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Characteristics and mechanisms of phosphate removal by calcium-iron layered double hydroxides and their hydrolysis products

Abstract : The development of an efficient removal material for phosphate from wastewater to prevent the eutrophication in surface waters is very important. In this study, CaIIFeIII layered double hydroxide containing chloride and nitrate as intercalated anions (CaFe-LDH-Cl and CaFe-LDH-NO3) were used as removal materials for phosphate. Both forms were designed and synthesized at different CaII: FeIII molar ratios (2:1, 3:1, and 4:1) following three simple co-precipitation methods. The materials were evaluated for the removal of phosphate by batch equilibrium sorption experiments and kinetic measurements. The efficiency of the phosphate removal from aqueous solution was investigated in the range pH 4-12. As a result, it was found that pseudo-second-order kinetic model described well the phosphate removal. The isotherms of adsorption of PO43- ions showed that CaFe-LDH-Cl and CaFe-LDH-NO3 at CaII: FeIII molar ratio of 2:1 revealed the highest rate of phosphate uptake of 385 and 402 mg g-1, respectively, comparing to other CaII: FeIII molar ratios. Equilibrium data were well fitted with Freundlich and Langmuir isotherms. In the case of high phosphate concentration ([PO43-] [> or =] 100 mg L-1), the comprehensive analysis of the phosphate-uptake products with different techniques revealed that CaFe-LDH dissolve first and then released Ca2+ ions reacting with PO43- anions to form Ca5(PO4)3OH (hydroxyapatite) which is the main mechanism for phosphate removal. Also, phosphate was removed partially via a subsidiary process other than precipitation of hydroxyapatite. The excess in phosphate removal was attributed to the formation of a disordered Ca doped ferrihydrite which removed phosphate via simple surface adsorption. In the case of initial low phosphate concentration ([PO43-] < 100 mg L-1), the analysis showed that PO43- removed mainly via simple surface adsorption over disordered Ca doped ferrihydrite which was the main component in the residual solid after partial Ca2+ releasing from LDH
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Submitted on : Friday, March 30, 2018 - 9:56:31 AM
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Muayad Al-Jaberi. Characteristics and mechanisms of phosphate removal by calcium-iron layered double hydroxides and their hydrolysis products. Other. Université de Lorraine, 2016. English. ⟨NNT : 2016LORR0056⟩. ⟨tel-01754654⟩



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