Calcium Oxide Research Articles

Pyrolysis of polystyrene using low-cost natural catalysts: Production and characterisation of styrene-rich pyro-oils

This work aims to study the catalytic pyrolysis of polystyrene (PS) in order to obtain a styrene-rich liquid appealing for re-polymerisation processes. The process was performed in a fixed-bed reactor using low-cost materials such as ilmenite, olivine, calcium oxide (CaO) and dolomite as catalysts at 600 ºC. A non-catalytic test with sand was also conducted for comparison purposes. The resulting pyro-oil yield was between 89 and 96 wt%, and consisted mainly of styrene monomer, styrene dimer and styrene trimer, as well as other light aromatic compounds depending on the catalyst used. Olivine and CaO were capable to increase the styrene monomer concentration in the pyro-oil by about 10–12 % compared to non-catalytic pyrolysis, reaching up to 74.5 and 71.4 wt%, respectively. Furthermore, these catalysts reduced the concentration of styrene dimer and styrene trimer in the pyro-oil, which could be useful for further re-polymerisation processes. However, the presence of polyaromatics (PAHs) in the pyro-oils obtained from ilmenite, olivine and CaO was also identified, and other families such as mono-aromatics, di-aromatics, BTX, and nitrogen heterocyclic compounds were also increased in all pyro-oils obtained with catalysts compared to those obtained by non-catalytic pyrolysis. In addition, several inorganic species in the pyro-oil were reduced by the addition of the catalysts. This effect was observed after the addition of olivine and CaO, especially in the reduction of S, Mg, Ca and Fe. These results clearly demonstrate the potential of pyrolysis to convert PS waste into valuable building blocks for the production of new plastics.

Calcium oxide enhances the anaerobic co-digestion of excess sludge and plant waste: performance and mechanism.

The study investigates the effect of the oxidant calcium oxide (CaO) on the codigestion of excess sludge (ES) and plant waste (PW) under mesophilic anaerobic conditions to enhance methane production. The findings indicate that CaO significantly elevated methane yield in the codigestion system, with an optimum CaO addition of 6% resulting in a maximum methane production of 461 mL/g volatile solids, which is approximately 1.3 times that of the control group. Mechanistic exploration revealed that CaO facilitated the disintegration of organic matter, enhanced the release of soluble chemical oxygen demand, and increased the concentrations of soluble proteins and polysaccharides within the codigestion substrate. The presence of CaO was conducive to the generation and biological transformation of volatile fatty acids, with a notable accumulation of acetic acid, a smaller carboxylic acid within the VFAs. The proportion of acetate in the CaO-amended group increased to 32.6-36.9%. Enzymatic analysis disclosed that CaO enhanced the activity of hydrolytic and acidogenic enzymes associated with the ES and PW codigestion process but suppressed the activity of coenzyme F420. Moreover, CaO augmented the nutrient load in the fermentation liquid. The study provides an alternative scheme for the efficient resource utilization of ES and PW.

Low-Cost and Eco-Friendly Calcium Oxide Prepared via Thermal Decompositions of Calcium Carbonate and Calcium Acetate Precursors Derived from Waste Oyster Shells.

Waste oyster shells were utilized to produce calcium carbonate (CaCO3) by grinding. This CaCO3 was then reacted with acetic acid to yield calcium acetate monohydrate (Ca(CH3COO)2·H2O). Both CaCO3 and Ca(CH3COO)2·H2O were used as precursors for synthesizing calcium oxide (CaO) through thermal decomposition at 900 °C and 750 °C, respectively. The yields of CaO from both precursors, determined through calcination experiments and thermogravimetric analysis (TGA), exceeded 100% due to the high purity of the raw agents and the formation of calcium hydroxide (Ca(OH)2). X-ray fluorescence (XRF) analysis revealed a CaO content of 87.8% for CaO-CC and 91.5% for CaO-CA, indicating the purity and contamination levels. X-ray diffraction (XRD) patterns confirmed the presence of CaO and minor peaks of Ca(OH)2, attributed to moisture adsorption. Fourier-transform infrared (FTIR) spectroscopy identified the vibrational characteristics of the Ca-O bond. Scanning electron microscopy (SEM) showed similar morphologies for both CaO-CC and CaO-CA, with CaO-CA displaying a significant amount of rod-like crystals. Based on these results, calcium acetate monohydrate (CA) is recommended as the superior precursor for synthesizing high-purity CaO, offering advantages for various applications.

