Stabilization And Synergistic Utilization Of Unstable Components In Circulating Fluidized Bed Fly Ash-blast Furnace Slag-red Mud Based Cementitious Materials

Circulating fluidized bed fly ash(CFA),blast furnace slag,and red mud are solid waste with large emissions,complex composition,and low utilization rate,which occupy a large amount of land,pose a threat to the environment and seriously restrict the sustainable development of the metallurgical and power industries.The rapid development of green and low-carbon industries was proposed to pass the 20th National Congress of the Communist Party of China.Thus,the preparation of materials using CFA,blast furnace slag,and red mud was an important way to promote the development of low-carbon.The issues such as high content of unstable components(f-CaO and SO3)in CFA,low utilization rate of high added value of blast furnace slag,and difficulty in utilizing alkaline red mud and its high concentration of Na+have been focused on in this article.The stabilization and synergistic utilization of unstable components in CFA-blast furnace slag-red mud based cementitious materials have been investigated.The main content is as follows:Firstly,the problem of poor volume stability in the preparation of cementitious materials with high dosage of CFA has been addressed.The stabilization method of unstable components in CFA was adopted by blast furnace slag.The reaction characteristics of f-CaO silicification and SO3 calcification in CFA have been investigated.Thus,the stabilization mechanism of unstable components in CFAblast furnace slag based cementitious material(CCM)has been revealed.The properties showed that the basic performance of CCM40 was optimal when the Ca/(Si+Al)mass ratio was 0.72.The compressive strength,expansion value,and residual of f-CaO at CCM40 were 47.30MPa,0.5mm,and 0.19%,respectively,which meet the Chinese standard of 42.5 fly ash Portland cement(P.F 42.5).The microscopic analysis demonstrates that the main hydration products in CCM40 were C-(A)-S-H gel and ettringite.Additional C-S-H gel and ettringite were generated by active Si-Al in blast furnace slag based on f-CaO silicification and SO3 calcification.Thermodynamic mass ratio and polymerization degree in CCM40-28d were increased to 71.92%and 46.28%,respectively.The volume stability and basic properties of cementitious materials have been improved.Secondly,the issues of slow stabilization rate about unstable components and difficulty in utilizing alkaline red mud and its Na+ in CCM40 have been focused.The way of providing alkaline conditions from red mud to accelerate the stabilization rate of unstable components has been applied.The stabilization rate of unstable components in CFA-blast furnace slag-red mud based cementitious material(CGM)and the utilization of Na+ in red mud have been researched.Hence,the acceleration mechanism of the stabilization about unstable components has been clarified.At the same time,the performance and volume stability of cementitious materials have been improved by the formation of hydrated sodium aluminosilicate(N-A-S-H)gel from Na+in red mud.The results showed that the performance of CGM10 was excellent when(Ca+Na)/(Si+Al)mass ratio was 0.90.The compressive strength,expansion value,and f-CaO residual of CGM 10 were 49.35MPa,0.3mm,and 0.13%,respectively.It is worth noting that the performance of CGM10 was superior to that of CCM40.The micromorphology and 27Al coordination structure showed that the microstructure density and AlⅣ1,AIⅥcontent of CGM10-28d were higher under the action of alkaline(OH-)red mud.The degree of amorphous(DOA)and GEMS thermodynamic mass ratio of gel products were increased to 75.28%and 73.39%,respectively.The stabilization rate of unstable components in CGM 10 was higher than that of CCM40.Meanwhile,Na+in red mud was utilized by[Si(Al)O4]structure to form N-A-S-H gel.Thirdly,the problems of low reactivity and poor frost resistance of CGM 10 have been proposed.The method of promoting the hydration of CGM 10 using active mixtures has been adopted.The influence of fine blast furnace slag,phosphorus slag,and gasification slag as active mixtures on the hydration characteristics of CGM10 has been investigated.Therefore,the strengthening mechanism of reaction activity and frost resistance of CFA-blast furnace slag-red mud-phosphorus slag based cementitious material(CWM2)has been dissected.The macroscopic performance showed that the compressive strength of CWM2-28d containing phosphorus slag was 51.15 MPa(Higher than CGM 10),and strength,strength loss,and mass loss of CWM2 after 25 freeze-thaw cycles were 49.95 MPa,2.35%,and 0.36%,respectively,which are better to other CWMs.The dosage of total solid waste in CWM2 was 70 wt.%,and it is volume stability,performance,and frost resistance still meet the P.F 42.5.The microscopic results manifested that the main hydration products of CWM were C-S-H gel,C/N-A-S-H gel,and ettringite.The polymerization degree and microstructure density in CWM2 were higher than those in CGM 10.This result indicated that the reactivity of the CWM2 was enhanced by phosphorus slag,which improved the frost resistance in CGM 10.Finally,the high content of unstable components(f-CaO and SO3)in CFA and the difficulty in utilizing Na+ of red mud have been focused.The method of synergistic utilization of unstable components in CFA and Na+ in red mud has been adopted.The performance and hydration mechanism of CFA-red mud-metallurgical solid waste based road base material(CRM)have been investigated.The microstructure design mechanism and technology for the preparation of CRM from high dosage CFA,red mud,and metallurgical solid waste have been obtained.The results showed that the compressive strength(6.14MPa),volume stability(0.070%),durability,and environmental performance of CRM37-7d were the optimal when the(Ca+Na)/(Al+Si)mass ratio was 0.39.The dosage of solid waste in the CRM37 was 97 wt.%,and its performances still meet the standards of expressway and heavy traffic of first-class highway.The reason for this phenomenon was that the 7-day strength of CRM has been increased by SO3 in CFA.Shrinkage of CRM volume was compensated by f-CaO expansion from CFA.At the same time,the CRM performance was further improved by Na+ in red mud.The microscopic analysis noted that the main hydration products of CRM37 were ettringite and C/N-A-S-H gel.The DOA of the hydration products,[Si(Al)O4]polymerization degree,and micro-morphology density in CRM37 were the excellent.These results indicated that there was a synergistic effect between CFA,red mud,and metallurgical solid wastes.The theoretical development of the stabilization and synergistic utilization of unstable components in CFA-blast furnace slag-red mud based cementitious materials has been promoted by this work,and the transformation of scientific and technological achievements has been achieved.It is important for the green and sustainable development of metallurgy and power industry.