Search Results (22)

The sustainable conversion of biogenic waste into high-value materials presents a promising approach for addressing environmental and industrial challenges. This work reports an advancement into antioxidant-enriched phosphate minerals derived from green conversion of biogenic calcium carbonates of crustaceans. We demonstrate the effectiveness of Raman technology in controlling conversion using phosphoric acid treatment. The effects of reaction parameters—including acid stoichiometry, granular size distribution, and thermal treatment at 700 °C and 1200 °C—were systematically evaluated. Raman spectroscopy results validated by X-ray diffraction (XRD) and SEM-EDX analyses revealed mixed-phase minerals monetite, brushite, whitlockite or hydroxylapatite, respectively. Notably, reducing particle size enhanced conversion efficiency by increasing the reactive surface area, while the use of excess phosphoric acid facilitated conversion to monocalcium phosphate and promoted the degradation of the organic matrix. Thermal treatment further altered the product composition: heating at 700 °C produced a whitlockite-rich phase, whereas treatment at 1200 °C shifted the balance toward hydroxylapatite. The synthesized calcium phosphate compounds, including hydroxylapatite, monocalcium phosphate, whitlockite, and brushite, hold significant practical utility in biomedical applications (such as bone grafts and dental implants), agriculture, and industrial processing. Moreover, we have proven that by controlling the reaction parameters the final product composition can be tailored according to the specific needs. A greener approach yields brushite, monetite, or monocalcium phosphate, while a more energy-demanding process, including heating to 1200 °C, yields a high-purity hydroxylapatite. This research offers a sustainable analytical route for producing high-purity calcium phosphate materials from wasted biomaterials, contributing to both the bioeconomy as well as scientific innovation. Full article

Due to the explosive growth of software quantity and the mixed ability of software developers, a large number of software defects emerge during the later stages of software maintenance. The search method based on genetic programming is one of the most popular in search algorithms, but it also has some issues. The single-objective approach to validate and select offspring patches without considering other constraints can affect the efficiency of patch generation. To address this issue, this paper proposes an automatic software repair method based on Multi-objective Genetic Programming (MGPRepair). Firstly, the method adopts a lightweight context analysis strategy to find suitable repair materials. Secondly, it decouples the replacement statements and insertion statements in the repair materials, using a lower-granularity patch representation method to encode the patches in the search space. Then, the automatic software defect repair is treated as a multi-objective search problem, and the NSGA-II multi-objective optimization algorithm is used to find simpler repair patches. Finally, the test case filtering technique is used to accelerate the patch validation process and generate correct patches. MGPRepair was experimentally evaluated on 395 real Java software defects from the Defects4J dataset. The experimental results show that MGPRepair can generate test case-passing patches for 51 defects, of which 35 defect patches are equivalent to manually generated patches. Its repair the efficiency and success rate are higher to other excellent automatic software defect repair methods such as jGenProg, RSRepair, ARJA, Nopol, Capgen, and SequenceR. Full article

This experimental study explores the mitigation of membrane fouling in membrane bioreactors (MBRs) through the combined use of granular activated carbon (GAC) and powdered activated carbon (PAC). The research assesses the impact of these materials on the fouling resistance, critical flux, and permeate quality using various mixed liquor suspended solids concentrations and carbon dosages. The results indicate that the GAC-PAC combination significantly reduces the total filtration resistance, particularly the cake layer resistance, by 11.7% to 13.6% compared to setups without activated carbon or with the individual carbon types. The study also reveals that this combination decreased the fouling rate by 15% to 24% at critical flux steps, demonstrating substantial improvements in fouling mitigation and operational efficiency. Furthermore, the GAC-PAC combination, which produces an adsorption process, enhances the permeate quality, achieving the near-complete removal of organic matter, total nitrogen, and turbidity, with total phosphorus removal reaching 99%. These findings demonstrate that the combined use of GAC and PAC not only reduces membrane fouling but also improves the overall MBR performance, making it a viable strategy for enhancing the efficiency of wastewater treatment processes. Full article

