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•RC-450 °C cement can reduce more than 94% of the CO2 emission compared to OPC.•RC-450 °C cement had much less CO2 emission than RC-800 °C cement.•RC-450 °C paste had a similar ...strength as OPC paste.
The production of ordinary Portland cement (OPC) is responsible for a significant part of global CO2 emission. For decades, the raw material and high burn temperature (up to 1500 °C) for OPC production have not been changed to reduce the CO2 emission significantly. In order to reduce the CO2 emission for cement production, two types of recycled cements (RC-450 °C and RC-800 °C) were produced in this study. It is hoped that the potential application of recycled cement could help to mitigate the CO2 emission in cement production. The application of recycled cement could significantly reduce the environmental impacts caused by the landfills of demolished waste concretes. The recycled cements RC-450 °C and RC-800 °C were produced through burning waste old OPC pastes at 450 °C and 800 °C respectively and then grinding into powder through a ball mill. The CO2 emissions from producing OPC, RC-450 °C and RC-800 °C were calculated and compared through considering the CO2 emissions from both fuel burning and the clinker materials. Compared to the production process of OPC, the production of RC-450 °C can reduce 94% of CO2 emission. By mixing with water, an additional 4% CO2 by weight of RC-450 °C can be captured in the RC-450 °C paste through the formation of calcium carboaluminate and additional calcite. RC-450 °C showed lower CO2 emission but a higher strength of paste than RC-800 °C. Besides, RC-450 °C paste was found to have a similar strength as the OPC paste, and this suggests that the RC-450 °C could be used to totally replace OPC.
The interfacial adhesion between oxidised bitumen and mineral surfaces at dry and wet conditions was investigated using molecular dynamics (MD) simulations. Molecular models were built for virgin and ...oxidised bitumen components including saturate, aromatic, resin and asphaltenes. The bitumen models and four representative mineral substrates (namely quartz, calcite, albite and microcline) were employed to construct bitumen-mineral interface systems. These models were validated by the experimental results and MD simulations reported in the literature. The hardening mechanism of the aged bitumen was analysed by comparing the density, cohesive energy density and fraction of free volume between the virgin and oxidised bitumen. Work of adhesion was computed to quantify the adhesive bonding property of the bitumen-mineral interface systems for the virgin, lightly oxidised and heavily oxidised bitumen models under dry and wet conditions. Results show that the oxidised products (carbonyl and sulfoxide) strengthen the intermolecular bonding, resulting in molecular aggregation and physical hardening of the aged bitumen. When bitumen becomes oxidised at the dry condition, the interfacial adhesion of bitumen-acidic minerals (quartz) is dominated by van der Waals interaction which decreases due to the increased bitumen-quartz intermolecular distance caused by the aggregated bitumen molecules during aging. In comparison, the interfacial adhesion of bitumen-strong alkali minerals (albite and microcline) is dominated by electrostatic energy which increases due to higher polarity introduced by the oxidised products. For the bitumen-weak alkali mineral (calcite), the interfacial adhesion is attributed to both electrostatic energy and van der Waals energy, where compared to the virgin bitumen, the electrostatic energy becomes lower for the lightly-oxidised bitumen due to the increased bitumen-mineral distance but becomes higher for the heavily-oxidised bitumen due to higher polarity. At wet condition, water is the dominating factor that affects (weakens) the interfacial adhesion between the bitumen and the acidic minerals (quartz), and the oxidative aging of bitumen is the major factor that affects (strengthens) the interfacial adhesion between the bitumen and the strongly alkaline minerals (albite and microcline). For the weak alkali minerals such as calcite, both water and bitumen aging can significantly affect the interfacial adhesion.
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•Van der Waals forces dominate interfacial interaction of bitumen with acidic minerals.•Electrostatic forces dominate interfacial interaction of bitumen with alkali minerals.•Oxidation causes molecular aggregation and higher polarity of the bitumen.•Water weakens while oxidation strengths bitumen-mineral interfacial adhesion.•Coupled effect of water and oxidation on adhesion depends on mineral's acid-base.
