Environmental management science program FY1997 progress report

Abstract

Research ObjectiveThe objective of this work is to determine the fundamental data needed to predict the behavior of Sr at temperature and time scales appropriate to thermal remediation, because 9oSr is a major contaminant at Hanford and INEL sites (Duncan, 1995) and thermally-enhanced technologies used to remediate organic contaminants (Newmark and Aines, 1995) may improve the efficiency and speed of metal remediation as well. Research StatementOur approach combines macroscopic sorption/precipitation and desorption/dissolution kinetic experiments, which track changes in solution composition, with direct molecular characterization of Sr in the solid phase using X-ray absorption spectroscopy. These experiments will be used to identify mechanistic geochemical reactions and their thermochemical properties that will be incorporated into geochemical computer codes. Research ProgressThis report consists of three sections: 1. Results of Sr sorption to kaolinite and goethite from pH 4 to 10 at 25,50, and 80-C and atmospheric CO,(g); 2. Preliminary spectroscopy results; and 3. Review of the available thermodyanimc data in the is Fe-Sr-Na-N03-C02-H20 system. 1.Strontium sorption to goethite and kaolinite at 25, 50, and 80-C. In our goethite and kaolinite experiments, Sr-uptake begins in solutions undersaturated with respect to strontianite (SrCO,) and increases in more supersaturated solutions. We know that Sr-uptake is enhanced by kaolinite and goethite, because Sr is not removed from solution over the same experimental run conditions in the absence of solid phases. It is possible that ternary Sr-carbonate complexes form at the kaolinite and goethite surfaces, and that they provide the needed "seed carbonate" to precipitate strontianite.This idea builds from direct observation of multinuclear-cobalt-surface complexes on kaolinite (O'Day et al. 1994) and the formation of a mixed nickel-aluminum hydroxide during pyrophyllite dissolution and nickel-uptake (Scheidegger et al. 1996). We expect Sr-uptake to involve the formation of multinuclearSr-carbonate complexes because strontianite is much less soluble than Sr(OH),(s).Temperature-dependence of Sr-uptake to goethite and kaolinite is minimal. This is consistent with the small (about 0.2 orders of magnitude) temperature-dependence of strontianite solubility from 25 to 80-C.Figures l-4 show the results of Sr sorption to goethite and kaolinite at atmospheric pCO,(g) as a function of pH and temperature.In the presence of goethite, significant Sr-uptake occurs at 25, 50, and 80-C from solutions containing pH > 8 and [Sr], = 10T7 to 10m4 M ( Fig. 2 and 3). The absolute Sr-2 uptake increases with increasing [Sr], at constant temperature and at pH 2. There is a slight increase in Sr-uptake with increasing temperature for 65 -1 lo-lo -2 lo'ot""""""""""""""""'~' 3 4 5 8 9 10Figure 1 (continued).-510-8""""I',"""(","""""',, 3;H fincll Similar to goethite, significant Sr-uptake occurs at 25, 50, and 80-C from solutions containing pH > 8 and [Sr], = 10m6 to 10e4 M (Fig. 5 and 6). Minim...