Carboxylate Anions Research Articles

Hydroxyl carboxylate anion catalyzed depolymerization of biopolyesters and transformation to chemicals.

Upcycling biopolyesters (e.g., polyglycolic acid, PGA) into chemicals is an interesting and challenging topic. Herein, we report a novel protocol to upgrade biopolyesters derived from hydroxyl carboxylic acids over ionic liquids with a hydroxyl carboxylate anion (e.g., glycolate, lactate) into various chemicals under metal-free conditions. It is found that as hydrogen-bond donors and acceptors, hydroxyl carboxylate anions can readily activate the ester group via hydrogen bonding and decompose biopolyesters via autocatalyzed-transesterification to form hydroxyl carboxylate anion-based intermediates. These intermediates can react with various nucleophiles (e.g. H2O, methanol, amines and hydrazine) to access the corresponding acids, esters and amides under mild conditions (e.g., 40 °C). For example, 1-ethyl-3-methylimidazolium glycolate can achieve complete transformation of PGA into various chemicals such as glycolic acid, alkyl glycolates, 2-hydroxy amides, 2-(hydroxymethyl)benzimidazole, and 1,3-benzothiazol-2-ylmethanol in excellent yields via hydrolysis, alcoholysis and aminolysis, respectively. This protocol is simple, green, and highly efficient, which opens a novel way to upcycle biopolyesters to useful chemicals.

Preparation of La/Mg modified sheep dung activated carbon and its adsorption characteristics for phosphorus in wastewater

The resource utilization of sheep dung from farming waste was evaluated in adsorption of total phosphorus (TP). Four types of modified sheep dung activated carbon (SDAC) were prepared: SDAC without metal (SDAC-N), SDAC with lanthanum (SDAC-La), SDAC with magnesium (SDAC-Mg), and SDAC with La and Mg (SDAC-La-Mg). The various SDACs prepared were tested in the adsorption TP from wastewater. The main components of the SDAC-La-Mg surface were MgO and La2O3. The SDAC-La-Mg surface was rich in functional groups such as CC and CO and acquired a negative charge. At 25 °C and pH of 4, the TP adsorption capacity of SDAC-La-Mg was 1.94 mg/g. Among the four SDAC adsorbents, SDAC-La-Mg exhibited the highest adsorption capacity. TP adsorption by SDAC-La-Mg followed the secondary kinetic and Langmuir isothermal adsorption models, primarily through chemisorption mechanisms such as ion exchange, chemical precipitation, and covalent bonding. SDAC-La-Mg was regenerated, and the TP removal rate remained at 65% after three regeneration cycles. Mg and La ions combine with carboxylate ions to form ligand compounds, enabling TP adsorption by displacing the -OH group on the surface of SDAC-La-Mg to form an inner complex. Thus, SDAC-La-Mg can be used as an effective adsorbent for TP in wastewater treatment.

Surfaces of Atmospheric Droplet Models Probed with Synchrotron XPS on a Liquid Microjet.

