Insoluble Calcium Research Articles

Evaluating the Chemical Stability and Performance of Zinc Phosphate-Coated Steel Fibers in Concrete Corrosion Simulations

This study investigates the impact of zinc phosphate-coated steel fibers on corrosion performance and bond strength within concrete subjected to corrosive environments. Results indicate that the coating enhanced corrosion resistance in various environments, including saturated Ca(OH)2, 10% Na2SO4, and 3.5% NaCl solutions. The zinc phosphate coating resulted in a more positive corrosion potential and a lower corrosion rate, likely due to galvanic coupling between the coating and the steel fiber matrix. Furthermore, the improved corrosion resistance in Ca(OH)2 solution may also be related to the formation of insoluble calcium phosphate compounds. The bond strength and pullout energy in the zinc phosphate-coated fiber-reinforced pre-corrosion specimens enhanced by 19.3% and 90.92%, respectively, compared to the bare fiber-reinforced ones. Upon exposure to a simulated seawater environment that induces corrosion, the interfacial bond strength and pullout energy of zinc phosphate-coated steel fibers and cement mortar experienced marginal decreases of 4.2% and 4.6%. Zinc phosphate coatings demonstrate considerable promise for extensive application in concrete structures exposed to highly corrosive environments.

Immobilization of arsenic wastes and retardation effect on cement hydration: Experimental and molecular dynamic analysis

AbstractThis work was designed to investigate the influence of arsenic dosage, variety on the mechanical properties, hydration, and solidification from the perspective of Portland cement (PC) performance evolution. The results demonstrate that using PC could solidify the arsenic wastes effectively, with arsenic leaching concentrations consistently below 5 mg/L. Arsenic wastes retard cement hydration, leading to a slower rate of hydrates formation, disrupting the calcium silicate hydrate (C–S–H) stacking structure, and thus detrimental to strength development especially at early age. The adverse effect is highly dependent on the arsenic variety. The insoluble calcium arsenate exhibits the least impact, while the arsenates show the largest challenging to immobilization due to the instability of hydrates. Molecular dynamic simulation indicates that arsenic can be chemically immobilized with Ca2+, and be physically adsorbed onto the positively charged C–S–H by forming As‐O···Ca···Si‐O units, accompanied by a significant reduction in adsorption energy by 46.5%. The arsenic solidification behavior provides a basis for the resource utilization of arsenic wastes in cementitious materials.

Quince (Cydonia oblonga Mill.) Waste By-Product Characterization as a Potential Functional Ingredient

Currently, the production of waste in the food industry is increasing, which is a serious problem. However, most of these residues, especially those derived from fruits and vegetables, have great unknown properties that are not used. The main objective of this article is the analysis and characterization of the waste from quince after its processing to observe its properties and its potential use in different industries as a functional ingredient, thus favoring the circular economy and sustainability. Quince by-product nutritional parameters such as proteins, fibers, sugars, vitamins, and minerals were analyzed. Also, the antioxidant capacity was measured by various methods: 1,1-diphenyl-2-picrylhydrazyl radical scavenging activity (DPPH), antioxidant capacity in Trolox equivalent antioxidant capacity (TEAC/ABTS), and total polyphenol content (TPC). Finally, the antimicrobial capacity against different postharvest-pathogenic fungi was measured in direct sample and extract. The nutritional results showed a nutritional profile rich in soluble and insoluble fiber, potassium, calcium, and magnesium, and low in fat. The antioxidant results from the extract showed significant levels of phenols and higher antioxidant capacity from the extracted sample. No positive results were found in the antimicrobial capacity study. Quince by-products could be a potential ingredient in the industry due to their nutritional composition and antioxidant content.

