Research On Preparation Of The Load Of Double Metal Ions Polysaccharide Microsphere And Its Adsorption Performance For Uranium And Fluoride

The wastewater resulted from uranium purification and transformation in the production of nuclear fuel contains not only uranium but fluorine.The emission of this type of wastewater causes the fluorine and uranium pollution in the water and will do harm to the health of people and the organisms.Therefore.the efficient removal of uranium and fluorine from fluoro-uranium mixed aqueous solution has received great attention.Adsorption is mostly utilized owing to its high removal efficiency to low concentration of radioactive wastewater,high flexibility,regeneration of adsorbent,and low cost.The existing adsorbent achieved the goal of fluoride or uranium removal,but could not attain the goal of the two kinds of ions removal simultaneously.Therefore,it is of great significance to search for a double-functional adsorbent with high efficiency and low cost.Two kinds of adsorbents are prepared in this study,one is carboxymethyl konjac glucomannan loaded with lanthanum and aluminum microsphere(CMKGM-La-A1),the other is alginate/carboxy methyl cellulose sodium composite microsphere loaded with calcium and aluminum(S A/C MC-Ca-Al).The adsorption properties,mechanism and regeneration and recycling process of the adsorbents are investigated.Results are shown as follows:1.CMKGM-La-Al microsphere adsorbent was synthesized via the sol-gel method using static-electricity spraying pump.Effects of mass ratio of Al3+ and La3+ and mass fraction of CMKGM on gel strength were investigated,and the adsorption performances on uranium and fluoride were also investiganted.4 wt%of CMKGM and the mass ratio of Al3+ and La3+ of 2:1 were selected as the conditions for preparation of the CMKGM-La-Al microspheres with high compressive strength.The results of adsorption demonstrated that the maximum adsorption amount of uranium was found to be 45.451 mg g-1 at pH 5,initial concentration of 40 mg L-1 and 15 h of contant time while that for F-was 20.37 mg g-1 at pH 2.0,concentration of 40 mg L-1 and 4 h.The asorption isotherm,adsorption kinetic and Thermodynamics of uranium and fluoride adsorption onto CMKGM-La-A1 was studied.Results indicated that the adsorption process could be well described by Langmuir isotherm model.while the kinetic data conformed successfully to the pseudo-second-order equation.both of the adsorption of uranium and fluoride on CMKGM-La-Al was spontaneous process.The adsorption capacity of the adsorbent only changed slightly in the presence of other co-existing anions or cations in fluoro-uranium mixed solution.The results of regeneration and recycle of CMKGM-La-Al showed that the adsorbent possessed a superior recycling ability,and the removal efficiency could be remained more than 72%after 4 cycles for fluride,while that for uranium was more than 800%after 5 cycles.The volume reduction rate of adsorbents after burnt can be reached more than 90%.The mechanism of La(?)and A1(?)immobilized and adsorption of uranium and fluoride on CMKGM-La-Al was analyzed by SEM,FT-IR,EDX,pHpzc and XPS.Results suggest that the CMKGM-La-Al adsorbent had a great potential in removing uranium and fluoride from aqueous solution.2.The SA/CMC-Ca-Al composite microsphere adsorbents were synthesized from S A and CMC through sol-gel method using static-electricity spraying pump.Effects of mass ratio of SA and CMC,mass concentration of Ca2+ and Al3+ on gel strength were studied.Results showed that the optimum synthesis conditions of the composite microsphere with high gel strength were SA/CMC mass ratio of 9:1 and the concentration of SA/CMC solution was 2.5 wt%,mass concentration of Ca2+ was 3 wt%and the mass concentration of Al3+ was 7.5 wt%.The result of studies for uranium and fluoride adsorbed onto dual functional microsphere adsorbents of SA/CMC-Ca-Al from fluoro-uranium mixed aqueous solution system showed that the maximum adsorption amount for uranium was 101.76 mg g-1 at pH 4.0,298.15 K,concentration 100 mg L-1 for 15 h,while that for fluoride is 35.98 mg g-1 at pH 2.0,298.15 K,concentration 100 mg L-1 for 4 h.The asorption isotherm,adsorption kinetic and Thermodynamics of uranium and fluoride onto SA/CMC-Ca-Al were investigated.Results indicated that both of the adsorption process could be well described by Langmuir model.The adsorption kinetic data was fitted well with pseudo-first-order model for uranium and pseudo-second-order model for fluoride.The adsorption capacity only changed slightly in the presence of other co-existing anions or cations in fluoro-uranium mixed solution.The results of regeneration and recycle of SA/CMC-Ca-Al showed that the desorption efficiency was more than 75%after 5 cycles for fluride,while that for uranium was more than 98%after 5 cycles.The volume reduction rate of the adsorbents after burnt can be reached more than 89%.The mechanism of modification of SA/CMC and adsorption of uranium and fluoride on SA/CMC-Ca-Al was analyzed by SEM,FT-IR,EDX and XPS.Results suggested that the SA/CMC-Ca-Al adsorbent had a great potential in removing uranium and fluoride from fluoro-uranium mixed aqueous solution.3.Then adsorption performance of SA/CMC-Ca-Al adsorbents in the packed column was measured under variable operating conditions,such as bed depths,initial influent ions concentration and flow rates.The results showed that the breakthrough time and depletion time were extended with an increase in bed heights but obviously shortened with an increase in influent concentration and flow rates,respectively.The equilibrium uptake of SA/CMC-Ca-Al increased with an increase in initial influent concentration and flow rates but decreased with increase in bed depth,respectively.