The carbonation of steel slag to produce building material is a useful way to increase the utilization of steel slag and absorb carbon dioxide. In this study, gypsum, steel slag, and water were ...mixed, compaction-shaped, and carbonation-cured as a means of improving the strength of the steel slag. It was observed that gypsum promoted an increase in both the compressive strength and the CO2 uptake of steel slag. CO2 uptake was positively correlated with strength. Microanalysis indicated that the main hydration product were C-S-H phases and ettringite, while the main carbonation products were calcite and monocarbonate (C3A. CaCO3.11H2O). Gypsum is speculated to promote the rapid hydration of steel slag to form ettringite (C3A.3CaSO4.32H2O), which then reacts with CO2 to produce monocarbonate; thus, gypsum plays a catalytic role in this system. The results of this study therefore provide theoretical guidance for the preparation of steel slag–gypsum carbide building materials.
•Biostimulation was adopted for the first time in accelerating MICP in Cu immobilization in soil.•MiSeq Illumina sequencing confirmed significant number and types of ureolytic bacteria in ...soil.•Soluble-exchangeable fraction of Cu decreased from 45.54 mg kg−1 to 1.55 mg kg−1 in soil.•Biostimulation induced carbonate precipitation was characterized in Cu immobilization.
The urease-based microbially induced carbonate precipitation (MICP) is known as effective remediation strategy in soil metals remediation; however, all related studies confined to bioaugmentation. In the present study, biostimulation process was adopted for the first time in accelerating MICP in copper (Cu) immobilization in soil. The abundance, composition, and diversity of the bacterial community after biostimulation were assessed with MiSeq Illumina sequencing analysis that confirmed number and types of ureolytic and calcifying bacteria grown significantly leading to MICP process, compared to untreated soil. The results demonstrated that biostimulation induced calcite precipitation in soil that immobilized Cu mainly in carbonated fraction of soil, while soluble-exchangeable fraction decreased from 45.54 mg kg−1 to 1.55 mg kg−1 Cu in soil. Scanning electron microscopy (SEM) cum energy-dispersive X-ray spectroscopy (EDX) evaluated structure and elemental composition in Cu immobilization after biostimulation. Fourier Transform-Infra Red (FTIR) spectroscopy depicted functional chemical groups involved in copper immobilization, while X-Ray Diffraction (XRD) identified main crystalline phases or biominerals formed during biostimulation in order to carryout Cu remediation from soil.
The effect of depressant 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA) on the flotation separation of smithsonite from calcite was studied by micro-flotation and electro-kinetic tests. The ...micro-flotation results showed that good floatability of both smithsonite and calcite were achieved in the presence of sodium oleate. The depressant PBTCA selectively depressed calcite without interfering the floatability of smithsonite. The mixed minerals flotation results showed that efficiency separation of smithsonite from calcite was achieved using PBTCA as the depressant. Zeta potential measurements indicated that NaOl was able to adsorb on the PBTCA pre-treated smithsonite surface, but failed to adsorb on the PBTCA pre-treated calcite surface.
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•Both smithsonite and calcite floated well in the presence sodium oleate•Separation of smithsonite and calcite using PBTCA depressant was attempted•Calcite can be selectively depressed by PBTCA•This might be attributed to the matched-degree of PBTCA with calcite
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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.
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•EP particles as a novel bacteria carrier on crack-healing in concrete was studied.•EP particles exert more positive effects on the healing capacity over EC particles.•Microstructures ...of the mineral precipitations on the crack surface were analyzed.•Completely healed crack widths were maximized in EP-B specimens.
Immobilization has been reported to be an efficient approach for bacteria-based self-healing concrete to maintain the high-efficiency mineral-forming capacity of incorporated bacteria over a period of time. However, the relatively high-cost, local unavailability, and low adsorption capacity of the current bacteria carriers make them impractical for potential implementation in large-scale concrete structures. In this study, the feasibility of expanded perlite (EP) as a novel bacteria carrier on quantifying cracks-healing in concrete via immobilization of Bacillus cohnii was demonstrated. The effects of two other self-healing techniques, i.e., direct introduction of bacteria and expanded clay (EC) immobilized bacteria, on the efficiency of crack-healing were also investigated. Experimental results showed that specimens incorporated with EP-immobilized bacteria exhibited the most efficient crack-healing after each healing time. The values of completely healed crack widths were up to 0.79mm after 28days of healing, which is larger than the value of 0.45mm for specimens incorporated with EC-immobilized bacteria. Field emission scanning electron microscope (FESEM) and X-ray diffraction (XRD) analysis confirmed that mineral precipitations on their crack surfaces are calcite crystals. The findings obtained in this study may provide a scientific basis for the potential implementation of expanded perlite, as a new microorganism carrier, in bacteria-based self-healing concrete.