Impact of preacidification on the functionality and insoluble calcium levels of Low-Moisture Part-Skim Mozzarella made from high-casein milk

The use of low-concentration factor ultrafiltered (LCF-UF) milk for cheesemaking has become popular in recent years. Research on using LCF-UF milk to make low-moisture part-skim (LMPS) Mozzarella manufacture is limited due to concerns about the negative impact of the higher casein content on functional properties, such as melt and stretch. Pre-acidification (PA) (reflects acid added to milk before the addition of the starter culture) has been used in low-fat and nonfat Mozzarella cheeses to lower calcium levels and improve their texture and melting properties. We explored the use of PA to reduce the insoluble calcium content of cheese (calcium that is a crosslinking material for the casein proteins) and its impact on the functionality of LMPS Mozzarella made from high casein (4.2%) milk. Seven vats of LMPS Mozzarella, with a control (no PA), 2 pH values for PA (6.40 and 6.00) and 3 different acidification methods (use of acetic, citric, or carbonic acid from carbon dioxide) were evaluated for their impact on solubilization of colloidal calcium phosphate during LMPS manufacture. Composition, proteolysis, microstructural and functional changes in the LMPS cheeses were monitored during 90 d of refrigerated storage. All cheeses had similar composition except for the cheese made with milk PA with carbonic acid, which had a lower fat-in-dry matter probably due to foaming observed in this sample during the gas sparging. The cheese made with milk PA with citric acid to pH 6.00 had the lowest amount of total and insoluble calcium compared with other cheeses at all steps during cheese manufacture and storage, likely due to the calcium chelating ability of citric acid. The cheese that was made with milk PA with citric acid to pH 6.40 had a trend of slightly lower (not significant) total and insoluble calcium during cheese manufacture compared with other cheeses that were made with milk PA to pH 6.40. The pH value in all the cheeses remained similar throughout 90 d of storage, whereas the cheese that was made with milk PA with citric acid to pH 6.00 had the lowest pH values during storage. Treatment significantly (P < 0.05) impacted instrumental hardness, the maximum loss tangent during heating, the melting temperature and the storage modulus values measured at 70°C. Proteolysis was not impacted by treatment suggesting that typical aging should occur. Cheese that was PA with citric acid to pH 6.00 initially had lower maximum loss tangent values and higher hardness, possibly due to the lower pH value of this cheese. The performance of cheeses on pizza was assessed using Sensory Spectrum® method and quantitative descriptive analysis. The PA of cheese milk with citric acid helped to reduce the insoluble Ca level and at 30 and 90 d of storage, these cheeses had lower first chew hardness, lower chewiness, and lower strand thickness values compared with other cheeses. The use of PA could help improve the functionality of LMPS Mozzarella made from milk high in casein with citric acid being the most efficient in dissolving the insoluble calcium from casein.

The impact of calcium sequestration on the material and structural properties of acid milk gels and corresponding cream cheeses

SummaryWe report on the role of ethylenediaminetetraacetic acid (EDTA) in addition to the structural and material properties of acid milk gels formed via addition of glucono‐delta‐lactone (GDL) and these properties of corresponding analogue cream cheeses prepared from these gels. Increasing addition of EDTA to cheese milks prior to acidulation reduced the concentration of insoluble calcium in the milks. Acid gelation of milks, as measured by small deformation rheology, showed a decreased rate of gelation and lower relative elastic modulus of gels with increasing EDTA concentration. The sequestration of colloidal calcium phosphate from the casein micelle by the addition of EDTA led to the lower gelation rate and elastic modulus. The lower extent of ionic binding is considered the causative mechanism for formation of weaker gel structures. Cream cheeses prepared using acid gels with GDL acidulant were compositionally unaffected by EDTA concentration. However, variations in G′ observed in the acid gels containing increasing levels of EDTA correlated with large deformation material property changes in cream cheese analogues. In addition, the increasing inclusion of EDTA in cheese milks translated to reduced water‐holding capacity of the cream cheeses prepared from those milks. These results provide insights on the specific role of milk calcium on the structure, material and physical properties of acid milk gels and corresponding cream cheese analogues.

