Hydroxide Research Articles

Isolation and Electrochemical Analysis of a Facultative Anaerobic Electrogenic Strain Klebsiella sp. SQ-1.

Electricigens decompose organic matter and convert stored chemical energy into electrical energy through extracellular electron transfer. They are significant biocatalysts for microbial fuel cells with practical applications in green energy generation, effluent treatment, and bioremediation. A facultative anaerobic electrogenic strain SQ-1 is isolated from sludge in a biotechnology factory. The strain SQ-1 is a close relative of Klebsiella variicola. Multilayered biofilms form on the surface of a carbon electrode after the isolated bacteria are inoculated into a microbial fuel cell device. This strain produces high current densities of 625 μA cm-2 by using acetate as the carbon source in a three-electrode configuration. The electricity generation performance is also analyzed in a dual-chamber microbial fuel cell. It reaches a maximum power density of 560 mW m-2 when the corresponding output voltage is 0.59 V. The facultative strain SQ-1 utilizes hydrous ferric oxide as an electron acceptor to perform extracellular electricigenic respiration in anaerobic conditions. Since facultative strains possess better properties than anaerobic strains, Klebsiella sp. SQ-1 may be a promising exoelectrogenic strain for applications in microbial electrochemistry.

A sustainable bioprocessing system leveraging gas fermentation and bipolar membrane electrodialysis system for direct recovery of acetic acid

This study examined the integration of gas fermentation with bipolar membrane electrodialysis (BPMED) for sustainable production of acetic acid and bases, focusing on medium recycling and ion-exchange membrane optimisation. Gas fermentation was performed using an acetogenic microbe, Eubacterium callanderi KIST612, in a custom-designed gas bioreactor. The BPMED system was operated under specific voltage conditions to evaluate the proton and hydroxyl ion generation, ion concentration, and residual ratios. Gas fermentation consistently generated acetate with a stable CO2 consumption rate (0.167 mmol gcell−1) and an increased rate of conversion of carbon into biochemicals via methanol. The BPMED system efficiently produced acetic acid (acetate extraction rate of 99.72 %–99.82 %) and hydroxide ions (from 8 to 18 V), with operational challenges identified at higher voltage levels (≥20 V). The BPMED process, which includes additional membranes and exhibits a lower acetate flux than the ED process, had remarkable cost-effectiveness, surpassing the ED integration process by 17.6 %. This economic advantage was paralleled by a significant environmental benefit, where the BPMED process reduced carbon dioxide emissions by 7.4 % compared with the ED process. These results suggest that integrating gas fermentation with BPMED is a viable and sustainable approach for acetic acid production.

Dimeric ethyl-tin(IV)-dibromide-hydroxide-N,N-di-methyl-formamide.

Di-μ-hydroxido-bis-[di-bromido-(di-methyl-formamide-κO)ethyl-tin(IV)], [Sn2Br4(C2H5)2(OH)2(C3H7NO)2], was prepared from ethyl-tin(IV) bromide and N,N-di-methyl-formamide (DMF) in air. The crystal structure exhibits the typical structural features of dimeric Lewis-base-stabilized monoorganotin(IV)-dihalide-hydroxides, RSnHal2(OH), i.e. two octa-hedrally coordinated Sn atoms are linked together via two bridging hydroxide groups, resulting in a centrosymmetric four-membered rhomboid-like Sn-OH ring with acute angles at the Sn atom, obtuse angles at the O atoms and two different tin-oxygen bond lengths. With the shorter bond trans to the ethyl group, this observation underlines once more the so-called trans-strengthening effect in monoorganotin(IV) com-pounds with octa-hedrally coordinated Sn atoms. Differences and similarities in the bond lengths and angles in the four-membered Sn-OH rings have been worked out for the rings in dimeric diorganotin(IV)-halide-hydroxides, [R 2SnHal(OH)]2, and hydrates of dimeric tin(IV)-trihalide-hydroxide-aqua-hydrates, [SnHal3(OH)(H2O)]2·nH2O.

