Mineral Reactions Research Articles

Experimental study on the effect of hydrothermal activation on the physicochemical properties and mineralization efficiency of fly ash-supercritical CO2

To address the challenge of low mineralization efficiency of fly ash-supercritical carbon dioxide (CO2), a hydrothermal activation method was proposed to enhance fly ash-supercritical CO2 mineralization. The study systematically investigated the mechanism through which hydrothermal activation parameters influenced the efficiency of fly ash-supercritical CO2 mineralization through a series of experimental reactions. The effects of hydrothermal activation temperature and time on mineralization efficiency were investigated macroscopically. The results indicated that the mineralization efficiency increased by 202.93 % when hydrothermally activated at 220 °C for 30 min. Furthermore, when the activation time was ≤10 min, 220 °C exhibited a significant effect on the mineralization efficiency. For activation time ≥20 min, mineralization efficiency exhibited high stability with increasing temperature. Subsequently, under 220 °C conditions, mineralization efficiency reached 18.79 % for 5 min and 21.69 % for 30 min, representing only a 15.43 % increase despite a six-fold increase in time. Microscopic analysis of the pore structure of hydrothermally activated fly ash indicated that pore parameters (volume, specific surface area, and volume change rate) exceeded those of original fly ash for pore diameters ≥9 nm, and the opposite was observed for pore diameters <9 nm. Additionally, compared with the pristine fly ash, the pore size and volume fraction of the mineralized fly ash macropores increased, while mesopores decreased, and small pores exhibited a slight decrease in volume fraction and size. This indicated that pores ≥9 nm were primarily affected by hydration expansion, while pores <9 nm were primarily affected by mineralization precipitation. The hydrothermal activation mineralization reaction predominantly affected medium and large pores ≥9 nm, exhibiting less effect on smaller pores.

A preliminary exploration of waste red-bed as a supplementary cementitious material

A red-bed is a type of continental clastic sedimentary stratum, with red serving as the main color. This type of stratum accounts for 20% of the land area in China. In the process of infrastructure construction, a large amount of waste red-bed is generated. Waste red-bed exacerbates the shortage of land resources and is a misuse of resources. In this study, a preliminary exploration of the recycling of waste red-bed in central Yunnan Province was conducted. The studied red-bed contains approximately 30% clay minerals and was used as supplementary cementitious material (SCM) instead of clay after calcination. Through laboratory characterization, environmental impact assessment, and cost analyses, the feasibility of using the red-bed as a type of SCM was demonstrated. The results show that the dehydroxylation reaction of clay minerals in the red-bed was almost complete after calcination at 800 °C. A pozzolanic reaction occurred, and additional heat was released after the addition of the calcined red-bed (CRB) to the cement mortar. When the cement replacement ratio increased from 10% to 30%, the strength activity index decreased from 98.2% to 82.2%, which met the relevant requirements. However, compared with the control samples, the samples with replacement ratios of 40% and 50% had lower mortar fluidities by 57.3% and 75.5% and higher porosities by 33.3% and 20.0%, respectively. Owing to the dilution effect of the cement and the decrease in the mortar fluidity, the internal structure of the sample porosity increased, and the strength decreased dramatically. In addition, the environmental impacts, energy consumption, and cost of using waste red-bed as a SCM were quantitatively analyzed via a carbon emission index and a cost index.

Multi-field and multi-scale dynamic numerical modeling of supercritical CO2 and fly ash mineralization

Fly ash-CO2 mineralization technology can effectively control gas–solid waste emissions and improve the climate environment. However, rationally describing the evolution mechanism of the fly ash-supercritical CO2 mineralization reaction and accurately predicting the efficiency of the mineralization reaction are of great significance for improving and evaluating the supercritical CO2 mineralization sequestration capacity. Fly ash micro- and nanopore multi-scale effects are the key to influencing the supercritical CO2 seepage-mineralization reaction mechanism. None of the current theoretical models consider the pore multi-scale effects, thus the validity and accuracy of predicting and describing the evolutionary mechanism of supercritical CO2 mineralization rates and efficiencies are questionable. To address this scientific issue, a multi-scale continuous pore structure theoretical model was established based on the structural characteristics of fly ash micro- and nanopores. Additionally, a new model of supercritical CO2 multi-field and multi-scale dynamic mineralization theory was developed by considering parameters such as temperature, pressure, and humidity. The accuracy of the model was verified through the mineralization experiments. The new model effectively describes the dynamic evolution mechanism of supercritical CO2 mineralized fly ash. The effects of parameters such as temperature, pressure, water vapor diffusion coefficient, supercritical CO2 permeability, and pore multi-scale effect on the efficiency and mineralization rate were investigated through numerical simulation. The results showed the following: The mineralization efficiency exhibited a parabolic increase with temperature, with 72℃ being the turning point for the growth rate of mineralization efficiency, and 82℃ being the optimal effective temperature to promote the mineralization efficiency of supercritical CO2. A 3.5-fold increase in supercritical CO2 pressure changes the mineralization efficiency by a maximum of only 0.0493 %. Increasing the water vapor diffusion coefficient by 5 orders of magnitude changes the mineralization efficiency by only 8.3 %. The pore attenuation coefficient increases by 3 orders of magnitude, and the supercritical CO2 mineralization efficiency changes by a factor of 2.27. A model that does not account for pore multi-scale effects overestimates the fly ash- supercritical CO2 mineralization efficiency by a factor of 2.47 at a permeability of 3 × 10-10 m2. Therefore, neglecting the pore continuum multi-scale effect can lead to a serious overestimation of the mineralization efficiency of supercritical CO2.

