Study On Preparation Of Sludge-Based Iron-aluminum Nanomaterials And Its Removal Of Fluoride And Arsenic From Drinking Water

The drinking water plant can produce a large amount of sludge during the process of water purification.If it is not properly disposed,it will cause secondary pollution to the environment.Due to the large amount of coagulant added during the operation of the drinking water plant,the content of iron and aluminum in the sludge is high.In this study,sludge from waterworks was used as a raw material.The Fe and Al contained in the sludge and the remainder were separated.The magnetic sludge-based nano-iron-aluminum composites obtained by different methods,which can be used for the removal of F and As（V）in water,respectively.The study aims to use solid waste to treat contaminated water.The iron salt and the aluminum salt contained in the sludge can be sufficiently extracted by acid leaching the pyrolysis sludge.The remainder is acid leached carbonized sludge（ALCS）.The magnetic sludge-based nano-iron-aluminum composite materials（ALCS-Fe-Al and ALCS-Al-Fe）can be obtained through different nanocrystallization methods with nano-precursors of iron salt and aluminum salt and a carrier of ALCS.The two composite materials were used to adsorb fluorine and arsenic ions in water,respectively.The optimum conditions for fluoride removal by ALCS-Fe-Al can be determined with the content of iron and aluminum of ALCS:Fe=1:1&ALCS-Fe:Al=1:2（mass ratio）and the adsorbent dosage of 3.0 g/L.Under this condition,when the initial fluorine concentration was 10mg/L,the fluoride removal rate can reach 96.2%.The residual fluoride ion concentration in the water can meet the WHO safe drinking water standard.The adsorption kinetics study showed that the adsorption process followed the pseudo second-order kinetic model.The adsorption isotherm was more consistent with the Langmuir isotherm model and the adsorption capacity was 30.49mg/g.The existence forms of nano-iron and nano-aluminum on ALCS-Fe-Al can be determined by means of SEM,BET,VSM,FT-IR and XPS and the mechanism of fluorine removal was explored.After 6 cycles of regeneration,the adsorption efficiency of ALCS-Fe-Al can still reach 85.6%.The p H of the aqueous solution（4～9）and the coexisting anions had no significant effect on the adsorption effect.The optimum conditions for As（V）removal by ALCS-Fe-Al can be determined with the content of iron and aluminum of The optimum conditions for fluoride removal by ALCS-Fe-Al can be determined with the content of iron and aluminum of ALCS:Fe=1:1&ALCS-Fe:Al=1:2（mass ratio）and the adsorbent dosage of 0.6 g/L.Under this condition,when the initial arsenic concentration is 1mg/L,the arsenic removal rate can reach 96.6%.The residual arsenic ion concentration in water can be in line with China’s standard for distributed drinking water supply（GB5749-2006）.The kinetic study showed that the adsorption process of arsenic on ALCS-Fe-Al followed the pseudo-second-order kinetics model.The adsorption isotherm was consistent with the Langmuir isothermal model and the adsorption capacity was 20.24mg/g.The existing forms of nano-iron and nano-aluminum on ALCS-Al-Fe can be determined by SEM,BET,VSM,FT-IR and XPS.The p H of aqueous solution（4～9）had little effect on arsenic removal.The common anions Cl^-,HCO₃^-,CO₃^2-,and PO₄^3-had almost no effect on the adsorption of As（V）by ALCS-Al-Fe.But SO₄^2-and SiO₃^2-inhibit the adsorption of arsenate.After three regeneration cycles of ALCS-Fe-Al,the arsenic removal rate can still reach 90.5%.The results show that the magnetic sludge-based nano-iron-aluminum composites can remove fluoride and arsenic from drinking water effectively.Consequently,this work can not only realize the recycling of drinking water sludge,but also provide a new method for the removal of fluoride and arsenic in aqueous solution.