Synthesis And Photocatlytic Properties Of CaTiO₃ Powders With Desulfurization Ash As Raw Materials

The flue gas pollution has been solved effectively due to the development of sintering flue gas desulfurization?FGD?technology.However,a large number of FGD ash has been produced,resulting in new solid waste pollution.At present,the treating technology on FGD ash is immature,most of them can only be stored,which not only occupies a lot of valuable land resources,but also causes secondary pollution to the environment.The utilization of FGD ash mainly focus on cement,wall filling materials,soil modification,etc.,and the added value of the products is relatively low.In consideration of a large amount of calcium ion,sulfite or sulfate ion,chloride ion and potassium sodium ion in the FGD ash,this thesis attempts to use the FGD ash as the calcium source to synthesize CaTiO₃ photocatalyst powders by the molten salt method.The sulfite or sulfate ions,chloride ions,potassium and sodium ions in the FGD ash improves the formation of low melting point materials during the heating process,which can lower the synthesis temperature.The photocatalytic activity of the synthesized CaTiO₃powders for the degradation of organic pollutants will also be investigated.The method proposed in this thesis can not only transform the FGD ash into functional materials with higher added value,but also provide agent for the initial treatment of industrial waste water.It is a new idea of"treating waste with waste".It is significant in the treatment of industrial pollutants.In this thesis,CaTiO₃ powders were synthesized by molten salt method at low temperature with chemical reagent CaCO₃,CaSO₃.1/2H₂O and FGD as calcium sources,and TiO₂ with different crystal phases as titanium sources,respectively.The effects of raw materials,synthesis temperature,synthesis time and the salt amount on the phase composition,particle morphology and the photocatalytic performance under ultraviolet light irradiation were investigated.The main contents of the thesis are summarized as follows:?1?CaTiO₃ powders were synthesized by molten salt method with chemical reagent CaCO₃ and CaSO₃.1/2H₂O as calcium sources,and KCl/Na₂SO₄ as molten salt,respectively.The results show that the molten salt created a liquid environment for the reaction and accelerated the diffusion of the reactants to the reaction interface,which played an important role in reducing the reaction temperature and removing impurities.Pure CaTiO₃ powder was obtained at 750?by molten salt method,which is about 600?lower than that required by traditional solid-state method.The amount of molten salt had obvious effect on the phase composition of the synthesized product,and the optimal amount of molten salt is twice the mass of the target product.With increasing synthesis temperature and holding time,the particle size of the product grew up gradually,but the photocatalytic activity of the product only changed a little.When CaCO₃ was used as the calcium source,the CaTiO₃ powder obtained at 850?for 3 h with P25?rutile phase and anatase phase coexist?as titanium source had the best photocatalytic activity.After 60 min UV irradiation,the degradation rate of methylene blue?MB?solution was 97.3%.When CaSO₃·1/2H₂O was used as calcium source,the CaTiO₃ powder obtained at 750?for 3 h with anatase TiO₂ as titanium source had the best photocatalytic activity.After 60 min UV irradiation,the degradation rate of methylene blue?MB?solution was 90.2%.?2?CaTiO₃ powder was synthesized by molten salt method using FGD ash as calcium source.The results show that pure phase CaTiO₃ powder was obtained at 650?with FGD ash as calcium source,which is lower than that with pure chemical reagent CaCO₃ and CaSO₃·1/2H₂O as calcium source.The possible reason is that the impurity ions contained in the FGD ash further reduced the melting point of molten salt.Liquid formed at lower temperature and promoted the solid-state reaction.Different titanium sources greatly influenced the properties of the synthesized products.When anatase phase TiO₂ was used as titanium source,the photocatalytic activity of the synthesized product decreased with increasing reaction temperature and holding time.The CaTiO₃ prepared at 750?for 5 h had the best UV photocatalytic activity with a MB degradation rate of 61.9%in 60 min.When P25 was used as titanium source,the photocatalytic activity of the synthesized product firstly increased then decreased with increasing calcination temperature and holding time.The CaTiO₃ prepared at 750?for 3 h had the best UV photocatalytic activity with a MB degradation rate of 61.0% in 60 min.