Improved chloralkaline reversible electrochemical cells featuring a catalytic-coating-free 3-D printed titanium gas diffusion electrode

This study presents a novel resin 3-D printed chloralkaline reversible electrochemical cell featuring a 3-D printed titanium (3DP-Ti) cathode and a mixed-metal oxide anode. It evaluates the capability of this cell for electricity production (using hydrogen and bleach as fuel and comburent, respectively) and electrolysis of NaCl brine (producing hydrogen, chlorine, and retaining carbon dioxide). Parameters including NaCl concentration, bleach pH, and temperature were varied for examination. Despite the assembled 3DP-Ti does not contain any cathodic catalytic layer, the cell shows outstanding performance and it reaches maximum power densities of 7.38 mWcm−2 and maximum current densities of 12.7 mAcm−2. Hydrogen is flowed through small pores and electricity production dependence on feeding solution pH, electrolyte concentration, and temperature are observed. The system proved as a reversible chloralkaline electrochemical cell by confirming its good performance as an electrolyzer, with faradic efficiencies of 100 % for hydrogen production and 70 % for chlorine production. Energy efficiencies reached 196.54 mg Cl2/Wh and 7.48 mg H2/Wh. During operation as an electrolyzer (stream feeding to the gas diffusion cathode), it also demonstrated the capacity to fix carbon dioxide contained in gaseous streams by reacting with hydroxyl ions produced during the electrochemical hydrogen production. The fixation efficiency was 220.0 mg CO2 fixed/Wh. These findings demonstrate progress in electrochemical cell technology, highlighting its potential for various electrochemical applications.

Evaluation of structural characteristics BaFe(12-x)InxO19 hexaferrite compounds at high temperatures

BaFeO-based hexaferrite compounds were synthesized by partially replacing Fe atoms with In atoms in barium hexaferrite, and their structural characteristics, thermal, and magnetic properties were studied. The crystal structure and lattice parameters of the hexaferrite were investigated using the X-ray diffraction method. Thermal property investigations were conducted at high temperatures. The results obtained by the Differential Scanning Calorimetry (DSC) method were analyzed, and the mechanisms of formation and decomposition of hydroxide groups in these crystals were explained. These effects were also determined by Thermogravimetric Analysis (TGA) studies. The vibrational magnetometry method studied the magnetic properties of BaFe11.4In0.6O19 and BaFe10.8In1.2O19 compounds. As the concentration of In atoms in the samples increases, the temperature of the ferrimagnetic-paramagnetic phase transition decreases. The observed effect in the temperature range of RT to 800 °C is attributed to weight loss due to the decomposition of structural water molecules through an endothermic reaction in hexaferrite compounds. The value of the Curie temperature for the BaFe11.4In0.6O19 compound was 383 °C, and for the BaFe10.8 In1.2O19 compound, it was 323 °C. Increasing In concentration from x = 0.6 to x = 1.2 increases the In3+ ionic radius in the structure, and due to the replacement of Fe3+ ions with more In3+ ions at x = 1.2, the magnetic hyperfine field area decreases.

Impact of Mg‐doping on morphology, structure, optical properties, and enhancing photocatalytic performance of ZnO thin films, prepared by sol–gel spin‐coated method

AbstractThin films of pure and Mg‐doped ZnO (MZO) were successfully fabricated on glass substrates by sol–gel spin coating method. Microstructure, surface morphology, elemental composition, optical analysis, and Mg doping effect on the photocatalytic performance of the thin films have been measured by XRD, SEM, EDS, and UV–Vis, respectively. XRD analysis showed that ZnO and MZO thin films have a hexagonal wurtzite structure, and the intensity of the (0 0 2) peak moved from higher to lower angle and right to left with rising Mg‐dopant concentration, and crystallinity was enhanced with doping, whereas micro‐strain and dislocation density dropped. SEM analysis found that ZnO had spherical and agglomerated structures, and the increased size of the grains was observed with increasing doping. The optical analysis demonstrated that the band gaps increased as the dopant percentage increased. Methylene blue, a dye pollutant, examined the thin films’ photocatalytic performance. It was demonstrated that the addition of the Mg to the ZnO lattices increased the absorption of the hydroxyl ions at the surface of the thin film and hence acted as a trap site, leading to a decrease in the electron–hole pair and consequently enhancing the photodegradation.

