Study on Preparation and Photocatalytic Performance of Alkali-activated Steel Slag and Magnesium Slag Based Cementitious Material

Author:Kang Le

Supervisor:zhang yao jun


Degree Year:2017





In 2016,China’s steel slag emissions are about 100 million tons and the amount of magnesium slag is more than about 6 million tons.The long-term accumulation of steel slag and magnesium slag not only takes up a large amount of land resources,but also causes serious ecological damage and environmental pollution.Therefore,exploring steel slag and magnesium slag high value-added new ways of application is great significance to the sustainable development of China’s iron and steel and metal magnesium industry.In the present paper,steel slag,magnesium slag and steel-slag-magnesium-slag are used as raw materials,NaOH and Na2SiO3·9H2O as alkali activators,silica fume as toughening agent,the alkali-activated steel slag-based cementitious material(ASSCM),alkali-activated magnesium slag-based cementitious material(AMSCM)and alkali-activated-steel-slag-magnesium-slag-based composite cementitious material(ACCM)were successfully synthesized through hydration reaction.The chemical composition,pore structure,mineral phase,microstructure,optical and electrical properties of cementitious materials were characterized by various modern methods,such as TGA/DSC、XRF、BET、XRD、IR、UV-Vis DRS、PL、FESEM、TEM and XPS.At the same time,photocatalytic degradation and photocatalytic decomposition of water to hydrogen performances were evaluated.The reaction mechanism of photocatalytic oxidation degradation of dyes and hydrogen production by photocatalytic decomposition of water were explored.Its main research contents and the results are as follows:(1)XRD and FESEM results showed that steel slag,silica fume and NaOH reacted with acrylic resin emulsion to form calcium silicate(CSH)and porous alkali-activated steel slag-based cementitious material(PASSCM).The mechanical property and pore structure of alkali-activated steel slag-based cementitious material with different dosage of pore forming agent was investigated.The experimental results indicated that adding pore-forming agent of acrylic resin emulsion could effectively adjust the pore structure and mechanical property of the alkali-activated steel slag-based cementitious material.When the incorporation content of pore-forming agent was 0.1wt%(0.1PASSCM),the compressive strength and the flexural strength were 23.5 MPa and 4.6 MPa for the curing period of 3 days,respectively.0.1PASSCM specimen had the largest SBET and highset mesoporous volume,and showed a relatively homogeneous pore structure.The0.1PASSCM exhibited the highest degradation rate under UV irradiation and the degradation rate of 4 mg/L malachite green solution could reach 95.13%after 60 min photocatalytic degradation reaction.The photocatalytic reaction belongs to the first-order reaction kinetics.(2)The synthesized PASSCM was used as carrier,Ce(NO3)3·6H2O as precursor,CeO2-loaded porous alkali-activated steel slag-based cementitious material(CeO2/PASSCM)was innovatively prepared through impregnation method.The performances of photocatalytic degradation of malachite green dye and photocatalytic decomposition of water for hydrogen production were evaluated.The results showed that BET specific surface area and mesoporous volume of CeO2/PASSCM series catalyst increased,about 80%of the pore volume was concentrated in the range of mesoporous(2-50 nm).8CeO2/PASSCM catalyst specimen displayed the highest photocatalytic activity.The degradation rate of 6 mg/L malachite green solution was up to 100%after 80 min photocatalytic degradation reaction.When the catalyst dosage is0.1 g,8CeO2/PASSCM specimen exhibited the highest photocatalytic hydrogen production activity(7653μmol/g)and hydrogen generation rate(1275.5μmol/(g?h)).It may be attributed to the synergistic effects of high SBET,large mesoporous volume,and the coupled semiconductors formed by Ce O2 and FeO in the photocatalyst carrier.(3)The photocatalytic activity as the main index,NH4VO3 as the V source,and on the basis of the optimum CeO2 load content,V-doped CeO2-loaded porous alkali-activated steel slag-based cementitious material(V-CeO2/PASSCM)was firstly synthesized,and it was used as a novel catalyst for photocatalytic degradation malachite green dye.The photocatalytic degradation performance of series catalysts was evaluated by response surface methodology.The order of the main factors affecting photocatalytic degradation malachite green dye was as follows:catalyst dosage>V doping content>malachite green dye concentration.The regression coefficient R2 was up to 0.9681,implying that the regression model had great reliability.The optimal experimental condition of photocatalytic degradation reaction was as follows:malachite green dye concentration was 10 mg/L,catalyst specimen was 0.1 g,and V doping content was 1wt%.The degradation rate of malachite green dye was 100%.1V-CeO2/PASSCM catalyst has excellent reuse performance.After repeated 5 times,the degradation rate of 10 mg/L malachite green dye solution after 140 min photocatalytic degradation reaction,and the degradation rate still maintained at about80%.(4)Subsequently,alkali-activated magnesium slag-based cementitious material was used as a carrier,Ni(NO3)2·6H2O and Cu(NO3)2·3H2O as precursor,a novel type of NiO and CuO co-loaded alkali-activated magnesium slag-based cementitious material((CuO+NiO)/AMSCM)was successfully synthesized through impregnation method,and the photocatalytic degradation performance of the series catalysts was evaluated.The results showed that 10(NiO+CuO)/AMSCM catalyst specimen showed the highest photocatalytic activity.When the catalyst specimen dosage was 0.8 g,the concentration of methyl orange solution was 3 mg/L and the reaction time was 100 min,the degradation rate of methyl orange dye was 92.78%.It may be attributed to the synergistic effect between the active species of NiO and CuO and the network of formed by calcium silicate hydrate in AMSCM matrix which improved the separation efficiency of photogenerated electron hole pairs.The photocatalytic reaction accorded with the first-order reaction kinetics.(5)In order to couple with the mechanical property,conductivity property and photocatalytic performance of the cementitious material,the mixture of magnesium slag and steel slag was used as raw material,Na2SiO3·9H2O as alkali activator,silica fume as toughening agent,conductive carbon black as conductive medium,a novel conductive alkali-activated-steel-slag-magnesium-slag-based composite cementitious material(CACCM)was also successfully prepared.The effects of carbon black content on the mechanical property and electrical conductivity of the conductive composite cementitious material were explored.The results indicated that the interface effect was caused by carbon black and the gel phase of ACCM specimen,which leaded to the compressive strength of the test block decreased.The electrically conductive property of CACCM specimen was improved significantly by proper incorporation of carbon black.When the amount of carbon black was 4.5wt%,the electrical conductivity was0.3997 S/m for the curing period of 28 days and the conductivity remained basically the same with the increase of age after 28 days.It may be attributed to the conductive medium in the conductive composite cementitious material formed a connected conductive network.The incorporation of carbon black could improve the photocatalytic degradation rate of the composite cementitious material,and the conductivity of the catalyst is positive correlation with the degradation rate of the dye.4.5CB/CACCM specimen showed the best photocatalytic degradation activity and the degradation rate of malachite green dye could reach 90.58%at 80 min.The kinetics analysis indicated that the photocatalytic degradation reaction belongs to the second-order reaction kinetics.