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DOE OSTI2026

How exudates production along a phosphorus gradient influences mineral dissolution across contrasting soil development stages

Harnessing rhizosphere processes offers a valuable opportunity to optimize nutrient use efficiency in agroecosystems. In nutrient-limited soils, plants discharge part of photosynthate surplus via root exudation, including carboxylates, which may enhance mineral dissolution and nutrient mobilization. We aimed to assess how plant responses to nutrient limitation translated into changes in exudate profiles, and how these exudates, in turn, drive bioweathering processes across soils of contrasting mineralogy and weathering degree. We conducted a hydroponic experiment with Lupinus albus grown under five phosphorus (P) concentrations (5, 10, 20, 30, and 50 µM) over seven weeks. We measured plant biomass and root traits, performed a metabolomics analysis and quantified seven carboxylates in root exudates using gas chromatography-mass spectrometry. To assess bioweathering processes across contrasted soil domains, we conducted batch dissolution tests with exudates using three soil horizons—35 each with distinct physicochemical properties: enriched in organic matter, iron oxides, or primary silicates. At the intermediate level of P supply, shoot biomass was comparable to that under high P, but plants produced more root biomass and a higher total carboxylate exudation rate. Despite low carboxylate concentrations (<100 ppb), exudates promoted the dissolution of Ca, Mg, Si, Fe, P and K in all horizons. Yet, the degree of element released varied among horizons. These findings highlight the importance of root exudates in enhancing mineral dissolution, with effects dependent on soil physicochemical properties. The results suggest that managing agroecosystems under moderate nutrient limitation could be a sustainable strategy to increase root-to-shoot ratios, enhance bioweathering processes and nutrient release in soil solution.

Pollet, Sasha L.↗

DOE OSTI2013

Electrochemistry of soluble UO 2 2+ from the direct dissolution of UO 2 CO 3 in acidic ionic liquid containing water

The direct dissolution of UO 2 CO 3 in neat and “wet” ionic liquid (IL) trimethyl-n-butylammonium bis(trifluoromethansulfonyl)imide [Me 3 N n Bu][TFSI] is examined. The ionic liquid serves as both the solvent for the direct dissolution of UO 2 CO 3 (s) and the electrolyte solution for the electrochemical analysis of the soluble uranyl species. The solubility data indicate that displacement of the CO 3 2- occurs slowly due to the low concentration of protons available from residual water in the pristine IL. Enhanced dissolution of UO 2 CO 3 through the formation of carbonic acid H 2 CO 3 is achieved after the addition of acid, bis(trifluoromethanesulfonyl)amide (HTFSI) and water. The soluble uranyl cation can then coordinate with the TFSI anion in place of the displaced CO 3 2- anion following the decomposition of carbonic acid and purging of CO 2 (g) and water from the IL. The solubility of UO 2 CO 3 was examined using liquid scintillation counting of 233 U for the pristine ionic liquid. The “wet” ionic liquid containing HTFSI and soluble UO 2 CO 3 was evaluated using UV/vis spectroscopy before and after dissolution. The electrochemical deposition of uranium species from ionic liquid was evaluated using cyclic voltammetry. The potential mediated deposition of uranium species was achieved and verified using scanning electron microscopy (SEM) and the solid uranium deposits were evaluated using energy dispersive X-ray emission spectroscopy (EDX).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2026

Cobalt Dissolution from Metal Oxides and Battery Cathode Materials with Acetic Acid-Based Deep Eutectic Solvents

