Preparation Of Hydrotalcite From Aluminum Dross And Its Adsorption Properties

In the aluminum industry,aluminum dross is an unavoidable by-product.Due to its complex and diverse components,recycling it into aluminum production seems to be elusive.However,if it is piled up or buried untreated,it will lead to environmental pollution,negative impacts on human health,and the waste of aluminum resources.As a solid waste,aluminum contains rich aluminum resources.Therefore,it is practically significant to research the approach to comprehensively utilize the aluminum dross and generate valuable products.This thesis intends to synthesize zinc-aluminum hydrotalcite using aluminum ash as raw material.Firstly,X-ray fluorescence elemental analysis was carried out on the aluminum ash slag from different aluminum profile factories,and the aluminum element content in the aluminum dross was found to be 28%to 52%.X-ray diffraction analysis and its phase analysis revealed that the main forms of aluminum are elemental aluminum,aluminum oxide,aluminum nitride,and magnesium-aluminum spinel.Moreover,the morphology of the aluminum dross with severe agglomeration was observed through the scanning electron microscope.Then,the aluminum dross was extracted with two extractants:hydrochloric acid and sodium hydroxide.After using XRD to compare the phase before and after the extraction,it was found that the phase related to aluminum almost disappeared,indicating that most of the aluminum had been extracted.Furthermore,the aluminum content of the two extraction solutions was measured with ICP,which was 14.03 g/L and13.82 g/L using the sodium hydroxide extract and the hydrochloric acid extract respectively,while the latter contained more types and contents of impurities.Since the extract contains a variety of non-Al metal ions,by selecting divalent ions(Mg²⁺)and trivalent ions(Fe³⁺)to verify the influence of impurity ions in aluminum dross on the synthesis of zinc-aluminum hydrotalcite,the following conclusions are drawn.The addition of Mg²⁺and Fe³⁺has a certain effect on the relative intensity of the peaks of the XRD pattern,and the relative intensity decreases slightly with the increase of the additional amount.According to the structural parameters,it is calculated that Mg²⁺and Fe³⁺have little effect on the interplanar spacing and unit cell parameters but have a greater effect on the grain size in the a-axis and c-axis directions.Both declining trends were also observed in the zinc-aluminum hydrotalcite synthesized using alkaline extracts and those synthesized using acidic extracts.In addition,it can be concluded from the SEM images that the addition of Mg²⁺and Fe³⁺and the use of alkaline and acidic extracts have little effect on the morphology of zinc-aluminum hydrotalcite synthesized.According to the experiments above,under the condition that the use of aluminum dross to synthesize zinc-aluminum hydrotalcite had little effect,the influence of its reaction temperature and reaction time on hydrotalcite was explored.It can be concluded that with the prolongation of synthesis time,the XRD results demonstrated that the relative intensity of the peaks increased,especially for the 003-crystal plane,the peak increased significantly,and the grain size also increased.With the increase in synthesis temperature,XRD results showed that the intensity of diffraction peaks decreased,the samples began to appear impurity peaks at 150?,and there were no characteristic peaks of hydrotalcite at 170?.In addition,the results suggested that the crystallinity of the zinc-aluminum hydrotalcite synthesized by the alkali extraction solution was better because the alkali extraction solution contained fewer impurity metal ions.The hydrotalcite synthesized under different conditions showed different adsorption capacities of F^-,and the synthesis temperature significantly affected the adsorption capacity.The adsorption amount was the largest at 18.3mg/g when the reaction time of the zinc-aluminum hydrotalcite synthesized by the alkali extract was 6 hours and the reaction temperature was 130?.The synthesized zinc-aluminum hydrotalcite was tested according to the industry standard HG/T 5549-2019,and the measurement result met the requirements of the first-class product.Finally,the adsorption behavior of fluoride ions was investigated.The results showed that the adsorption equilibrium was reached at 20 hours,the adsorption capacity of LDHs(OH^-)was 19.35 mg/g,and the adsorption capacity of LDHs(H⁺)was 19.09 mg/g;using pseudo-first-order and pseudo-second-order kinetics of the adsorption kinetics,the fitting results proved that it was more consistent with the pseudo-second-order kinetics,indicating that the mechanism controlling the adsorption efficiency is chemisorption;the Langmuir isotherm and the Freundlich adsorption isotherm equation model were used to fit the adsorption data,and the fitting results displayed that it was more in line with the Langmuir isotherm adsorption;in addition,the adsorption temperature can increase LDHs(OH^-)and LDHs(H⁺)on the adsorption capacity of fluoride ions,but the improvement effect was not significant.