With the growing interest in geothermal energy as a renewable and sustainable energy source, nowadays engineers and researchers are facing technological and environmental challenges during geothermal wells’ operation or energy recovery improvement by optimizing surface installations. One of the major problems encountered is the degassing of geothermal brines which are often loaded with dissolved gases, resulting in technical problems (scale formation, corrosion, reduced process efficiency, etc.) and environmental problems through the possible emission of greenhouse gases (CO₂, CH₄ and water vapor) into the atmosphere. In this work, a method to predict, from readily available information such as temperature and GLR, the bubble point pressure of geothermal fluids as well as the GHG emission rate depending on the surface conditions is presented. This method is based on an extended version of the Soreide and Whitson model with new parameters optimized on the solubility data of several gases (CO₂, CH₄, N₂, O₂ and H₂) in brine (NaCl + CaCl₂ + KCl). The developed approach has been successfully used for the prediction of water content of different gases and their solubilities in different types of brines over a wide temperature and pressure range, and has been applied for the prediction of bubble point pressure and GHG emissions by comparing the results with available industrial data of geothermal power plants including the Upper Rhine Graben sites.

Geothermal energy has been a subject of great interest since the 1990s in the Upper Rhine Graben (URG), where the first European Enhanced Geothermal System (EGS) pilot site has been developed, in Soultz-sous-Forêts (SsF), France. Several studies have already been conducted on scales occurring at the reinjection side at the geothermal plants located in the URG. It has been observed that the composition of the scales changes as chemical treatment is applied to inhibit metal sulfate. The purpose of this study was to model the scaling phenomenon occurring in the surface pipes and the heat exchangers at the SsF geothermal plant. PhreeqC, a geochemical modelling software, was used to reproduce the scaling observations in the geothermal plant during exploitation. A suitable database was chosen based on the availability of chemical elements, minerals, and gas. A thermodynamic model and a kinetic model were proposed for modelling the scaling phenomenon. The thermodynamic model gave insight on possible minerals precipitated while the kinetic model, after modifying the initial rates equation, produced results that were close to the expected scale composition at the SsF geothermal plant. Additional laboratory studies on the kinetics of the scales are proposed to complement the current model.

K-jarosite (KFe₃(SO₄)₂(OH)₆), the most common jarosite-type mineral in natural and industrial settings, has been widely studied to understand its dissolution behavior in both environmental and industrial contexts. However, reported kinetic data remain inconsistent due to the combined influence of kinetic factors, despite the importance of such data for optimizing system conditions and improving process control and environmental management. The present work aims to help elucidate K-jarosite dissolution by carrying out new experiments in sulfuric acid medium (pH 1 and 2) at different temperatures (296, 323 and 343 K) and using two initial concentrations (0.4 and 1 g of K-jarosite/kg of solution). K-jarosite was synthesized and characterized by analytical techniques (XRD, SEM and BET), and the composition was determined by induction-coupled plasma optical emission spectroscopy (ICP-OES). Derivative (DVKM), Noyes–Whitney (NWKM) and Shrinking Core (SCKM) kinetic models previously used in the literature of jarosite-type compounds were adjusted to the data obtained here and compared. The results showed that higher temperatures and lower pH led to faster dissolution rates. Smaller initial concentrations decreased the rates slightly but had less impact than the other variables. Experiments at pH 1 led to the dissolution of all jarosite solids, while at pH 2 they led to incomplete dissolution. Remarkably, at pH 2 and at higher temperatures (mainly at 343 K), there was slight reprecipitation of the iron. XRD analysis identified no peak other than K-jarosite peaks after dissolution. DVKM and NWKM represented the effect of the studied parameters well. However, only using SCKM was a kinetic equation describing the dissolution process obtained. While the behavior of the kinetic curve is well established, the model fails to correctly describe the induction period. Under extreme conditions (>323 K, pH 1), dissolution is described by a chemical reaction controlling stage and it changes to mass transport in mild conditions. As theoretically expected, the results obtained in this work give important information about the prediction of the behavior of jarosite dissolution in terrestrial environments (acid mine and acid rock drainages) and hydrometallurgical process in mild acidic conditions and high temperatures.