Recovery of critical metals with alternative solvents beyond those in traditional pyrometallurgy and hydrometallurgy is needed in consideration of environmental challenges and the growing demand for metals in energy technologies. Deep eutectic solvents (DESs) have emerged as sustainable alternatives for solvometallurgy in metal separation and recovery. In this study, DESs based on hydrogen bond acceptors (HBAs) including choline chloride (ChCl), acetylcholine chloride (AChCl), and betaine (Bet) were investigated for their effectiveness when paired with acetic acid (AA) as the hydrogen bond donor (HBD) for the dissolution of cobalt from cobalt oxide (CoO), lithium cobalt oxide (LiCoO 2 ), and lithium nickel manganese cobalt oxide (LNMC). Based on the spectroscopic analysis of the metal dissolution and coordination, Bet:AA was found to provide the highest solubility for CoO (0.33 M) in the form of an octahedral complex. On the other hand, ChCl:AA solvent was more effective at dissolving LiCoO 2 with 0.04 M Co 2+ corresponding to 17% dissolution efficiency and LNMC with 0.06 M Co 2+ corresponding to 72% dissolution efficiency at 50 °C, compared to Bet:AA (9% for LiCoO 2 and 31% for LNMC). Although the solubilities of LiCoO 2 and LNMC have not significantly improved in ChCl:AA, this difference in effectiveness between the solvents clearly reveals the role of the HBA in solubilization. The coordination synergy between the chloride and the –OH moiety facilitates the breakdown of the LiCoO 2 driven by the alteration of the solvent polarity. Cobalt in these solutions was found dominantly as a tetrahedral [CoCl 4 ] 2– complex. A chemical separation of cobalt oxalate from a mixed-metal oxide system based on Co, Fe, and Ni was also demonstrated, confirming the potential of these solvents for practical metal recovery.

Cobalt separation↗

DOE OSTI2018

Convective carbon dioxide dissolution in a closed porous medium at low pressure

Motivated by the persistence of natural carbon dioxide ( $\text{CO}_{2}$ ) fields, we investigate the convective dissolution of $\text{CO}_{2}$ at low pressure (below 1 MPa) in a closed system, where the pressure in the gas declines as convection proceeds. This introduces a negative feedback that reduces the convective dissolution rate even before the brine becomes saturated. We analyse the case of an ideal gas with a solubility given by Henry’s law, in the limits of very low and very high Rayleigh numbers. The equilibrium state in this system is determined by the dimensionless dissolution capacity, $\unicode[STIX]{x1D6F1}$ , which gives the fraction of the gas that can be dissolved into the underlying brine. Analytic approximations of the pure diffusion problem with $\unicode[STIX]{x1D6F1}>0$ show that the diffusive base state is no longer self-similar and that diffusive mass transfer declines rapidly with time. Direct numerical simulations at high Rayleigh numbers show that no constant flux regime exists for $\unicode[STIX]{x1D6F1}>0$ ; nevertheless, the quantity $F/C_{s}^{2}$ remains constant, where $F$ is the dissolution flux and $C_{s}$ is the dissolved concentration at the top of the domain. Simple mathematical models are developed to predict the evolution of $C_{s}$ and $F$ for high-Rayleigh-number convection in a closed system. The negative feedback that limits convection in closed systems may explain the persistence of natural $\text{CO}_{2}$ accumulations over millennial time scales.

Mechanics↗

DOE OSTI2018

Pore-scale modelling of multiphase reactive flow: application to mineral dissolution with production of CO 2

A micro-continuum approach is proposed to simulate the dissolution of solid minerals at the pore scale in the presence of multiple fluid phases. The approach employs an extended Darcy–Brinkman–Stokes formulation that accounts for the interfacial tension between the two immiscible fluid phases and the moving contact line at the mineral surface. The simulation framework is validated using an experimental microfluidic device that provides time-lapse images of the dissolution dynamics. The set-up involves a single-calcite crystal and the subsequent generation of CO 2 bubbles in the domain. The dissolution of the calcite crystal and the production of gas during the acidizing process are analysed. We then show that the production of CO 2 bubbles during the injection of acid in a carbonate formation may limit the overall dissolution rate and prevent the emergence of wormholes.

bio-inspired, mechanical behavior, carbon sequestr↗

DOE OSTI2018

Complexity of Uranyl Peroxide Cluster Speciation from Alkali-Directed Oxidative Dissolution of Uranium Dioxide

Solid UO 2 dissolution and uranium speciation in aqueous solutions that promote formation of uranyl peroxide macroanions was examined, focusing on the role of alkali metals. UO 2 powders were dissolved in solutions containing XOH (X = Li, Na, or K) and 30% H 2 O2. Inductively coupled plasma optical emission spectroscopy (ICP-OES) measurements of solutions revealed linear trends of uranium versus alkali concentration in solutions resulting from oxidative dissolution of UO 2 , with X:U molar ratios of 1.0, showing that alkali availability determines the U concentrations in solution. The maximum U concentration in solution was 4.36 x 10 5 parts per million (ppm), which is comparable to concentrations attained by dissolving UO 2 in boiling nitric acid, and was achieved by lithium hydroxide-promoted dissolution. Lastly, Raman spectroscopy and electrospray ionization mass spectrometry (ESI-MS) of solutions indicate that dissolution is accompanied by formation of various uranyl peroxide cluster species, the identity of which is alkali concentration-dependent, revealing remarkably complex speciation at high concentrations of base.

