Study On The Technologies Of Extraction Of Aluminum Hydroxide From The Alum Sludge

A large number of residual solids,usually called alum sludge,are yielded from the operation unit of waterlogging and separation during the process of alum ore.Alum sludge mainly consists of undecomposed silicates and oxides of aluminium with small amounts of ferric oxide.In recent years,the management of alum sludge has become a significant issue in environmental engineering due to the enormous quantities generated and the associated disposal costs and constraints.At present,the alum sludge has been utilized partly by our country,the majority is piled up in the open.On the one hand,raw alum sludge is highly acidic,which will cause the pollution of the atmosphere,water body and soil.On the other hand,alum sludge has potassium,aluminum and other elements,which can be used as a potential reuse of resources.In order to solve the problem of low value-added of alumina slurry,in this paper,a new route to synthesize aluminium hydroxide using alum sludge as raw material was reported.The work took alum sludge as raw material and Al2O3 in material converted into NaAlO2 by means of acid-melting reaction at first.The influence of granularity of raw material,concentration of sulfuric acid,solid-liquid mass ratio,reaction temperature on extraction rates of aluminum hydroxide were obtained by using orthogonal and single-factor experiments.The optimum technological conditions of aluminium hydroxide extracting process are as follows:the granularity of raw material 60-80 mesh,the concentration of sulphuric acid 60%,the solid-liquid mass ratio 1:3,the reaction temperature 175 ?,the reaction time for 3h.After reaction under the optimum conditions,the extraction efficiency of Al(OH)3 amounted to 87.07%.According to the the differences of the precipitation value between aluminium hydroxide and iron hydroxide,99.59%iron can be removed by adjustiong the pH.Aluminum hydroxide sol obtained using sodium aluminate and sulphuric acid reaction system,then aluminum hydroxide were synthesized at room temperature and pressure or hydrothermal environment.The structure of the materials were characterized by using modern physical and chemical techniques,such as X-ray diffraction(XRD),Fourier transformation infra-red spectra(FT-IR),Thermal analyses(TG-DSC),Scanning electron micrograph(SEM)and Grainsize analyses.The results indicated that amorphous aluminum hydroxide were synthesized at room temperature and pressure,however under hydrothermal conditions,pseudo-boehmite were prepared,which the specific surface area is 101m2/g.The influence of type of the dispersing agents on the granularity and distribution of aluminum hydroxide were investigated.When adding 8%sodium dodecyl sulfate,aluminum hydroxide obtained the smallest particle size of 1.76?m.After reasonable synthetically benefit estimation on this subject,the conclusion that the acid-melting method is an ideal method to extract aluminum hydroxide from alum sludge can be got.This item can bring good economic benefit and environmental benefit.