| For many cement enterprises in China, the limestone mineral resources are low grade limestone with high MgO. Although the autoclave soundness qualified through cement production control, but often will bring difficulties to the production control. The belts with high MgO are stripped also will reduce the mining income, and may bring about the environmental impact, and the late strength of high magnesium clinker is lower. Therefore, to study how to use high magnesium limestone to produce qualified cement is of vital importance.This article rely on the "973" project (2009CB623101):The Formation, Structure and the Properties of the High Metastable Alite in the Clinker System. Attempt was made to use the ion doping make magnesium oxide solid solution in a favorable direction. With the directional solid solution of Mg2+caused by chemical doping, as far as possible to promote the absorption of the f-CaO and the development of silicate phase. And, try to change the crystal structure of the silicate and increase the hydration activity of Alite. Ultimately achieve the goal of optimization of the strength of the magnesia clinker and realize the comprehensive and high value-added utilization of low grade raw materials. After the test analysis, several conclusions could be obtained:(1) With the increasing of SM, the concentration f-MgO presents an obvious increasing process within the scope of the SM=2.2～3.2when the total MgO in clinker was5%. The solid solution of MgO is decreaseing from2.94%to1.94%. Low SM and IM are conducive to the solid solution of MgO, but KH has little effect on it. Along with the increase of SM, the28d compressive strength of clinker increases from60.2Mpa to64.0Mpa and the90d compressive strength gradually increases from64.1Mpa to71.8Mpa.However, when the SM is higher than3.0, the28d and90d compressive strength of clinker change little with the increase of SM. In addition, with the increase of KH, the3d and28d compressive strength is increasing, but the28d compressive strength of cement basically remains unchanged. Combination of solid solution and strength, to produce high alite and high-Magnesia clinker should be used in the high KH, slightly lower SM and IM.(2) Fixed a certain amount of SO3, doping appropriate content of SO3and CaF2can effectively promote the solution of MgO in clinker. On the basis of the doping of CaF2, the solid solution of MgO show a trend of increases with the increase of SO3when CaF2<0.25%. The highest amount of solid solution is approximately3.97%. However, with the increase of CaF2is fixed in the clinker, the impact of SO3on the MgO solid solution is increasingly weak. When the content of SO3is smaller (SO3≤1.2%), the increased doping amount of CaF2is more conducive to the solid solution of MgO in the clinker. When doping with SO3independent, the28days compressive strength decrease obviously with the increase of SO3. When adding suitable amount of CaF2, adding a certain amount of SO3help improve the compressive strength of clinker, but there is a optimal amount (SO3=0.8%). When the content of SO3is equal, the strength of the samples which doped with0.25%CaF2are higher than which not about2-6MPa. And the higher content of CaF2in the clinker, later strength of cement clinker is also higher. The clinker containing with SO3and MgO, Alite can stable at M1-M3type in the room temperature. And, when mixed with a certain amount of SO3, with the improvement of content of CaF2in the clinker, the symmetry of Alite is also gradually improves.(3) When doping with Ca(H2PO4)2·H2O independent, the28days compressive strength increase slightly with the increase of P2O5. To obtain high strength magnesia clinker, single doped P2O5require higher levels. In the case of the same content of F, composite mixing Ca(H2PO4)2·H2O or CaHPO4.2H2O are conducive to high magnesium clinker late strength, and the highest strength can reach about70Mpa. But, the content of phosphorus ion exist the best dosage (0.2%-0.4%), too high or too low, effect is not obvious. When adding suitable amount of CaF2in the clinker, composite mixing CaHPO4.2H2O or Ca(H2PO4)2.H2O are conducive to the clinker in the MgO solid solution. The highest amount of solid solution is approximately4.76%. But, adding CaHPO4.2H2O is more advantageous than Ca(H2PO4)2·H2O on the solid solution of MgO in the clinker. When the content of f-MgO in clinker is low (<2%), the slightly change of content of f-MgO is not the main factor which affects the strength of clinker. In the scope of this experiment, single doped CaF2can only stable C3S at between M2and M3type. But on this basis, appropriate mixing with0.2%Ca(H2PO4)2.H2O can make the C3S solid solution stable at between M3-R type. However, the content of Ca(H2PO4)2.H2O exists the best dosage. When its content is too high (0.80%), the crystal structure of C3S solid solution reduce to between the M2and M3type.(4) Slag doped solution applies not only to the high magnesium clinker, is also applicable to the normal clinker which with low magnesium. In the case of low KH (KH=0.87), use the PZR+F slag solution or PG+F slag solution can be obtained of the cement clinker which strength is higher than57Mpa when the limestone is high magnesium and low calcium. But if you want to obtain high strength clinker (≥60Mpa), KH value or the content of slag should be improved. It is also capable of producing a clinker which compressive strength is more than75MPa even if the KH is relatively low (KH=0.87) when using the scheme of F slag+PS. And the factory can produce a clinker which compressive strength is more than68MPa under normal conditions when using the scheme of PZR+F slag. And the scheme has a good easy to burn and kiln adaptability. When using this scheme, the sand, ring and other abnormal conditions is better than the plan without slag admixture. Compared with normal production before the experiment, the plan of PZR+F slag can be accomplished by the production does not reduce and the heat consumption does not increase. |
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