Comparison of mineral transformation in CO2 geological storage under CO2–water–sandstone and mudstone reactions

Carbon dioxide (CO2) mineral trapping was considered the most secure and stable mechanism for CO2 geological storage. The previous studies lacked clarity regarding the mechanisms and processes of transformation for various types of minerals involved in CO2–water–sandstone and mudstone reactions during CO2 geological storage. Additionally, it didn't clear the different stages of mineral reactions in reservoir and caprock. We utilized experimental and numerical simulation methods to analyze the mechanisms, processes, and stages of CO2–water–rock reactions involving various types of minerals in the mudstone from Chang 4 + 5 members and the sandstone from Chang 6 member of the Triassic Yanchang Formation in the Ordos Basin. The experimental simulation demonstrated the dissolution of feldspar minerals in sandstone led to precipitate of carbonate, clay, and other minerals. Contrary, mudstone primarily underwent the dissolution of clay minerals and the precipitation of feldspar minerals, whereas carbonate content remained relatively stable. The numerical simulation consisted of experimental results in the short term, but over a longer timescale, The reaction processes of carbonate and clay minerals in the reservoir and caprock dissolved first and then precipitated. Conversely, other minerals behaved oppositely; feldspar minerals continuously dissolved in the reservoir but precipitated first and then dissolved in the caprock. The reaction stages of mineral change in both the reservoir and caprock could be divided into dissolution, rapid precipitation, and stable precipitation. The reservoir's dissolution stage was shorter than the caprock, which entered the stable precipitation stage earlier. With increasing storage time, continuous CO2–water–rock reactions gradually transformed physically sequestered CO2 in the formation into chemically sequestered mineralized CO2.

Experimental Investigation of Amine Regeneration for Carbon Capture through CO2 Mineralization

Summary The most common method for point-source carbon capture involves the absorption of CO2 from flue gas by amine solutions. The CO2 is then stripped from the amine solution by desorption with steam or heat. While amine solvents exhibit high CO2 absorption efficiency, their desorption process consumes a substantial amount of energy. A more energy-efficient alternative for the regeneration of the amine can be done through a mineralization process. Past studies have shown the feasibility of mineralizing captured CO2 from amine solution using calcium oxide (CaO) or other CaO-containing industrial waste. This study aims to show experimentally the extent of mineralization over time in near-ambient conditions and develop a mechanistic model. Lab-scale experiments are conducted to determine the absorption characteristics of CO2 in monoethanolamine (MEA) solutions and the extent of mineralization. We observe that pH serves as an indicator for CO2 loading in amine solutions. At high concentrations of MEA, CO2 absorption efficiency is about 0.5 mol CO2/mol MEA. Under ambient pressure and a temperature of 40°C, CaO effectively mineralizes CO2 and regenerates MEA. The CaO initially reacts with water to produce calcium hydroxide (Ca(OH)2) and subsequently reacts with dissolved CO2, forming calcium carbonate (CaCO3). Both 13C nuclear magnetic resonance (NMR) and FTIR indicate that MEA can be regenerated with an efficiency close to 69 to 98%, by comparing the carbamate and bicarbonate peaks in the 13C NMR response. A model to describe the absorption and mineralization reaction is proposed using the PHREEQC software; the pH is matched within less than 3% error. This study demonstrates that CO2 desorption from MEA solutions can occur through mineralization, converting CO2 into carbonates at low pressure and temperature with CaO. This method has lower energy consumption and results in the most stable form of CO2, making it a safer sequestration strategy than supercritical CO2 storage in reservoirs.