Enhancing compressive strength of phosphogypsum-based geopolymer cement with five alkaline activator combinations

Phosphogypsum (PG) is a bulk industrial solid waste generated during phosphoric acid manufacturing. This study investigated a novel phosphogypsum-based geopolymer (PBG) cement through L16(45) orthogonal experiments. The impact of five alkaline activators, including Portland cement clinker (PCC), sulfate alumina cement clinker (SACC), aluminate cement (AC), magnesium oxide (MgO), and calcium oxide (CaO), on the performance of PBG cement was analyzed, and the optimal mix ratio was determined. Results indicate that all four alkaline activators, excluding CaO, can enhance unconfined compressive strength (UCS) of PBG cement. Factor index analysis revealed that an optimal composition comprising 4 % PCC, 6 % SACC, 2 % AC, and 4 % MgO yielded the highest 28-day UCS of 45.63 MPa. PBG cement primarily consists of dihydrate gypsum (CaSO4·2H2O), ettringite (Ca6(Al(OH)6)2(SO4)3(H2O)25.7), and polymers. Of these constituents, the polymers accounted for 61.9 wt% of the total composition and provided most of the strength. This study provided a new approach for making better use of waste PG.

Preparation and Research on Mechanical Properties of Eco-Friendly Geopolymer Grouting Cementitious Materials Based on Industrial Solid Wastes.

Red mud (RM), a hazardous solid waste generated in the alumina production process, of which the mineral composition is mainly hematite, is unable to be applied directly in the cement industry due to its high alkalinity. With the rise of geopolymers, RM-based grouting materials play an essential role in disaster prevention and underground engineering. To adequately reduce the land-based stockpiling of solid wastes, ultrafine calcium oxide, red mud, and slag were utilized as the main raw materials to prepare geopolymers, the C-R-S (calcium oxide-red mud-slag) grouting cementitious materials. The direct impact of red mud addition on the setting time, fluidity, water secretion, mechanical properties, and rheological properties of C-R-S were also investigated. In addition, a scanning electron microscope (SEM), X-ray diffraction (XRD), three-dimensional CT (3D-CT), Fourier transform infrared spectroscopy (FT-IR), and other characterization techniques were used to analyze the microstructure and polymerization mechanism. The related results reveal that the increase in red mud addition leads to an enhanced setting time, and the C-R-S-40 grouting cementitious material (40% red mud addition) exhibits the best fluidity of 27.5 cm, the lowest water secretion rate of 5.7%, and a high mechanical strength of 57.7 MPa. The C-R-S polymer grout conforms to the Herschel-Bulkley model, and the fitted value of R2 is above 0.99. All analyses confirm that the preparation process of C-R-S grouting cementitious material not only substantially improves the utilization rate of red mud, but also provides a theoretical basis for the high-volume application of red mud in the field of grouting.

Harnessing the potency of eco-friendly calcium oxide derived from eggshells for enhanced photocatalytic activity and biocompatibility evaluation in HepG2 cell line

Efforts towards sustainable development and pollution prevention are driving the exploration of bio-Calcium oxide (CaO) production from eggshell waste. This work investigates the thermal conversion of eggshell derived CaCO3 into CaO. Powder X-ray diffraction and Fourier transform infrared spectroscopy confirm CaO composition, displaying a cubic structure with 2.405 Å bond length and a mid-bond electron density of 0.2298 e/ų. Electron density studies corroborate this, revealing a three-dimensional distribution and one-dimensional profile. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) confirms spherical CaO particles and EDAX spectra displays the presence of calcium and oxygen. UV absorption spectra reveal a 3.3 eV energy bandgap, showcasing CaO's photocatalytic potential. It demonstrates exceptional photocatalytic against congo red and methylene blue dyes, degrading them by 96.4 % and 98 %, respectively, via pseudo first-order kinetics. Additionally, CaO demonstrates promising anticancer activity against HepG2 liver cancer cells, with an IC50 value of 31.2 μg/mL, positioning it as a cost-effective and potent agent for both wastewater treatment and cancer therapy.

