Characteristics of Circulating Fluidized Bed Combustion (CFBC) Ash as Carbon Dioxide Storage Medium and Development of Construction Materials by Recycling Carbonated Ash.

This study validates the attributes of the mineral carbonation process employing circulating fluidized bed combustion (CFBC) ash, which is generated from thermal power plants, as a medium for carbon storage. Furthermore, an examination was conducted on the properties of construction materials produced through the recycling of carbonated circulating fluidized bed combustion (CFBC) ash. The carbonation characteristics of circulating fluidized bed combustion (CFBC) ash were investigated by analyzing the impact of CO2 flow rate and solid content. Experiments were conducted to investigate the use of it as a concrete admixture by replacing cement at varying percentages ranging from 0% to 20% by weight. The stability and setting time were subsequently measured. To produce foam concrete, specimens were fabricated by substituting 0 to 30 wt% of the cement. Characteristics of the unhardened slurry, such as density, flow, and settlement depth, were measured, while characteristics after hardening, including density, compressive strength, and thermal conductivity, were also assessed. The findings of our research study validated that the carbonation rate of CFBC ash in the slurry exhibited distinct characteristics compared to the reaction in the solid-gas system. Manufactured carbonated circulating fluidized bed combustion (CFBC) ash, when used as a recycled concrete mixture, improved the initial strength of cement mortar by 5 to 12% based on the 7-day strength. In addition, it replaced 25 wt% of cement in the production of foam concrete, showing a density of 0.58 g/cm3, and the 28-day strength was 2.1 MPa, meeting the density standard of 0.6 grade foam concrete.

Coagulation Behavior of Antimony Oxyanions in Water: Influence of pH, Inorganic and Organic Matter on the Physicochemical Characteristics of Iron Precipitates.

The presence of inorganic and organic substances may alter the physicochemical properties of iron (Fe) salt precipitates, thereby stabilizing the antimony (Sb) oxyanions in potable water during the chemical treatment process. Therefore, the present study aimed to examine the surface characteristics, size of Fe flocs and coagulation performance of Sb oxyanions under different aqueous matrices. The results showed that surface properties of Fe flocs significantly varies with pH in both Sb(III, V) suspensions, thereby increasing the mobility of Sb(V) ions in alkaline conditions. The negligible change in surface characteristics of Fe flocs was observed in pure water and Sb(III, V) suspension at pH 7. The key role of Van der Waals forces of attraction as well as hydration force in the aggregation of early formed flocs were found, with greater agglomeration capability at higher more ferric chloride dosage. The higher Sb(V) loading decreased the size of Fe flocs and reversed the surface charge of precipitates, resulting in a significant reduction in Sb(V) removal efficiency. The competitive inhibition effect on Sb(III, V) removal was noticed in the presence of phosphate anions, owing to lowering of ζ-potential values towards more negative trajectory. The presence of hydrophobic organic matter (humic acid) significantly altered the surface characteristics of Fe flocs, thereby affecting the coagulation behavior of Sb in water as compared to the hydrophilic (salicylic acid). Overall, the findings of this research may provide a new insight into the variation in physicochemical characteristics of Fe flocs and Sb removal behavior in the presence of inorganic and organic compounds during the drinking water treatment process.

Use of ballasted flocculation (BF) sludge for the manufacturing of lightweight aggregates.

Ballasted flocculation (BF) is an efficient way to remove the turbidity from surface water. The objective of the present study is to optimize the ballast (magnetite), coagulant (poly aluminum chloride) concentration and pH for efficient turbidity removal from surface water. To do this, the sludge produced from an optimized dose of a BF treatment was utilized for the production of lightweight (LW) aggregates by combining it with hard clay and sewage sludge. The LW aggregates were formed by means of rapid sintering in the temperature range of 1000-1200 °C with an exposure time of 10 min. The physical properties of the LW aggregates, in this case the leaching of heavy metals, the bulk density and the microstructure, were investigated. The results indicated that corresponding ballast and coagulant concentrations of 0.75 g/L and 30 mg/L (poly aluminum chloride (PAC)) resulted in the maximum removal efficiency of ≈95%. Using a mixture of BF sludge (30 wt%), dry sewage sludge (20 wt%), and hard clay (50 wt%), aggregates with a density of around 1.0 g/cm3 could be produced. In addition, it was confirmed that the manufactured aggregate was environmentally stable as the elution of heavy metals was suppressed.

