Research On The Behavior Of Iron In The Formation Process Of Calcium Aluminate

In China, the iron-bearing resources reserve is huge. It is significant for the sustainable development of our bauxite resource and ore resource if we make a comprehensive utilization of them. However, the content of iron oxide and alumina is relatively less in iron-bearing resources. They couldn’t be used for alumina or iron production with traditional methods because their industrial grade doesn’t match the demands. However, the total content of useful constituent is considerable. The process of "rotary heath furnace reduction-calcium aluminatc slag-iron separation at high temperature-leaching alumina from calcium aluminate slag" has been put forward to utilize the iron-bearing resources in tandem. The composition of iron-bearing bauxite is simulated by analytical reagents to research the phase transformation law, self-disintegrating and leaching property, and the behavior of iron in the formation of calcium aluminate clinker in sintering process. What’s more, the technological parameters are used in the sintering process of iron-bearing bauxite and high-iron-content red mud. The main results are showed as follows.At1250℃, the metallization ratio of pelletizing is increasing with the carbon content rising as well as prolonging of sintering time. However, the accumulation of reduced iron is hindered at high temperatures with too much carbon. From the content of residual iron in the calcium aluminate, the reasonable reducing conditions are got that the C/O is1.0～1.2and the reduction time is15-30min and the reduction temperature is1250℃. The phases of pre-reduced pellets are Fe, β～2CaOSiO2, CaO, Fe3O4,12CaO·7Al2O3and2CaO·Al2O3·SiO2. What’s more, the phases change little as the change of the C/O.The C/A is studied in the conditions of1250℃for20min. It shows that the reduced iron gathers worse and wore and the size of iron grains is smaller and smaller while the quantity of slag and energy consumption is increasing with C/A increasing. However, the phase of2CaO·Al2O3·SiO2, which hinders the leaching of Al2O3in the calcium aluminate, would be formed in the sintering process when C/A is lower. The best C/A is1.2.After sintered at1250℃, the pre-reduced pellets are heated at higher temperature to separate the slag-iron. The temperature has a great effect on the formation of calcium aluminate. When the temperature is below1500℃, the reduced iron gathers worse and the iron grains have little. What’s worse, the phase of2CaOAl2O3·SiO2is formed in the calcium aluminate. When the temperature is more than1500℃, the content of residual iron in the calcium aluminate is only2%-4%and the main phases are that12CaO·7Al2O3、CaO·Al2O3、2CaOSiO2、3CaO Fe2O3·3SiO2. The activity of calcium aluminate is better and the best leaching of Al2O3is97.24%. When the reduction time is between10min and50min, the content of residual iron is decreasing with the increase of reduction degree. The content of residual iron in the calcium aluminate is only2.21%when the reduction time is20min. But the reduction time doesn’t affect the phase formation and self-disintegrating and leaching property of the calcium aluminate. The best activity of calcium aluminate is got in the condition that the pellets are sintered at1250℃for15min then sinered at1500℃for20min.In the sintering process, most of Fe2O3is reduced to metallic iron and only a little Fe2O3isn’t reduced but combine with CaO and SiO2to form3CaO Fe2O3·3SiO2when the iron in the simulated ore is Fe2O3. If FeOOH takes place of Fe2O3, there are a small number of Ca3Al0.84Fe1.16(SiO4)3、Ca1.92Fe1.08Fe2(SiO4)3except for3CaO Fe2O3·3SiO2in calcium aluminate.When the iron-bearing bauxite is studied, the results are similar to the results got by analytical reagents. When C/A is1.2, the gathering of iron and the self-disintegrating property of calcium aluminate achieve the desired effect. Most of iron is separated by magnetic separation in metallic iron while the residual iron exists in andradites. The main phases of calcium aluminate are12CaO·7Al2O3, CaO·Al2O3,2CaOSiO2and andradites. The leaching of Al2O3is92.38%. When the ferric red mud is studied, the behavior of Fe is also similar to the results got by analytical reagents. Most of iron is separated by magnetic separation in metallic iron. When C/A is1.2, there is lots of2CaO·Al2O3·SiO2leading to the leaching of Al2O3only about50%. However,2CaO·Al2O3·SiO2disappears as C/A increasing. A better leaching of Al2O383.89%is got in C/A=1.6. The phase of CaO·Al2O3isn’t formed in calcium aluminate. It may be due to the Al2O3in red mud existing in the form of katoite, resulting in a great difference in the phases of calcium aluminate.