Dissolution Kinetics of a Simple Analogue Nuclear Waste Glass as a Function of Ph, Time and Temperature

Abstract

We have measured the dissolution rate of a simple five-component borosilicate glass (Na 2 0, CaO, A1 2 0 3 , B 2 0 3 , Si0 2 ) using a flow-through system. The experiments were designed to measure the dissolution rate constant over the interval pH 1 through pH 13 at 3 temperatures (250, 500 and 70 0 C). Dilute buffers were used to maintain a constant pH. Analyses of solutions and solid surfaces provided information that is used to develop a kinetic model for glass dissolution.Under all conditions we eventually observed linear dissolution kinetics. In strongly acidic solutions (pH 1 to pH 3) all components but Si were released in their stoichiometric proportions and a thick, Si-rich gel was formed. In mildly acidic to neutral solutions the gel was thinner and was both Si-and Al-rich, while the other components were released to solution in stoichiometric proportions. In mildly to strongly alkaline solutions all components were released to solution in stoichiometric proportions. By varying the flow rate at each pH we demonstrated a lack of transport control of the dissolution rate.The dissolution rates were found to be lowest at near-neutral pH and to increase at both low and high pH. A rate equation based on transition-state theory (TST) was used to calculate dissolution rate constants and reaction order with respect to pH over two pH intervals at each temperature. At 25 0 C between pH 1 and pH 7 based on the Si release rate the log rate constant for glass dissolution (g glass/m2od) was -0.77 and the order with respect to pH was -0.48. Between pH 7 and pH 13 the log rate constant for glass dissolution was -8.1 and the order with respect to pH was +0.51. The measured simple glass dissolution rate constants compare very well with constants estimated by fitting the same TST equation to experimental results obtained for SRL-165 glass and to dissolution rate estimates made for synthetic basaltic glasses.

Evaluation of the Non-Transient Hydrologic Source Term from the CAMBRIC Underground Nuclear Test in Frenchman Flat, Nevada Test Site

“…This forces the curve to shift to the left. This was been observed in borosilicate glass dissolution experiments of Knauss et al (1990) and is likely to occur in the case of nuclear melt glass dissolution as well. As mentioned earlier, the rate of glass dissolution slows as the solution approaches saturation with respect to the glass.…”

Modeling of Groundwater Flow and Radionuclide Transport at the Climax Mine sub-CAU, Nevada Test Site

“…This forces the curve to shift to the left with increasing temperature. This was observed in borosilicate glass dissolution experiments of Knauss et al (1990) and is likely to occur in the case of nuclear melt glass dissolution as well. …”

Determination of the Forward Dissolution Rate for International Simple Glass in Alkaline Solutions

“…In KOH solutions, we observe a general increase of the forward dissolution rate with the increase of the pH, as previously observed in literature [1,4,[8][9][10][11][12][13][14] and especially for SON68 glass in similar tests [4]. Figure 2 shows a comparison between the forward dissolution rates obtained for the first series of data obtained for ISG and SON68 in KOH solutions: a good agreement of the results is obtained for moderately alkaline pH values.…”