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It is widely accepted that oil recovery during waterflooding can be improved by modifying the composition of the injected brine. A typical approach is diluting the formation water to ...a specific lower salinity. However, recent experimental studies report the adverse effect of formation water dilution on oil recovery for specific oil/brine/rock systems. The adverse effect depends on the interactions within the system and is more pronounced in carbonates. In this study, we investigated the effect of water composition on the performance of low salinity water injection by considering the complex interaction of oil, brine, and rock system.
A surface complexation model (SCM) is developed to calculate the zeta-potential at oil and rock surfaces. Considering a water film between oil and rock and using DLVO theory, attractive/repulsive forces between oil/brine and brine/rock interfaces are calculated. Contact angle is predicted employing the augmented Young-Laplace equation. Our zeta potential calculations based on the SCM reproduced the experimental data of oil/brine and brine/calcite zeta potential measurements. Our contact angle calculations using the DLVO theory and the augmented Young-Laplace equation accurately estimated the dynamic trend of contact angle during low salinity flood. Modeling wettability alteration as a function of contact angle was sufficient to predict the low salinity effect. The developed model is implemented in a comprehensive compositional reactive transport simulator to validate the proposed approach.
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Selective separation of smithsonite from gangue, especially calcite, remains a difficult problem in practice due to the fact that selectivity of depressants currently used is not ...good. In this study, fenugreek gum (FGM) was used as a new depressant to separate smithsonite from calcite when using cationic collector octadecylamine acetate (ODA). Flotation results show that FGM can excellently separate smithsonite from calcite. The selective interaction mechanism of FGM was disclosed by zeta potential measurements, adsorption amount measurements and FTIR studies. The results of adsorption amount measurements indicate that FGM adsorbs much more on calcite than smithsonite and the interaction of FGM with calcite lowers the adsorbed amount of ODA on calcite surface. The zeta potential measurements results show that FGM hardly interferes with the surface charge of smithsonite but has conspicuous influence on that of calcite. The FTIR studies confirm the chemisorption of FGM on calcite surface and weak adsorption on smithsonite surface, possibly caused by electrostatic interaction or hydrogen bond.
•Use CO2 to treat harden cement powder as a supplemental cementitious material.•The incorporation of carbonated cement powder enhances the compressive strength.•Replacement of cement with carbonated ...cement powder shows a denser microstructure.
Recovering aggregates from recycled concrete produces a large amount of powder, which contains hardened cement paste and is classified as a corrosive hazardous material. This study used CO2 to treat hardened cement paste powder and to investigate how the incorporation of uncarbonated and carbonated hardened cement paste powder into cement affects the hydration and microstructure development of cement. Carbonated hardened cement paste powder consists mainly of calcite and silica gel. Replacement of cement by uncarbonated cement paste powder content from 10 to 30% by the mass of cement decreases, while replacement of cement with 10–20% carbonated hardened cement paste powder increases the strength of cement up to 90 days. The replacement of cement with 30% carbonated waste paste powder slightly decrease the strength of the cement. The silica gel in carbonated hardened cement paste powder quickly reacts with calcium hydroxide and results in the formation of more C-S-H. The presence of calcite in carbonated hardened paste powder leads to the formation of calcium aluminate hemi-carbonate (CAHC) and calcium aluminate mono-carbonate (CAMC) thus to a stabilization of ettringite (AFt) compared with the control cement paste, in which portion of AFt converts to mono-sulphoaluminate. CAHC is less stable than CAMC and transforms to CAMC in about one week after its formation. These chemical actions lead to a lower porosity and a higher compressive strength for cement paste with carbonated hardened paste powder compared with the control cement paste.
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