Hydrotalcite-like Phase Research Articles

Insight into migration of Cr(VI) in self-hardening slurry materials for trench cutoff wall.

The migration and immobilization of heavy metals in soil and groundwater pose significant environmental challenges, particularly in the context of Cr(VI), a highly toxic and mobile contaminant. Self-hardening slurry materials, commonly used for trench cutoff walls, have gained great attention due to their potential for pollutant containment. However, the relationship between their adsorption properties and pollutant diffusion behaviors remains poorly understood. This study investigates the adsorption properties and free-diffusion behaviors of Cr(VI) in two self-hardening slurry materials, SCB (slag-cement-bentonite) and MASB (MgO activated slag-bentonite), to better understand the pollutant migration and immobilization mechanisms. Adsorption experiments reveal that MASB exhibits a higher Cr(VI) adsorption capacity than SCB, resulting in greater retardation factors and longer breakthrough times, improved by 57.6% and 94.9% at Cr(VI) concentrations of 2600mg/L and 26000mg/L, respectively. However, free-diffusion tests show that MASB has a larger migration depth and shorter breakthrough times, reduced by 68.2% and 57.9%. Microscopic analysis reveals that the presence of stable and ion-exchangeable hydration products (hydrotalcite-like phases) in MASB enhances its Cr(VI) adsorption capacity but provides favorable conditions for Cr(VI) diffusion. SCB demonstrates superior retardation to Cr(VI) in free-diffusion due to the transformation of AFm phases absorbed with Cr(VI) into stable AFt phases.

Hydrotalcite-derived well-dispersed and thermally stable cobalt nanoparticle catalyst for ammonia decomposition

Hydrotalcite-derived well-dispersed and thermally stable cobalt nanoparticle catalyst for ammonia decomposition

Influence of magnesite/limestone addition on the hydration characteristics of ternary slag cement systems

Influence of magnesite/limestone addition on the hydration characteristics of ternary slag cement systems

Efficient utilization of coral waste for internal curing material to prepare eco-friendly marine geopolymer concrete

To address shortages in construction materials for island engineering, tackle the accumulation of solid waste, and inhibit the shrinkage of geopolymers, coral waste was utilized as the internal curing material to prepare high-performance marine geopolymer concrete (MGC) with seawater, sea-sand, and normal limestone aggregate (LsA). The coral coarse aggregate (CorA) used in this investigation has a total porosity ranging from 50% to 58.3% with internal pore diameters spanning 50-400μm. The water desorption of CorA followed a two-stage pattern within a relative humidity (RH) range of 75%-85%, becoming nonlinear above 90% RH, which released about 85% of its moisture within 200h at 97% RH, demonstrating potential for internal curing. Adding a small amount of CorA to MGC increased slump and setting time by providing internal curing water. However, as CorA content exceeded 30%, the slump significantly decreased due to reduced mixing water and elevated activator concentration, while the initial setting time slightly decreased. Furthermore, the inclusion of saturated CorA in MGC significantly reduced autogenous shrinkage, with higher CorA contents (exceeding 30%) leading to slight expansion in the early stages and nearly eliminating shrinkage at contents above 40%. The greater drying shrinkage in geopolymer systems compared to ordinary Portland cement is due to capillary pressure compressing the product framework, converting larger gel pores into smaller ones. Additionally, the layered calcium aluminosilicate hydrate (C-A-S-H) gel exhibits more pronounced creep characteristics under low internal humidity conditions. The higher CorA content in MGC promoted the formation of hybrid C, N-A-S-H gel and hydrotalcite-like phases, and reduced carbonation issues. The interfacial transition zone (ITZ) between CorA and the geopolymer matrix formed a robust mechanical interlock, enhancing tensile strength and minimizing shrinkage-induced cracks. Based on overall performance and marine material utilization, an optimal substitution rate of CorA between 40% and 50% is recommended.

Hybrid Organic-Inorganic Blast Furnace Slag Binders Activated with Alkali Acetates.

Hybrid organic-inorganic binders based on blast furnace slag were produced using sodium (NaAc) or potassium (KAc) acetate as the sole activator, and their properties were compared with those of sodium- or potassium hydroxide-activated slag pastes. The acetate-activated binders showed significantly lower cumulative heat release and extended setting time (∼230 h) than the hydroxide-activated binders. The main reaction products forming in all binders were calcium aluminosilicate hydrate-type gels and a hydrotalcite-like phase, independently of the activator type used. Compressive strengths of the acetate-activated pastes (∼40 MPa at 180 days) were lower than those of the hydroxide-activated binders (∼80 MPa at 180 days). However, the acetate-based binders exhibited superior impermeability and reduced wettability at 28 days, likely due to hydrophobic acetate groups. It is hypothesized that acetates dissociate in water, forming calcium acetate and alkali silicates via a reaction with species dissolving from the slag. This study demonstrates alkali acetates are effective activators for creating hybrid slag-based binders with reduced permeability.