Nowadays, almost all countries in the world are intensifying their search for locally available energy sources to become independent of external supplies. The production of alternative fuels from biomass and waste by thermal treatment or direct use in the combustion process is still the simplest method for fast and cheap heat production. However, the different characteristics of these fuels can cause problems in the operation of the plants, resulting in increased air pollution. Therefore, the analysis of the thermal treatment of solid fuels is still an important issue from a practical point of view. This work aimed to study biomass combustion in a small-scale reactor using the in-house Extended DEM (XDEM) method based on mixed Lagrangian–Eulerian approaches. This was provided by a novel, independently developed coupling computational interface. This interface allows for a seamless integration between CFD and DEM, improving computational efficiency and accuracy. In addition, significant advances have been made in the underlying physical models. Within the DEM framework, each particle undergoes the thermochemical processes, allowing for the prediction of its shape and structural changes during heating. Together, these changes contribute to a more robust and reliable simulation tool capable of providing detailed insights into complex multi-phase flows and granular material behavior. Numerical results were obtained for a non-typical geometry to check the influence of the walls on the distribution of the parameters in the reactor. The results show that XDEM is a very good tool for predicting the phenomena during the thermal treatment of solid fuels. In particular, it provides information about all the moving particles undergoing chemical reactions, which is very difficult to obtain from measurements. Full article

The Hongtoushan Cu-Zn volcanogenic massive sulfide (VMS) deposit, located in the Hunbei granite–greenstone terrane of the North China Craton, has undergone a complex, multi-stage metallogenic evolution. The deposit comprises three main types of massive ores: Type-1 ores, characterized by a sulfide matrix enclosing granular quartz and dark mineral aggregates; Type-2 ores, distinguished by large pyrite and pyrrhotite porphyroblasts and a small amount of gangue minerals; and Type-3 ores, mainly distributed in the contact zone between the ore body and gneiss, featuring remobilized chalcopyrite and sphalerite filling the cracks of pyrite. The metallogenic process of the Hongtoushan deposit is divided into three main stages: (1) an early mineralization stage forming Type-1 massive ores; (2) a metamorphic recrystallization stage resulting in Type-2 massive ores with distinct textural features; and (3) a late-stage mineralization event producing Type-3 massive ores enriched in Cu, Zn, and other metals. This study integrates sulfur isotope, trace elements, and fluid inclusion data to constrain the sources of ore-forming materials, fluid evolution and metallogenic processes of the deposit. Sulfur isotope analyses of sulfide samples yield ${\delta }^{34}$S values ranging from −0.7 to 4.2 (mean: 1.8 ± 1.5, 1$\sigma$), suggesting a predominant magmatic sulfur source with possible contributions from Archean seawater. Trace element analyses of pyrite grains from different ore types reveal a depletion of rare earth elements, Cu, and Zn in Type-2 massive ores due to metamorphic recrystallization, and a subsequent re-enrichment of these elements in Type-3 massive ores. Fluid inclusion studies allowed for identifying three types of ore-forming fluids: Type-1 (avg. $T_h$: 222.9; salinity: 6.74 wt.% NaCl eqv.), Type-2 (avg. $T_h$: 185.72; salinity: 16.56 wt.% NaCl eqv.), and Type-3 (avg. $T_h$: 184.81; salinity: 16.22 wt.% NaCl eqv.), representing a complex evolution involving cooling, water–rock interaction and fluid mixing. This multi-disciplinary study reveals the interplay of magmatic, hydrothermal and metamorphic processes in the formation of the Hongtoushan VMS deposit, providing new insights into the fluid evolution and metallogenic mechanisms of similar deposits in ancient granite–greenstone terranes. Full article

