報告書番号

N10021

タイトル（和文）

地下水年代測定評価技術の開発（その13）－36Cl/Cl測定前処理法としてのカラム法における共存イオンの影響評価とその対策－

タイトル（英文）

Research and development on groundwater dating(Part13) -Estimation of impact of coexistent anions to "Column method" and improvement of pretreatment method-

概要 （図表や脚注は「報告書全文」に掲載しております）

著者らは既報で硫酸イオンと塩化物イオンを精度良く分離可能なカラム法を開発し、これによって36Clを用いた地下水年代評価を高精度化することができた。本研究では、カラム法を実サンプルに適用するため、カラム法の阻害要因である塩化物イオン以外の陰イオン濃度が高いサンプルへの適用法について検討した。高濃度の硝酸イオンやフッ化物イオン濃度がカラム法の阻害要因となるサンプルについては、塩化銀として塩化物イオンを回収する方法を提案した。また、炭酸水素イオンが阻害要因となる、塩化物イオン濃度が低い天然水では、pHを制御して炭酸水素イオンを除去する手法を開発し、カラム法の適用を可能とした。これらの前処理手法の開発によって、カラム法を全てのサンプルに対して適用可能とすることができた。

概要 （英文）

The column method that is the methodology to separate Cl- and SO42- ions resin in solution based on column chromatography with anion exchange resin has been developed in our previous study. This method has following advantages over the BaSO4 method: (1) complete and stable separation of Cl- and SO42-, (2) less operator influence on results, (3) short processing time (<6 h), (4) high (almost 100 %) recovery of Cl-and (5) concentration of Cl- and separation from SO42- in the one system for dilute solutions. However this method is not applicable to solutions those have high anion concentration because exchangeable-sites on resin were occupied by anions other than Cl-. In this study, pre-treatment method was developed so that column method is applicable to solutions with high anion concentration.
Concentrated HF and HNO3 solutions were used to dissolve rock matrix to analyze 36Cl/Cl in rock samples. Thus Cl solution extracted from rock samples contains F- and NO3- ions with high concentration. For such solutions, F- and NO3- ions can be removed by using AgCl precipitation. AgCl was dissolved by 3.0mol/L NH3 solution to obtain solution with Cl- ion solution. We have found this NH3 solution with Cl- ion can be treated by column method directly because OH- produced from NH3 has little influence on Cl chromatogram in column method.
Application of column method to groundwater with low Cl- concentration was also investigated. HCO3- ion was found to affect the retention time of Cl- ion at column method and it can be removed by using exchange reaction between ion exchange resin and cations in groundwater without changing the concentration of Cl- in groundwater. After the removal of HCO3- ion, column method was confirmed to be applicable to groundwater with low Cl- concentration.

報告者

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