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•Preparation of nanofluids (different nanoparticles concentration in different brine concentration).•SEM and AFM images (images taken before and after nano-modification).•EDS analysis ...(data were taken after nano-modification of the surfaces).•Effect of exposure time, brine concentration and nanoparticle concentration on contact angle.•Efficiency of used nanofluid (sustainability of silica nanoparticles).
Changing oil-wet surfaces toward higher water wettability is of key importance in subsurface engineering applications. This includes petroleum recovery from fractured limestone reservoirs, which are typically mixed or oil-wet, resulting in poor productivity as conventional waterflooding techniques are inefficient. A wettability change toward more water-wet would significantly improve oil displacement efficiency, and thus productivity. Another area where such a wettability shift would be highly beneficial is carbon geo-sequestration, where compressed CO2 is pumped underground for storage. It has recently been identified that more water-wet formations can store more CO2.
We thus examined how silica based nanofluids can induce such a wettability shift on oil-wet and mixed-wet calcite substrates. We found that silica nanoparticles have an ability to alter the wettability of such calcite surfaces. Nanoparticle concentration and brine salinity had a significant effect on the wettability alteration efficiency, and an optimum salinity was identified, analogous to that one found for surfactant formulations. Mechanistically, most nanoparticles irreversibly adhered to the oil-wet calcite surface (as substantiated by SEM–EDS and AFM measurements). We conclude that such nanofluid formulations can be very effective as enhanced hydrocarbon recovery agents and can potentially be used for improving the efficiency of CO2 geo-storage.
The temperature dependence of composition, unit cell parameters, thermal expansion coefficients and microstructure during complete thermal decomposition of calcite has been investigated by in-situ ...high-temperature X-ray powder diffraction. The respective X-ray diffractograms were obtained from 675 to 800 °C at 25 °C intervals. Results indicate that the thermal conversion of calcite to calcium oxide is initiated at a slow rate and rapidly decomposed beyond the temperature of 750 °C. During the period of thermal decomposition, positive and negative expansion of the unit cell is detected parallel to c-axis and perpendicular to a-axis, respectively. A substantial reduction in unit cell volume by 69% is observed during the conversion from trigonal calcite to cubic calcium oxide. It is also found that the rapid composition change and unit cell volume reduction simultaneously accounted for polynomial behavior of thermal expansion coefficients of calcite. Both crystallite size and lattice strain of calcite are increased simultaneously during thermal decomposition. A considerably higher lattice strain is observed for calcite compared to calcium oxide at all decomposition temperatures. The uniform arrangement of small cubic unit cells in newly materialized calcium oxide is accounted for moderate crystallite size and lowest lattice strain at the completion of thermal decomposition.
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•Decomposition of calcite is initiated slowly and rapidly decomposed above 750 °C.•CO2 gas emission catalyzed the conversion of trigonal CaCO3 (calcite) to cubic CaO.•Polynomial behavior in thermal expansion coefficients is observed for calcite.•Lattice strain and crystallite size of calcite increased rapidly with temperature.•Stabilization of CaO is achieved by moderate crystallite size and lowest lattice strain.
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The efficient separation of scheelite from calcium-bearing minerals, especially calcite, remains a challenge in practice. In this work, a novel reagent scheme incorporating a ...depressant of sodium hexametaphosphate (SHMP) and a collector mixture of octyl hydroxamic acid (HXMA-8) and sodium oleate (NaOl) was employed in both single and mixed binary mineral flotation, and it proved to be highly effective for the separation. Furthermore, the role of the pH value in the separation was evaluated. Additionally, the mechanism of the selective separation was investigated systemically via zeta potential measurements, fourier transform infrared (FTIR) spectroscopy analysis, X-ray photoelectron (XPS) spectroscopy analysis and crystal chemistry calculations. It turns out that the selective chemisorption of SHMP on calcite (in the form of complexation between H2PO4−/HPO42− and Ca2+) over scheelite is ascribed to the stronger reactivity and higher density of Ca ions on the commonly exposed surfaces of calcite minerals. The intense adsorption of HXMA-8 on scheelite over calcite due to the match of the OO distances in WO42− of scheelite and CONHOH of HXMA-8 holds the key to the successful separation. We were also interested in warranting the previous claim that NaOl is readily adsorbed on both minerals via chemisorption. Our results provided valuable insights into the application of mixed collectors and an effective depressant for flotation separation.