The global focus on geopolymer binder production has increased due to the adoption of waste materials and industrial byproducts. Given the gradual decline in the availability of fly ash and ground granular blast furnace slag (GGBFS) resulting from the decarbonization process in electricity and steel production, waste clay brick powder (WCBP) could be a viable substitute for these pozzolanic by-products. This study presents the economic and environmental benefits of the use of WCBP as a replacement for conventional pozzolanic by-products in geopolymer binder production by assessing its techno-eco-efficiency, environmental impact, and cost-effectiveness performances. The favorable mechanical characteristics exhibited by the fly ash–GGBFS–WCBP-based geopolymer binder emphasize the importance of assessing its sustainability alongside its technical viability. The study employed life cycle analysis (LCA), following ISO framework, and using the Simapro software 9.2, to evaluate the environmental implications of the use of WCBP-based geopolymer mixtures. Human toxicity emerged as the primary impact. Moreover, the analysis of life cycle costs highlighted key financial factors, with around 65–70% attributed to alkaline activators of the total cost. The production of alkaline activators was identified as a critical point for both environmental impact and economic considerations due to energy consumption. While WCBP-rich samples exhibit a 1.7–0.7% higher environmental impact compared to the control mix (CM), their high mechanical strength and cost-effectiveness make them technologically and economically efficient geopolymer mixes. In conclusion, the portfolio analysis for techno-eco-efficiency affirms that mixes containing 40%, 30%, and 20% WCBP are more efficient than those using 10% and 0% WCBP, respectively. Full article

Cement hydration within particle bed concrete 3D printing processes can be benefited by storing water in the otherwise dry aggregate bulk material. Additional water also has the advantage of acting as a source of passive cooling. However, even small amounts of liquid lead to detrimental effects on bulk properties, such as the flowability. For that reason, this study proposes implementing dry water (DW) in order to store large amounts of water in a bulk material of non-absorbent, coarse sand whilst maintaining its initial bulk properties. DW is essentially created by mixing water and hydrophobic fumed silica in a high shear process, leading to water droplets surrounded by a protective silica shell. Herein, several DW variants, distinguished by their deionised water to hydrophobic silica ratio, were mixed with non-absorbent, coarse sand particles. In addition, mixtures were produced to contain a specific overall water content of up to w_H2O = 5% within the bulk material. It was shown that dry water can be used to incorporate large amounts of water into a granular bulk material and simultaneously preserve flow properties. The decisive factor is the proportion of hydrophobic silica for a given water content as the DW capsules may otherwise not endure mechanical stress during mixing. However, even minimal quantities of silica can prevent liquid capillary bridges from forming and, thus, inhibit bulk property degradation. Full article

Zero valent iron (ZVI) is widely used in permeable reactive barriers (PRBs) for the remediation of contaminated groundwater. The hydraulic conductivity of ZVI can be reduced due to iron corrosion processes activated by water and its constituents including pollutants. To overcome this issue, ZVI particles can be mixed with granular materials that avoid a drastic reduction in the hydraulic conductivity over time. In light of the most recent studies concerning iron corrosion processes and recalling the basic principles of century-old chemistry of iron corrosion, we have revised the results of 24 long-term column tests investigating the hydraulic and reactive behavior of granular mixtures composed of ZVI and pumice or lapillus. From this analysis, we found a clear correlation between the reactive behavior, described by the retardation factor (i.e., the ratio between flow velocity and propagation velocity of the contamination front), and the hydraulic behavior, described by means of the permeability ratio of the reactive medium (i.e., the ratio between the final and initial value of hydraulic conductivity). In particular, the permeability ratio decreased with the increase in the retardation factor. Moreover, it was found that the retardation factor is a useful parameter to evaluate the influence of flow rate, contaminant concentration, and ZVI content on the reactive behavior of the granular medium. Full article