Supramolecular architecture of Mn(II) complex with 5,5´-dimethyl-2,2´-bipyridine and 4-hydroxybenzoic acid: Synthesis, crystal structure, Hirshfeld surface analyses, catalytic and antimicrobial activities

A novel complex [Mn(5,5´-dmbipy)2Cl2](4-hba)2 (1) (5,5´-dmbipy=5,5´-dimethyl-2,2´-bipyridine and 4-hba=4-hydroxybenzoic acid) was successfully synthesized using methanol by steam reflux. The complex is characterized using SC-XRD, IR, UV and thermogravimetric analysis. Single crystal X-ray analysis of 1 indicates a distorted octahedral coordinated Mn2+ centre with two molecules of 5,5´-dmbipy and two chlorine ions and the presence of two uncoordinated 4-hba in the complex. The two chlorine atoms (Cl1 and Cl2) form intermolecular H-bonding with 4-hba. The complex crystallizes in monoclinic space group P21/c forming a helical like 1D polymeric supramolecular architech through H- bonding. Presence of halogen-hydrogen bond C(sp2)-OH—Cl-M between uncoordinated -OH and Cl ion in 1 significantly provides a path of extending supramolecular network forming a unique architect of the complex. Interestingly, presence of pyridine-benzene system forming π-π stacking is confirmed from SC-XRD. Hirshfeld surface analysis is carried out to explore the noncovalent interactions in the crystal. Mn3O4 nanoparticles synthesized from complex 1 are characterized using PXRD and HRTEM, and successfully employed as catalyst for the degradation of dyes. Both complex 1 and Mn3O4 nanoparticles show appreciable biological activities.

Removal of arsenic from water by silver nanoparticles and Fe-Ce mixed oxide supported on polymeric anion exchanger

By encapsulating nanoscale particles of goethite (α-FeO(OH)), hydrous ceric oxide (CeO2·H2O, HCO) and silver nanoparticles (AgNPs) in the pores of polystyrene anion exchanger D201, a novel nanocomposite FeO(OH)-HCO-Ag-D201 was prepared for the effective removal of arsenic from water. The isotherm study shows that FeO(OH)-HCO-Ag-D201 has excellent adsorption performance for As(III) and As(V), with an increased adsorption capacity of As(III) to 40.12 mg/g compared to that of 22.03 mg/g by the composite adsorbent without AgNPs (FeO(OH)-HCO-D201). The adsorption kinetics data showed that the sorption rate of FeO(OH)-HCO-Ag-D201 for As(III) is less than that for As(V), and the adsorption of As(III) and As(V) were consistent with the pseudo-second-order model and the pseudo-first-order model, respectively. Neutral or basic conditions are favored for the adsorption of As(III/V) by FeO(OH)-HCO-Ag-D201. Compared with nitrate/chloride/bicarbonate, sulfate/silicate/phosphate showed more remarkable inhibition of arsenic removal by FeO(OH)-HCO-Ag-D201, whereas natural organic matter showed no interference to the arsenic removal. The As(V) adsorption involved different interactions such as electrostatic attraction and surface complexation, while the adsorption of As(III) involved the part oxidization of As(III) to As(V) and the simultaneous adsorption of As(III) and As(V). In addition to the Ce(IV) in CeO2·H2O acted as an oxidant, the synergistic effect of α-FeO(OH) and AgNPs also contributed to the oxidization of As(III) to As(V). Moreover, the reusable property suggested that this FeO(OH)-HCO-Ag-D201 nanocomposite has great potential for arsenic-contaminated water purification.

