Effect of experimental technique on the determination of strontium distribution coefficients of a surficial sediment from the Idaho National Engineering Laboratory, Idaho

The effect of experimental technique on strontium distribution coefficients (Kdʹs) was determined as part of an investigation of strontium geochemical transport properties of surficial sediment from the Idaho National Engineering Laboratory, Idaho. The investigation was conducted by the U.S. Geological Survey and Idaho State University, in cooperation with the U.S. Department of Energy. Batch experiments were conducted to quantify the effect of different experimental techniques on experimentally derived strontium Kdʹs at a fixed pH of 8.0. Combinations of three variables were investigated: method of sample agitation (rotating-mixer and shaker table), ratio of the mass-of-sediment to the volume-of-reaction-solution (1:2 and 1:20), and method of sediment preparation (crushed and non-crushed). Strontium Kdʹs ranged from 11 to 23 mlg−1 among all three experimental variables examined. Strontium Kdʹs were bimodally grouped around 12 and 21 mlg−1. Among the three experimental variables examined, the mass-to-volume ratio appeared to be the only one that could account for this bimodal distribution. The bimodal distribution of the derived strontium Kdʹs may occur because the two different mass-to-volume ratios represent different natural systems. The high mass-to-volume ratio of 1:2 models a natural system, such as an aquifer, in which there is an abundance of favorable sorption sites relative to the amount of strontium in solution. The low mass-to-volume ratio of 1:20 models a natural system, such as a stream, in which the relative amount of strontium in solution exceeds the favorable surface sorption site concentration. Except for low mass-to-volume ratios of non-crushed sediment using a rotating mixer, the method of agitation and sediment preparation appears to have little influence on derived strontium Kdʹs.