Internally-crosslinked alginate dialdehyde/alginate/gelatin-based hydrogels as bioprinting inks for prospective cardiac tissue engineering applications

Cardiovascular diseases represent a worldwide social and economic challenge, due to heart tissue limited regenerative capabilities. 3D bioprinted cell-laden constructs are a promising approach to develop patches for cardiac regeneration or in vitro models for new drug preclinical discovery and validation. However, the development of bioinks with optimal mechanical, rheological, and biological properties is still a challenge. Although alginate (Alg)-based bioinks have been extensively explored, such hydrogels lack cell adhesion properties and degradability. Additionally, 3D Alg structures are usually obtained by micro-extrusion bioprinting exploiting conventional external cross-linking methods, which introduce inhomogeneities and unpredictability in construct formation. This work exploits Alg internal ionic gelation mechanism to obtain homogeneous self-standing multilayered 3D printed constructs without employing support baths or post-printing crosslinking treatments, combining an insoluble calcium salt (calcium carbonate, CaCO3) with an acidifying agent (D-(+)-Glucono-1,5-lactone, GDL) to promote controlled release of calcium ions. Alg was blended with oxidized alginate (ADA) and gelatin (Gel) to achieve degradable and cell adhesive hydrogels for cardiac tissue engineering. Firstly, ADA/Alg bioink composition was tailored by varying polymer weight ratio (keeping ADA as the main component) and calcium ions concentration to achieve cardiac tissue-like viscoelastic properties. Then, the amount of Gel in ADA/Alg hydrogels was optimized to support adult human cardiac fibroblasts (AHCFs) adhesion, producing shear thinning inks with tunable viscoelastic properties (G&amp;rsquo; 650-1300 Pa) and degradation profile (40-80% weight loss after 21 days in phosphate buffered saline, PBS) by varying Gel concentration. ADA/Alg/Gel hydrogels showed a shear thinning behavior suitable for 3D bioprinting and dependent on ink stabilization time, due to the gradual pH-triggered release of calcium ions over time. AHCFs-laden ADA/Alg/Gel bioinks could be successfully printed producing scaffolds with high shape fidelity and good cell viability post-printing. Finally, 3D AHCF-laden and H9C2-laden ADA/Alg/Gel bioinks with the highest gelatin content (25% w/w) allowed cell adhesion after 24 hours of incubation, showing potential application for cardiac tissue modelling. This research presented a comprehensive framework for advancing the design of bioink formulations enabling the printing of cell-adhesive and self-supporting constructs.

Designing calcium-fortified milk for improving stability and calcium bioaccessibility by solid dispersion emulsification

Approximately 70 % of the calcium intake in the adult diet worldwide is derived from dairy products. However, insoluble calcium salts, which are usually added directly during dairy production, have poor suspension stability and are prone to precipitation. The current study aimed to address the constraints of conventional production methods by utilizing solid dispersion emulsification technology to inhibit the aggregation of calcium salts. Calcium-fortified milk samples with different calcium content were prepared and compared with the commercial calcium-fortified milk, and their physicochemical, microstructural, and digestive properties were characterized. The results of this study demonstrated that all the prepared calcium-fortified milk samples exhibited a particle size of approximately 270 nm and a zeta-potential of approximately −40 mV. The calcium-fortified milk, which has been produced using solid dispersed emulsion technology, has been found to have 1.8 times more physical stability than commercial milk. Microstructural studies showed that aggregation of milk with more than 225 mg/100 mL calcium content occurred. During in-vitro digestion, it was found that the increasing calcium loading did not impact protein digestion without the creation of new fragments in the calcium-fortified milk. Calcium bioaccessibility was enhanced by approximately 50 % in comparison with the commercial product. While the release of free fatty acids was found to decrease with increasing calcium content. This study facilitates the development and utilization of calcium-fortified and low-fat foods and provides a new idea for the addition of milk minerals in dairy products.

Selective Dissolution of Calcium Pyrophosphate Dihydrate Crystals Using a Pyrophosphate Specific Receptor.