ConspectusThe atmosphere is a key part of the earth system comprising myriad chemical species in all basic forms of matter. Ubiquitous nano- and microscopic aerosol particles and cloud droplets suspended in the air play crucial roles in earth's climate and the formation of air pollution. Surfaces are a prominent part of aerosols and droplets, due to the high surface area to bulk volume ratios, but very little is known about their specific properties. Many atmospheric compounds are surface-active, leading to enhanced surface concentrations in aqueous solutions. Their distribution between the surface and bulk may determine heterogeneous chemistry and many other properties of aerosol and cloud droplets, but has not been directly observed.We used X-ray photoelectron spectroscopy (XPS) to obtain direct molecular-level information on the surface composition and structure of aqueous solutions of surface-active organics as model systems for atmospheric aerosol and cloud droplets. XPS is a vacuum-based technique enabled for volatile aqueous organic samples by the application of a high-speed liquid microjet. In combination with brilliant synchrotron X-rays, the chemical specificity of XPS allows distinction between elements in different chemical states and positions within molecular structures. We used core-level C 1s and N 1s signals to identify the alkyl and hydrophilic groups of atmospheric carboxylic acids, alkyl-amines, and their conjugate acids and bases. From this, we infer changes in the orientation of surface-adsorbed species and quantify their relative abundances in the surface. XPS-derived surface enrichments of the organics follow trends expected from their surface activities and we observed a preferential orientation at the surface with the hydrophobic alkyl chains pointing increasingly outward from the solution at higher concentrations. This provides a first direct experimental observation of well-established concepts of surface adsorption and confirms the soundness of the method.We mapped relative abundances of conjugate acid-base pairs in the aqueous solution surfaces from the respective intensities of distinctive XPS signals. For each pair, the protonation equilibrium was significantly shifted toward the neutral form in the surface, compared to the bulk solution, across the full pH range. This represents an apparent shift of the pKa in the surface, which may be toward either higher or lower pH, depending on whether the acid or base form of the pair is the neutral species. The surface shifts are broadly consistent with the relative differences in surface enrichment of the individual acid and base conjugates in binary aqueous solutions, with additional contributions from nonideal interactions in the surface. In aqueous mixtures of surface-active carboxylate anions with ammonium salts at near-neutral pH, we found that the conjugate carboxylic acids were further strongly enhanced. This occurs as the coadsorption of weakly basic carboxylate anions and weakly acidic ammonium cations forms ion-pair surface layers with strongly enhanced local abundances, increasing the probability of net proton transfer according to Le Chatelier's principle. The effect is stronger when the evaporation of ammonia from the surface further contributes to irreversibly perturb the protonation equilibrium, leaving a surplus of carboxylic acid. These surface-specific effects may profoundly influence atmospheric chemistry mediated by aqueous aerosols and cloud droplets but are currently not taken into account in atmospheric models.

Intramolecular electrostatic effects on reduction of CO2 to CO by iron porphyrin complexes: Insights from DFT calculations

Iron porphyrin (Por) complexes were found to be highly efficient molecular catalysts for electrocatalytic CO2 reduction and the catalytic performance can be modulated by the modification of ligands. Herein, density functional theory calculations were employed to investigate how the presence of second-sphere anionic carboxylate groups influences the CO2-to-CO conversion by Fe porphyrins. The kinetics and thermodynamics of individual chemical steps in the reaction cycle were systematically studied. Computations indicated that the catalytic active species is the ferrous complex with the two extra electrons being stored in the π system of porphyrin and the rate-determining step is the CO2 binding. The synchronization of the Fe-to-CO2 and ligand-to-Fe electron transfers leads to the formation of FeIII(CO22−)(Por•−). The experimentally observed activity trend could be rationalized by the Brønsted-Evans-Polanyi principle. The electrostatic repulsive between the negatively charged hanging group and the CO2 moiety destabilizes the CO2 adduct and thereby raises the binding energy. Then, the two-step protonation occurs easily to give Fe(II)-CO. The further one-electron reduction triggers the dissociation of CO to regenerate of the formal Fe(I) porphyrin catalyst. The insights gained from this study may be helpful in designing efficient electrocatalysts for CO2 reduction.

Mechanical Strength and Conductivity of Cementitious Composites with Multiwalled Carbon Nanotubes: To Functionalize or Not?

The incorporation of carbon nanotubes into cementitious composites increases their compressive and flexural strength, as well as their electrical and thermal conductivity. Multiwalled carbon nanotubes (MWCNTs) covalently functionalized with hydroxyl and carboxyl moieties are thought to offer superior performance over bare nanotubes, based on the chemistry of cement binder and nanotubes. Anionic carboxylate can bind to cationic calcium in the hydration products, while hydroxyl groups participate in hydrogen bonding to anionic and nonionic oxygen atoms. Results in the literature for mechanical properties vary widely for both bare and modified filler, so any added benefits with functionalization are not clearly evident. This mini-review seeks to resolve the issue using an analysis of reports where direct comparisons of cementitious composites with plain and functionalized nanotubes were made at the same concentrations, with the same methods of preparation and under the same conditions of testing. A focus on observations related to the mechanisms underlying the enhancement of mechanical strength and conductivity helps to clarify the benefits of using functionalized MWCNTs.

