title: Performance of phosphoric acid activated montmorillonite as buffer materials for radioactive waste repository.
abstract: In this study, the performance of phosphoric acid activated montmorillonite (PAmmt) was evaluated by cesium ions adsorption experiments. The PAmmt samples were obtained by activating with 1, 3 and 5 mol L(-1) of phosphoric acid, respectively under reflux for 3, 12, and 24h. Experimental results demonstrated that the treatment of raw K-10 montmorillonite with phosphoric acid increased the materials' affinity for Cs uptake and no significant amount of suspension solids were produced. A relatively insignificant variation in the CEC value was observed. Furthermore, PAmmt also showed high adsorption selectivity toward Cs ions. The improved sorptive properties were mainly related to the increased surface area and the relatively higher surface charge density. Increased specific surface area was the resulted from partial decomposition of lamellar structure of mmt; while the higher surface charge density was caused by the protonation of octahedral Al-OH sites during the acid activation. Generally speaking, stronger acid concentration and longer activation times would produce relatively more decomposed PAmmt particles. However, as the activation exceeds 3h, the precipitation of Si(4+) would passivate PAmmt against further acid attacks. Based upon our results, acid activation by phosphoric acid could produce PAmmt samples with high sorption capacity and selectivity, and good structural integrity, which are beneficial to be used at radioactive waste repository.
authors.affiliation: Institute of Nuclear Engineering and Science, National Tsing Hua University, Hsinchu 300, Taiwan.
authors.forename: Tsing-Hai
authors.initials: TH
authors.lastname: Wang
authors.forename: Tsung-Ying
authors.initials: TY
authors.lastname: Liu
authors.forename: Ding-Chiang
authors.initials: DC
authors.lastname: Wu
authors.forename: Ming-Hsu
authors.initials: MH
authors.lastname: Li
authors.forename: Jiann-Ruey
authors.initials: JR
authors.lastname: Chen
authors.forename: Shi-Ping
authors.initials: SP
authors.lastname: Teng
mesh_terms: D000143:Acids; D000327:Adsorption; D001546:Bentonite / Q000737:chemistry*; D002021:Buffers; D002586:Cesium / Q000737:chemistry; D005459:Fluorides / Q000737:chemistry; D010756:Phosphoric Acids / Q000737:chemistry*; D016062:Porosity; D011850:Radioactive Waste / Q000032:analysis*; D012037:Refuse Disposal / Q000379:methods*; D017550:Spectroscopy, Fourier Transform Infrared; D013431:Sulfates / Q000737:chemistry; D013499:Surface Properties; D013816:Thermodynamics; D014961:X-Ray Diffraction
chemical_list: D000143:Acids; D002021:Buffers; D010756:Phosphoric Acids; D011850:Radioactive Waste; D013431:Sulfates; D001546:Bentonite; D002586:Cesium; D005459:Fluorides