Temporal effects on the micro- and nano-structural cement-slag pastes subjected to microwave curing over 7 years

Temporal effects on the micro- and nano-structural cement-slag pastes subjected to microwave curing over 7 years

Hydration mechanism and microstructure evolution of recycled brick powder blended cement toward low-carbon and cleaner production

Hydration mechanism and microstructure evolution of recycled brick powder blended cement toward low-carbon and cleaner production

Compressive Strength and Microstructure of Carbide Slag and Alkali-Activated Blast Furnace Slag Pastes in China

The alkali-activated blast furnace slag is attracting significant attention in replacing Portland cement due to several characteristics similar to cement hydration. However, there are a few practical problems with commercial alkali activators, such as the fast setting time, relatively high costs, and significant CO2 emissions during preparation. Thus, discovering industrial residues possessing inherent alkalinity are urgent. This study proposes the use of carbide slag at levels of 0%, 5%, 10%, 15%, 20%, and 30% and alkali at levels of 1%, 2%, 3%, 4%, 5%, 6%, 8%, and 10% activated blast furnace slag. The compressive strength and microstructure of carbide slag and alkali-activated blast furnace slag (CAB) pastes were examined using X-ray diffraction analysis (XRD), Differential Scanning Calorimetry/Thermogravimetric Analysis (DSC/TG), Fourier transform infrared spectroscopy (FTIR) and Scanning electron microscopy (SEM). The results revealed that the addition of carbide slag produced more hydrotalcite-like phase as well as decreased the content of ettringite (AFt) and the calcium–silicate–hydrate (C-S-H) gel, which decreased the compressive strength of the CAB pastes. At the age of 28 days, when the dosage was 5%, 10%, 15%, 20%, and 30%, the compressive strength of CAB mixes decreased by 2.1%, 7.1%, 9.2%, 9.8%, and 28.1%, respectively. The addition of NaOH promoted the formation of AFt, and there was an optimum level of NaOH corresponding to the high compressive strength of paste. At the age of 3 days and 7 days, the compressive strength reached its maximum at the dosage of 6% NaOH, which was 24.8 MPa and 36.3 MPa, respectively. However, at the ages of 14 days and 28 days, the compressive strength increased as the dosage of NaOH increased to 5%, which was 43.3 MPa and 44.5 MPa, respectively. The water curing could both enhance the early and later strength, the compressive strength of 23.3 MPa was gained at 3 days, and this increased by 16.3%, 24.0% and 36.9% at 7 days, 14 days and 28 days, respectively. Therefore, water curing was suitable for the strength development of CAB pastes.

Valorization of biomass bottom ash in alkali-activated GGBFS-fly ash: Impact of biomass bottom ash characteristic, silicate modulus and aluminum-anodizing waste

Valorization of biomass bottom ash in alkali-activated GGBFS-fly ash: Impact of biomass bottom ash characteristic, silicate modulus and aluminum-anodizing waste

Dissolution-precipitation hydration mechanism of steel slag based on ion exchange of a layered alkali-activator

Dissolution-precipitation hydration mechanism of steel slag based on ion exchange of a layered alkali-activator

Characterizing two types of zonation within slag rims of aged alkali-activated slag pastes through SEM and TEM

Characterizing two types of zonation within slag rims of aged alkali-activated slag pastes through SEM and TEM

3-Dimensional insight into zonation within slag rims of aged blended cement

3-Dimensional insight into zonation within slag rims of aged blended cement

Formation and Evolution of the Hydrotalcite-Like Phase During Ageing of Dolomite-Cement Mortars under Various Conditions

This work considers the reactions of dolomite powder mixed with Portland cement during ageing under accelerating conditions (60 °C, water or alkaline medium). The phase composition and microstructure of cement-dolomite mortars were studied using X-ray diffraction (XRD), thermogravimetric analysis (TGA), and scanning electron microscopy with X-ray microanalysis (SEM-EDS). The results showed that the alkalinity of the medium increased the dolomite reaction degree but did not affect the reaction products’ composition. The formation of the hydrotalcite-like phase with the general formula Mg4Al2(CO3)1−x(OH)12+2x·nH2O proved to be the predominant route of dolomite consumption in the presence of available aluminium in the hardened cement paste. Then, after three months of ageing, an interlayer anions replacement became noticeable: carbonate anions in the structure of hydrotalcite are gradually replaced by hydroxide ones.