Alloyed Trimetallic Nanocomposite as an Efficient and Recyclable Solid Matrix for Ideonella sakaiensis Lipase Immobilization.

In this work, a trimetallic (Ni/Co/Zn) organic framework (tMOF), synthesized by a solvothermal method, was calcinated at 400 and 600 °C and the final products were used as a support for lipase immobilization. The material annealed at 400 °C (Ni-Co-Zn@400) had an improved surface area (66.01 m2/g) and pore volume (0.194 cm3/g), which showed the highest enzyme loading capacity (301 mg/g) with a specific activity of 0.196 U/mg, and could protect the enzyme against thermal denaturation at 65 °C. The optimal pH and temperature for the lipase were 8.0 and 45 °C but could tolerate pH levels 7.0-8.0 and temperatures 40-60 °C. Moreover, the immobilized enzyme (Ni-Co-Zn@Lipase, Ni-Co-Zn@400@Lipase, or Ni-Co-Zn@600@Lipase) could be recovered and reused for over seven cycles maintaining 80, 90, and 11% of its original activity and maintained a residual activity >90% after 40 storage days. The remarkable thermostability and storage stability of the immobilized lipase suggest that the rigid structure of the support acted as a protective shield against denaturation, while the improved pH tolerance toward the alkaline range indicates a shift in the ionization state attributed to unequal partitioning of hydroxyl and hydrogen ions within the microenvironment of the active site, suggesting that acidic residues may have been involved in forming an enzyme-support bond. The high enzyme loading capacity, specific activity, encouraging stability, and high recoverability of the tMOF@Lipase indicate that a multimetallic MOF could be a better platform for efficient enzyme immobilization.

Influence of Phosphate on Arsenic Adsorption Behavior of Si-Fe-Mg Mixed Hydrous Oxide.

The arsenic adsorption performance of silicon (Si), iron (Fe), and magnesium (Mg) mixed hydrous oxide containing a Si: Fe: Mg metal composition ratio of 0.05:0.9:0.05 (SFM05905) was investigated. SFM05905 was synthesized by the co-precipitation method. Batch experiments on arsenic adsorption were conducted at various temperatures and concentrations. Adsorption isotherms models were represented by a linearized equations and were insensitive to temperature change. The anion selectivity of SFM05905 at single component was high for arsenite (III), arsenate (V), and phosphate (PO4), indicating that PO4 inhibits arsenic adsorption. The adsorption amount of As (III), As (V), and PO4 were compared using a column packed with granular SFM05905, and an aqueous solution was passed by a combination of several anions that are single, binary, and ternary adsorbate systems. As (III) had the highest adsorption amount; however, As (III) and PO4 were affected by each other under the ternary mixing condition. Although the adsorption amount of As (V) was smaller than that of As (III), it was not affected by other adsorbates in the column experiments. Finally, although the adsorption of both arsenic continued, the adsorbed PO4 gradually desorbed.

Interpretation by literature review of the use of calcium hydroxide as an intra-ductal medication

The effectiveness of calcium hydroxide as an antiseptic agent in endodontics has recently gained relevance, being crucial to ensure optimal results in endodontic treatments. The aim of the study was to interpret the use of calcium hydroxide as an intra-endodontic medication by means of a literature review. A narrative review of the updated literature was performed, with the aim of describing the effects of CaOH and exposing the different clinical procedures in which it is used, as well as the results of its application in endodontic therapy. Clinical trials, meta-analyses and original and published articles from 2018 to 2023, in English or Spanish, were included. It was found that calcium hydroxide plays a key role in endodontics due to its dissociation into calcium and hydroxyl ions, which contributes to its antimicrobial and biological efficacy. Its clinical application is extensive, including preventive endodontics, direct and indirect pulp capping, pulp curettage and pulpotomies, especially in teeth with incomplete apical development. The mechanism behind its antimicrobial action lies in the diffusion of calcium ions and the increase in pH, which limit the rate and enhance the antimicrobial effect in root canals. It was concluded that, for an effective endodontic treatment, it is necessary to eliminate all microorganisms from the root canal. In addition, the microorganism such as E. faecalis has a high resistance to endodontic treatment, which is due to its ability to penetrate into the dentinal tubules, tolerate high alkalinity, and form biofilms