36 MATERIALS SCIENCE↗

DOE OSTI2026

Kinetic Pathways to Diblock Copolymer Micelles via Thin Film Dissolution and Cosolvent Variation

We investigate how processing pathways control micelle formation during dissolution of lamellar diblock copolymers using dissipative particle dynamics (DPD) simulations and DPD-selfconsistent field theory (DPD-SCFT). Comparing thin film (TF) and cosolvent-assisted (CS) dissolution reveals fundamentally different micellization mechanisms and final states. In the TF pathway, dissolution proceeds through a metastable cylindrical intermediate that dictates final micelle dimensions. The lamellar melt first transforms into cylindrical micelles, which then fragment into spherical micelles. The final spherical radius is intrinsically linked to the cylinder radius by a constant ratio, Rsphere ≈ 1.4Rcylinder. DPD-SCFT confirms that both cylinders and spheres are near their equilibrium dimensions. In contrast, CS dissolution produces kinetically trapped micelles with sizes significantly below equilibrium. Micellization is hindered by high free energy barriers to single-chain exchange and fusion. Growth occurs primarily via fusion, but increasing corona repulsion suppresses further coarsening, preventing equilibration. These results demonstrate that, when starting from a bulk copolymer phase, the metastable cylindrical intermediate plays a central role in determining final micelle size.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2022

Transition Metal Dissolution Mechanisms and Impacts on Electronic Conductivity in Composite LiNi 0.5 Mn 1.5 O 4 Cathode Films

The high-voltage LiNi 0.5 Mn 1.5 O 4 (LNMO) spinel cathode material offers high energy density storage capabilities without the use of costly Co that is prevalent in other Li-ion battery chemistries (e.g., LiNi x Mn y Co z O 2 (NMC)). Unfortunately, LNMO-containing batteries suffer from poor cycling performance because of the intrinsically coupled processes of electrolyte oxidation and transition metal dissolution that occurs at high voltage. In this work, we use operando electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) spectroscopies to demonstrate that transition metal dissolution in LNMO is tightly coupled to HF formation (and thus, electrolyte oxidation reactions as detected with operando and in situ solution NMR), indicative of an acid-driven disproportionation reaction that occurs during delithiation (i.e., battery charging). Leveraging the temporal resolution (s-min) of magnetic resonance, we find that the LNMO particles accelerate the rate of LiPF 6 decomposition and subsequent Mn 2+ dissolution, possibly due to the acidic nature of terminal Mn-OH groups. X-ray photoemission electron microscopy (XPEEM) provides surface-sensitive and localized X-ray absorption spectroscopy (XAS) measurements, in addition to X-ray photoelectron spectroscopy (XPS), that indicate disproportionation is enabled by surface reconstruction upon charging, which leads to surface Mn 3+ sites on the LNMO particle surface that can disproportionate into Mn 2+ (dissolved) and Mn 4+ (s) . During discharge of the battery, we observe high quantities of metal fluorides (in particular, MnF 2 ) in the cathode electrolyte interphase (CEI) on LNMO as well as the conductive carbon additives in the composite. Electronic conductivity measurements indicate that the MnF 2 decreases film conductivity by threefold compared to LiF, suggesting that this CEI component may impede both the ionic and electronic properties of the cathode. Ultimately, to prevent transition metal dissolution and the associated side reactions in spinel-type cathodes (particularly those that operate at high voltages like LNMO), the use of electrolytes that offer improved anodic stability and prevent acid byproducts will likely be necessary.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Crystal dissolution by particle detachment

Crystal dissolution, which is a fundamental process in both natural and technological settings, has been predominately viewed as a process of ion-by-ion detachment into a surrounding solvent. Here we report a mechanism of dissolution by particle detachment (DPD) that dominates in mesocrystals formed via crystallization by particle attachment (CPA). Using liquid phase electron microscopy to directly observe dissolution of hematite crystals — both compact rhombohedra and mesocrystals of coaligned nanoparticles — we find that the mesocrystals evolve into branched structures, which disintegrate as individual sub-particles detach. The resulting dissolution rates far exceed those for equivalent masses of compact single crystals. Applying a numerical generalization of the Gibbs-Thomson effect, we show that the physical drivers of DPD are curvature and strain inherently tied to the original CPA process. Based on the generality of the model, we anticipate that DPD is widespread for both natural minerals and synthetic crystals formed via CPA.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2023