Hydrogen bond reorientations driven phase transitions leading to dielectric anomaly in bis(glycinium)oxalate at high pressure and low temperature

Glycine complexes are of immense importance to fundamental science and technological applications. Bis(glycinium)oxalate is stabilized by an unusually strong hydrogen bond at ambient conditions in a centrosymmetric crystal structure. Here, using high pressure and low temperature infrared spectroscopic studies, supported by first principles density functional theory calculations, we present the mechanism of phase transformation in dense Bis(glycinium)oxalate, both at a pressure of 1.7 GPa and at temperatures below 50 K. The transition is governed by reorientations in strong hydrogen bonding network mediated by displacements in carboxylate ions, which modifies glycine conformation driving the loss of inversion symmetry. Further, we have carried out dielectric measurements, which show that the phase transformation is accompanied with a dielectric transition in the non-centrosymmetric phase of the crystal, making it a potential candidate to search for a new ferroelectric material in glycine family.

A hierarchical C-S-H/organic superstructure with high stiffness, super-low porosity, and low mass density

Herein, a hierarchical cementitious calcium silicate hydrate (C-S-H) superstructure with high Young's modulus, super-low porosity, and low mass density is reported. It has a very high Young's modulus at 47.5 GPa, three times higher than our reference synthetic C-S-H. Its specific surface area is merely 0.4509 m2/g, two orders of magnitude smaller than our reference synthetic C-S-H and the most common construction materials. In addition, the skeletal density of this composite is 1.96 g/cm3, much lower than C-S-H and hardened cement paste. In a density-Young's modulus diagram, this composite is located at the intersection of metals, ceramics, and polymers, approaching the carbon fiber region, implying lightweight and stiff characteristics. The cryogenic stability is also evaluated. It shows a satisfying applicability potential for cryogenic engineering with stable pore structure and nanoscopic mechanical properties. We confirm that the assembly of hierarchical C-S-H superstructure requires both hydrophilic amide and anionic carboxylic groups.

Super-Structured Wet-Adhesive Hydrogel with Ultralow Swelling, Ultrahigh Burst Pressure Tolerance, and Anti-Postoperative Adhesion Properties for Tissue Adhesion.

Wet-adhesive hydrogels have been developed as an attractive strategy for tissue repair. However, achieving simultaneously low swelling and high burst pressure tolerance of wet-adhesive hydrogels is crucial for in vivo application which remains challenges. Herein, a novel super-structured porous hydrogel (denoted as PVA/PAAc-N+ ) is designed via facile moisture-induced phase separation-solvent exchange process for obtaining porous polyvinyl alcohol (PVA) hydrogel as dissipative layer and in situ photocuring technology for entangling quaternary ammonium-functionalized poly(acrylic acid)-based wet-adhesive layer (PAAc-N+ ) with the porous surface of PVA layer. Benefitting from the ionic crosslinking between quaternary ammonium ions and carboxylate ions in PAAc-N+ wet-adhesive layer as well as the high crystallinity induced by abundant hydrogen bonds of PVA layer, the hydrogel has unique ultralow swelling property (0.29) without sacrificing adhesion strength (63.1kPa). The porous structure of PVA facilitates the mechanical interlock at the interface between PAAc-N+ wet-adhesive layer and tough PVA dissipative layer, leading to the ultrahigh burst pressure tolerance up to 493mm Hg and effective repair for porcine heart rupture; the PVA layer surface of PVA/PAAc-N+ hydrogel can prevent postoperative adhesion. By integrating ultralow swelling, ultrahigh burst pressure tolerance, and anti-postoperative adhesion properties, PVA/PAAc-N+ hydrogel shows an appealing application prospect for tissue repair.

Thermal decomposition kinetics and mechanisms of long alkyl chain ionic liquids with carboxylate anions

This work presents the synthesis and analysis of the thermal decomposition kinetics and mechanisms of long alkyl chain ionic liquids (ILs) with cations 1-decyl-3-methylimidazolinium ([C10MIM]+), 1-dodecyl-3-methylimidazolinium ([C12MIM]+), and 1-hexadecyl-3-methylimidazolinium ([C16MIM]+) and butanoate ([C3COO]−) and heptanoate ([C6COO]−) anions. The kinetics analysis was performed using the Kissinger-Akahira-Sunose isoconversional methodology. The results indicated that the carboxylate ILs are less thermally stable than their bromide analogues and the order of thermal stability was explained by the values of the kinetic parameters (Ea and lnA) and their variation with α. For most of the studied carboxylate ILs there was a considerable variation in Ea as the decomposition progressed, indicating multiple decomposition steps. The thermal decomposition mechanism was studied by analyzing the thermal degradation residue from 1H NMR spectroscopy.

