Additive-free hydrothermal leaching method with low environmental burden for screening of strontium in soil

Kato, Takuma*; Nagaoka, Mika  ; Guo, H.*; Fujita, Hiroki; Aida, Taku*; Smith, R. L. Jr.*

In this work, hydrothermal leaching was applied to simulated soils (clay minerals vermiculite, montmorillonite, kaolinite) and actual soils (Terunuma, Japan) to generate organic acids with the objective to develop an additive-free screening method for determination of Sr in soil. Stable strontium (SrCl) was adsorbed onto soils for study and ten organic acids were evaluated for leaching Sr from simulated soils under hydrothermal conditions (120 to 200C) at concentrations up to 0.3 M. For strontium-adsorbed vermiculite (Sr-V), 0.1 M citric acid was found to be effective for leaching Sr at 150C and 1 h treatment time. Based on these results, the formation of organic acids from organic matter in Terunuma soil was studied. Hydrothermal treatment of Terunuma soil produced a maximum amount of organic acids at 200C and 0.5 h reaction time. To confirm the possibility for leaching of Sr from Terunuma soil, strontium-adsorbed Terunuma soil (Sr-S) was studied. For Sr-S, hydrothermal treatment at 200C for 0.5 h reaction time allowed 40% of the Sr to be leached at room temperature, thus demonstrating an additive-free method for screening of Sr in soil. The additive-free hydrothermal leaching method avoids calcination of solids in the first step of chemical analysis and has application to both routine monitoring of metals in soils and to emergency situations.