The dissolution kinetics of natural gypsum: a case study of Eocene facies in the north-eastern suburbs of Paris

Abstract

The dissolution kinetics of different varieties of natural gypsum samples with different porosity and content of insoluble impurities are experimentally investigated under unsaturated conditions. The main goal of this work is to verify whether and how the petrophysical and petrographic nature of gypsum influence its dissolution rate. Gypsum samples were taken from Priabonian (Ludian) and Lutetian formations located in the north-eastern suburbs of Paris, where the development of sinkholes due to gypsum dissolution is a common phenomenon. Experiments using the rotating disk technique allow us to determine the kinetic rate model parameters of each sample in pure water following the empirical rate expression derived from mixed kinetic theory. The kinetic order n shows a dispersion around a mean value n = 1.2 and k, the pure dissolution rate coefficient varies according to the facies and the experimental conditions (k≈1×10 −6 to 8×10 −6 mmol/cm 2 /s). These results are adjusted according to the specific roughness and texture of each sample, for the results to be more representative of in-situ conditions. Batch experiments are also performed in order to evaluate the extremely low dissolution rates when the solution is close to equilibrium. The results reveal a double kinetics: far from equilibrium, the dissolution rates show that the linear behavior and the kinetic parameters are relatively close with the values found using the rotating disk method. For concentrations greater than 0.94±0.02 of the equilibrium concentration C re f , the dissolution rates show a linear behavior but with greater slope depending on the texture of the mineral. No changes of the dissolution rates were observed on pure gypsum crystals when non soluble solid impurities are added. However, a small degree of uncertainty around the value of C re f show a significant effect on the parameters of the second kinetics.

Assessment and Prediction of the Water Quality Index for the Groundwater of the Ghiss-Nekkor (Al Hoceima, Northeastern Morocco)

“…This could be due to ion discharge, coastal zone development, seawater intrusion, agricultural input contamination, human waste, or sewage from homes and septic tanks, among other things (Table 3) [27]. This process is also associated with rock salt, since gypsum-containing rock formations are effectively infiltrated and resolved [52][53][54].…”

Gypsum Precipitating From Volcanic Effluent as an Archive of Volcanic Activity

“…This is also in agreement with optical and electron microscopy, which does not show dissolution surfaces, but rather continuous growth of gypsum laths with idiomorphic growth surfaces preserved within individual gypsum crystals. There is, therefore, no evidence for gypsum dissolution, which is surprising given the abundance of rain and the resulting effect of dilution on the saturation state of the seepage fluids, and the gypsum dissolution rates determined by Zaier et al (2020). This strongly suggests that dissolution is hindered.…”

“…Moreover, fluid dilution by rainfall would lead to undersaturation, and potential dissolution of gypsum. Indeed, a full day of undersaturation would be predicted to dissolve 0.2 mm of gypsum as calculated from the experimentally-determined dissolution rate data of Zaier et al (2020) for low-porosity, crystalline gypsum. With 176 rainy days per year and a total precipitation of 2,416 mm/year at the nearby city of Banyuwangi (data from www.climate-data.org), dissolution should be an important process.…”

“…Vigorous gas injection into the lake was observed by Takano et al (2004) in echo-soundings of the lake, and is further evident from bubbling of lake waters at the dam and fumaroles. Measurements of volcanic gas Rn activity show it to be high; 1.2-2.3 • 10 5 dpm/m 3 for Etna fumaroles (Giammanco et al, 2007) and 2.4-9.0 • 10 5 dpm/m 3 for 500 °C Merapi fumaroles (Zimmer and Erzinger 2003). Volcanic gas is thus a viable source for the 210 Pb in the lake waters, and fluctuations in this volcanic flux (Merapi fumaroles varied from 2.4 to 8.4 • 10 5 dpm/m 3 within a single day-Zimmer and Erzinger 2003) will lead to variations in the 210 Pb 0 in the seepage waters from which the gypsum grew.…”

Water Quality Assessment Using the Water Quality Index, and Geographic Information Systems in Nador Canal, Morocco

“…The occurrence may result from factors such as ion discharge, coastal zone development, seawater intrusion, agricultural input contamination, human waste, or sewage from homes and septic tanks, among other causes [47] . Additionally, this phenomenon is linked to rock salt, as gypsum-containing rock formations are prone to infiltration and dissolution due to the aforementioned factors [48][49][50] .…”