Pseudo-gout is caused by the deposition of highly insoluble calcium pyrophosphate dihydrate (CPPD) crystals in the joints of sufferers. This leads to inflammation and ultimately joint damage. The insolubility of CPPD is driven by the strong attraction of di-cationic calcium ions with tetra-anionic pyrophosphate ions. One of the challenges of dissolving CPPD is that a related mineral, hydroxy apatite (HA) is present in larger amounts in the form of bone and also contains strongly interacting calcium and phosphate ions. Our aim in this work was to selectively dissolve CPPD in preference to HA. To accomplish this, we used a known receptor for pyrophosphate that contains two complexed zinc ions that are ideally spaced to interact with the tetra-anion of pyrophosphate. We hypothesized that such a molecule could act as a preorganized tetra-cation that would be able to outcompete the two calcium ions present in the crystal lattice of CPPD. We demonstrate both visually and through analysis of released phosphorous that this molecule is able to preferentially dissolve CPPD over the closely related HA and thus can form the basis for a possible approach for the treatment of pseudo-gout.

35. Efficacy of phytase in growing pig and lactating sow diets is improved by a source of insoluble calcium carbonate

35. Efficacy of phytase in growing pig and lactating sow diets is improved by a source of insoluble calcium carbonate

Calcinosis in dermatomyositis.

To provide the most recent literature on our understanding behind the pathogenesis and the treatment of calcinosis in dermatomyositis. Early diagnosis and controlling the overall disease activity are cornerstones to prevent calcinosis in juvenile dermatomyositis. Observational cohort studies showed that prolonged state of inflammation and features of vascular dysfunction like digital ulcers and abnormal nailfold capillaries are associated with calcinosis. Neutrophil activation and mitochondrial dysfunction have recently emerged as potential mechanistic pathways involved in calcinosis pathogenesis. Few recent case series have alluded to the efficacy of topical and intralesional sodium thiosulfate, while JAK inhibitors appear to be newer promising therapy in juvenile dermatomyositis. Calcinosis in dermatomyositis consists of deposition of insoluble calcium compounds in the skin and other tissues. It is prevalent in up to 75% of patients with juvenile dermatomyositis and up to 20% in adult dermatomyositis. While it leads to significant patient morbidity, we do not yet understand the pathogenesis in its entirety. Surgical excision although palliative is the mainstay of treatment and should be offered to patients. All available treatment options are only based on very low level of evidence.

Effect of phosphate impurities on the properties of β-hemihydrate gypsum pastes plasticized by polycarboxylate superplasticizer

This study aims to investigate the effect of HPO42-/PO43- on the working performance and mechanical strength of β-hemihydrate gypsum pastes containing polycarboxylate superplasticizer (PCE) and reveal its underlying mechanism. The results showed that HPO42-/PO43- has a detrimental effect on the fluidity, compressive strength, and softening coefficient of β-hemihydrate gypsum pastes. However, in the presence of PCE, all properties were improved compared to the blank group when the HPO42-/PO43- content was less than 0.3 %. The fluidity and compressive strength of the pastes can be increased by up to 95 % and 32 %, respectively. It was found that HPO42-/PO43- reacted with Ca2+ to form insoluble calcium phosphate salt (ICPS), and the adsorption of PCE on the surface of ICPS increased the total adsorption amount, thereby enhancing the dispersion ability of PCE and increasing the fluidity of fresh slurry. In addition, the adsorption behavior of PCE on the surface of ICPS weakened its inhibitory effect on the hydration of hemihydrate gypsum, which was confirmed by TG-DSC. The increased hydration products and reduced water requirements significantly improved mechanical properties. These findings enhance the understanding of the interaction between phosphorus impurities and PCE, which can guide the improvement of the performance of β-HPG and promote the resource utilization of phosphogypsum.

Determination of insoluble (INSOL) calcium content in Cheddar, Feta, Juustoleipa, and Mozzarella cheeses using acid-base buffering curves