Operando characterization and regulation of metal dissolution and redeposition dynamics near battery electrode surface

Mn dissolution has been a longstanding, ubiquitous issue that negatively impacts the performance of Mn-based battery materials. Mn dissolution involves complex chemical and structural transformations at the electrode-electrolyte interface. The continuously evolving electrodeelectrolyte interface has posed great challenges for characterizing the dynamic interfacial process and quantitatively establishing the correlation with battery performance. In this study, we visualize and quantify the temporally and spatially resolved Mn dissolution/redeposition (D/R) dynamics of electrochemically operating Mn-containing cathodes. The particle-level and electrode-level analyses reveal that the D/R dynamics is associated with distinct interfacial degradation mechanisms at different states of charge. Our results statistically differentiate the contributions of surface reconstruction and Jahn-Teller distortion to the Mn dissolution at different operating voltages. Introducing sulfonated polymers (Nafion) into composite electrodes can modulate the D/R dynamics through trapping the dissolved Mn species and rapidly establishing the local Mn D/R equilibrium. This work represents an inaugural effort to pinpoint the chemical and structural transformations responsible for Mn dissolution via an operando synchrotron study and develops an effective method to regulate Mn interfacial dynamics for improving battery performance.

25 ENERGY STORAGE↗

DOE OSTI2020

Arsenite oxyanions affect CeO 2 nanoparticle dissolution and colloidal stability

While highly reactive cerium oxide nanoparticles (CeO 2 NPs) are widely used in industry, their transport in aquatic systems is not well understood. To fill this knowledge gap, the interactions of CeO 2 NPs with arsenite (As 3+ ), a toxic metalloid and potential co-present contaminant, were investigated with respect to CeO 2 NP colloidal stability, dissolution, and surface redox reactions. Arsenite showed distinctive effects at different concentrations, with a high As 3+ concentration (10 –4 M) inducing 90% of CeO 2 NPs to settle from solution after 8 hours, while lower As 3+ concentrations (10 –5 or 10 –6 M) led to only 20% of CeO 2 NPs settling. The dissolution of NPs was most significant in the 10 –5 M As 3+ system owing to a lesser extent of aggregation, exposing more CeO 2 surface for dissolution. In the three As 3+ concentration systems, >97% of aqueous arsenic remained as As 3+ over 6 hours. On the NP surface, adsorbed As III was oxidized to As V , resulting in 58–70% of the adsorbed arsenic remaining as As III . Simultaneously Ce IV was reduced to Ce III , increasing Ce III on the CeO 2 NP surface from 17% (without arsenite) to 21–25% (with arsenite). Further mechanistic analyses revealed that the adsorption of arsenite was the main contributor to neutralizing the CeO 2 NP surface potential, enhancing particle sedimentation. These findings suggest that the fate and transport of CeO 2 NPs in our experimental systems are strongly affected by arsenite concentration and its adsorption on NPs. Here, the results also highlight the importance of the interplay between NP aggregation, oxidation, and dissolution in predicting the behaviors of CeO 2 NPs and associated toxic elements in aquatic systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2022

Atomistic level aqueous dissolution dynamics of NASICON-Type Li 1+ x Al x Ti 2– x (PO 4 ) 3 (LATP)

Advancing the atomistic level understanding of aqueous dissolution of multicomponent materials is essential. Here, we combined ReaxFF and experiments to investigate the dissolution at the Li 1+ x Al x Ti 2– x (PO 4 ) 3 -water interface. We demonstrate that surface dissolution is a sequentially dynamic process. The phosphate dissolution destabilizes the NASICON structure, which triggers a titanium-rich secondary phase formation.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Effects of surface charge and cluster size on the electrochemical dissolution of platinum nanoparticles using COMB3 and continuum electrolyte models

