Effect of Iron on Waste‐Glass Leaching

Abstract

The interactive effects between ductile iron and PNL 76-68 borosilicate glass were investigated as a function of time in 90°C static deionized, tuff, and basalt groundwaters. A synergistic effect occurs between the two materials, i. e. iron enhances glass dissolution and glass enhances iron corrosion. An iron silicate precipitate forms, part of which is colloidal in nature. This precipitate effectively removes many of the elements from solution and therefore inhibits the saturation effects which normally cause decreases in elemental removal rates. Thus, the effects of initial solution composition on the glass leach rates are significantly reduced and the relatively high early leach rates normally observed in deionized water are maintained for longer times due to the suppression of saturation effects. This results in more total elemental removal from the glass in all of the groundwaters evaluated. The precipitate and its colloidal form require further characterization.

The effects of the glass surface area/solution volume ratio on glass corrosion: A critical review

“…Rather, the corrosion accelerates because of the effects other phases that form during glass corrosion have on the silicic acid activity. Attainment of the "residual rate" is known to be prevented in the presence of silicon-consuming phases that may be present as part of the test system, such as clay [189][190][191][192] and iron [193,194], and upon the formation of secondary phases form the leachate solution as the glass corrodes The formation of secondary phases is an unavoidable result of glass corrosion. They form as the glass converts to a more stable assemblage of phases to reduce the free energy of the system.…”

“…Colloidal materials that occur naturally in the groundwater or are generated during corrosion of engineered barrier materials will be available to sorb radionuclides [193,269]. This material may remain suspended in solution, or may eventually be sorbed by immobile phases, may be filtered from the solution by microprobes, or may flocculate and settle out of solution.…”

“…Sorption may result in a change in the oxidation state of the radionuclide. Competition between actinides and other metal ions in complexation and sorption reactions results in complex chemistries in real systems, and will, in general, decrease the amounts of radionuclides removed from solution.Colloidal materials that occur naturally in the groundwater or are generated during corrosion of engineered barrier materials will be available to sorb radionuclides [193,269]. This material may remain suspended in solution, or may eventually be sorbed by immobile phases, may be filtered from the solution by microprobes, or may flocculate and settle out of solution.…”

Critical review of glass performance modeling

“…However, other dissolved species also affect glass dissolution rates [7,[19][20][21][22][23][24][25]. For example, the dissolution rates of silicate glasses are strongly decreased in the presence of dissolved Mg, Pb, and Zn and strongly enhanced, under some conditions, by dissolved Fe (see Section III.G.4).…”

“…Likewise, anions such as ph sphate and sulfide are known to affect mineral dissolution rates and may likewise affect glass dissolution rates. The effects of metals may be attributable to several processes depending upon the metal, including the formation of surface complexes, the precipitation of a surface layer providing a transport barrier, and the reaction of dissolved glass species with the dissolved metals causing the precipitation of colloids or secondary phases that affect the glass dissolution affinity [22]. Other mechanisms are also possible.…”