The amount of colloidal calcium phosphate (CCP) complex associated with caseins (INSOL Ca) determines the body, texture, flavor and breakdown of cheese constituents during aging. The continuous pH decline during cheese making because of lactic acid fermentation results in solubilization of insoluble (INSOL) calcium. Measuring INSOL Ca in such a dynamic and wide range pH system (6.6 to 5.3) is challenging. The purpose of this study was to test utility of acid-base auto-titration method in differentiating INSOL Ca content in cheeses with a wide range of pH (i.e., Juustoleipa 6.6, Mozzarella 5.6, Cheddar 5.3, Feta 4.8) and also to understand the relationship between pH, protein content, and INSOL Ca. A positive relationship was obtained for pH (R2 = 0.62) and protein content (R2 = 0.85) with INSOL Ca, suggesting concomitant release of CCP content at lower pH values and association of higher amount of CCP with higher protein content. Despite having a pH slightly closer to Mozzarella (pH 5.56), Cheddar cheese (pH 5.25) had more INSOL Ca (0.67%) owing to the highest amount of protein (26%) and low moisture content (33%). Feta had the lowest amount of INSOL Ca (0.15%) owing to a low pH (4.79), higher moisture content (55%), and low protein content (14%). Juustoleipa had the highest percentage of INSOL Ca out of total calcium (88%) due to higher pH (6.62) and more intact casein. It was evident that the acid-base titration method was able to differentiate INSOL Ca between different types of cheeses with varying pH and protein content. Findings of this work will help tracking the proportion of INSOL Ca at various stages of cheese making and understanding kinetics of INSOL Ca solubilization and its role in causing pH variation in the early stage of cheese ripening.

The Influence of Potassium Sulfate, as Activator, on the Hardening Process of Insoluble Calcium Sulfate

The Influence of Potassium Sulfate, as Activator, on the Hardening Process of Insoluble Calcium Sulfate

Treatment of calcinosis cutis associated with autoimmune connective tissue diseases.

Calcinosis cutis is a condition that is commonly associated with autoimmune connective tissue diseases. It is characterized by the deposition of insoluble calcium salts in the skin and subcutaneous tissue, which can cause pain, impair function, and have significant impacts on quality of life. Calcinosis cutis is difficult to manage because there is no generally accepted treatment: evidence supporting treatments is mostly comprised of case reports and case series, sometimes yielding mixed findings. Both pharmacologic and procedural interventions have been proposed to improve calcinosis cutis, and each may be suited to different clinical scenarios. This review summarizes current treatment options for calcinosis cutis, with discussion of recommendations based on patient-specific factors and disease severity.

Creation of plant-based meat analogs: Effects of calcium salt type on structure and texture of potato protein-alginate composite gels

Due to environmental and ethical concerns with current meat production practices, there is a need to create plant-based meat analogs that accurately simulate the textural attributes of animal-derived meat. This study therefore assessed the impact of different insoluble calcium salts on the structural and rheological properties of plant protein-polysaccharide hydrogels formed via internal gelation. Potato protein (10 wt%) was used as a sustainable source of heat-set gelling proteins, whereas sodium alginate (1 wt%) was used as a sustainable source of ion-set gelling polysaccharides. Initially, CaCO3, Ca3(PO4)2, or CaHPO4 were used to crosslink the alginate in the protein-polysaccharide mixtures at ambient temperature by slowly releasing Ca2+ ions as the pH was reduced due to the action of D-glucono-δ-lactone (GDL). When the same amount of GDL and calcium were used, the pH trends, as well as the appearance and texture, were similar for Ca3(PO4)2 and CaHPO4 induced gels, whereas CaCO3 induced gels showed different characteristics, which was mainly attributed to the release of CO2 bubbles during the dissociation of this insoluble calcium salt. At the same calcium and GDL concentration, the gel strength increased in the following order: CaCO3 < Ca3PO4 < CaHPO4. This change in gel strength was mainly related to differences in the pH-time profiles produced by the dissolution of the different calcium salts. Micro-computed tomography analysis showed that the textural characteristics were related to the porosity of the composite hydrogels produced. When the final pH of all the samples was set at pH 5.5 by controlling the GDL concentration, the CaCO3 induced hydrogels had a higher gel strength than the Ca3(PO)4 and CaHPO4 induced ones. However, CaCO3 induced gels also released a large amount of CO2 bubbles, which disrupted the gel structure both before and after the heating process. Overall, our results showed that the pH, appearance, structure, and texture of potato protein/alginate hydrogels can be controlled by manipulating the type of insoluble salt and the amount of added GDL used. These potato protein-alginate hydrogels may therefore be suitable for creating meat analogs in the plant-based food industry.