A new kind of low-carbon bainite steel with excellent strength and toughness was developed, serving as the bogie of the next-generation high-speed train. However, the softening of the heat-affected zone (HAZ) in laser-arc hybrid welding (LAHW) needs to be overcome. In this study, the effect of the cooling rate of the LAHW process on the microstructure and mechanical properties in the HAZ was explored via thermal simulation. The results showed that with increased cooling rate, the grain size increased, the content of lath martensite decreased, and the lath bainite gradually changed to a granular shape in the thermal simulation specimen. With the decrease in the cooling rate, i.e., with the increase of t_8/5, the strength–toughness matching of the material showed a downward trend. The thermal simulation specimen with a t_8/5 of 6~8 s had higher strength and good toughness, which can be considered a potential welding parameter reference. The content of martensitic austenite (M-A) constituents was the main factor that determined the strength and toughness of the joint. During the tensile test, the axial force caused the material to tighten, and the transverse stress as obvious in the part of the M-A constituents that are prone to microcracks and many defects, resulting in cracks, paths, and multi-component layers in the center. As a result, the thermal cycle specimens had mixed fracture characteristics. Full article

In this work, the performance of discrete and continuum computational models for addressing granular flow dynamics in a rotating drum at different regimes is studied. The results are compared to the experimental observations obtained by image processing of a high-speed camera on a pilot plant rotating drum. For the discrete modeling, Discrete Elements Method (DEM) through the open-source software LIGGGHTS(R) is used, while for the continuum model, the $\mu \left(I\right)$-rheology is implemented in the general structure of a Volume-Of-Fluid (VOF) solver of the OpenFOAM(R) platform. Four test cases consisting of different sets of particles filling and rotational speed are considered and the results are analyzed in terms of solids distribution, the velocity of the particles, and mixing patterns. The solids distribution and velocities for each one of the tests considered are fairly similar between both computational techniques and the experimental observations. In general, DEM results show a higher level of agreement with the experiments, with minor differences that might be irrelevant in some cases (e.g., more splashing of particles for the fastest regimes). Among the drawbacks of the continuum model, it was unable to predict the slumping regime observed experimentally which can be attributed to the lack of a yield criterion and a slower dragging of the granular material when the drum is being accelerated, which can be attributed to the need of adding non-local effects to the rheology. On the other hand, the dynamic of the bed in the rolling and cascading regimes are accurately predicted by the continuum model in less time than DEM, even in a pilot plant scale system. These results suggest that the use of a continuum model with granular fluid rheology is more suited for simulating industrial-scale rotating drums at different regimes than DEM, but only if all the phenomenological features (i.e., yield criteria and non-local effects) are taken into account in the model. Full article

Improvement of stirring performance is one of the primary objectives in solid–liquid mixing processes, such as the preparation of phase change materials (PCMs) for energy saving in refrigeration and heat pump systems. In this paper, three novel impellers are proposed: pitched-blade punched turbine (PBPT), bionic cut blade turbine (BCBT) and bionic cut punched blade turbine (BCPBT). An experimental test was conducted to validate the stirring system model based on the Eulerian–Eulerian method with the kinetic theory of granular flow. Then the performance of the novel impellers was predicted, studied, and compared. The outcomes indicate that a novel impeller, specifically BCPBT, can effectively suspend particles and dramatically reduce power consumption. A better solid–liquid suspension quality was obtained with an aperture diameter of 8 mm and aperture ratio of 13%. Within the range of impeller speeds and liquid viscosity studied in this this paper, higher impeller speeds and more viscous liquids are more conducive to particle dispersion. One of the most important contributions of this work lies in the design of novel impellers, an extent of energy conservation to 17% and efficient mixing was achieved. These results have reference significance for improving the energy efficiency of temperature regulation systems. Full article