Effects of engineering injection and supplement mode of in-situ biogeochemical transformation enhancement EVO-FeSO4 on the remediation of tetrachloroethylene contaminated aquifer

Traditional in situ biogeochemical transformation suffers from competition among crucial microorganisms and inadequate formation of reactive minerals, thus leading to the accumulation of toxic intermediates. In this study, three regulation schemes were proposed to solve these problems from the perspective of engineering mode. Results showed intermittent injection mode effectively reduced the accumulation of toxic intermediates but the reduction rate of tetrachloroethylene was decreased. And periodical supplementation of carbon and sulfur sources accelerated the removal of tetrachloroethylene but failed to reduce the accumulation of toxic products. While, regular supplementation of sulfate effectively weakened the competition of methanogens and increased the iron sulfide proportion on the surface of the minerals, thus reducing the accumulation of toxicity. Based on the results, this study obtained an effective engineering approach for practical site application. In addition, the main forms of active minerals capable of β-eliminating contaminants during biogeochemical transformation were identified in this study, including FeS, FeS2, and Fe3S4. Furthermore, the engineered regulatory mechanism of this study was summarized through the analysis of microbial community structure and mineral morphology. The amendment promotes the production of minerals and thus controls the transformation pathway of contaminants by altering the abundance of sulfate-reducing bacteria and dissimilatory iron reducing bacteria. This mechanism can provide a basis for subsequent theoretical studies.

Influence of Reservoir Salinity, Mineralogy, Temperature, and Pressure on Geochemical Hydrogen Loss in Depleted Carbonates

Summary Underground hydrogen storage (UHS) is a cost-effective and safer system vital for the growth of the hydrogen market and its role as an essential transitional fuel. Presently, depleted hydrocarbon reservoirs (DHR) account for more than 75% of all UHS sites due to their higher prevalence and readiness for use. However, hydrogen (H2) loss primarily due to abiotic interactions poses a significant challenge to the integrity of DHR sites, and while the underlying conditions have been investigated in some studies, the conclusions have been inconsistent, particularly for carbonate reservoirs. In this study, we analyzed the impact of reservoir physical and chemical parameters, (i.e., salinity, mineralogy, temperature, and pressure) on H2-brine-mineral interactions and the extent of H2 loss in carbonate formations. Static batch simulations were performed using PHREEQC and MATLAB® for a 1-year storage cycle period with three different brine and rock samples at 50–130°C and 15–30 MPa. The results showed that the dissociation of H2 and formation of CH4 and H2S increased with increasing temperature, at a two times higher rate compared to pressure. Also, markedly, in various brine compositions and reactive mineralogy, a 20% or less H2 loss could be attained in temperatures &amp;lt;50°C and 115–130°C, with pressure below 17 MPa; meanwhile, the pressure condition 18 MPa and greater (at 50°C) would risk at least 50% loss, with &amp;gt;86% from 19 MPa. Second, H2 loss increased to 80% after about 50 days for all the brines, and pressure and temperature conditions in the mineral sample with the largest composition of reactive minerals (i.e., pyrite, anhydrite, etc.) suggested a 50% loss risk in such mineralogy during the storage cycle period of about 1 month. Lastly, in the mineral sample with &amp;gt;90 wt% calcite and 0–2 wt% reactive minerals composition, H2 molality increased at least fourfold on average across the storage period and reservoir brine/temperature/pressure conditions. This result further indicates that reactive mineralogy has a more significant effect on the stability of hydrogen relative to temperature and pressure in a carbonate UHS formation. In summary, the findings suggest that a minimal reactive mineral composition, 100°C or higher, and 17 MPa or lower constitutes a set of reservoir physical and chemical conditions with the potential for a limited risk of H2 loss (&amp;lt;20%) in carbonate DHR. However, the extension of the present work to the dynamic UHS conditions is necessary to further ascertain these conclusions.

Iron-rich Ca[sbnd]Mg skarns from the SW East European Craton (Lithuania): Microstructural study, mineral reactions and direct age constraints of ore-forming events using LA-ICPMS

