Study On Reaction Kinetics,Hydration Kinetics And Properties Of Sulphoaluminate Cement Prepared From Petroleum Coke Desulfurization Slag

Calcium sulphoaluminate（CSA）cement has shown rapid setting,high early-age strength,slight expansion,freeze-thaw resistance and low alkalinity during hydration of calcium sulphoaluminate.Furthermore,the manufacture of CSA cements is more environmentally friendly than that of OPC as their sintering temperature is less than the latter up to 100–200 ℃.Therefore,CSA cements is mainly used in many spectial engineering progects,such as rapid construction,winter construction,marine engineering,underground engineering,et al.The main component of the sulphoaluminate cement clinker is the ye’elimite（3Ca O·Al2O3·Ca SO4,C₄A₃（?） in cement notation）and 2Ca O·Si O2（C2S）.In general,the clinker is produced by burning mixtures of limestone,bauxite and gypsum to provide the necessary Ca O,SO3,Al2O3 and Si O2 required for phase formation.However,the exploitation and burning of the natural mineral emitting large amounts of CO2.Therefore,the study of using solid waste to prepare CAS cement have been received wide attention by researcher.Petroleum coke desulphurize slag（PCDS）is the solid waste residue of the power plants,which use petroleum coke as fuel.Various methods have been suggested for utilization of the PCDS waste,but none of them can consume it in quantities large enough to equal the rate of production.Through analysized the chemical composition of the PCDS thoroughly,we prepared the CSA cement by using PCDS as raw materials in this paper.Effect of PCDS on synthesis dynamics,synthesis process,sintering temperature,hydration process and hydration dynamics model of the C₄A₃（?） mineral have been investigated.CSA cement clinker with different mineral composition have been prepared.At the same time,we learn about the relationship among the synthesis process,mineral composition,and mechanical properties of the CSA cement.Firstly,we studied the synthesis dynamics and activation energy of the C₄A₃（?）,which prepared by three different raw materials,that is,chemical reagent（proportion scheme A）,PCDS with chemical reagent（proportion scheme B）and PCDS withindustrial materials（proportion scheme C）.The results showed that,the optimal sintering temperature of the C₄A₃（?） using proportion scheme C is about 1100¹200 ℃.And the synthesis dynamics model of the C₄A₃（?） mineral using proportion scheme C satisfied Glinstling model.Moreover,some impurity elements with low melting point,such as,Fe2+,Si2+,Mg2+ et al.,will form liquid phase in sintering process of C₄A₃（?）mineral.At the same time,the reactants will reacted each other in the liquid phase.So,the coefficient of reaction rate have been achieved 11.90×10-4 s-1 at 1200℃.The synthesis activation energy of the C₄A₃（?） mineral using proportion scheme C is only 85.63 k J /mol,lower than that（170.97 k J/mol）of C₄A₃（?） mineral using proportion scheme A.Secondly,the hydration process and hydration dynamics of the C₄A₃（?） mineral using different raw materials have been studied.Results showed that the hydration heat of the C₄A₃（?） mineral prepared by PCDS was significantly lower than that prepared by chemical reagents.At the same time,the maximum rate of heat release was delayed,hydration temperature also decreased significantly.In early stage of hydration acceleration period,the hydration reaction model of the C₄A₃（?） mineral consistent with the phase boundary reaction process.But in later stage of hydration acceleration period,the hydration reaction model of the C₄A₃（?） mineral prepared by PCDS was changed to meet the Kondo model and no longer conform to the common crystallization nucleation and crystal growth process（NG model）,due to the impurity ions enter into ettringite（AFt）lattice,retard the formation of hydration products.In deceleration period of hydration,the hydration process of C₄A₃（?） mineral prepared by three kinds of raw materials met the Kondo model.However,the reaction mechanism coefficient of the C₄A₃（?） mineral prepared by PCDS was only 1.42,that means it is still in the stage of transition from autocatalytic reaction to diffusion reaction.The FT-IR and TG-DSC analysis results showed that the main hydration products of the C₄A₃（?） mineral wasettringite（AFt）and aluminum gel（AH）.But,the time of hydration product from the C₄A₃（?） mineral prepared by PCDS is delayed.Thirdly,we studied the formation process of sulphoaluminate cement clinker and its microstructure under different raw material composition.Study results showed that,the burning temperature of cement clinker can be reduced and the decomposition temperature of clinker minerals decreases with the use of PCDS at the same mineral composition.The grain size of clinker minerals prepared by PCDS is smaller（about 3⁶ nm）than that of cement clinker prepared by chemical reagent（about 8¹0 nm）.And then,the physical properties and the mechanical properties of the cement prepare by different raw materials were studied.The setting time of CSA cement prepared by PCDS is longer than that of cement prepared by other materials,and the standard consistency is slightly lower.Furthermore,the retarding effect of gypsum at this cement is not obvious.The mechanical properties test showed that the early strength of CSA cement is low because of the trace elements in PCDS inhibit the hydration reaction of cement.The compressive strength of the cement is only between 24.4²7.8 MPa at 1d curing time.But,with the increase of C2 S content,the later strength increases rapidly,and the compressive strength of 28 d reaches 40.5MPa.Finally,we analyzed the economic and social benefits through the perspectives of energy consumption,CO2 emission and the saving of natural mineral resources.The results showed that the use of PCDS can reduce the sintering energy consumption of cement and the power consumption of raw meal grinding.When 1 tons of CSA cement clinker was produced,only 451.3kg of CO2 was released,which is reduced by 35% compared with the ordinary raw material.Meanwhile,the use of PCDS will solve many environment problems of power enterprises.Furthermore,it will also reduce the amount of natural gypsum and limestone,and solves the serious environmental pollution caused by mining when the PCDS was get full utilization as resources.