Efficient Recovery Of Sr(Ⅱ) Ion From Aqueous Medium Using Grafted Functional Sorbents

The removal of strontium from different aqueous media is one of the important problems of the scientific community since radioactive strontium is one of the radionuclides released after nuclear accidents that can significantly affect human health by entering the food chain.The purpose of this study is to synthesize a chemically and mechanically stable sorbents（based on silicacore）,with enhanced reactivity（due to the bifunctionality effects of methacrylicacidandamidoxime groups）for efficient removal of strontium from water resources.This work contributes to the development of bi-functional sorbents for the sorption of Sr（Ⅱ）.Silica microspheres are functionalized through the grafting of either polymethacryli cacid or amidoxime groups（mono-functional composite,PMAA/SiO₂ and PAO/SiO₂,respectively）or in combination(bi-functional composite,PAO_xMAA_100-x/SiO₂).The materialsare characterized by texturalanalysis,TGA,SEM-EDX,elementalanalysis,FTIR,XPS,pH_PZC in order to confirm the synthesis route,identify the reactive groupsand support the interpretation of sorption mechanisms toward Sr（Ⅱ）.The sorption of Sr（Ⅱ）,at optimum pH8,involvesamine groupsand hydroxyl/carboxyl groups in the bi-functional composite sorbent.The comparison of sorption properties shows that maximum sorption requiresamajority of carboxylic groups from polyacrylic compared withamidoxime functions;optimum formulation:PAO₂₀MAA₈₀/SiO₂ sorbent.Sorption isothermsare efficiently fitted by the Langmuirand Sips equations:the maximum sorption capacity reachesaround 1.38mmol Sr g^-1.Kinetic profiles for sorptionare modeled using the pseudo-first order rate equation;equilibrium isachieved within 40–60 min.Complete desorption of Sr（Ⅱ）using 1M HCl solutions is even faster;equilibrium time being 15–20 min.The sorbent can be recycled for 5 cycles withalimited decrease in the sorption performance,with full desorption.In fixed-bed column,the breakthrough curvesare fitted by the Thomas equation.In equimolar multi-сomponent solutions,the sorption is seleсtive for Sr（Ⅱ）overalkaliandalkaline earth metal ions.In multi-component solutions,the sorbent shows a preferred selectivity according the sequence:K（Ⅰ）>Ba（Ⅱ）>Na（Ⅰ）>Ca（Ⅱ）.Tested on seawater from Fangchenggang,a prefecture-level city in the south of Guangxi Zhuang Autonomous Region,People’s Republic of China;the sorbent shows high distribution ratio for Sr（Ⅱ）,B（Ⅲ）and Mo（Ⅵ）.