The Varena Iron Ore deposit in the SW East European Craton is a significant ore body that occurs within metamorphosed and hydrothermally reworked Paleoproterozoic dolostones. We have performed microstructural investigations supplemented with mineral chemistry and geochronological investigations (LA-ICP-MS) to obtain age constraints on the ore-forming event(s) and improve the understanding of the conditions during mineralization process. Mineral chemistry and textures suggest a drop in pressure after the event of peak metamorphic skarn formation. Influx of oxidized, iron-rich H2O fluids resulted in (1) Mg mobility that caused secondary dolomitization of calcite, (2) dissolution of metamorphic magnetite and formation of a new, inclusion-rich (Mag-1) and inclusion-poor (Mag-2) magnetite, and (3) replacement of the peak skarn assemblages. During these fluid-related processes, accessory phases of monazite, baddeleyite, and zircon were formed. Their UPb dating yield individually robust ages of 1721 ± 9 Ma (monazite, 23 spots), 1703 ± 10 Ma (baddeleyite, 18 spots) and 1706 ± 54 Ma (zircon, 14 spots), respectively. The weighted mean age of 1713 ± 7 Ma (2σ internal) is considered to represent the best age estimate of the iron-ore mineralization in the Varena Iron Ore deposit, and possibly also dates influx of P, REEs etc. into the system. This mineralization event is contemporaneous with ca. 1.73–1.70 Ga metamorphic reworking of the host rocks in the region and may be linked to regional continental-margin type Transscandinavian Igneous Belt (TIB) magmatism in south-central Sweden.

Metamorphic mineral reactions and mineral paragenesis in the rocks of the Meyeri tectonic zone (the south-eastern part of the Fennoscandian shield, Russia)

Metamorphic mineral reactions and mineral paragenesis in the rocks of the Meyeri tectonic zone (the south-eastern part of the Fennoscandian shield, Russia)

Techno-economic assessment of supercritical, cold liquid, and dissolved CO2 injection into sub-seafloor basalt

Injecting CO2 into subsea basalt can provide permanent storage via multiple trapping mechanisms, including mineralization reactions which convert the CO2 into solid carbonates over time. Injecting CO2 together with water can accelerate the process of mineralization, but presents additional challenges, such as high energy and water requirements. A techno-economic model of CO2 transport and injection into ocean basalt was developed to compare injection strategies using pure supercritical CO2, pure liquid CO2, and CO2 dissolved in seawater. The model was applied to a representative injection site off the coast of British Columbia, Canada. Injection of CO2 dissolved into seawater was found to be more energy and cost intensive than injection of supercritical or liquid CO2; this is primarily due to the reduced quantities of CO2 that can be injected into each well, and additional pumping energy required for the accompanying seawater. For the base assumptions, transport and storage costs for supercritical, liquid, and dissolved injection were estimated as $43/t, $38/t, and $250/t respectively. Their energy requirements were estimated as 93 kWh/t, 90 kWh/t, and 213 kWh/t respectively. The current best estimates of geological parameters for ocean basalt suggest good injectivity and very large storage capacities per well. This may help to compensate for the additional project expenses incurred by deep water, allowing cost-effective liquid and supercritical injection. However, this result is sensitive to high uncertainties in both geological parameters and component cost data.

High-efficiency metal-free CO2 mineralization battery using organic redox catalysts

CO2 batteries offer a promising avenue for mitigating CO2 emissions and conversion, but encounter challenges such as high costs, dendrite, corrosion, flooding and slow kinetics stemming from the use of metal electrodes. CO2 mineralization is thermodynamically favorable (ΔGCO2), presenting an opportunity for processing solid waste and reducing CO2 emissions while potentially producing energy. However, the lack of direct electron transfer in the CO2 mineralization reaction hinders the direct generation of electrical energy. Here, we propose an organic CO2 mineralization battery (OCMB) without using metal, which efficiently harnesses CO2 to mineralize solid waste carbide slag, maximizing the recovery of mineralization reaction energy to generate electricity and produce carbonate products, without requiring renewable electricity charging. We employ a high-solubility, stable under strong alkaline conditions, and fast kinetics organic phenazine derivative—DSPZ as the electron and proton carrier, which facilitates the conversion of ΔpH between electrodes by interacting with alkaline wastes and CO2 into electricity. Simultaneously, the OCMB undergoes regeneration cycles through mineralization reactions. The theoretical model predicted the open circuit voltage (OCV) and discharge behavior of OCMB, offering insights for improved battery engineering. We demonstrate an impressive peak power density exceeding 227.5 W/m2 for the OCMB, with an estimated electricity production of ∼ 178.03 kWh per ton of CO2 mineralization. This research underscores the potential integration of OCMBs into CO2 energy systems, waste treatment processes, and chemical production, offering both economic and environmental benefits.