We study the site-dependent dissolution of platinum nanoparticles under electrochemical conditions to assess their thermodynamic stability as a function of shape and size using empirical molecular dynamics and electronic-structure models. The third-generation charge optimized many-body potential is employed to determine the validity of uniform spherical representations of the nanoparticles in predicting dissolution potentials (the Kelvin model). To understand the early stages of catalyst dissolution, implicit solvation techniques based on the self-consistent continuum solvation method are applied. It is demonstrated that interfacial charge and polarization can shift the dissolution energies by amounts on the order of 0.74 eV depending on the surface site and nanoparticle shape, leading to the unexpected preferential removal of platinum cations from highly coordinated sites in some cases.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2019

Dissolution of silica component of glass network at early stage of corrosion in initially silica-saturated solution

Corrosion of glass in silica-saturated solution has been performed with the assumption that dissolution of silicate species from the glass network would not occur. Using surface-sensitive analytical techniques, we report experimental evidence suggesting the dissolution of silicate network species from a model nuclear waste glass, called international simple glass (ISG), in an aqueous solution initially saturated with soluble silica species. Results from low energy ion scattering and X-ray photoelectron spectroscopy reveal a complete depletion of mobile element species (B, Na) from the ISG surface and an enrichment of Zr on the outmost surface. In support of spectroscopic analyses, results from topographic imaging with atomic force microscopy show a stochastic dissolution of glass surface resulting in a higher surface roughness with increasing corrosion time in aqueous solution. This study shows that a true equilibrium between soluble silica species in the solution phase and silicate species in the glass network could not be warranted by performing corrosion experiments in the solution where dissolved silica species are initially equilibrated with amorphous silica in the presence of KOH. The leaching of mobile species (B, Na) could affect the saturation level of aqueous solution and induce further dissolution of the glass surface.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Topological controls on aluminosilicate glass dissolution: Complexities induced in hyperalkaline aqueous environments

Abstract Fly ash, an aluminosilicate composite consisting of disordered (major) and crystalline (minor) compounds, is a low‐carbon alternative that can partially replace ordinary portland cement (OPC) in the binder fraction of concrete. Therefore, understanding the reactivity of fly ash in the hyperalkaline conditions prevalent in concrete is critical to predicting concrete's performance; including setting and strength gain. Herein, temporal measurements of the solution composition (using inductively coupled plasma‐optical emission spectrometry: ICP‐OES) are used to assess the aqueous dissolution rate of monophasic synthetic aluminosilicate glasses analogous to those present in technical fly ashes, under hyperalkaline conditions (10 ≤ pH ≤ 13) across a range of temperatures (25°C ≤ T≤45°C). The dissolution rate is shown to depend on the average number of topological constraints per atom within the glass network (n c , unitless), but this dependence weakens with increasing pH (>10). This is postulated to be on account of: (a) time‐dependent changes in the glass’ surface structure, that is, the number of topological constraints; and/or (b) a change in the dissolution mechanism (eg from network hydrolysis to transport control). The results indicate that the topological description of glass dissolution is most rigorously valid only at very short reaction times (ie at high undersaturations), especially under conditions of hyperalkalinity. These findings provide an improved basis to understand the underlying factors that affect the initial and ongoing reactivity of aluminosilicate glasses such as fly ash in changing chemical environments, for example, when such materials are utilized in cementitious composites.

Oey, Tandré↗

DOE OSTI2021

Seeded Stage III glass dissolution behavior of a statistically designed glass matrix

The glass dissolution rate of some glasses accelerates after prolonged time spent at a slow, residual glass dissolution rate. This phenomenon is referred to as Stage III behavior. Here, the acceleration in glass dissolution rate linked to Stage III behavior is significant and may be the most impactful to long-term performance of glass in a repository. This work is aimed at understanding the effect of glass composition on Stage III behavior to add a level of technical defensibility to glass disposal. To this end, a set of twenty-four glass compositions were statistically designed, where eight glass components (SiO 2 , B 2 O 3 , Al 2 O 3 , CaO, Na 2 O, SnO 2 , ZrO 2 , and Others) have been independently varied in order to study the individual effects of each. These glasses have been subjected to static dissolution tests at 90 °C in deionized water and then seeded with zeolite Na-P2 28 days into the testing to induce Stage III behavior. The response of the glasses to the zeolite seeds fell into four primary types: 1) no response to seeds; 2) an immediate linear sustained acceleration in the rate; 3) an immediate linear acceleration in the rate followed by a decrease; and, 4) a progressive acceleration in the rate that is concurrent with the addition of the seeds. The main glass components observed to influence these behaviors were CaO, Al 2 O 3 , B 2 O 3 , and ZrO 2 , where: 1) CaO influenced which glasses showed a Stage III response to seeds (high CaO: Types 2, 3, and 4) or did not respond to seeds (low CaO: Type 1), 2) Al 2 O 3 and B 2 O 3 influenced which glasses showed a sustainable Stage III response (high Al 2 O 3 : Types 2 and 4) versus transitory response (low Al 2 O 3 and high B 2 O 3 : Type 3), and 3) ZrO 2 concentration influenced whether glasses showed a linear (high ZrO 2 : Type 2) versus progressive (low ZrO 2 : Type 4) response to seeds.

