Study On The Influence Of Fe,Mg,Na,K On The Formation Of Clinker Minerals And The Hydration Process Of Sulfur-aluminum-ferric Cementitious Materials

With the aggravation of climate change and environmental pollution problems,there is an urgent need to find innovative and effective technological routes to promote the green upgrading of high carbon emission industries such as the cement industry in China.There are studies showing that the use of industrial solid wastes to prepare sulfur aluminum ferric cementitious materials（SAFCM）greatly reduces production costs and contributes to the promotion and application of low-carbon cementitious materials.In addition,this technology can also effectively promote China’s solid wastes treatment change from "pollution reduction single goal" to "green,low-carbon and health multi-goal synergistic management",so as to achieve the pollutants renewable resources cycle process,in line with the "green,low-carbon,recycling" sustainable development concept.However,the "complex composition and low quality" of solid wastes determine that they contain more Fe,Mg,Na and K multiple components in addition to CaO,SiO₂,Al₂O₃ and CaSO4,which are necessary for SAFCM preparation.It seriously affects the mineral phase formation characteristics and hydration characteristics of SAFCM,resulting in instability of its properties,limiting the promotion and application of the technology.Addressing the above problems,this paper investigates the effects of Fe,Mg,Na and K on the mineral phase formation and hydration characteristics of SAFCM,reveals the mechanism of the influence of multiple components on the mineral phase formation and hydration process of SAFCM,and clarifies the direction of optimization of the mineral phase and properties of it.The work carried out in this paper is as follows:（1）The effects of Fe content and its present forms and the alkalinity coefficient of the raw materials on the formation of SAFCM mineral phases are investigated.The results show that Fe3+replaces Al3+ in CAS crystals and forms C4A3-XFXS,and stabilizes CAS in cubic morphology.As flux,Fe2O3 accelerate the mineral reaction at the low temperature,but with the increase of Fe2O3 dosage（>4.9 wt.%）,excessive Fe phases appear in the clinker and lead to the decrease of CAS content.Fe3O4 and C2F are better fluxes compared to Fe2O3,which improve the reactivity of high-Fe clinker at low temperature as raw materials.Decreasing the alkalinity coefficient of raw meal can increase the solid solution of Fe3+ in CAS,thus increasing the content of CAS in clinker.（2）The effects of single and multiple incorporation of Mg,Na and K on the mineral phase formation characteristics of SAFCM are investigated.The results indicate that both Na2O and K2O are mineralizers,and their moderate blending（≤0.8 wt.%）promotes the mineral reaction of the clinker at low temperature,while the excessive blending inhibits the generation of active mineral phases.With the increase of MgO,the generation of active minerals is promoted first and then inhibited,and the optimal dosage is 4 wt.%.In the case of compounding,low alkali dosage increases the optimal dosage of MgO to 6 wt.%,while high alkali dosage inhibits the production of active minerals.（3）The effects of Fe content and its present forms and Mg,Na and K on the hydration process of SAFCM are revealed.The results show that SAFCM has the fastest hydration rate and highest hydration degree when the Fe2O3 dosage is 4.9 wt.%,and the first hydration acceleration period of SAFCM is delayed from 2～6 h to 6～12 h with the increase of Fe2O3.SAFCM prepared with C2F has higher early hydration rate of CAS,and the early hydration of CAS is suppressed when the Fe present form is Fe3O4,which mainly depends on the content of CAS-c in the clinker.The incorporation of Na2O and K2O destroys the grain structure of CAS and causes severe lattice distortion,thus increasing its early hydration rate,and the optimal dosage is 0.8 wt.%.MgO（≤6 wt.%）provided more crystallization points for AFt and improved the crystallinity of native AFt.When Fe,Mg,Na,and K are compounded,the accommodation of MgO to SAFCM is increased to 8 wt.%at low alkali content,while the high MgO dosage at high alkali content suppresses the degree of hydration of CAS.