.06%, Pb<0.05%. The test material Mo44.49%, the calcined molybdenum oxide agglomerate composition was Mo49.51%, S<0.089%, Cu 0.16%, Sn 0.0054%, Pb 0.092%. (Pb did not change before and after sintering).
The molybdenum dioxide content in the tested molybdenum oxide agglomerate accounted for about 20%. The molybdenum dioxide content can be further increased by the adjustment of the ingredients and the strict control of the atmosphere in the furnace.
The sales prospect of molybdenum oxide agglomerates is broad and the economic benefits are considerable. According to the trial results of heavy steel mills, the use of molybdenum oxide agglomerates as steelmaking additives can reduce the amount of ferromolybdenum by 30%. 80% of the total amount of molybdenum used in Chongqing Steel Plant is used in the additive of refined steel.
The work that should be continued to study the molybdenum oxide agglomerate is to further improve the production efficiency of the molybdenum oxide agglomerate and increase the content of molybdenum dioxide in the molybdenum oxide agglomerate.
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