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Selective adsorption of tannic acid (TA) on calcite surfaces and the implications of this process for the separation of fluorite ore were studied by microflotation tests, surface ...adsorption experiments, zeta potential measurements, UV–vis analysis, and X-ray photoelectron spectroscopy (XPS) analysis. The microflotation tests indicated that TA, when added before sodium oleate (NaOl), could selectively depress calcite from fluorite at pH 7. Surface adsorption experiments revealed that TA hinders the interaction of NaOl with calcite. The zeta potential of calcite became more negative with TA than with NaOl. However, the characteristic features of TA adsorption were not observed on fluorite, suggesting that the dominant adsorption sites are dissimilar on the fluorite and calcite surfaces in the pulp. UV–vis spectroscopy, XPS, and solution chemistry analysis were utilized to obtain a better understanding of the mechanism for selective adsorption of TA as well as the key factors determined by the Ca2+ and Ca(OH)+ components on the mineral surfaces. A possible adsorption mechanism along with an adsorption mode is proposed for the surface interaction between TA and calcite.
•Alfalfa and bermudagrass-derived biochars were used for removal of tetracycline.•Based on the physicochemical properties, adsorption mechanisms were explained.•The alfalfa-derived biochar has ...exhibited outstanding TC adsorption capacity.•Adsorption capacity of alfalfa-derived biochar was compared to commercial ACs.•Alkaline regeneration led to effective adsorption–desorption for multiple cycles.
The biochars derived from alfalfa (AF) and bermudagrass (BG), the abundant grass hays to cows, were prepared, characterized and used for removal of tetracycline (TC) in water. The alfalfa-derived biochar (AF-BC) has exhibited outstanding TC adsorption capacity (372 mg/g), which was about 8-fold higher than that of bermudagrass-derived biochar (BG-BC). In addition, the TC adsorption capacity of AF-BC was comparable with those of the commercial activated carbons under the same conditions. The surface structure, chemistry and high ash contents of AF-BC suggested the hydrogen bonding, electrostatic interactions and surface complexation between AF-BC and TC. Furthermore, hydroxyapatite (HAP; Ca5(PO4)3OH) and calcite (CaCO3) on the surface of AF-BC may also contribute to adsorption of TC via surface complexation, hydrogen bonding and electrostatic interactions. The alkaline desorption-driven regeneration of TC-spent AF-BC led to effective adsorption–desorption for multiple cycles, which indicated AF-BC could be a cost-effective adsorbent for TC in water and wastewater.
CO2 geo-sequestration is a promising technology to permanently store CO2 in geological formations to control the atmospheric carbon footprint. In addition, CO2 is frequently utilized in enhanced oil ...recovery operations to accelerate oil production. Both, CO2 geo-storage and EOR, are significantly influenced by the wettability of the associated rock/CO2/brine systems. Wettability drives the multiphase flow dynamics, and microscopic fluid distribution in the reservoir. Furthermore, while wettability is known to be influenced by varying in-situ conditions and surface chemistry of the rock/mineral, the current state-of-the-art indicates wider variabilities of the wetting states.
This article, therefore, critically reviews the published datasets on CO2 wettability of geological formations. Essentially, the rock/CO2/brine and rock/crude-oil/CO2-enriched-brine contact angle datasets for the important reservoir rocks (i.e. sandstone and carbonate rocks), as well as for the key minerals quartz and calcite are considered. Also, the parameters that influence wettability are critically analyzed, and the associated parametric trends are discussed and summarized. Finally, we identify pertinent research gaps and define the outlook of future research. The review, therefore, establishes a repository of the recent contact angle data, which thus assists to enhance our current understanding of the subject.
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•Overview of wettability characterization using contact angle measurements•Experimental rock/CO2/brine contact angle data for sandstone carbonate, quartz and calcite•Rock/CO2/brine contact angle prediction using MD simulation•Experimental rock/oil/CO2-enriched-brine contact angle data•Parametric analysis of factors influencing rock wettability•Current research gaps and future outlook
Despite the broad range of interest and applications, controls on calcite surface charge in aqueous solution, especially at conditions relevant to natural systems, remain poorly understood. The ...primary data source to understand calcite surface charge comprises measurements of zeta potential. Here we collate and review previous measurements of zeta potential on natural and artificial calcite and carbonate as a resource for future studies, compare and contrast the results of these studies to determine key controls on zeta potential and where uncertainties remain, and report new measurements of zeta potential relevant to natural subsurface systems.