Unique production strategy of Pt/C electrocatalysts via pulsed laser for hydrogen generation: Insights screening by DFT calculations

Design and optimizing the components and structure of highly-active electrocatalysts is a prevalent approach for reducing the input electrical energy consumption and concurrently H2 fuel production. An efficient and sustainable method is a water-electrolyzer for H2 generation, but still restricted by the stable electrode materials. In this study, a green chemistry approach for one-pot production of Pt/C nanospherical with controllable ratios of Pt and C was demonstrated using simple pulsed laser ablation in liquid (PLAL) process, during which Pt target ablation in diverse solvents (water, methanol, ethanol, and 1-propanol) without external carbon source and reducing/capping agents. The carbon-rich solvents are acted as both C-source and solvent, which are decomposed during the PLAL process, producing C, H, and OH ions inside the cavitation bubble which condenses as C-shells on the Pt surface. The optimal Pt/C proportions have the highest electrochemical H2-evolution in acidic media with an overpotential of 59 mV at 10 mA/cm2, Tafel slope of 41 mV/dec, and j0 of 0.686 mA/cm2. The exceptional electrocatalytic concert of optimal Pt/C was further supported by the density functional theory. Optimized C-content in Pt/C reveals good dispersion and strong interaction of C with Pt can make efficient electron transfer, structural stability, and electrochemical durability, resulting in superior electrocatalytic performance in electrolyzer devices.

Growth kinetics of novel nickel oxide (NiO) nano fibers on glass substrates by SILAR process: A solution to remove AZO dye

This article presents the growth of uniformly distributed nickel oxide (NiO) nanofibers on a glass substrate by the Successive Ionic Layer Adsorption and Reaction (SILAR) process and explores its photocatalytic features towards an AZO dye. The nanofiber grown by the SILAR process is subjected to annealing at 400°C to decompose the hydroxide group into oxide. X-ray diffraction pattern divulges the Face-Centered Cubic (FCC) structure of NiO, and its average crystallite size (46–61 nm). The fibrous morphology with the width varying from 37.83 to 42.05 nm is confirmed through FESEM micrographs. The existence of nickel and oxide, with atomic percentages in the ratio 40:60 is confirmed by EDX analysis. From the UV–visible spectrum, the band gap energy Eg is determined using a Tauc plot and the values are varied between 3.38 eV and and 3.41 eV. Photocatalytic degradation efficiency for the Congo red dye is found to be 93% for reusable NiO nanofibers under the illumination of UV light. The photodegradation pathway of Congo red dye is presented based on gas chromatography-mass spectrometry (GC-MS) analysis. The prospective applications of the current work in wastewater treatment make it significant.

Lead and zinc chemical fraction alterations in multi-metal contaminated soil with pomelo peel biochar and biochar/apatite incubation

