Preparation And Safety Evaluation Of Baking-Free Brick From Incineration Fly Ash And Secondary Aluminum Dross By Harmless

With the accelerated industrial process,the annual production of incineration fly ash and secondary aluminum dross produced in China exceeds 10 million tonnes and 3 million tonnes respectively.Incineration fly ash and secondary aluminum dross are complex in composition and contain high concentrations of heavy metals and other harmful substances,which are classified as hazardous waste in China,and difficult to use directly.At the same time,the increasing demand for natural sand and gravel in China has led to a series of environmental problems,such as landslides and serious damage to the natural landscape and vegetation caused by large-scale rock mining.Therefore,the search for an efficient way to use incineration fly ash and secondary aluminum dross in a harmless and resourceful way is of great significance for the health of the environment.This paper proposes the use of non-hazardous treatment agents and wrap-shell technology to prepare incineration fly ash and secondary aluminum dross free bricks,which not only broadens the way of incineration fly ash and secondary aluminum dross resource utilization but also fills part of the demand for natural sand and gravel.The specific research content and results are as follows.(1)The effect of harmless treatment on the performance of incineration fly ash,secondary aluminum dross and incineration fly ash baking-free grey brick(IFAB),secondary aluminum dross baking-free grey brick(SADB),and incineration fly ash-secondary aluminum dross baking-free grey brick(IFA-SADB)were investigated.The results show that the harmless treatment has a low impact on the basic properties of fly ash and aluminium ash,but significantly reduces the content of pollutants such as chloride salts,heavy metals and dioxins.The harmless treatment can enhance the safety of baking-free ash bricks,improve the leaching water quality and the leaching concentration of harmful substances of baking-free ash bricks.It also enhances the strength of IFAB and IFA-SADB,but reduces the strength of SADB.(2)The optimum raw material ratios for three types of baking-free grey bricks were determined through single-factor experiments.The optimal formulation for IFAB is:incineration fly ash 70%,cement 10%,fly ash 4%,metakaolin 16%,sodium hydroxide1.8%(dry basis mass ratio),water glass 1.2%(dry basis mass ratio).The optimal formulation of SADB is:secondary aluminum dross 70%,cement 10%,metakaolin 4%,gypsum 16%,water glass 1.5%(of the dry basis mass ratio).The optimal formulation of IFA-SADB is:incineration fly ash 50%,secondary aluminum dross 20%,cement 10%,fly ash 4%,metakaolin 8%,gypsum 8%,sodium hydroxide 1.8%(of the dry basis mass ratio),water glass 1.2%(of the dry basis mass ratio).The compressive strength of IFAB and SADB meets the MU 20 standard of GB/T 21144-2007"Solid Concrete Bricks",the compressive strength of IFA-SADB satisfies the MU 15 standard.(3)Incineration fly ash was used as a raw material to prepare incineration fly ash non-sintered lightweight aggregates(IFALAs)through the wrap-shell process and applied to incineration fly ash non-sintered lightweight aggregates baking-free brick(IFALAB),and the optimum process parameters were determined as follows:aggregate/cement ratios6.0:4.0,forming pressure 12.5 MPa,aggregate grading(1-3 mm:3～5 mm)under the condition of 3:7.The prepared IFALAB has the best properties,with a density of 1786kg/m~3,24 h water absorption of 7.1%,compressive strength of 21.8 MPa,flexural strength of 4.7 MPa,reaching the MU 20 strength grade in GB/T 21144-2007.(4)The mineral composition and morphological characteristics of the baking-free bricks were analysis by XRD and SEM.It was found that the main factors affecting the mechanical properties of baking-free bricks are the mineral composition and chloride content of the baking-free bricks.The IFALAs core-shell interface is relatively porous and loose,resulting in the low strength of the IFALAs itself,but the core-shell structure of IFALAs allows for a tight connection between the IFALAs and cementite interfaces,thus compensating for the relatively loose structure and low strength of the IFALAs core-shell interface.(5)The environmental safety of the four types of baking-free bricks was investigated.The safety evaluation results show that the leaching water quality test results and harmful substances test results of baking-free bricks meet the requirements of GB 3838-2002“environmental quality standards for surface water”and do not produce secondary pollution to the environment.The results show that the environmentally safe preparation of baking-free bricks from incineration fly ash and secondary aluminum dross is feasible.