Plasma Modification of Biomass-Based Starfish Catalysts for Efficient Biodiesel Synthesis.

This study investigated biodiesel production via the transesterification of grapeseed oil with plasma-modified biomass-based catalysts originating from starfish. Dried starfish was first converted into magnesium and calcium oxide through heat treatment and then further modified by plasma engineering to improve the catalyst's surface area and active sites via zinc addition. The Zn content was added via plasma engineering in the ratios of starfish (Mg0.1Ca0.9CO3): ZnO varying from 5:1, 10:1, to 20:1. The structure and morphology of the catalyst were confirmed through XRD, SEM, and XPS analysis. After the Zn addition and activation process, the surface area and the basicity of the synthesized catalysts were increased. The plasma-modified catalyst showed the highest basicity at the ratio of 10:1. Based on HPLC analyses, the optimized biodiesel yield in transesterification demonstrated 97.7% in fatty acid conversion, and its catalytic performance maintained 93.2% even after three repeated runs.

CaO catalysts supported on ZSM-5 zeolite for biodiesel production via transesterification of rapeseed oil

This paper deals with the effect of Si/Al ratio and form of zeolite support on the catalytic properties of the CaO catalysts in transesterification reaction of rapeseed oil with methanol. The reaction was conducted at 180 and 220 °C. To get the intended purposes of the work a various calcium oxide (CaO) catalysts supported on the ammonium and hydrogen forms of ZSM-5 zeolites with different Si/Al ratios were prepared by impregnation method. The results showed that the most active zeolite-based catalyst was 10%CaO/ZSM-5 (Si/Al = 50) system in the transesterification reaction at both temperatures 180 and 220 °C, which exhibited triglycerides (TG) conversion equal to 72.7 and 95.2% and fatty acid methyl esters (FAME) yield of 56.9 and 91.1%, respectively. High reactivity of this catalyst is explained by its acid-base properties, crystallite size of active phase, large external surface area and uniform distribution of the CaO on catalyst surface compared to the other investigated CaO systems supported on ZSM-5 zeolites. In addition, the analysis of the product obtained in the transesterification process carried out on the 10% CaO/ZSM-5 (Si/Al = 280) catalyst at 220 °C confirmed the presence of the following methyl esters of higher fatty acids: methyl oleate, methyl linoleate, methyl linolenate, methyl stearate, methyl eicosenoate, methyl palmitate, methyl palmitoleate, methyl nervonate and methyl arachidate.

Utilization of cow bone waste and calcium oxide for the solidification and stabilization of MSWI fly ash: Towards sustainable practices

The quest for sustainable waste management practices has catalysed the development of innovative approaches to transform waste into resourceful products. This study explores the effectiveness of cow bone waste and calcium oxide (CaO) as agents in the stabilization/solidification (S/S) process of Municipal Solid Waste Incineration (MSWI) fly ash derived from two distinct cities employing both grate-type and circulating fluidized bed incinerators in China. Employing a robust experimental framework, the research evaluated the stabilization efficacy for heavy metals, monitored the progression of pH, and quantified the compressive strength of the treated MSWI fly ash. Moreover, it conducted risk assessment and economic analyses. Incorporating CBW and CaO into the MSWI fly ash from grate-type incinerators significantly enhanced the Pb stabilization efficiency, achieving up to 99.7 % when adding 31 % CBW and 7 % CaO. This treatment resulted in the leaching of other heavy metals, which were also below the standard landfill limits. In the circulating fluidized bed incinerator fly ash, the leaching concentrations of heavy metals in the treated samples were reduced by up to 98.6 % for Cd and 64.4 % for Ni.Additionally, an increase in CaO content was found to substantially improve the compressive strength of the solidified samples across all tested curing periods (7, 14, and 28 days). The optimal compressive strength result, observed at 28 days, reached 1.2 MPa, compared to the raw fly ash, which exhibited only 0.77 MPa when adding just 9 % CaO. This highlights CaO's critical role in enhancing the mechanical integrity of the treated MSWI fly ash. The study concludes that strategically calibrated ratios of cow bone waste and CaO attenuate the environmental hazard presented by MSWI fly ash and bolster its mechanical attributes, thereby repurposing the waste into a viable material for construction.