Numerical investigation on the influence of CO2-induced mineral dissolution on hydrogeological and mechanical properties of sandstone using coupled lattice Boltzmann and finite element model

The impact of CO2-induced mineral reactions, specifically the CO2-water-rock interactions, has been widely recognized for its potential to compromise the hydrogeological and mechanical properties of porous media, thereby deteriorating their integrity and mechanical characteristics. This raises concerns regarding the safety of numerous projects such as CO2 geological storage. However, the mechanism underlying the influence of CO2-induced mineral reactions on these parameters is still not fully understood, thereby introducing uncertainty into the reliability of predicted outcomes. Direct pore-scale simulation plays a crucial role in deepening the understanding of CO2 -water-rock interaction and its associated impacts. The present study proposes a novel simulation model that integrates the lattice Boltzmann and finite element methods to simulate the dissolution of calcite in a 3D sandstone sample invaded by saturated CO2 solution, aiming to investigate the resulting evolution of hydrogeological parameters (i.e., porosity and permeability) and mechanical properties (i.e., bulk and shear moduli). The injection rates of reactive fluid (i.e., CO2 solution) were varied in the model to simulate different operational conditions of CO2 geological storage project. The simulation results demonstrate that the decrease in injection velocity inhibits the dissolution of calcite in the middle and downstream regions, concentrating it near the inlet. These distinct modes of calcite dissolution result in differentiated permeability and mechanical properties within rocks possessing identical porosity levels. In general, the increase in fluid injection velocity leads to a more pronounced enhancement in permeability and a greater attenuation in bulk and shear moduli under the same porosity. Thus, it is confirmed that the utilization of porosity is inadequate in accurately characterizing the evolution of rock permeability and mechanical properties resulting from mineral reactions. We ascertain that the application of fractal parameters, i.e., succolarity and fractal dimension, can more precisely depict the progression of permeability and bulk/shear modulus, respectively.

New insights into the controversy of reactive mineral-controlled arsenopyrite dissolution and arsenic release

Serious arsenic (As) contaminations could commonly result from the oxidative dissolution of As-containing sulfide minerals, such as arsenopyrite (FeAsS). Pyrite (Py) and calcite (Cal) are two typically co-existing reactive minerals and represent different geological scenarios. Previous studies have shown that a high proportion of Py can generate a stronger galvanic effect and acid dissolution, thereby significantly promoting the release of arsenic. However, this conclusion overlooks calcite's antagonistic effect on the release of As in the natural environment. That antagonistic effect could remodel the linear relationship of pyrite on the oxidative dissolution of arsenopyrite, thus altering the environmental risk of As. We examined As release from arsenopyrite along a gradient of Py to Cal molar ratios (Py:Cal). The results showed that the lowest As release from arsenopyrite was surprisingly found in co-existing Py and Cal systems than in the singular Cal system, let alone in the singular Py system. This phenomenon indicated an interesting possibility of Py assistance to Cal inhibition of As release, though Py has always been regarded as a booster, also evidenced in this research, for As release from arsenopyrite. In singular systems of Py and Cal, As continued to be released for 60 days. However, in co-existing Py and Cal systems, As was released non-linearly in three stages over time: initial release (0–1 Day), immobilization (1–15 Days), and subsequent re-release (>15 Days). This is a new short-term natural attenuation stage for As, but over time, this stage gradually collapses. During the re-release stage (> 15 Days), a higher molar ratio of Py:Cal (increasing from 1:9 to 9:1) results in a lower rate constant k (mg·L−1·h−1) of As release (range from 0.0011 to 0.0002), and a higher abundance of secondary minerals formed (up to 26 mg/g goethite and hematite at Py: Cal=9:1). This demonstrates that increasing the Py:Cal molar ratio results in the formation of more secondary minerals which compensate for the higher potential antagonistic mechanisms generated by pyrites, such as acid dissolution and galvanic effect. These results explain the mechanisms of the high-risk characteristics of As both in acidic mine drainage and karst aquifers and discover the lowest risk in pyrite and calcite co-existing regions. Moreover, we emphasize that reactive minerals are important variables that can't be ignored in predicting As pollution in the future.

Acceleration of chelator on mineralization reaction of cement paste at different CO2 pressures

In order to further improve the mechanical properties of CO2-cured cement paste, effects of chelator on the compressive strength of cement paste cured under different CO2 pressures were investigated, and the mechanism of chelator in accelerating the mineralization reaction was deduced from the analysis of the degree of mineralization reaction, microstructures, and phase compositions, with the contribution of chelator in reducing the net CO2 emissions of cement industry being evaluated. The results showed that the use of chelator could significantly enhance the compressive strength of cement paste cured at different CO2 pressures compared with other methods for improving the compressive strength of CO2-cured cement paste, and the compressive strength of cement paste cured for 48 h at 0.1 MPa and 0.4 MPa CO2 could be enhanced by 23.2 % and 9.4 %, respectively. Chelator could migrate Ca2+ from smaller pores and pore channels to larger pores, decreasing the Ca2+ content and degree of mineralization reaction in smaller pores and pore channels, avoiding the blockage of the stomata by generated CaCO3, and allowing more CO2 to penetrate and diffuse into the cement paste, thereby promoting mineralization reaction and significantly improving compressive strength of cement paste cured at atmospheric pressure. The use of chelator in mineralization curing cement-based materials could further reduce net CO2 emissions from cement production, making significant contribution to the advancement of mineralization curing technology and environmental sustainability.