Structure and Physico-Mechanical Properties of Polyelectrolyte Complexes Based on Sodium Carboxymethylcellulose Polysaccharide and Polyacrylamide

In this paper, the structure and physico-mechanical properties of films of polyelectrolyte complexes (PEC) based on sodium carboxymethylcellulose (Na-CMC) with linear polyacrylamide (PAA) have been studied. Polyelectrolyte complexes were obtained by mixing aqueous solutions of Na-CMC and PAA components in various ratios of components and pH of the medium. The structure of the obtained products was determined using IR spectroscopy and electron microscopy. IR spectra in the range 400–4000 cm-1 were recorded on NIKOLET Magna-560 IR and Specord-75IR spectrophotometers (Carl Zeiss, GDR). The mechanical properties of films of polyelectrolyte complexes were determined by stretching at a constant speed of movement of the lower clamp, 50 mm/min, on an Instron-1100 automatic dynamometer (England) at room temperature. IR spectroscopic data showed that polyelectrolyte complexes based on Na-CMC and PAA were stabilized due to the cooperative ionic bond between Na-CMC carboxylate anions (-COO-) and amine groups (-NH2) of polyacrylamide. It is shown that PEC films with an equimolar ratio of Na-CMC and PAA components have an increased value of mechanical strength (σр = 38 MPa), elastic modulus (Е = 73 MPa) and a minimum relative elongation (ε = 0.5%). And in excess of Na-CMC or PAA leads to a decrease in mechanical strength and elastic modulus, which is associated with a decrease in the frequency of intermolecular bonds. It has been ascertained that water-soluble polyelectrolyte complexes based on Na-CMC and PAA with increased strength properties can be obtained from solutions of components taken at an equimolar ratio of interacting components. By changing the ratio of components, properties such as mechanical strength, modulus of elasticity and elongation can be controlled. This can serve as one of the means of controlling the structure and properties of Na-CMC and PAA polyelectrolyte complexes. The regulation of the physico-mechanical properties of PEC films opens up wide opportunities for their use as a soil structure former in agriculture and water management and as the basis for soft drugs in pharmacy.

Lanthanum and some lanthanides 2,4-dichlorophenoxyactetates: Structure and luminescent properties

The exchange interaction of lanthanum and some lanthanides salts (neodymium, samarium, europium, gadolinium, terbium and dysprosium) with sodium salt of 2,4-dichlorophenoxyacetic acid (HL) in dimethylformamide medium produced lanthanum and lanthanide carboxylates. The compounds were studied by elemental and thermal analysis, infrared spectroscopy and X-ray structure analysis. It was found that the complexes form two isostructural series: [Ln2L6(DMF)3]∙Solv (Ln = La, Nd, Sm, Eu) and [LnL3(H2O)2]∙2DMF∙Solv (Ln = Gd, Tb, Dy). Both series have a one-dimensional polymer structure in which the central atoms are connected by bridging carboxylate anions. The crystal structures of the complexes have a branched network of noncovalent D-H…A and Cl…Cl interactions. An analysis of the photophysical properties of all compounds revealed a bright luminescence with a quantum yield up to 39.5 % and an excited state lifetime of 1330 μs for the europium polymer enhanced by 2,4-dichlorophenoxyacetate ligands.

Formation of Polyion Complex Aggregate Formed from a Cationic Block Copolymer and Anionic Polysaccharide.

