The Thermal Decomposition Behavior Of Dolomite And Application

As we all known, dolomite is an important raw materials of reducing the metalmagnesium and also an important auxiliary of reducing steel and sintering ore.There isa large quantity of high purity dolomite stones in the area of Changbaishan. But it is ashortage of experimental data for this dolomite. Therefore, we take some experiments tostudy the decomposition behavior and mechanism of this dolomite using DTA-7thermal analysis, XRD and some other instruments. We also perform the kinetics,SEMand TEM in order to study the microstructure of dolomite in this paper. The averagemagnesium content of Changbaishan dolomite is13.04%;the atomic ratio ofmagnesium and calcium is1:1.There are many tiny particles of different size in thebluk of Changbaishan dolomite and its size is distribution in3～10μm.It also has somerecrystallization phenomenon in the bluk. According to the research of microstructure,Changbaishan dolomite belongs to crystal dolomite, presenting the typical surface ofrhombohedron and the particles structure is compact.We can observe two group ofcleavage seam in the bluk, appearing a special morphology.The main impurities ofChangbaishan dolomite are SiO₂and Al₂O₃. Therefore, Changbaishan dolomite is anideal raw material for the smelting of magnesium.The process of decomposition can be divided into two steps. The generalreaction path for the first half thermal decomposition of a natural dolomite is differentfrom what people used to persist in. The amount of MgO that can be extracted fromdolomite is less than the theoretical one. This finding may be ascribed to a solid solutionof MgO in calcite. The first step of decomposition is controlled by boundary surfacecontraction in the beginning, followed by diffusion rate-contracting as thedecomposition temperature increases. The contraction step is the diffusion of CO₃^2-.Thesecond step of decomposition is controlled by three-dimensional diffuse （ballsymmetry）. The diffusion of CO₂is a rate-controlling step.At the constant temperature of662℃and calcined for2h, weightlessness is notapparent; at the constant temperature of714℃and calcined for2h,weightlessness ratereaches11.11%.It indicates the decomposition can undertake at this condition but the process is slow. However,at the constant temperature of734℃and calcined for2h,weightlessness reaches23.2%,which is close to the theory weight loss of MgCO₃in thedolomite.Meanwhile, there is a change in the curve of weightlessness.As a result, thelow temperature of the thermal decomposition of dolomite is between714℃and734℃.Accurding to the result of experiments,we can also conclude that the hightemperature of the thermal decomposition of dolomite is between774℃and796℃.On the basis of calcining experiment, the result indicate that the temperaturetakes a more obvious influence on the low thermal decomposition stage than that of thehigh thermal decomposition stage,because the weightlessness rate increases obviouslywith the rise of temperature.It suggests that the proper decomposition temperature forthe low stage of dolomite is restricted. When the dolomite was calcining for an hour, nomatter what temperature it was, the decomposition process was nearly completed,especial the high temperature decomposition stage,so it is appropriate to take a shorttime for the calcining of dolomite, otherwise it may be a waste of the fuel.