Experimental Investigation of Amine Regeneration for Carbon Capture through CO2 Mineralization

Summary The most common method for point-source carbon capture involves the absorption of CO2 from flue gas by amine solutions. The CO2 is then stripped from the amine solution by desorption with steam or heat. While amine solvents exhibit high CO2 absorption efficiency, their desorption process consumes a substantial amount of energy. A more energy-efficient alternative for the regeneration of the amine can be done through a mineralization process. Past studies have shown the feasibility of mineralizing captured CO2 from amine solution using calcium oxide (CaO) or other CaO-containing industrial waste. This study aims to show experimentally the extent of mineralization over time in near-ambient conditions and develop a mechanistic model. Lab-scale experiments are conducted to determine the absorption characteristics of CO2 in monoethanolamine (MEA) solutions and the extent of mineralization. We observe that pH serves as an indicator for CO2 loading in amine solutions. At high concentrations of MEA, CO2 absorption efficiency is about 0.5 mol CO2/mol MEA. Under ambient pressure and a temperature of 40°C, CaO effectively mineralizes CO2 and regenerates MEA. The CaO initially reacts with water to produce calcium hydroxide (Ca(OH)2) and subsequently reacts with dissolved CO2, forming calcium carbonate (CaCO3). Both 13C nuclear magnetic resonance (NMR) and FTIR indicate that MEA can be regenerated with an efficiency close to 69 to 98%, by comparing the carbamate and bicarbonate peaks in the 13C NMR response. A model to describe the absorption and mineralization reaction is proposed using the PHREEQC software; the pH is matched within less than 3% error. This study demonstrates that CO2 desorption from MEA solutions can occur through mineralization, converting CO2 into carbonates at low pressure and temperature with CaO. This method has lower energy consumption and results in the most stable form of CO2, making it a safer sequestration strategy than supercritical CO2 storage in reservoirs.

Treating waste with waste: adsorption behavior and mechanism of phosphate in water by modified phosphogypsum biochar.

The use of green methods to treat industrial waste and waste reuse has become a key environmental issue. In order to achieve this goal, this study treated waste phosphogypsum (PG) and produced modified PG biochar to adsorb and remove phosphorus from PG leachate, so that the PG pollution problem was controlled. In this study, PG was modified with sodium carbonate (Na2CO3) to prepare a modified PG biochar that was used for the removal of phosphorus-containing wastewater. An X-ray diffraction (XRD) analysis of the modified PG revealed that the main component was calcium carbonate (CaCO3), and a suitable amount of modified PG could load calcium oxide (CaO) onto the biochar and improve its physical properties. The experimental results showed that the modified PG biochar had a maximum phosphorus adsorption capacity of 132mg/g. A further investigation of the mechanism of adsorption revealed the importance of electrostatic attraction and chemical precipitation, and it was found that the CaO in the modified PG biochar could effectively facilitate the conversion of phosphate to hydroxylapatite (Ca5(PO4)3OH) in water. The phosphorus removal rate from leachate obtained from a landfill containing PG was 99.38% for a specific dose of the modified PG biochar. In this study, a PG pollution control technology was developed to realize the goal of replacing waste with waste.

Mitigating low-temperature hydrothermal degradation of 2 mol% yttria stabilised zirconia and of 3 mol% yttria stabilised zirconia/nickel oxide by calcium oxide co-doping and two-step sintering

Hydrothermal degradation deteriorates the fracture toughness and strength of tetragonal stabilised zirconia. The phase transformation to the monoclinic phase is particularly critical for materials with lower stabiliser content such as 2 mol% and 3 mol% yttria stabilised zirconia (2YSZ and 3YSZ). In this work, two routes in two-step sintering and co-doping with calcium oxide are analysed to mitigate the degradation. Both strategies show a reduction in average grain size of the 2YSZ while maintaining a comparable densification. The achieved smaller grains suppress the hydrothermal degradation rates. In addition, a mitigating effect beyond the reduction in grain size of YSZ is found for CaO doping. 1.6 mol% CaO co-doped 2YSZ shows less than 4% of monoclinic phase after 50 h in an autoclave with H2O at 134 °C. Pure 2YSZ contrarily reaches 100% monoclinic phase after 20 h at the same conditions. A suppression of degradation by CaO doping was also observed for the composite of nickel oxide and 3 mol% yttria stabilised zirconia. Hence, CaO co-doping can be an interesting strategy to increase resistivity against hydrothermal degradation for both biomedical and renewable energy applications. The findings further outline a route to achieve tetragonal YSZ with lower yttria contents than 2 mol%.