Adsorption Capacities of Iron Hydroxide for Arsenate and Arsenite Removal from Water by Chemical Coagulation: Kinetics, Thermodynamics and Equilibrium Studies.

Arsenic (As)-laden wastewater may pose a threat to biodiversity when released into soil and water bodies without treatment. The current study investigated the sorption properties of both As(III, V) oxyanions onto iron hydroxide (FHO) by chemical coagulation. The potential mechanisms were identified using the adsorption models, ζ-potential, X-ray diffraction (XRD) and Fourier Transform Infrared Spectrometry (FT-IR) analysis. The results indicate that the sorption kinetics of pentavalent and trivalent As species closely followed the pseudo-second-order model, and the adsorption rates of both toxicants were remarkably governed by pH as well as the quantity of FHO in suspension. Notably, the FHO formation was directly related to the amount of ferric chloride (FC) coagulant added in the solution. The sorption isotherm results show a better maximum sorption capacity for pentavalent As ions than trivalent species, with the same amount of FHO in the suspensions. The thermodynamic study suggests that the sorption process was spontaneously exothermic with increased randomness. The ζ-potential, FT-IR and XRD analyses confirm that a strong Fe-O bond with As(V) and the closeness of the surface potential of the bonded complex to the point of zero charge (pHzpc) resulted in the higher adsorption affinity of pentavalent As species than trivalent ions in most aquatic conditions. Moreover, the presence of sulfates, phosphates, and humic and salicylic acid significantly affected the As(III, V) sorption performance by altering the surface properties of Fe precipitates. The combined effect of charge neutralization, complexation, oxidation and multilayer chemisorption was identified as a major removal mechanism. These findings may provide some understanding regarding the fate, transport and adsorption properties onto FHO of As oxyanions in a complex water environment.

The Experimental Process Design of Artificial Lightweight Aggregates Using an Orthogonal Array Table and Analysis by Machine Learning.

The purpose of this study is to experimentally design the drying, calcination, and sintering processes of artificial lightweight aggregates through the orthogonal array, to expand the data using the results, and to model the manufacturing process of lightweight aggregates through machine-learning techniques. The experimental design of the process consisted of L18(3661), which means that 36 × 61 data can be obtained in 18 experiments using an orthogonal array design. After the experiment, the data were expanded to 486 instances and trained by several machine-learning techniques such as linear regression, random forest, and support vector regression (SVR). We evaluated the predictive performance of machine-learning models by comparing predicted and actual values. As a result, the SVR showed the best performance for predicting measured values. This model also worked well for predictions of untested cases.

Optimum Bloating-Activation Zone of Artificial Lightweight Aggregate by Dynamic Parameters.

The purpose of this study is to compare the bloating mechanism of artificial lightweight aggregate under sintering and rapid sintering conditions to identify the factors behind the bloating of the lightweight aggregate under these sintering conditions, and to find suitable temperature ramping conditions. The aggregate had an average particle size of 10 mm as formed using acid clay, and it was fired by a rapid sintering method and a normal sintering method. The bulk density and water absorption ratio of the specimen were measured, and the cross section was observed. No black core was observed under the rapid sintering condition, and it was lightened at an inflection point of 1150 °C. A reduction in the bulk density was observed in a shorter period of time when the input temperature was high under the normal sintering conditions. Regardless of the input temperature, the bulk density change was divided into three sections and a bloating-activation zone was observed in which the density abruptly decreased.