Calcinosis Prevalence in Autoimmune Connective Tissue Diseases-A Retrospective Study.

Background/Objectives: Calcinosis cutis is the deposition of insoluble calcium salts, which may cause inflammation, ulceration, pain, and restricted joint mobility. It rarely develops in damaged tissues (dystrophic subtype), most frequently in autoimmune connective tissue diseases (CTDs), but there is very limited data on the prevalence. Also, therapy remains an unsolved issue. In this study, we aimed to collect data on the prevalence of calcinosis in CTD patients to highlight that it is a considerable problem. Methods: A retrospective study was conducted in our department to assess the epidemiology of dystrophic calcinosis in CTDs between January 2003 and January 2024. Results: A total of 839 CTD patients were identified, of whom 56 had calcinosis (6.67%). The mean age of the calcinosis patients at diagnosis of underlying CTD was 41.16 ± 19.47 years. The mean time interval from the onset of calcinosis was 5.96 ± 8.62 years. Systemic sclerosis was the most common CTD complicated by calcinosis (n = 22). Conclusions: Our results are comparable to those reported previously in the literature. Although calcinosis is rare in the overall population, it is a present and unsolved problem in CTD patients. Therefore, further studies are needed on the factors involved in the development and progression of calcinosis as well as its treatment.

Use of high-pressure processing and low-temperature storage to extend the performance shelf life of 2 types of string cheese

The manufacturing method of string cheese is similar to mozzarella, but the hot curd is extruded through narrow tubes or pipes, which align the protein fibers that provide the characteristic ability for consumers to pull strings from this cheese. Firmness is another important performance attribute for consumers who just bite into the string cheese without peeling off strings. There have only been a few studies on string cheese, but it is known that stringiness and firmness decrease during prolonged storage, which is a particular challenge for exporting string cheese. We explored 2 treatments to try to retain the stringiness and firmness of string cheese for longer storage periods. The techniques used were high-pressure processing (HPP; 600 MPa for 3 min) and reduced storage temperature (0°C). In other cheese varieties, these techniques have helped extend the performance shelf life. We tested these techniques using the 2 main types of commercial string cheese: direct acid string cheese (DASC) and cultured string cheese (CSC), which were obtained from 2 different manufacturing facilities. The DASC had higher fat (∼2.2%) and higher pH values (∼0.2 units) compared with the CSC. The CSC had higher protein content (∼3.4%), higher insoluble calcium content (∼8 mg insoluble Ca/g protein) and higher texture profile analysis (TPA) hardness values (∼4 N) compared with the DASC. Due to the compositional differences, the 2 varieties were statistically analyzed separately for all other attributes. In both cheese types, HPP caused an immediate reduction in stringiness, some solubilization of insoluble calcium, and a slight increase in the cheese pH values. High-pressure processing also caused a slight increase in TPA hardness of the CSC samples until 14 d (possibly due to a slight increase in cheese pH). The use of the 0°C storage temperature reduced proteolysis and helped retain firmness during storage. Low-temperature storage could help extend the performance shelf life of string cheese by a couple of months, but HPP was not suitable, as the process caused an immediate reduction in stringiness due to the disruption of the matrix induced by the HPP treatment.

Experimental Study on Ecological and Biogeochemical Role of Calcimycocavites in Understanding Carbon Fluxes in the Age of Global Warming and Climate Change

The present work reports the results of calcimycocavitological studies on the seashells from beaches of north Goa, India yielding distinct microfungal forms known as calcimycocavites which are important in global climate change studies. SEM studies of the calcareous shell fragments revealed the micro tunneling behavior of the fungi. Digital analysis of SEM images using Mountain Premium 7.2 software revealed the fine topography of calcimycocavites hyphae along with unidentified presumptive biomineral encrustations. The biodegradation of mycocavitogenic insoluble Calcium Oxalate by oxalotrophic members of bacterial communities may occur using bacterial Oxalate decarboxylase and formate dehydrogenase finally releasing Carbon Di Oxide and water and Calcium oxide to the local nutrient pool. Calcimycocavites may be thus involved in the biogeochemical cycling of Carbon and Calcium in the Ocean-Beach environment. The ecological, biological, and biogeochemical implications of the findings are presented concerning the possible role of calcimycocavites in Calcium and Carbon cycling by breakdown of the calcareous shells and release of inorganic and organic components in the ecosystem. The role of calcimycocavites is stressed in global climate studies.

