Recovery Of Silicon, Aluminum And Iron In Feedwater Sludge And Preparation Of Its Derived Nanomaterials

Water plant produces much Drinking-water treatment sludge（DWTS） by coagulation-sedimentation everyday, the constituent of it about coagulant and organic have great impact on the environment. It produces about 1.5-2.4 million tonnes of dry DWTS every year in China. it is regarded as waste and discharged directly into the river for a long time, so it brings great environmental impact about the aquatic environment. Today, in order to reduce the cost of DWTS and avoid secondary damage, its utilization has attracted much attention. The main constituents of the DWTS are clay, humus and coagulant, so the main chemical element are Si, Al and Fe. We can produce more environmental benefits if recycle, purify and make use of it. Therefore, how to scientifically and reasonably use of DWTS is very hot.In this work, the concentration of main inorganic elements leached from DWTS was investigated. Firstly, acid extraction was applied to obtain sodium aluminate and then alkaline extraction was applied to obtain sodium silicate, and using them as raw material. Specific surface area and pore volume of mesoporous silicon dioxide（1241.2 m2/g, 1.2 cm3/g）, mesoporous alumina（332.9 m2/g, 0.52 cm3/g） and mesoporous silica-alumina oxide（743.4 m2/g, 0.73 cm3/g） is good. As a result of these porous materials with abundant surface functional groups and porous structure, which can be used in many aspects such as adsorption and carriers. And large amounts of iron waste generated can be further extracted.The Fe was extracted from DWTS by acid, and it was synthesized to Fe3O4 and Fe2O3 magnetic particles. The Si composition of DWTS was extracted by alkali and mixed with the magnetic particles. The mixture was prepared for Fe3O4@SiO₂ and Fe2O3@SiO₂ composite, SiO₂ layer on Fe3O4 magnetic particles work as protective effects to avoid magnetic particles oxidize and retain magnetic responsiveness. Magnetic crystal structure of Fe3O4@SiO₂（390.0 m2/g） or Fe2O3@SiO₂（220.9 m2/g） is not influenced by the coated porous SiO₂ layer. Peaks of Fe-O stretching vibration（580 cm-1） and asymmetric Si-O-Si stretching vibrations（1080 cm-1） of Fe3O4@SiO₂ indicate the successful coating of thin silica layer（20-150 nm）. Adsorption capacity of RRX-3B and NaNO2 by Fe3O4@SiO₂ is better than that of Fe2O3@SiO₂ and both of composites can be recycled through an external magnetic field. This method is an efficient and environmentally friendly method for recycling DWTS.These raw materials of nano-materials were obtained by acid extraction and alkaline of water sludge, which provide a solution to DWTS reuse. It is an environmentally friendly, economical, and sustainable method of sludge disposal. It turns out that preparation of nano-materials of the excellent performance can deal with the problems of environmental pollution and is important to environmental protection.