Block copolymers (PmMn; P20M101 and P100M98) comprising poly(2-(methacryloyloxy)ethylphosphorylcholine) (PMPC, P) containing biocompatible phosphorylcholin pendants and cationic poly((3-acryloylaminopropyl) trimethylammonium chloride) (PMAPTAC, M) were synthesized via a controlled radical polymerization method. The degrees of polymerization of the PMPC and PMAPTAC segments are denoted by subscripts (PmMn). The mixture of cationic PmMn and anionic sodium chondroitin sulfate C (CS) with the pendant anionic carboxylate and sulfonate groups formed polyion complex (PIC) aggregates in phosphate-buffered saline. A charge-neutralized mixture of P20M101 with CS formed P20M101/CS PIC vesicles with a hydrodynamic radius (Rh) of 97.2 nm, zeta potential of ca. 0 mV, and aggregation number (Nagg) of 23,044. PMPC shells covered the surface of the PIC vesicles. The mixture of P100M98 and CS formed PIC spherical micelles with the PIC core and hydrophilic PMPC shells. The Rh, zeta potential, and Nagg of the PIC micelles were 26.4 nm, ca. 0 mV, and 404, respectively. At pH < 4, the carboxylate anions in CS were protonated. Thus, the charge balance in the PIC micelles shifted to decrease the core density owing to the electrostatic repulsions of the excess cations in the core. The PIC micelles dissociated at a NaCl concentration ≥0.6 M owing to the charge screening effect. The positively charged PIC micelles with excess P100M98 can encapsulate anionic dyes owing to electrostatic interaction.

Deep removal of dichloromethane using ionic liquids: Thermodynamic and molecular insights

In this work, the efficient capture of dichloromethane (DCM) with ionic liquids (ILs) was proposed and systematically investigated. The carboxylic acid-based anion and quaternary phosphonium cation were screened out, and on this basis the designed tetrabutylphosphonium hexanoate ([P4444][C5COO]) and tetrabutylammonium hexanoate ([N4444][C5COO]) ILs were finally synthesized. The results demonstrate that [P4444][C5COO] exhibits the optimal absorption performance (1400 mg·g−1 at 30 °C and 0.3 bar). Notably, the Henry's law constant for DCM in [P4444][C5COO] (3.02 Pa·m3·mol−1 at 25 °C) is the lowest among all solvents documented in the literature. The microscopic mechanism was explored by 1H NMR spectra, quantum chemical (QC) calculations and molecular dynamics (MD) simulations. The results suggest that anion plays a dominant role, while weak cation–anion interaction and large free volume of cations are conducive to the absorption of DCM. The proposed IL was considered as a promising alternative absorbent to achieve high absorption capacity, suitable physicochemical properties and excellent recyclability.

Plasmon induced decarboxylation of aromatic carboxylic acids on bipolar electrodeposited Au- and Ag-film monitored by SERS

This study delves into the intersection of plasmonics and catalysis, offering insights into tailoring nanoscale chemical reactions. Employing Surface Enhanced Raman Spectroscopy (SERS), we track the decarboxylation process of 4-mercaptobenzoic acid (4-MBA) and its isomers. Using a specially designed thin film platform of gold and silver, prepared via bipolar electrodeposition (BP-ED), we investigate the influence of laser-power, solution pH, and exposure duration. Decarboxylation predominantly occurs in alkaline pH environments, attributed to deprotonation. Notably, 2-MBA exhibits swift decarboxylation, even without alkaline conditions, likely due to its closer proximity to the nanostructured surface. The significance of the carboxylate anion (–COO–) is underscored, as experiments with ester forms of 2- and 3-MBA exhibit similar behavior. Additionally, experiments with linear chain thiocarboxylic acids highlight the necessity of a benzene ring for stable reaction intermediates. A key finding lies in the effectiveness of the bipolar electrodeposition technique for monitoring decarboxylation reactions across various compositions on a unified platform. This research sheds light on the potential of SERS in understanding chemical reactions near metal nanostructures, ultimately advancing our grasp of reaction pathways and the identification of new reactive species.

Zwitterionic polymers as high-performance coatings for hemoperfusion adsorbents and their chemisorption of protein-bound toxins through computational simulations

It remains a challenge for commercial hemoperfusion adsorbents to efficiently remove multiple protein-bound toxins in the clinical treatment of liver and kidney failure. Here, polystyrene divinylbenzene microspheres (PS-DVB) were surface-modified by poly(carboxybetaine methacrylate) (poly-CBMA) through controlled polymerization, named PCBMA. PS-DVB served as a supporting backbone and provided enormous specific surface, while a layer of the poly-CBMA aimed at efficiently removing various toxins and attaining better biocompatibility. After modification, the mesoporous analysis revealed a high specific surface area of 527 m2/g. More notably, compared with PS-DVB, PCBMA showed an 830%, 130%, and 26% increase in the adsorption capacity of p-cresol sulfate (PCS), indoleacetic acid (IAA), and bilirubin (BR), respectively, in the presence of 40 g/L bovine serum albumin. Further molecular dynamics simulations and DFT calculations showed that poly-CBMA exhibited stronger intermolecular forces for all three toxins. The hydrogen bonds formed between the negatively charged carboxylate ions from PCBMA contributed to its excellent adsorption performance. This study not only provides a new idea to study the adsorption mechanism of toxins by zwitterionic polymers but also demonstrates the promising application of microspheres modified by zwitterionic polymers in clinical hemoperfusion therapy.

