Preparation Of Iron And Cementitious Materials Synergistically Through Iron Ore Direct Reduction Process

In our country, the geological reserves of iron ore resources are abundant, but ore grade are scarce and lean, difficult to exploit and concentrate. It is hard to effectively use such iron ores through conventional ironmaking process. As the dwindling of rich ore reserves, we have to consider how to achieve efficiently ecological utilization of lean ore resources. The future trend is not only to recover iron and value metals, but also to make effective use of the gangue. So, it is of great practical significance and application value to explore a kind of reliable technology, to attain high-efficient comprehensive utilization of iron ores with reasonable economic cost, energy saving and emissions reduction.In this work, extract iron and prepare cementitious material synergistically from hematite with carbon as reductant through direct reduction process was investigated. Phase equilibria related to direct reduction process and the thermodynamic possibility for collaborative preparation of iron and gelled material response were calculated using FACTSage software. Effects of varied process parameters, such as reaction temperature, reaction time, ratio of reductant, reducing atmosphere, the cooling method, on production rate of iron and gelled ingredient Ca3 Si O5 were investigated also by continuous rising temperature control and two-phase rising temperature control method. Possible mechanisms that affect Ca3 Si O5 forming were discussed. The main results are as follows:(1) Thermodynamic calculation results in this work show that recovery rate of iron enlarge with the amount of carbon adding increasing when carbon was 0.75~1.0 times that of theoretical value at temperature of 1250℃~1450℃. Theoretical reduction rate of Fe can reach more than 99% when carbon addition is more than theoretical reducing agent requirement. There are no Ca3SiO5 can be detected when the temperature below 1350℃ but more than 58% when temperature is up to 1450℃ in theory. Iron can be completely reduced at 1450℃, the existing of iron have an influent on the generation of Ca3SiO5.(2) Experiment results showed that iron reduction rate could reach 90% when the continuous heating temperature was set at 1250℃~1450℃. Iron reduction rate was as high as 91% under the condition of three times theoretical requirements of reducing agent addition, holding 120 min at 1250℃. Low content of CO in the atmosphere was not favor to iron reduction. No Ca3SiO5 could be detected in the continuous rising temperature experiment ending at1250℃.(3) In two-phases rising temperature reduction experiment, the first temperature stage was set at 1000℃ holding 120 min, the second temperature stage was set at 1450℃ holding 60 min. The experiment results showed that the reaction products of Iron and Ca3 Si O5 could be obtained simultaneously, in which iron reduction rate reached 88%, Ca3 Si O5 content was up to 42%. The main factor hindering Ca3SiO5 production can be attributed to that bivalent iron ions occupy the lattice of Ca3SiO5.(4) The optimum temperature for Ca3SiO5 generated is about 1450℃. Cooling rate have great impact on the phase forming of Ca3SiO5 and Ca2SiO4. Due to the crystal transfer from beta-Ca2 Si O4 to gamma-Ca2SiO4 crystal, volume augmenting and then pulverization phenomenon were observed when cooling along with the furnace; However when cooling rate were rapid, Ca3SiO5 phase and β-Ca2 Si O4 could be retained to room temperature because of short staying time at Ca3 Si O5 decomposition temperature of 1250℃ and Ca2SiO4 crystal transition temperature of 525℃.It is feasible to gain iron and cementitious material simultaneously through Iron ore direct reduction process under theoretical and experimental conditions. It may provide some theory references for effective utilizing of iron ores especially lean resources, energy conserving and emission reducing, and furthermore, for alleviating the pressure of domestic iron ore resources.