Kinetics of In-Situ Calcium Magnesium Carbonate Precipitation and the Need for Desulfation in Seawater-Flooded Carbonate Reservoirs

Summary Mixing of incompatible injection and formation brines leads to the deposition of inorganic sulfate scales such as barite, celestite, and anhydrite in and around production wells. This process is well documented in seawater-flooded clastic reservoirs. One technique to avoid the resulting formation damage is to remove sulfate from seawater before injection using nanofiltration; however, this process is costly. We identify in this paper that it may not always be necessary in higher-temperature carbonate reservoirs. In this paper, we describe the use of reactive transport reservoir simulation to investigate the impact of carbon dioxide (CO2) partitioning and changes in pH, ionic concentrations, and temperature on carbonate reactivity and the sulfate scaling risk in waterflooded carbonate reservoirs. Dissolution and precipitation of calcite, dolomite, gypsum, anhydrite, barite, and celestite are all modeled and found to be coupled through (various) common ion effects. The produced brine compositions are used to calculate the saturation ratios (SRs) and mass of precipitate that may form in the production system. Sensitivity to mineral reaction kinetics, particularly for the dolomite reactions, is accounted for. Results identify that there is a strong relationship between calcite dissolution and dolomite (or other calcium/magnesium carbonate mineral) precipitation reactions, which drive each other and are affected by the availability of CO2 in the residual oil phase. This evolves over time, and as the thermal front propagates, impacts the concentration of calcium and magnesium in the brines traversing the reservoir. Temperature changes around the injection wellbore impact CO2 and mineral solubilities. The concentration of calcium in the displaced brine mix is thus determined more by contact with rock and temperature than by mixing between injection and formation brines. Depending on location relative to the thermal front, this may lead to gypsum or anhydrite precipitation, thereby stripping sulfate out of the injection brine. Thus, the sulfate scaling risk at the production wells is significantly reduced by this sulfate depletion process: The sulfate is stripped out of the seawater as it warms up in the reservoir before it mixes extensively with the formation water and significantly before any mixture of the two brines reaches the production zone. Thus, any loss of permeability is restricted to deep within the reservoir, where the pore volume (PV) that can accommodate mineral precipitation is very large. In this work, we identify that for carbonate reservoirs above 90–100°C, stripping of sulfate due to coupled mineral reactions may reduce or eliminate the need for use of a sulfate reduction plant (SRP). The process is modeled for the first time, accounting for the impact of CO2 partitioning and thermal front propagation. Knowledge of the kinetics of calcium/magnesium carbonate precipitation is shown to be critical in predicting the extent of sulfate depletion.

Formation of zinc carbonate phases on dissolving calcite, aragonite, and vaterite in acidic aqueous solutions

Calcium carbonate (CaCO3) minerals serve as a major sink to retain metal ions through mineral-water interfacial reactions in which the capacity and long-term stability of contaminant uptake are influenced by coupled dissolution and precipitation reactions of both primary and secondary carbonate minerals (i.e., mineral replacement). Notably, recent studies of calcite reactivity in acidic solutions containing high levels of metal ions demonstrated complex behavior under conditions of sustained disequilibrium. We explored the reactivity of three CaCO3 polymorphs (calcite, aragonite, and vaterite) with acidic Zn2+-containing aqueous solutions using a suite of imaging techniques including optical and scanning electron microscopies, synchrotron-based micro X-ray fluorescence, and transmission X-ray microscopy. Zn uptake by calcite occurred through a two-step process: the formation of a thin layer of the zinc precipitate on the substrate surface followed by the growth of fibrous and radiating hydrozincite particles from the layer. In contrast, Zn uptake by aragonite occurred by mineral replacement where the secondary Zn carbonate phase preserved the external morphology of the original crystal (i.e., a pseudomorph). The replacement of vaterite by hydrozincite occurred within the confined space beneath the porous shell of vaterite, signifying that the primary mechanism driving Zn carbonate precipitation was chemical exchange through the pores. When multiple CaCO3 polymorphs coexisted, the replacement of aragonite and vaterite occurred preferentially over that of calcite. These results demonstrate the distinct morphological and mineralogical controls over the reactivities of calcium carbonate minerals with Zn2+ under acidic conditions.

