Preparation And Dye Removal Performance Of Fly Ash Based Zeolite Composites

Dye wastewater is one of the major hazardous industrial wastewater from the dye production and application industries.The ash is solid waste from coal-fired power plants and industrial waste from current displacements.Exploring green,cost-effective and efficient ways to remove organic dyes from dye wastewater and achieve resource utilization of solid waste fly ash is a pressing issue.Common treatment methods for dye wastewater include adsorption and photocatalysis.As a common adsorbent,zeolite is widely used in the treatment of dye wastewater.Zeolite is a silica-alumina compound consisting of three atoms of silicon,aluminum and oxygen in a three-dimensional skeleton structure.The main components of fly ash are silica and alumina,which together account for more than 80 wt.%.Therefore,fly ash can be used to prepare zeolite-based adsorbent,so as to achieve the purpose of "treating waste with waste".The main results of the study are as follows.(1)The effect of Si:Al on the crystal structure,microstructure and adsorption properties of methylene blue dye and the mechanism of zeolite were studied by alkali melt-hydrothermal method using solid waste fly ash as raw material and sodium silicate and sodium aluminate to control the ratio of Si:Al in raw material.The results show that zeolite A in cubic configuration(ZA)is synthesized when Si:Al is 1:1,zeolite X in octahedral configuration(ZX)and zeolite Y in octahedral configuration(ZY)are synthesized when Si:Al is 1.5:1 and 3:1.The specific surface areas of ZY and ZX zeolites are up to 386.7149 m2 g-1 and 373.8945 m2 g-1,which are 21.2 times and 20.5 times higher than those of ZA,respectively,indicating that zeolites with octahedral configuration have larger specific surface areas.The adsorption properties of ZA,ZX and ZY on methylene blue dyes have been investigated.The adsorption properties of ZA,ZX and ZY on methylene blue were found to be up to 16.973 mg g-1,41.309 mg g-1 and 49.266 mg g-1 respectively.The adsorption properties of ZY are about 15 percent higher than the highest values reported in the literature.It can be seen that Y-zeolite prepared from fly ash has excellent adsorption properties for methylene blue dye.The adsorption behavior of methylene blue dye by ZA,ZX and ZY zeolite was studied.The results showed that the adsorption behavior of ZA,ZX and ZY zeolite was consistent with pseudo-second-order kinetic model and Langmuir isotherm model,indicating that the adsorption behavior of ZA,ZX and ZY zeolite to methylene blue dye was a chemical adsorption occurring on the surface of a single layer.(2)Due to the high cost of regulating Si:Al with sodium silicate as a source of silicon,to further reduce the cost of synthesizing Y-zeolite,diatomite is used as a source of silicon to regulate the silica-sodium ratio and prepare Y-zeolite.Zeolite Y was synthesized from fly ash and diatomite by alkali melting-hydrothermal method.The effects of silica-sodium ratio(molar ratio of silicon in raw material to sodium hydroxide in alkali melting-process),alkali melting-temperature and hydrothermal crystallization time on the morphology of zeolite Y and on the adsorption properties of crystal violet,methylene blue and basic fuchsin dyes were studied.The results show that the crystallinity of Y-zeolite is higher when the silica-sodium ratio is 1:3,the alkali melting temperature is 550℃,and the hydrothermal crystallization time is 12 h.The theoretical adsorption capacity of crystal violet,methylene blue and basic fuchsin can reach 78.72 mg g-1,42.68 mg g-1 and 195.194 mg g-1.It can be seen that the Y-type zeolite adsorbent synthesized with low-cost diatomite as a silicon source has excellent adsorption capacity for a variety of dyes.The kinetics of adsorption and thermodynamics of dye production in Y-zeolite have been studied.It is shown that the Langmuir isotherm model and best fits the proposed secondary kinetic model.(3)In order to further improve the dye removal effect of zeolite,the optimal Y-type zeolite synthesized by fly ash and diatomite was used as the carrier,the solid phase dispersion method was used to support nano-titanium dioxide(TiO2)on the surface of Y-type zeolite(TiO2/ZY composite material),and the combined effect of adsorption and photocatalysis was used to improve the dye removal effect.The adsorption properties of TiO2/ZY composites on fundamental fuchsin and crystalline violet dyes have been investigated.It has been shown that TiO2/ZY composites exhibit excellent removal of organic dyes under the combined effect of adsorption and photocatalysis.