The issue of heavy metal soil contamination is widespread, and the negative effects of heavy metals on the ecosystem depend on their chemical speciation in contaminated soil. Pomelo peel-derived biochar produced at 300 °C (PPB300) and 500 °C (PPB500) and its combination with apatite ore (AP) was applied to immobilize lead (Pb) and zinc (Zn) in agricultural multi-metal polluted soil. Soil amendments including biochar (PPB300 and PPB500) at concentrations of 3%, 5%, and 10%, as well as a mixture of biochar and apatite (AP) at 3:3% and 5:5% weight ratios, were introduced into the soil matrix. The chemical forms of Pb and Zn in incubated soil samples and control soil (CS) were studied utilizing the Tessier’s sequential extraction procedure. The chemical partitioning of heavy metals was carried out using Tessier’s extraction protocol, yielding fractions representing exchangeable (F1), carbonate (F2), Fe/Mn oxide (F3), organic matter (F4), and residual (F5) forms. Quantification of Pb and Zn concentrations was accomplished via inductively coupled plasma mass spectrometry (ICP-MS). Observations revealed notable elevations in pH, organic carbon (OC), and electrical conductivity (EC) levels within the treated soil relative to the control soil (p < 0.05). After incubating PPB300, PPB500, and AP for 30 days, there was a reduction in the exchangeable fraction of Pb and Zn by approximately 64% and 58% respectively. This reduction was achieved by transforming heavy metals from mobile fractions to immobile fractions using five primary mechanisms: chemical and physical adsorption, electrostatic attraction, the formation of complexes via interactions with active groups, cation exchange processes, and precipitation events mediated by phosphate, carbonate ions, or hydroxyl ions within an alkaline environment. Therefore, pomelo peel-derived biochar and the blend of biochar/apatite show promise as materials for mitigating heavy metal pollution in soil.

Analisis pembuatan dan penggunaan koagulan poly aluminium chloride (PAC) pada proses penjernihan air

Background: Poly Aluminum Chloride (PAC) is a complex inorganic compound between hydroxyl (OH) ions and aluminum ions which undergo gradual chlorination. PAC is able to coagulate suspended substances or colloidal dispersions to produce floc that easily settles. Methods: The raw materials used in the manufacture of PAC consist of alumina hydrate Al (OH) 3, hydrochloric acid (HCl), sulfuric acid (H2SO4), and calcium carbonate (CaCO3). The experiments were carried out by reacting Al (OH) 3 as much as 100 grams, HCl as much as 180 ml, and H2SO4 as much as 127.1 grams at 90 ° C and 100 ° C temperature variations with time variations of 30s, 60s, and 90s. The characterization was tested in the form of a jar test and FTIR test. Finding: In the Jar Test, the optimum temperature and time are obtained at 90 ° C and 60s and at 100 ° C and 60s. At the optimum jar test results, the FTIR test was performed. Conclusion: From the test results, this study meets PAC manufacturing standards.

Evaluation of Effect of Septilin™ and Calcium Hydroxide Intracanal Medicaments on Interappointment Flare-up and Healing of Apical Periodontitis-Pilot Study

ABSTRACT Background: Endodontic microflora comprises of multispecies, hence no single intracanal medicament can disinfect the root canal completely. Newer herbal medicaments need to be researched which may be more effective. Hence there was a need to evaluate and compare the effect of Septilin and calcium hydroxide intracanal medicaments on interappointment flare up and healing in apical periodontitis. Aim and objective: To evaluate and compare the effect ofcalcium hydroxide and septilin intracanal medicaments in interappointment flare up and periapical healing. Materials and Methods: Thirty patients with periapical lesions in the anterior region of jaw were selected. Intracanal medicaments were inserted as Group I -Calcium hydroxide(n=15) and Group IISeptilinTM (n=15). After 7 days the intracanal medicament was changed and obturation done after 15 days. Patients were evaluated clinically for VRS pain score at 1&amp;2 weeks and 1, 3 and 6 months. Radiographic evaluation using PAI index was done by two trained observers at interval of 1, 3 and 6 months. Results: showed no incidence of flare up. After three months there was significant change in the PAI score. At 6 months, 20% of calcium hydroxide group whereas 13.33% of SeptilinTM group had PAI score of 1. Conclusion: At 3 months the periapical healing in both groups was similar. At 6 months Calcium hydroxide group showed better healing as compared to SeptilinTM group.

