TESTING METHODS TO DETERMINE SR/BA IN NATURAL TERRESTRIAL BARITE SAMPLES

The purpose of this study was to measure the elemental ratio of Sr/Ba in the natural (continental microbially-mediated) barite (BaSO₄) by dissolving the samples and running them on the ICP-OES at Kent State University. Nearly pure barite residues were first separated from sediment samples following Paytan et al. (1993). Barite residues were then dissolved following the methods of both Averyt et al. (2003) and Bao (2006).

The first barite dissolution experiment followed the method of Averyt et al. (2003). One lab precipitated barite sample and seventeen natural barite samples were dissolved in an ethylenediaminetetraacetic acid-potassium hydroxide (EDTA-KOH) solution. The solution was prepared with 10 mM EDTA in 0.2 M KOH. The samples were analyzed using ICP-OES after 4-5 days of dissolution.

The second barite dissolution experiment followed the method of Bao (2006). The same set of samples that were dissolved in the EDTA-KOH solution were used in this experiment. The samples were dissolved in a diethylenetriaminepentaacetic acid-sodium hydroxide (DTPA-NaOH) solution. This solution was prepared with 50 mM DTPA in 1 M NaOH. The barite appeared to dissolve faster using this method and after three days of dissolution, the samples were analyzed using ICP-OES.

The solutions in both methods showed residue from the natural samples after 3-5 days. Solid that was left in the EDTA-KOH solution was analyzed using an Environmental SEM, which showed that in most samples the residue was < 1-10% barite.

Analysis of both solutions on the ICP-OES showed the plasma was more stable when running the EDTA-KOH solution. The relative standard deviation for Sr was around 3% for this method and was much higher when running the DTPA-NaOH solution. This leads to the conclusion that the method by Averyt et al. (2003) is recommended for future work.

The EDTA-KOH solution results from the ICP-OES were also studied. When comparing Sr/Ba of barite and Sr/Ba of the natural waters and other environmental data (e.g., saturation state of barite, temperature, conductivity, [Sr], [SO₄], [Ba], Δ^88/86Sr_barite-water), there were no significant relationships found. Currently, it is unknown if there is a relationship with microbial activity at these sites. Further studies may help to find the controlling factors of the Sr/Ba in these natural barite samples.