Synthesis and Characterization of Coenzyme Q10 onto Nanoporous Calcium Silicate-Based Systems for Wound Healing

This study explores the microstructure, spectroscopic, and bonding arrangements within bioactive calcium silicate and calcium magnesium silicate systems loaded with different values (1–2.5 wt%) Coenzyme (CoQ10) ratios, synthesized using sol-gel processes. The investigation utilizes X-ray diffraction (XRD), transmission electron microscopy, and Fourier transform infrared (FTIR) spectroscopy to analyze the samples. The study explores the assignment of FTIR bonds, examining changes in the silicate-based bonds environment under the effect of the CoQ10 ratio. The observed frequency shifts and intensity variations in FTIR bonds, linked with the bioactive silicate composition, are attributed to a reduction in local symmetry resulting from introducing the calcium and magnesium oxides and CoQ10 to the silica network. The XRD and FTIR results contribute valuable insights into the structural role of silicate-based materials loaded with CoQ10, thereby enhancing our understanding of the CoQ10 release process. Approval of the CoQ10 drug loading in both calcium silicate and calcium magnesium silicate nanosystems was recognized by shifts in FTIR bands, changes in particle distribution, and the valuation of drug release activity showed by the bioactive two calcium silicate-based nanoparticles. Additionally, wound healing studies revealed the biocompatibility and wound healing response of calcium magnesium silicate nanoparticles.

Effective capture of gaseous Se during spent nuclear fuel recycling using calcium oxide pellets: Optimization, performance, and practical implications

The continuous utilization of nuclear energy has led to the accumulation of spent nuclear fuel (SNF) containing uranium, transuranium, and fission products (FPs). Reprocessing and pyrochemical methods have shown the potential for SNF reuse, thereby reducing its environmental impact. Voloxidation, a pivotal step in SNF recycling, involves thermal treatment in an oxidizing atmosphere to enhance the reactivity. During voloxidation, Se-79, which is a FP with a long half-life, is released as SeO2 under oxidizing conditions, necessitating technologies to capture it. CaO pellets (CPs) were prepared to capture gaseous SeO2. The effects of operating conditions on SeO2 capture performance were investigated. The CP reacts strongly with SeO2 to form CaSeO3, exhibiting a high adsorption capacity of 17.5 mol kg−1 and > 99% efficiency at 700 °C. The mechanical strength and thermal stability assessments indicate suitability for practical applications. Depending on the flow rate, the CP required for SeO2 capture was estimated when processing 1 t of SNF, thereby contributing to the design of effective SeO2 capture systems for safe and sustainable nuclear waste management.

Effect of electrolytic manganese residue at different calcination temperatures on hydration characteristics and microstructure of cement mortar

This study investigates the hydration mechanism and microstructure of electrolytic manganese residue (EMR) cement mortar at different calcination temperatures. The results indicate that EMR cement mortar, when calcined at low temperatures (200 and 400 °C), demonstrates improved mechanical properties in the early stages. However, higher sulfate content results in poor setting time and reduced volume stability. Concurrently, there is a notable reduction in the number of gel pores and a considerable increase in capillary pores, leading to diminished mechanical properties in the later stages. Although EMR cement mortar calcined at 600°C exhibits superior mechanical properties, its hydration kinetics are poor. The primary reason for this is that the finer particles of EMR primarily serve a filling role, with no hydration reaction occurring. However, when calcined at 800 °C and 1000 °C, the high-temperature decomposition of dihydrate gypsum forms activated calcium oxide, thereby enhancing pozzolanic activity. Simultaneously, the smaller EMR particles contribute to filling and nucleation, refining the pore structure and enhancing the mechanical properties. Additionally, the incorporation of EMR in cement mortar effectively mitigates heavy metals and achieves the goal of harmlessness.