The results show that the potential determining ions (PDIs) for the carbonate mineral surface are the lattice ions Ca2+, Mg2+ and CO32−. The zeta potential is controlled by the concentration-dependent adsorption of these ions within the Stern layer, primarily at the Outer Helmholtz Plane (OHP). Given this, the Iso-Electric Point (IEP) at which the zeta potential is zero should be expressed as pCa (or pMg). It should not be reported as pH, similar to most metal oxides.
The pH does not directly control the zeta potential. Varying the pH whilst holding pCa constant yields constant zeta potential. The pH affects the zeta potential only by moderating the equilibrium pCa for a given CO2 partial pressure (pCO2). Experimental studies that appear to yield a systematic relationship between pH and zeta potential are most likely observing the relationship between pCa and zeta potential, with pCa responding to the change in pH. New data presented here show a consistent linear relationship between equilibrium pH and equilibrium pCa or pMg irrespective of sample used or solution ionic strength. The surface charge of calcite is weakly dependent on pH, through protonation and deprotonation reactions that occur within a hydrolysis layer immediately adjacent to the mineral surface. The Point of Zero Charge (PZC) at which the surface charge is zero could be expressed as pH, but surface complexation models suggest the surface is negatively charged over the pH range 5.5–11.
Several studies have suggested that SO42− is also a PDI for the calcite surface, but new data presented here indicate that the value of pSO4 may affect zeta potential only by moderating the equilibrium pCa. Natural carbonate typically yields a more negative zeta potential than synthetic calcite, most likely due to the presence of impurities including clays, organic matter, apatite, anhydrite or quartz, that yield a more negative zeta potential than pure calcite. New data presented here show that apparently identical natural carbonates display differing zeta potential behaviour, most likely due to the presence of small volumes of these impurities. It is important to ensure equilibrium, defined in terms of the concentration of PDIs, has been reached prior to taking measurements. Inconsistent values of zeta potential obtained in some studies may reflect a lack of equilibration.
The data collated and reported here have broad application in engineering processes including the manufacture of paper and cement, the geologic storage of nuclear waste and CO2, and the production of oil and gas.
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•The IEP should be expressed as pCa or pMg; not pH. The PZC can be expressed as pH•Ca2+ and Mg2+ behave identically and zeta potential varies linearly with pCa and pMg•pH varies linearly with pCa irrespective of sample type or solution ionic strength•pSO4 may affect zeta potential by moderating the equilibrium pCa•It is important to ensure equilibrium has been reached prior to taking measurements
The present study investigates the effects of the belite content and carbonation curing on the physicochemical properties of cement mortar. The results provide new insight, demonstrating that a ...higher belite content in cement increases CO2 uptake during the carbonation curing process and thus promotes microstructural densification. Carbonation-cured cement with a high alite content showed increased pore connectivity, while the cement with a high belite content experienced reduced pore connectivity and more instances of pore closure, resulting in a complex microstructure. The belite phase was mostly consumed by the carbonation reaction during the curing process, resulting in the production of calcite. As a result, the mechanical strength of the carbonation-cured belite-rich Portland cement mortar was significantly improved in comparison with that after normal curing for an identical period. In particular, the reaction of the belite phase influenced by hydration/carbonation interaction at an early age is discussed along with the experimental results.
This study investigated microstructural changes in alkali-activated slag (AAS) mortars after carbonation using XRD, FTIR, DTG, 1H NMR and SEM examinations. The results showed that decalcification of ...C-S-H was the main reaction in carbonation of AAS. The C-S-H with a low Ca/Si was more vulnerable to decalcification in AAS samples activated by waterglass. Besides, AAS mortars demonstrated a lower CaCO3 formation compared to Portland cement mortars. Calcite and vaterite were the major CaCO3 polymorphs produced by carbonation of AAS precipitated mainly in gel pores and spaces in C-S-H interlayers. Meanwhile, the carbonation also caused a certain volume of contraction in AAS mortars.
•Carbonation affected Portland cement and alkali-activated slag differently.•Carbonation decreased the compressive strength of alkali-activated slag mortar.•C-S-H was the main calcium source during carbonation of alkali-activated slag.•Calcite and vaterite were the major carbonation products of alkali-activated slag.
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