Radium attenuation and mobilization in stream sediments following oil and gas wastewater disposal in western Pennsylvania

The Role of Barite in the Post-Mining Stabilization of Radium-226: A Modeling Contribution for Sequential Extractions

“…As seen on Figure 1, the Ba did not remain in the deionized water solution but was sorbed onto the clay minerals at this step, allowing for barite to continue to dissolve. This could explain some of the Ba that was found in the exchangeable fraction during sequential extractions on samples containing both clay minerals and barite [3]: part of the Ba sorbed onto the clay minerals at the first step and then exchanged for Cs (or another cation, depending on the reactant used) on the clay mineral sorption sites. The low occurrence of barite in the tailing samples does not permit XRD identifications.…”

“…Most environmental studies aim to understand the mobility of the chemical elements and their environmental and human health risk. Such studies require (i) the analysis of the chemistry of solutions and the reactivity of solids and (ii) the linking of the in situ observations to experimental results and models [1][2][3][4]. The sequential extraction technique allows for the characterization of the binding phases and the retention capacity (solubility of phase, sorption, coprecipitation) of an element of interest in a solid sample.…”

“…This results in a variety of reactants, reaction time, solid/liquid ratio and number of extracting steps [15,16], making cross-comparison difficult. For example, Figure S1 in Supplementary Materials shows that when comparing 25 sequential extraction studies, the liquid to solid ratio values varied from 6 to 100 mL/g [2][3][4][6][7][8][9]12,[15][16][17][18][19][20][21][22][23][24][25][26]). An important experimental constraint is also the number of replicates required, making this technique time consuming.…”

“…226 Ra is an alpha emitter with a high specific activity (3.7 × 10 10 Bq/g) [29]. This is an issue for U mining, and also for other extractive industries such as coal mining [27,30], the production of phosphate fertilizers [27] and of non-conventional oil and gas [3,17,23,31]. U-bearing ore usually presents 226 Ra in secular equilibrium with 238 U because most U mineralization is older than 1.5 million years [32][33][34][35].…”

“…Many studies have used sequential extractions to localize Ra [5,61]. 226 Ra was usually reported mainly in the residual phase [3,9,13,17,62], but also with high extraction rates (>10% of the total 226 Ra) in the soluble fraction [17,18], the exchangeable fraction (adsorbed on clay minerals surfaces) [9,63], the organic matter fraction [13,63], the reducible (Fe and Mn oxides) fraction [4,8] and the carbonate fraction [3]. Some conclusions clearly contradict each other [48,52,64,65].…”