Physico-chemical characterization of cupola slag: Enhancing its utility in construction

Cupola slag is a waste material of the steel and iron industries. Its composition is determined by the cupola furnace and other elements used in steel and iron manufacturing. This paper investigates the characterization behavior of various cupola slag materials. As a result, x-ray fluorescence (XRF), x-ray diffraction (XRD), thermogravimetry differential thermal analysis, and scanning electron microscopy (SEM) methods were used to characterize three cupola slag samples from distinct origins. In addition, various physical properties were used to compare different cupola slags. The specific gravity values of CS-1 (cupola slag-1 sample), CS-2 (cupola slag-2 sample), and CS-3 (cupola slag-3 sample) are 1.36, 2.5, and 2.917, respectively. The density and water absorption for CS-1, CS-2, and CS-3 are 1414.86, 1477.71, and 1796 kg/m3, and 0.37%, 0.32%, and 0.26%, respectively. Cupola slag also includes a larger percentage of lime, according to XRF data, which contributes to its improved binding characteristics. A higher calcium oxide content in CS-3 could facilitate the pozzolanic process. The presence of angular particles that aid in material binding is seen in the SEM image. Compounds with a nanostructure are then flawlessly blended into the mixture and grouped with calcium alumina silicates formed by cement hydration. The XRD pattern of cupola slag exhibits high peaks, indicating that the material is crystalline in character and can be utilized as sand. It also shows the presence of other chemical compounds, such as silica, which ranges from 30% to 45%. CS-1 and CS-2 have comparable XRD patterns. However, CS-3 has a somewhat different pattern because of the greater CaO content. Weight loss begins at higher temperatures, which shows that the material is stable at higher temperatures, according to a thermo-gravimetric study. The differential thermal analysis curve of CS-3 indicates that the material remains stable up to a temperature of 600 °C. The physical characteristics of all cupola slag samples show that cupola slag may be utilized to make sustainable building materials because of its lower specific gravity, density, and water absorption.

Comparative role of calcium oxide nanoparticles and calcium bulk fertilizer to alleviate cadmium toxicity by modulating oxidative stress, photosynthetic performance and antioxidant-defense genes expression in alfalfa

Cadmium (Cd) toxicity poses a significant threat to soil health and sustainable food production. Its bioaccumulation in plant tissues induces phytotoxicity by affecting physiological and biochemical attributes, leading to a reduction in plant biomass and production. Recently, nanotechnology has emerged as a promising approach for addressing heavy metal toxicity in an eco-friendly manner to enhance crop production. However, the comparative role of foliar applied calcium oxide nanoparticles (CaO-NPs) and bulk calcium fertilizer under Cd stress in alfalfa remains unexplored. Herein, we studied the ameliorative role of CaO-NPs and bulk calcium (50 and 100 mg L−1) to alleviate Cd stress (30 mg kg−1) in alfalfa seedlings. Plants exposed to Cd exhibited significant decreases in morpho-physiological traits, gas exchange attributes, and pigment contents as well as increase in Cd bioaccumulation in plant tissues. Notably, exogenous application of CaO-NPs ameliorates the toxic impact of Cd by enhancing plant biomass (45%), fluorescence efficiency and gaseous exchange attributes. The maximum dose of CaO-NPs induced Cd-tolerance response accompanied by a significant increase in antioxidative enzyme activities, such as superoxide dismutase (SOD; 29%), peroxidase (POD; 41%), catalase (CAT; 36%) and ascorbate peroxidase (APX; 49%), which play positive roles in ROS scavenging. TEM examination further revealed the protective role of these NPs in averting Cd-induced damage to leaf ultrastructure and mesophyll cells. Furthermore, CaO-NPs had a substantial influence on both Cd and Ca2+ accumulation in plant tissues, while qRT‒PCR analysis demonstrated higher expression of antioxidant defense genes viz. Cu/ZnSOD (0.38 fold change (FC)), MtPOD (0.51 FC), MtCAT (0.61 FC) and MtAPX (0.79 FC) under CaO-NPs application, over Cd control. Overall, our findings suggested that exogenous CaO-NPs could be effective in alleviating the adverse effects of Cd on alfalfa seedlings to ensure food safety and support sustainable agriculture.