Effect of Al2O3 content in slag on the relationship between slag reactivity and carbonation resistance

To understand the influence of slag chemistry on the carbonation resistance of slag-rich cement, this paper explored the carbonation characteristics of blended cement systems with different Al2O3 contents in slag through accelerated carbonation test. Irrespective of slag chemistry, three main CO2 binding phases were identified during accelerated carbonation test, i.e. carbonated Ca-Al AFm phases (amorphous or nano-crystalline), carbonated hydrotalcite-like phase, and calcium carbonate (amorphous calcium carbonate, vaterite, and calcite). Additionally, it was noted that the classification employed for slag reactivity (based on slag chemistry) cannot be extended to predict carbonation resistance of slag-rich cement directly. The main challenge occurred for slag with high alumina content. The experimental results showed that Al2O3-rich slag exhibited a high reactivity and can be considered as a reactive component in the blended mixture; however, it did not contribute to carbonation resistance of the mixture. Especially for CO2 binding capacity, it was similar for systems with varied alumina content in slag (from 3.69 to 18.19 wt.%) in the completely carbonated area.

Promoting the dissolution of slag in blended cement via adding polyaluminum sulfate and controlling the inner spatial zonation

Promoting the dissolution of slag in blended cement via adding polyaluminum sulfate and controlling the inner spatial zonation

A novel admixture to improve durability of alkali-activated slag by reducing water sorptivity and optimising the process of activation

A novel admixture to improve durability of alkali-activated slag by reducing water sorptivity and optimising the process of activation

Study on the composition of calcium alumina silicate hydrate (CASH) in lime-activated low carbon cementitious materials: The influence of alkaline additives

The composition of CASH in lime-activated low carbon cementitious materials (LCM) was investigated in this study, and the influence of alkaline additives on the composition of CASH in LCM was analyzed, particularly for the hydration rim of slag. Compared to LCM-control mixture, alkali additives effectively improved the hydration of GGBFS and significantly increased the thickness of the hydration rim as the inner hydration product. The enlargement of the hydration rim zone led to a lower Ca/(Si + Al) ratio of the hydrated gel mainly due to the interference of Al from intermixing phases in the rim. For LCM with alkaline additives, the hydration rim of slag contained C(N)ASH, ettringite, U-phase, and a minor amount of amorphous or poorly crystalline hydrotalcite-like phase, and the hydrated gel in paste was mainly composed of C(N)ASH due to the uptake of Na+ ions in CASH.

Pd-modified CuO-ZnO-Al2O3 catalysts via mixed-phases-containing precursor for methanol synthesis from CO2 hydrogenation under mild conditions

A series of palladium-modified (Pd-modified) CuO-ZnO-Al2O3 (CZA) catalysts with various Pd loadings (0.3 wt.% to 2.4 wt.%) were prepared using the wetness impregnation method, on two CZA supports with different structures that are CZA-aged precursor composed of a mixture of zincian-malachite and hydrotalcite-like phases (CZA-zH), and CuO/ZnO/Al2O3 metal oxide nanoparticles (CZA-MO). Enhancement on catalytic activity can be observed on both Pd-modified CZA catalysts in a temperature range of 180-240 °C for methanol synthesis via CO2 hydrogenation. Pd/CZA-zH catalysts exhibited a more efficient and stable production of methanol at a relatively low reaction temperature of 180 °C for 100 hrs of reaction. The improvement of activity is mainly ascribed to a higher surface area and abundant oxygen-containing functional groups (e.g., -OH) of CZA-zH support, which is beneficial for better adsorption and distribution of Pd promoter. Hydrogen temperature programmed reduction and X-ray photoelectron spectroscopy results demonstrated a better interaction between Pd and Cu on Pd/CZA-zH catalysts via enhanced reducibility of CuO, and peak shift of Cu to a lower binding energy. The difference in the efficient utilization of hydrogen spillover effect of Pd promoter over two CZA supports resulted in the different performances for methanol synthesis under mild reaction conditions.

Chloride penetration and binding behavior in unsaturated alkali-activated slag mortars

Chloride penetration and binding behavior in unsaturated alkali-activated slag mortars

Some Critical Reflections on the SEM-EDS Microanalysis of the Hydrotalcite-like Phase in Slag Cement Paste.

For a better understanding of the hydrotalcite-like phase with SEM-EDS microanalysis, the present research paid special attention to the data acquisition and interpretation of this technique. A lower Mg/Al ratio was obtained when using a higher accelerating voltage, and a beam energy of 10 kV was more appropriate than 15 kV for investigation when the slag rim was thin, to compromise to meet the requirements of obtaining an adequate overvoltage ratio and minimizing the interference. Additionally, it was noted that the Mg/Al ratio decreased from zones rich in hydrotalcite-like phase to zones rich in the C-S-H gel phase, and indiscriminately fitting scatter points selected from the slag rim would bias the Mg/Al ratio of the hydrotalcite-like phase. According to the standard-based microanalysis, it was concluded that the analysis total of the hydrates within the slag rim was in the range of 30-40%, lower than that located in the cement matrix. Besides the water chemically bound in the C-S-H gel phase, the hydrotalcite-like phase also contained a certain amount of hydroxide ions and chemically bound water.