Vegetation patterns associated with nutrient availability and supply in high-elevation tropical Andean ecosystems

Abstract. Plants absorb nutrients and water through their roots and modulate soil biogeochemical cycles. The mechanisms of water and nutrient uptake by plants depend on climatic and edaphic conditions, as well as the plant root system. Soil solution is the medium in which abiotic and biotic processes exchange nutrients, and nutrient concentrations vary with the abundance of reactive minerals and fluid residence times. High-altitude ecosystems of the tropical Andes are interesting for the study of the association between vegetation, soil hydrology, and mineral nutrient availability at the landscape scale for different reasons. First of all, because of low rock-derived nutrient stocks in intensely weathered volcanic soils, biocycling of essential nutrients by plants is expected to be important for plant nutrient acquisition. Second, the ecosystem is characterized by strong spatial patterns in vegetation type and density at the landscape scale and hence is optimal to study soil-water–vegetation interactions. Third, the area is characterized by high carbon stocks but low rates of organic decomposition that might vary with soil hydrology, soil development, and geochemistry, all interconnected with vegetation. The páramo landscape forms a vegetation mosaic of bunch grasses, cushion-forming plants, and forests. In the nutrient-depleted nonallophanic Andosols, the plant rooting depth varies with drainage and soil moisture conditions. Rooting depths were shallower in seasonally waterlogged soils under cushion plants and deeper in well-drained soils under forest and tussock grasses (&gt;100 cm). Vegetation composition is a relevant indicator of rock-derived nutrient availability in soil solutions. The soil solute chemistry revealed patterns in plant-available nutrients that were not mimicking the distribution of total rock-derived nutrients nor the exchangeable nutrient pool but clearly resulted from strong biocycling of cations and removal of nutrients from the soil by plant uptake or deep leaching. Soils under cushion plants showed solute concentrations of Ca, Mg, and Na of about 3 times higher than forest and tussock grasses. Differences were even stronger for dissolved Si with solute concentrations that were 16 times higher than forest and 6 times higher than tussock grasses. Amongst the macronutrients derived from lithogenic sources, P was a limiting nutrient with very low solute concentrations (&lt;1 µM) for all three vegetation types. In contrast K showed greater solute concentrations under forest soils with values that were 2 to 3 times higher than under cushion-forming plants or tussock grasses. Our findings have important implications for future management of Andean páramo ecosystems where vegetation type distributions are dynamically changing as a result of warming temperatures and land use change. Such alterations may lead not only to changes in soil hydrology and solute geochemistry but also to complex changes in weathering rates and solute export downstream with effects on nutrient concentrations in Andean rivers and high-mountain lakes.

Proposed Methods Accelerate Permanent CO2-Storage Process

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 215352,“ Accelerating the Permanent CO2 Storage Process: A Safer and Faster Route to Net Zero,” by Shubham Mishra, SPE, Boston Consulting Group. The paper has not been peer reviewed. _ The complete paper proposes two methods of accelerating the solidification (or mineralization) of CO2 in subsurface conditions, thus reducing the time required in the CO2 storage process. It also reviews industry and academic works devoted to the subject. Introduction Two main concerns with CO2 storage in subsurface reservoirs and CO2 sequestration are the large time cycle involved in its permanent storage and the associated environmental risks. Because other CO2 trapping mechanisms can be reversible, these concerns hinge heavily on the time required for solidification or mineralization of CO2 into a component such as calcite (CaCO3). Using current technologies and practices, it is practically impossible to complete the soaking period—or, in simpler words, a CO2 storage project—in one lifetime. Thus, technological development of CO2 storage, which depends on field validations, becomes an extremely long, multigenerational process. On the other hand, environmental safety is always a concern with underground CO2 storage. Three of four CO2 trapping mechanisms (structural, solubility-based, and residual) pose greater risk to the environment than does the fourth, which is mineralization or solidification. Therefore, from the point of view of environmental safety, mineralization is the most permanent form of CO2 storage that minimizes the risk of CO2 existing in gaseous form in the reservoir and thus flowing upward to shallower zones or the surface. Related Efforts Several research projects devoted to finding a commercial solution for accelerating the mineralization process are ongoing, including the following: - The CarbFix project in Iceland is based upon injection of CO2 dissolved in water streams into basalt rocks for accelerating mineral trapping. Through tracer surveys and mass calculations, the project has proposed that mineralization can be achieved in as little as 2 years for the size of the reservoir under consideration and the amount of CO2 injected. - A Canadian startup (Carbon Engineering) is turning carbon emissions into pellets that could be used as a synthetic fuel source, while a Swiss company called Climeworks is pumping extracted carbon to farms for agricultural use. - Another start-up is using calcium oxide, a waste product from the steel industry called steel slag, to react with CO2 and form CaCO3. This is used in controlled surface conditions in a cement-industry setup. This process, however, highlights how the reactions converting CO2 into solid can be sped up. - University research projects are ongoing that focus on use of various catalysts for increasing the rate of the mineralization chemical reaction, resulting in the formation of CaCO3. Proposed Methods While industry and academia are focusing on niche setups to solve this problem, not much focus is being placed on general large-scale applications such as increasing the mineralization chemical reaction rate in sandstone saline aquifers, where approximately 80% of potential carbon capture, utilization, and storage (CCUS) projects will be developed. Thus, technologies or workflows that can be applied in CO2 storage projects in saline aquifers to increase the mineralization reaction rate can be essential to bringing a shift to the larger vision of CCUS. In this effort, an integrated approach incorporating experience from oil and gas, cement, and other adjacent industries can help develop potential solutions.