We report on an open-source, publicly available C++ software module called Chrono::GPU, which uses the Discrete Element Method (DEM) to simulate large granular systems on Graphics Processing Unit (GPU) cards. The solver supports the integration of granular material with geometries defined by triangle meshes, as well as co-simulation with the multi-physics simulation engine Chrono. Chrono::GPU adopts a smooth contact formulation and implements various common contact force models, such as the Hertzian model for normal force and the Mindlin friction force model, which takes into account the history of tangential displacement, rolling frictional torques, and cohesion. We report on the code structure and highlight its use of mixed data types for reducing the memory footprint and increasing simulation speed. We discuss several validation tests (wave propagation, rotating drum, direct shear test, crater test) that compare the simulation results against experimental data or results reported in the literature. In another benchmark test, we demonstrate linear scaling with a problem size up to the GPU memory capacity; specifically, for systems with 130 million DEM elements. The simulation infrastructure is demonstrated in conjunction with simulations of the NASA Curiosity rover, which is currently active on Mars. Full article

Particle mixing process is critical for the design and quality control of concrete and composite production. This paper develops an algorithm to simulate the high-shear mixing process of a granular flow containing a high proportion of solid particles mixed in a liquid. DEM is employed to simulate solid particle interactions; whereas SPH is implemented to simulate the liquid particles. The two-way coupling force between SPH and DEM particles is used to evaluate the solid-liquid interaction of a multi-phase flow. Using Darcy’s Law, this paper evaluates the coupling force as a function of local mixture porosity. After the model is verified by two benchmark case studies, i.e., a solid particle moving in a liquid and fluid flowing through a porous medium, this method is applied to a high shear mixing problem of two types of solid particles mixed in a viscous liquid by a four-bladed mixer. A homogeneity metric is introduced to characterize the mixing quality of the particulate mixture. The virtual experiments with the present algorithm show that adding more liquid or increasing liquid viscosity slows down the mixing process for a high solid load mix. Although the solid particles can be mixed well eventually, the liquid distribution is not homogeneous, especially when the viscosity of liquid is low. The present SPH-DEM model is versatile and suitable for virtual experiments of particle mixing process with different blades, solid particle densities and sizes, and liquid binders, and thus can expedite the design and development of concrete materials and particulate composites. Full article

Calcite-induced precipitation methods (CIPMs) have recently become potential techniques in geotechnical engineering for improving the shear strength of sandy soil. One of the most promising methods among them is enzyme-induced calcite precipitation (EICP). In this technique, a mixed solution composed of reagents and the urease enzyme, which produces calcite, is utilized as the grouting material. The precipitated calcite in granular soil provides ties among the grains of soil and limits their mobility, thus promoting an improvement in strength and stiffness and also a reduction in the hydraulic conductivity of sandy soil. This paper discusses the potential increase in the strength and stiffness of the soil, the additional materials for grouting, the effect of these materials on the treatment process, and the engineering properties of the soil. The possible sources of the urease enzyme and the applicability of the EICP method to other soil types are also discussed in this paper. The environmental and economic impacts of the application of EICP are also presented. The envisioned plans for application, potential advantages, and limitations of EICP for soil stabilization are discussed. Finally, the primary challenges and opportunities for development in future research are briefly addressed. Full article

Lost-wax casting, also called precision casting, is the process of casting a duplicate metal sculpture cast an original sculpture. The ceramic shell mould used in lost-wax casting usually consists of several layers formed with fine zircon and granular mullite particles using silica gel as a binder. However, it is a complicated and time-consuming process. Large amounts of waste moulds that need to be disposed and recycled become an environmental concern. In this study, waste shell sand from the recycled mould and calcium carbonate/metakaolin were used as raw materials to prepare geopolymer slurry and coating. The influence of mixing ratio and the SiO₂/K₂O modulus of the alkali solution on the setting time and green/fired strength were evaluated. Ceramic shells with one to four layers of geopolymer slurry and waste sand sprinkling were fabricated and tested for their permeability and green/fired strength. It was found that geopolymer shells had higher green/fired strength and better permeability than the original zircon/mullite shell. For foundry practice, metal casts were fabricated using recycled ceramic shell moulds with one to four layers of geopolymer coating. All cast results have their dimensions all within tolerance limitation and up to 13 h can be saved for the preparation of shell moulds. Full article