The Adsorption Characteristics For Radionuclides On Collagen Fiber Immobilized Tannins

This research was supported by the National Key Technology R&DProgra m of China. The project is the preparation and study ofbioadsorbent for mining wastewater （No.2007BAB18808）.Collagenfiber immobilized tannins （CFIT）, which was a new type and renewablebiomass adsorbent. It’s physical and chemical characteristics, theadsorption characteristics and adsorption selectivity in the Th⁴⁺, U6⁺,Sr²⁺, Cs⁺four radionuclide ion single ion system, the the binary mixedion system and ternary mixed ion system solution. Using the CFITadsorbents as adsorption column packing, the adsorption characteristicsof Th⁴⁺, U6⁺, Sr²⁺three nuclides ion were studied. At last, theadsorption mechanism and material recycling of the adsorbent wasinvestigated.The results wereas follows:1. The particle size of the CFIT was mainly in220μ m nearby.Themicro-mo rphology analysis showed that the material was primarilymany fibers interwov enentwined and its specific surface area was only1.74m2/g.The adsorbent was mainly contained C, H, O, N four ele ments,only a s mall a mount of Cr3+elements, and contained a lot of easy withheavy me tal ions complexation functional groups, such as a mino,carboxyl, polyphenol hydroxyl.The zero potential of the CFIT waspH=2.3, and it belonged to the amorphous material. The decompositiontemperature of CFIT was262.54℃.2. The adsorption studies in a single radionuclide ion system (Th⁴⁺,U6⁺, Sr²⁺, Cs⁺) were showed that:when the experi mental conditionswere set as follows, the initial radionuclide ion concentrations（C0） forTh⁴⁺, U6⁺, Sr²⁺, Cs⁺were20mg/L, and the dose of the CFIT were0.1,0.03,0.1,0.05g, respectively. The adsorption ti me was24h, thetemperature was25℃and the pH value of the solution varied from1to8,the removal efficiency of t he collagen fiber immobilized tannins forfour nuclide ions were7.20⁹2.86%,4.93⁹2.20%,16.70⁴9.76%,5.97¹2.91%, and the optimum pH values were selected as3.0,5.5,6.0,5.0. When the experimental conditions were set as follows, the initial radionuclide ion concentrations（C0） for Th⁴⁺, U6⁺, Sr²⁺, Cs⁺were20mg/L, the adsorption ti me was24h, and the temp erature was25℃.The pH values were3.0,5.5,6.0,5.0, and the dosage was changedfrom0.02⁰.2g,0.005⁰.09g,0.05⁰.4g,0.05⁰.4g. The removalefficiency for Th⁴⁺, U6⁺, Sr²⁺, Cs⁺were78.86～97.90%,94.80～96.55%,29.82～44.15%,10.42～15.15%, and the best dosages wereselected as0.06,0.03,0.1,0.1g. The experi mental conditions were setas follows, the initial radionuclide ion concentrations（C0） for Th⁴⁺, U6⁺,Sr²⁺, Cs⁺were20mg/L, the doseages were0.06,0.03,0.1,0.1g, the pHvalues were3.0,5.5,6.0,5.0, and the adsorpti on time was24h. Thetemperature was all selected15,25,35,45,55℃.The results of theremoval efficiency for Th⁴⁺, U6⁺, Sr²⁺, Cs⁺at55℃,55℃,35℃,35℃reached the maximu m and the re moval efficiency were98.66%、98.58%、39.68%、15.02%, respectively. The removal efficiency for Th⁴⁺, U6⁺ofthe CFIT increased with the increasing of temperature. The adsorptionprocess was spontaneous and endother mic under the laboratoryconditions, while the removal efficiency for Sr²⁺and Cs⁺were l es saffected by temperature, and the adsorption perfor mance was theexothermi c reaction and was non-spontaneous at high te mperatures. Theexperimental conditions were set as fo llows, the initial radionuclideionconcentrations（C0） for Th⁴⁺, U6⁺, Sr²⁺, Cs⁺were20mg/L, thedoseages were0.06,0.03,0.1,0.1g, the pH values were3.0,5.5,6.0,5.0, and the temperature was25℃.The adsorption time was changedfrom10～720min,10～480min,10～720min,10～1200min, and thebest time of treatment were t(Th⁴⁺)=240min, t（U6⁺）=240mi n,t(Sr²⁺)=240min, t（Cs⁺）=180min, respectively. The