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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
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.
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.
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.
Mechanisms of nucleation from electrolyte solutions have been debated for more than a century. Recent discoveries of amorphous precursors and evidence for cluster aggregation and liquid-liquid ...separation contradict common assumptions of classical nucleation theory. Using in situ transmission electron microscopy (TEM) to explore calcium carbonate (CaCO₃) nucleation in a cell that enables reagent mixing, we demonstrate that multiple nucleation pathways are simultaneously operative, including formation both directly from solution and indirectly through transformation of amorphous and crystalline precursors. However, an amorphous-to-calcite transformation is not observed. The behavior of amorphous calcium carbonate upon dissolution suggests that it encompasses a spectrum of structures, including liquids and solids. These observations of competing direct and indirect pathways are consistent with classical predictions, whereas the behavior of amorphous particles hints at an underlying commonality among recently proposed precursor-based mechanisms.
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This study presents experiment and surface complexation modeling (SCM) of synthetic calcite zeta potential in brine with mixed potential determining ions (PDI) under various CO2 ...partial pressures. Such SCM, based on systematic zeta potential measurement in mixed brines (Mg2+, SO42−, Ca2+ and CO32−), is currently not available in the literature and is expected to facilitate understanding of the role of electrostatic forces in calcite wettability alteration. We first use a double layer SCM to model experimental zeta potential measurements and then systematically analyze the contribution of charged surface species. Calcite surface charge is investigated as a function of four PDIs and CO2 partial pressure. We show that our model can accurately predict calcite zeta potential in brine containing a combination of four PDIs and apply it to predict zeta potential in ultra-low and pressurized CO2 environments for potential application in enhanced oil recovery in carbonate reservoirs. Model prediction reveals that calcite surface will be positively charged in all considered brines in pressurized CO2 environment (>1atm). The calcite zeta potential is sensitive to CO2 partial pressure in the various brine in the order of Na2CO3>Na2SO4>NaCl>MgCl2>CaCl2 (Ionic strength=0.1M).
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