Estimating Sulfate Effective Diffusion Coefficients of Stabilized Fluorogypsum for Aquatic Applications

Abstract

The sulfate release from solidified/stabilized fluorogypsum was measured to develop the effective diffusion coefficients (De) as a parameter to assess the dissolution potential in aquatic applications. Specimens from 11 compositions consisting of 6–9% pH-adjusted fluorogypsum (pFG), 2–1% Type I/II portland cement (PC), and –38% Class C fly ash (FA) were exposed to solutions of 3 g L−1 (saltwater), 15 g L−1 (brackish water), and .5 g L−1 (freshwater) total dissolved solids (TDS). The effects of composition and salinity, measured as the TDS, on the sulfate De were determined to select the compositions for use in various aquatic environments. The results indicated that the solidified/stabilized pFG had a lower dissolution potential in saltwater and freshwater in comparison with brackish water. On the basis of the low De and low critical times (the time when the diffusion out of the specimen equals the precipitation onto the specimen), a composition of 8% pFG, 1% PC, and 1% FA is recommended as an alternative to limestone in saltwater and freshwater applications.