May 22 2019
Scientists from the University of Houston and the national laboratories across the United States discovered a new approach for removing toxins from water, as well as wastewater generated by hydraulic fracturing, to find a solution for a scientific problem.
Yandi Hu, assistant professor of civil and environmental engineering at the University of Houston, led a team of researchers in developing a better understanding of the presence of strontium-rich barite in the seawater. (Image credit: University of Houston)
The outcomes of the study focus on the mystery of why the mineral barite—often linked with the chemical element strontium—is extensively present in seawater and have been reported in an article published in the Proceedings of the National Academy of Sciences.
According to Yandi Hu, assistant professor of civil and environmental engineering at the University of Houston and corresponding author of the study, the seawater is undersaturated with regards to barite, meaning that the barium and sulfate ion concentrations are extremely low to form precipitates of barite. She reported that as strontium sulfate is highly water soluble compared to barium sulfate, thermodynamic levels of strontium in the precipitates of barium sulfate should also be low.
However, barite is often present in seawater as strontium-laced barite. She and her coworkers carried out the study based on the field-site findings that the presence of barite and high strontium levels in barite are connected with the presence of organic matter.
Along with Hu, the remaining coauthors of the study are Ning Deng and Bo Cao of University of Houston, Andrew Stack and Julian Weber of the Oak Ridge National Laboratory, and James De Yoreo of the Pacific Northwest National Laboratory.
The authors reported that “An understanding of barite precipitation in the ocean, which is globally undersaturated with respect to barite, is missing. Moreover, the reason for the occurrence of higher [strontium] content in marine barites than expected ... remains unknown.”
It was predicted by field data that barite precipitates were more likely to be found in seawater if organic material was within reach; however, the scientists explained that a particular mechanism for mineral-organic interactions was not clear.
For this reason, they used organic films in supersaturated and undersaturated solutions and determined barite nucleation. It was found from the analysis that there was a rapid growth of barite in the solution, with constant nucleation of barite at the solution-organic film interface.
According to Hu, this interface can develop a condition—a microenvironment—that differs from that of the main body of the solution.
The organics can enrich ions from the bulk solution, making the local solution at the interface supersaturated with respect to barite, even when the bulk solution was undersaturated.
Yandi Hu, Assistant Professor of Civil and Environmental Engineering, University of Houston
She explained that although the supersaturation along the organic film supported constant nucleation of barite at the interface, it is proven that the strontium sulfate that showed relatively lower nucleation energy caused the inclusion of strontium into the precipitates. “That explains the mysteries.”
Besides explaining the barite formation rich in strontium in marine environments, the scientists described that the research provides new insights for understanding and manipulating solid solution nucleation and growth, resulting in new techniques for the removal of toxins from water and other liquids. Hu stated that this includes the potentially feasible method of removing strontium from the produced water by hydraulic fracturing.
She expressed that strontium and barite are often present in the produced water. Although barite could be easily removed to an extent by adding sulfate, the removal of strontium is more complex. “We propose that with an organic presence, you can remove strontium more effectively.”
This study was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division.