Preparation of poly(lactic acid) (PLA)/poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV)/graphene oxide (GO) polymeric composites for the selective removal of lead ions (Pb(II)) in water

AbstractLead pollution in water has risen globally, due to industrialization and globalization. In this study, this problem was addressed by preparing poly (lactic acid) (PLA)/poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV)/graphene oxide (GO) composites and addressing their effectiveness in absorbing water, and adsorbing Pb(II) ions in water. In water absorption studies, increasing the GO content to above 1 wt.% (3 and 5 wt.%) resulted in the degradation of the composites. All blends, and composites with 1 wt.% GO loading showed good water intake properties, with the composites having the highest. Pb (II) ion intake analyses showed that all the materials adsorb Pb(II) ions significantly in 24 h contact time, but the composites with 1 wt.% GO loadings adsorbed the greatest (81.3%–86.5%). For the effect of pH on adsorption, the adsorption of Pb(II) ions increased with an increase in pH from acidic to basic. This was attributed to the abundance of hydroxyl ions in basic media, that will not compete with Pb(II) ions for adsorption sites. Conclusions were that the 49.5/49.5/1 w/w PLA/PHBV/GO composite was the most optimal adsorbent of Pb(II). This composite could be used in industrial water purification processes like membranes, to remove lead ions from water while conserving the environment.Highlights Melt mixed PLA/PHBV/GO composites for removing lead ions from water. 1 wt.% GO contents in the composites sufficiently absorbed water. 3 and 5 wt.% GO contents resulted in the hydrolytic degradation of composites. Contact time is directly proportional to the degree of lead ion adsorption. Basic pH media resulted in the optimal adsorption of lead ions from water.

Unraveling the Impact of Ethylenediaminetetraacetic Acid Chelating Agents on the Oil Recovery Processes: An Insight into Its Role in Fluid-Fluid and Rock-Fluid Interactions.

In recent years, chelating agents have garnered increasing attention due to their unique capabilities in addressing challenges associated with chemically enhanced oil recovery materials. Most previous studies have primarily focused on examining the influence of chelating agents on rock-fluid interactions. However, their effects on fluid-fluid interactions, specifically on interfacial tension (IFT) characteristics under various conditions, remain relatively unknown. This study investigates the effect of crucial reservoir parameters on the performance of ethylenediaminetetraacetic acid (EDTA) chelating agents in the IFT between crude oil and brine. Furthermore, the study evaluated the impact of varying concentrations of this agent on rock wettability alteration, zeta potential, and spontaneous imbibition. The results illustrated that introducing EDTA at high concentration into seawater (SW) solution reduced the IFT by 85%. Additionally, while higher pH levels contributed to IFT reduction due to increased hydroxyl ions, excessive salinity levels resulted in elevated IFT. Raising the temperature from 30 to 75 °C further decreased the IFT, changing the IFT for optimal EDTA concentration from 20.43 to 2.56 mN/m (∼88% reduction). The changes in zeta potential and contact angle measurements indicated that solutions of 5 and 7 wt % EDTA shifted rock wettability from oil-wet to strongly water-wet, resulting in the wettability alteration index of 1.01 and 1.02, respectively. Inductively coupled plasma analysis, on the other hand, revealed substantial chelation of metal ions from both the solution and rock when EDTA was added to the rock/SW system. This resulted in a significant increase in Ca2+ ions and a decrease in Mg2+ ions, attributed to the multi-ion exchange phenomenon.

INFLUENCE OF рН AND Ca&lt;sup&gt;2+&lt;/sup&gt; IONS ON CHEMICAL COMPOSITION AND SORPTION OF &lt;sup&gt;137&lt;/sup&gt;Cs BY CHERKASY BENTONITES (UKRAINE)