experimental datawere wellfitted by the pseudo-second-order model, and the equilibriumsorption capacities calculated by the model were al most the sa me asthose deter mined by experiments.The adsorption isother m resultsshowed that the adsorption for the radionuclides Th⁴⁺and U6⁺by theCFIT were agreed very well withthe Langmuir monolayer adsorptionmodel, but it did not fitted with the Freundlich multi-molecular layeradsorption model. Langmuir and Freundlich adsorption models were not agreed with the adsorption data for the radionuclides Sr²⁺and Cs⁺. Themaxi mu m adsorption capacities of the CFIT for Th⁴⁺, U6⁺, Sr²⁺, Cs⁺were41.3394mg/g,352.1127mg/g,9.2825mg/g,6.3930mg/g,respectively.3. Under the binary mixed ion system and ternary mixed ionsyste m, the adsorption properties and the effects of removing the heavymetal ions by the pH of t he solution, the adsorbent dosage, thetemperature, the adsorption time, the initial concentration of heavymetal ions were studied.The results showed that:the collagen fiberimmobilized tannins had a good selectivity for different heavy metalions, the adsorption behavior of the mixed radionucli de solution werewell agreed with the pseudo-second-order kinetics mod el, a n d t hefitting results by the adsorption isotherm model also showed that theadsorption of various radionuclides by the CFIT were fitted with theLangmuir isother m model.4. The adsorption effect of for Th⁴⁺, U6⁺and Sr²⁺using collagenfiber immobilized tannins as the adsorbent and the use of dynamicadsorption column experime nts under the initial concentration of theradionuclide, the flow rate and packing height three fact ors. The resultsshowed that: the penetration point and the exhaustion pointofthe bedvolume wereincreased with the increasing the initial concentration ofnuclides, and delayed with the increasing the height of the adsorptioncolumn. The adsorption of Th⁴⁺increased with the flow rate of theradionuclide solutionin advance. It may be provided a reference inhandling radioactive nuclides wastewater and the practical application.5. Combined with the physical and che mical pr operties of thecollagen fiber immobilized tannins and adsorption characteristics ofradionuclide ions, the adsorption mechanism of the CFIT wa s discussedunder the ionic radius of the radionuclide ions, ion valence, atomicmass, electronegativity in the existing form of the solution and thecoordination ability.The results showed that: the collagen fiberimmobilized tannins and radionuclide ion was mainly in complexationreaction and the ion exchange was only accounted a small proportion of physical adsorption.The larger of the nuclides ion mo lar mass, thesmaller of the ionic radius, the more easily comb ined the material. Theadsorbent was also correlated with ion electrospray negative,its stat epresented in the solution, the amount of adsorbent and the adsorbentmaterial in the enviro nment of the solution.6. Using the collagen fiber i mmobilized tannins column afteradsorbed the radionuclide saturation, the regeneration experimentsshowed that the adsorbent could be regenerated by0.1mol/L H₂SO₄,andreused at least eight cycles until the adsorption capacity47.92%forTh⁴⁺comp aring the initial use.The material was easily treated afterinactivation. TG analysis results showed that the weight lossratio was54%after deactivation of the CFIT, and its volume rate was1/13.With all the experimental data and theoretical analysis, it could beconcluded that the collagen fiber i mmo bilized tannins for re moving theradionuclides showed good adsorption and adsorption selective.Itshowed a good application prospects in the field of radioactive wast ewater treatment and environmental restoration.