Biosynthesized calcium oxide from calcined conch shells: A potential bactericidal agent against Escherichia coli

The occurrence of ineffective antibiotics and an abundance of waste shell has provided a research opportunity to study calcium compounds through natural recycling, derived from the abundant gleaned species of gastropod conch (Canarium urceus) shells. Particularly, calcium oxide from waste shells were investigated as a value-added application for inhibiting pathogenic Escherichia coli. Hence, this study investigated its bactericidal activity through the Kirby-Bauer disc diffusion method to measure its growth inhibition ability. Waste conch shells were collected from Maitum, Barangay Dahican, City of Mati, Davao Oriental. Conch shell powder was obtained through calcination in a muffle furnace for two hours at 800°C (CS800) and 900°C (CS900), both at 50% and 75% (w/v) concentrations, for comparison. Among the four tested samples with three replicates each, results indicated that CS800 (50%) exhibited the highest inhibitory effects against E. coli. Findings also revealed that samples at 50% concentration demonstrated higher antibacterial activity than those at 75%. This statistically suggests that concentration level significantly influenced the bactericidal activity, whereas the 100°C difference in calcination temperature did not. The antibacterial activity of calcined conch shells can be attributed to CaO through two mechanisms: primarily, the strong alkalinity of the medium, and secondarily, the generation of Ca2+ and reactive oxygen species (ROS) on the surface of CaO, which cause cell wall rupture. Another possible mechanism is also associated with generating superoxides

Chemical, mineralogical and geotechnical properties of volcanic ash of Tajogaite (La Palma, Canary Islands, Spain)

Volcanic eruption at La Palma island (Tajogaite, 2021) has produced tons of volcanic ash as natural sediments spread all around the island covering existing crops, roads, embankments, buildings, etc., by that way producing damage to environment. For the rehabilitation and reconstruction of island, and its application to adjacent areas, it is practical and economical to employ these volcanic ashes as construction material being encountered in abundant volume, and by that way could be considered as a resource material instead as a waste material, reducing necessary volume of landfills for its deposition. This paper defines the investigation of chemical, mineralogical and geotechnical properties of these deposited materials for its possible reuse by that way providing solution for its recovery. These young volcanic ashes are studied in its fresh natural state, prior to consolidation and cementation has taken place for its chemical, mineralogical and geotechnical characterization. Volcanic ash of Tajogaite is of a poorly graded sandy nature having difficulties for its compaction, having low improvement of relative density by the application of standard compaction methods. Mineralogy analysis indicates it is rich in silica, iron, calcium and alumina oxide, although being necessary the addition of mineral additives for its alkali-activation. Geotechnical characteristics of different samples vary depending on the sampling site, being resistance parameters determined by direct shear test (friction angle 30° to 34°) and deformational properties defined by one-dimensional consolidation test considered low values as of loose sand materials (deformation modulus range from 20 to 40 MPa).

Preparation of calcium aluminate and spinel by hydrolysis and calcination from secondary aluminum dross

AbstractThe direct extraction of alumina from secondary aluminum dross (SAD), which is a dangerous solid waste, is difficult. Moreover, this process easily produces a large amount of solid waste residue, which is not easily utilized. In this paper, a new green process was developed to prepare calcium aluminate and Mg‐Al spinel from SAD by hydrolysis–calcification roasting. The effects of calcium oxide (CaO) content, sintering temperature, and holding time on the properties of calcium aluminate were investigated by single‐factor experiments. The phase transformation mechanism of calcium aluminate was studied by thermodynamic analysis, X‐ray diffraction analysis, X‐ray fluorescence spectroscopy, and scanning electron microscopy. Under the optimal conditions (Ca/Al molar ratio of 0.8, sintering temperature of 1300°C, and holding time of 2 h), the main calcium aluminate phases are CaAl2O4 and Ca2Al2SiO7, the soluble alumina content of the calcium aluminate sample is 49.71 wt.%, and the main phases of the acid‐insoluble residue are Mg‐Al spinel and a very small amount of CaTiO3. The Ca/Al ratio is the key factor affecting the calcium aluminate phase—with increasing Ca/Al ratio, the calcium aluminate phase is transformed from CaAl4O7 to CaAl2O4 and eventually to Ca12Al14O33, and the Si‐containing phase changes from Ca2Al2SiO7 to CaSiO4.