Kinetics of zinc leaching from intermediate feedstocks

The aim of the work was to study the leaching kinetics of zinc from the compound CaO. ZnO, formed during the sintering of dust from electric arc furnaces with limestone, as well as to identify the mechanisms by means which such chemical interactions occur. The object of the study was the dust sinter of electric arc furnaces with limestone obtained at the Chelyabinsk Zinc Plant. It was found that zinc is contained in sinter in the form of readily soluble CaO. ZnO. The elemental composition of the initial dusts and sinter was determined by the spectral atomic emission method using inductively coupled plasma on a Spectroblue optical emission device and spark spectrometry. The phase composition of the materials was studied on a Bruker D8 Advance X-ray diffractometer. The initial sinter was milled to apowder state having a particle size of ~0.04 mm and with a yield of ~97% of the composition, %: 11.9 Zn; 28.5 Ca; 16.6 Fe; 0.38 Mg; 0.14 Pb; 0.05 Cl. Experiments on the leaching of Zn with NaOH solution were carried out at the following parameters: the initial concentration of zinc in the pulp was 0.202 g-ion/dm3 ; alkali concentration – 5‒9 mol/dm3 NaOH; L:S = 9:1; pulp mixing rate – 10‒20 rad. c-1; temperature – 333‒363 K; duration – 0.5–2.5 hours. It has been shown that zinc from sinter passes into solution as sodium tetrahydroxozincate Na2[Zn(OH)4], while calcium remains in the cake, mainly as insoluble Ca(OH)2, which reacts with carbon dioxide to form insoluble calcium carbonate CaCO3. The process of dissolving zinc from the sinter corresponds to the external diffusion mode of mutual transfer of the initial reagents and reaction products through the surface layer of the liquid at the interface of the “liquid–solid” phases with an activation energy value equal to 12.44 kJ/mol. Thus, with the studied parameters of zinc leaching with NaOH solution, the process proceeds in an external diffusion mode. The results are of interest when identifying conditions corresponding to the intradiffusion and kinetic modes of zinc leaching.

Microwave hydrothermal sulfuric acid leaching of spent cathode carbon from aluminum electrolysis for high efficiency removal of insoluble calcium fluoride

Toxic substances, like fluoride salts present in spent cathode carbon (SCC), have been a great risk to the environment and public health. Our approach involves alkali leaching to eliminate soluble fluoride, followed by microwave hydrothermal acid leaching to efficiently remove insoluble CaF2 from SCC. The optimized conditions, including a temperature of 353 K, a solid–liquid ratio of 1:20, and a 60-minute reaction time, resulted in an impressive 95.6 % removal of fluoride from SCC. Various characterization techniques were employed to analyze the composition, micro-morphology, and elemental content of the materials before and after the leaching process. Furthermore, critical process parameters on the leaching separation of insoluble CaF2 during microwave hydrothermal acid leaching were systematically investigated. The study removal mechanism revealed the transformation of insoluble CaF2 in the process of microwave oxidation insertion-hydrothermal acid leaching for SCC. The kinetic characteristics of the two-stage leaching process of CaF2 at different temperatures were analyzed according to the shrinkage kernel model. The results indicate that the two-stage leaching process of CaF2 is affected by mixing control and by diffusion control, severally. The expansion of the graphite flake layer of SCC through oxidative intercalation was identified as a critical process for the thorough removal of CaF2. Microwave hydrothermal acid leaching demonstrated a 17 % improvement over traditional hydrothermal acid leaching within the same reaction time, showcasing a noteworthy enhancement in fluoride removal. Consequently, the microwave oxidizing intercalation-hydrothermal acid leaching treatment of SCC, as explored in this study, offers an effective approach for achieving deep defluoridation of SCC.