36 MATERIALS SCIENCE↗

DOE OSTI2016

Phosphate Speciation under Organic‐Acid‐Promoted Dissolution of Phosphorus‐Sorbed Ferrihydrite–Boehmite Mixtures: Implications For Soil Phosphorus

Core Ideas Phosphate speciation determines its bioavailability in soils. Phosphate molecular speciation changes occur upon organic‐acid‐promoted dissolution. Results imply that phosphate in acid soils preferentially associated with Fe(III) oxides. Organic‐acid‐promoted dissolution of phosphate is a primary mechanism for enhancing the bioavailability of sorbed, inorganic soil phosphate. Bioavailability of P is, however, dependent on its speciation. Hence, the main objective of this study was to characterize changes in phosphate speciation as a function of pH levels (4–8) during citrate‐promoted dissolution of phosphate adsorbed on ferrihydrite–boehmite mixtures using two different sizes of ferrihydrite. A combination of batch dissolution kinetics and P K‐X‐ray absorption near‐edge structure (XANES) spectroscopy was used. Trends in shifts of white‐line peak energy and full width at half maximum height of P K‐XANES spectra indicated that the phosphate bonding configuration on ferrihydrite–boehmite as single minerals and mineral mixtures was predominantly binuclear–bidentate complexes at pH levels of 4, 6, and 8. When citrate was added to the ferrihydrite–boehmite mixtures with bound phosphate (pH 4 and 6), phosphate was preferentially released from boehmite, resorbed onto ferrihydrite, and precipitated to form noncrystalline FePO 4 minerals. A reverse trend was observed at alkaline pH. These results suggest the potential for excessive P release in P‐enriched acidic soils during a redox event due to preferential association of P to Fe(III) phases.

Adam, Nadia↗

DOE OSTI2013

Chlorite Dissolution Kinetics at Variable pH and Temperatures up to 275 °C

The objective of this suite of experiments was to develop a useful kinetic dissolution expression for chlorite that would be applicable over a wide range of solution pH and temperature conditions representative of subsurface conditions in natural and/or engineering geothermal reservoirs. The resulting rate equation is dependent on both pH and temperature and utilizes two specific dissolution mechanisms (an “acid” and a “neutral” mechanism). Rate parameters were derived from data collected at LLNL and available published data from Lowson et al. (2007). The form of this rate equation (Equation 1) should be easy to incorporate into most existing reactive transport codes for use in prediction of rock-water interactions in EGS systems. Specifically, we find that the dissolution of chlorite, a sheet-silicate, is relatively slow at elevated temperatures (100-275 °C), compared to other framework silicate minerals for which higher temperature kinetic data are available (e.g., quartz and feldspars; see Palandri and Kharaka, 2004). This finding is in conflict with previously reported high activation energies for chlorite based on extrapolation of low-temperature experimental data to higher temperatures. Additionally, we note that the dissolution of chlorite does not increase under alkaline conditions, as has been noted for other minerals, but rather remains at the same level as that noted for neutral conditions, with only a weak dependence on temperature. Future work includes similar rate measurements and the derivation of useful rate equations for illite, smectite, and biotite from pH 3 to 10 and 100 to 275 °C. Geochemical alteration, changing stress fields, mass transport and heat transfer incorporated into computational models are needed to optimize geothermal energy production for EGS systems. The resulting mineral rate equations from this work can be directly incorporated in modeling efforts to fully assess the impacts of geochemical alteration on long-term fracture permeability for EGS systems across the Geothermal Program. Chlorite rate equations and data have been submitted to the Geothermal Data Repository.

15 GEOTHERMAL ENERGY↗