Lanterna Rally

Author: Alissa J. O'Donnell

Publisher:

Published: 2014

Total Pages: 113

ISBN-13:

The occurrence and distribution of stable strontium around the United States was not well documented. Data from both the United States Geological Survey and United States Environmental Protection Agency from the past 10 years resulted in 39,256 samples that showed strontium was widely distributed with pockets of very elevated levels (= 10 mg/L) located along the Gulf Coast for surface water and in the Midwest for groundwater. Strontium removal data from a number of full-scale ion exchange, iron removal/coagulation, lime softening, and iron-based adsorption plants were examined. Point-of-entry ion exchange and iron removal, and point-of-use reverse osmosis effectiveness were also studied. Cation exchange and lime softening were effective strontium removal strategies, while iron removal/coagulation and iron-based adsorption approaches were not. The effectiveness of conventional coagulation and lime softening treatments on the removal of strontium at the bench-scale was needed. Alum and iron coagulants were able to achieve 18% and 6.0% strontium removal, respectively, from surface water after 0.2 æm vacuum filtering. No significant change in strontium removal was observed with the increase of coagulant dose, initial strontium concentration, pH, or initial turbidity. Lime softening was able to achieve 77% strontium removal after 0.2 æm vacuum filtering. Higher strontium removal efficiencies were seen at higher lime dosages which corresponded to a higher final pH. No significant changes in strontium removal was observed with the increase of initial strontium concentration. Fundamental studies were conducted with nanopure water to find the mechanism(s) for the lime softening strontium removal efficiencies. When calcium was not initially added, no significant change in strontium removal was observed with the increase of pH or initial strontium concentration. When calcium was initially added, the strontium and calcium removals were significantly increased above pH 11 to 65% and 98%, respectively. When calcium was initially added, a low initial dissolved inorganic carbon greatly reduced both strontium and calcium removal efficiencies to 8.1% and 29%, respectively. Scanning electron microscope (SEM) images for the fundamental experiments at a pH of 11 showed high spherical vaterite, the least stable polymorph of calcium carbonate, is prevalent in the samples compared to rhombohedron calcite, the most stable polymorph. Strontianite was only found in the sample with the lowest initial calcium concentration. X-ray diffraction patterns revealed that vaterite was shifted, indicating that strontium could be replacing calcium inside the crystal lattice. SEM images also revealed clusters of minerals in a transitional phase at the lowest and highest initial calcium concentrations. The possible mechanism(s) for strontium removal during the lime-soda ash softening treatment process includes surface adsorption into calcium carbonate precipitates, coprecipitation with the calcium carbonate precipitations, or surface-solution ion exchange within calcium carbonate.