Impact of mineral reactions and surface complexation on the transport of dissolved species in a subterranean estuary: Application of a comprehensive reactive transport modeling approach

Subterranean estuaries (STE) are hotspots of biogeochemical reactions. Here, dissolved constituents in waters of terrestrial and marine origin are transformed before they discharge to the coastal oceans. The involved biogeochemical reactions are complex and non-linear, calling for the application of numerical reactive transport modeling (RTM) to improve the process understanding. The aim of this study was to assess the roles of organic matter degradation and coupled secondary mineral reactions for the fate of dissolved species in STEs of sandy beaches. A comprehensive RTM approach was applied for this purpose, accounting for the effects of ion activities, pH, pe, redox reactions, mineral equilibria (calcite, goethite, siderite, iron sulfide, hydroxyapatite and vivianite) as well as surface complexation. Results show that the STE biogeochemistry and associated species fluxes are very sensitive to the assumed reaction network. For example, inorganic carbon and pH were largely controlled by calcite and siderite dynamics, and dissolved Fe2+ and HS- were precipitated as goethite, siderite and/or iron sulfides. Moreover, PO43- concentrations were affected by both the formation of vivianite or hydroxyapatite as well as surface complexation. This work helped to establish the relative importance of some of the major biogeochemical processes in the STE. However, further field studies are needed to understand which processes play a role in real-world STEs, including an exploration of the deep subsurface of STEs. Such field-based observations will improve our conceptual process understanding, which is key to developing well-constrained RTMs.

Effects of handheld nonthermal plasma on the biological responses, mineralization, and inflammatory reactions of polyaryletherketone implant materials

Background/purposeThe handheld nonthermal plasma (HNP) treatment may alter the surface properties, bone metabolism, and inflammatory reactions of polyaryletherketone (PAEK) dental implant materials. This study tested whether the HNP treatment might increase the biocompatibility, surface hydrophilicity, surface free energies (SFEs), and the cell adhesion and mineralization capability of PAEK materials. Materials and methodsDisk-shaped samples of titanium (Ti), zirconia (Zr), polyetheretherketone (PEEK [PE]), and polyetherketoneketone (PEKK [PK]) were subjected to HNP treatment and termed as TiPL, ZrPL, PEPL, and PKPL, respectively. Water-surface reactions were examined using a goniometer. MG-63 cells were cultured on all samples to assess the cell viability, cytotoxicity, cell attachment, and mineralization characteristics. The expression of pro-inflammatory cytokines (tumor necrosis factor-alpha and interleukin-6) and key mineralization markers (alkaline phosphatase [ALKP], osteopontin [OPN], and dentin matrix protein 1 [DMP1]) was measured using enzyme-linked immunosorbent assay kits. ResultsThe HNP-treated samples exhibited significantly enhanced surface hydrophilicities and SFEs compared to the untreated samples. The cell viability remained high across all samples, indicating no cytotoxic effects. The HNP treatment significantly enhanced MG-63 cell adherence and proliferation. Elevated levels of ALKP and OPN were observed for the plasma-treated PEPL and PKPL specimens, while DMP1 levels increased significantly only in the PKPL specimen. Pro-inflammatory cytokine levels were low across all samples, suggesting no inflammatory response. ConclusionThe HNP-treated PAEKs have enhanced the surface hydrophilicity and SFEs as well as superior cell adhesion and mineralization capability, and thus may be good clinical dental implant materials.