The safety of near-surface and deep radioactive waste storage facilities is based on a system of engineered and natural barriers. Significant degradation of the engineered barrier system composed of cemented waste matrixes covered by cement mixture, concrete compartments, and structures at the basement of the storage facility may cause radionuclide transfer from the facility to groundwater. Mixing of the cement and concrete with water leads to the formation of several various hydration products with subsequent leaching of Ca2+ ions and formation of hydroxyl ions (OH-), which affects the alkalinity of the water environment and the sorption properties of bentonite, as a component of the engineered barrier at the basement of near-surface facilities. The article presents the results of an experimental study of the influence of Ca2+ ion concentration and pH of the model solution (similar to groundwater composition at Vector Site in Chornobyl Exclusion Zone) on the elemental composition and sorption properties of natural (NB) and Na-modified (PBA-20) bentonites from the Cherkasy deposit concerning 137Cs at the Solid : Solution ratio of 1 : 100. Geochemical modeling suggests that addition of CaCl2 to test solution and resulting alkaline pH leads to precipitation of solids, mainly oxides, hydroxides, Fe oxyhydroxides (hematite, goethite, limonite), and Ca carbonates (calcite, aragonite, dolomite). Their role in Cs adsorption was evaluated. The concentration of structural elements (Si, Al) in bentonites practically does not change with Ca2+ ion concentration increase in the model solution, demonstrating the bentonite structure’s stability under these conditions. At the same time, an increase in the Ca concentration and a decrease in the Na concentration was found in the ion exchange complex of the bentonites if compared to the initial natural bentonite. This results in the transformation of Na-modified bentonite from Na, Ca-form to Ca, Na-form. The total sorption capacity of NB and PBA-20 bentonite concerning Cs+ ions at increased concentrations of Ca2+ ions and pH of the solution slightly decreases, though retaining high values of the degree of absorption (&gt; 90 %). The total adsorption of Cs+ ions on NB and PBA-20 bentonites from model groundwater with the addition of CaCl2 from 16 to 960 mg/dm3 and increase of рН from 7.4 to 11.8 decreases with the increase in ionic strength, in particular, due to competition with Са2+ and Na+ ions. NB and PBA-20 bentonites of the Cherkasy deposit remain a reliable component of the liner at the repository basement owing to their main functional property – high absorption capacity for 137Cs, which is an important dose-forming radionuclide of short-lived low- and medium-level waste.

Process for desulfurization and demineralization of low rank coal using oxidation assisted froth floatation technique

This study reports the desulfurization and deashing of Hangu coal by air oxidation assisted froth floatation technique applying performic acid (H2O2+HCOOH) as co-oxidant and Fe ions as catalysts in aqueous solution. This process led to the removal of up to 78.08% of total sulfur (TS) and 50.3% of ash at 60 °C, 30 min, a 2:2 ratio of H2O2+HCOOH (v/v), and 0.10% of Fe ions concentration. The sulfur and ash removal followed Fenton mechanism, wherein hydrogen peroxide (H2O2) dissociated into hydroxyl ions (OH-) and hydroxyl radicals (OH.), facilitated by the dissociation of ferrous ions (Fe2+). The reaction of HCOOH with OH. resulted in the formation of performic acid or peroxyl radical, selectively oxidizing sulfur compounds to sulfone and sulfoxide. In the subsequent phase, coal froth floatation was employed with the addition of surfactant i.e. Triton X-100 (TX-100) and collector i.e. diesel oil (DO), resulting in the removal of up to 49.83% of TS and 43.79% of ash. This was achieved under optimized conditions, specifically with a concentration of 400 ppm solution of TX-100 in the solution and a volume of 0.2 mL for DO. The emulsion of TX-100 and DO for the floatation of coal is a suitable option because TX-100 established polar interactions and hydrogen bonding with the oxidized functionalities of coal, whereas the hydrocarbons of diesel oil get attached to the unoxidized coal matrix through hydrophobic interaction. Onwards, simultaneous oxidation assisted by froth floatation in a two-step batch process at pre-optimized parameters resulted in TS and ash removal of 88.8% and 82.6%, and 62.2% and 39.3% in the froth and tailings, respectively. SEM, FTIR and XRD analyses revealed structural and morphological changes, modifications in chemical functionalities and mineralogical changes in the coal sample. The process can be scaled up for the up-gradation of low grade coal for industrial and power generation purposes.