Comparative analysis of EPR parameters in X-, Q-, W-bands for exchange-coupled copper(II) dimers

In this work, binuclear, polymeric binuclear, and molecular 16-nuclear copper(II) complexes [Py2Cu2(Piv)4] (1), {[(EtOH)2Cu2(Chda)2]·EtOH}n (2) and [K2(H2O)6(Py)8Cu16(OH)2(Chda)16]·EtOH·MeCN·3H2O (3) (piv is pivalate, Chda is 1,1-cyclohexanediacetate) have been studied by EPR spectroscopy in the X-, Q- and W-bands. Polynuclear copper(II) complexes are formed by binuclear fragments bonded by bridging carboxylate anions. In compounds 1–3, only pairwise interactions between copper ions are observed, despite the fact that in 2 and 3 there may be additional interactions between copper ions belonging to different dimers.

Chemical fixation of carbon dioxide into cyclic carbonates by multi-hydroxyl carboxylic acid ionic liquids under atmospheric pressure

Transformation CO2 to valuable chemical products is a favorable way for reducing CO2 emissions. However, the developed methodologies usually suffer from harsh reaction conditions. In this work, a series of ionic liquids featuring anions with multiple hydroxyl carboxylic acid moieties (MHCAIL1–5) were facilely synthesized, which exhibiting remarkable catalytic activity in conversion CO2 and various epoxides to cyclic carbonates without metal, co-catalysts, solvents and halogen under atmospheric pressure. The hydroxyl groups and carboxylate anion in ILs serve as hydrogen bond donors and nucleophiles to activate epoxides, ensuring exceptional conversion. Notably, the catalytic performance of MHCAIL-5 resulted in 99 % conversion of epichlorohydrin and 99 % selectivity of chloropropene carbonate at 80 ℃ within 3 h at atmospheric pressure. Proposed mechanism has been postulated according to NMR, FT-IR and Mass spectrometry results. Furthermore, due to the high thermodynamic and chemical stability of ionic liquids, this catalytic system demonstrated excellent recyclability.

Prediction Of Carboxylic Acid Toxicity Using Machine Learning Model

Carboxylic acids are organic compounds characterized by the presence of a carboxyl functional group capable of donating a proton and forming carboxylate ions in aqueous solutions. The carboxylic acid has widely been used in in manufacturing and medical applications. The rapid growth in carboxylic acid has established a need to predict its toxicity. The purpose of this paper to build predictive toxicity of carboxylic acid models by using five molecular descriptors (refractive index, The octanol/water partition coefficient (log P), acid dissociation constant (pKa), density, and dipole moment) through Machine Learning algorithms. The accuracy of the Machine Learning algorithm was determined by using three different types of models which are Decision Tree, Random Forest and k-Nearest Neighbour (k-NN). Among the machine learning algorithms used, we have determined that the decision tree is the best model for predicting the toxicity of carboxylic acid. This finding demonstrates that the decision tree model exhibits an acceptable level of performance in predicting toxicity within the field of toxicology.

Synthesis and characterization of polystyrene-b-poly(vinyldipicolinic acid) pH-responsive core-shell nanoparticles

The self-assembly of a new series of amphiphilic polystyrene-b-poly(4-vinyldipicolinic acid) PS-b-PVDPA diblock copolymers in aqueous solution is reported in order to obtain core–shell nanoparticles composed of a PS core and a PVDPA shell. Diblock copolymers were synthesized by Supplemental Activation Reducing Agent-Atom Transfer Radical Polymerization (SARA-ATRP) with a degree of polymerization (DP) of the PS block in the range 112–260 and a DP of PVDPA block of 10, 30 or 50. Anionic latex nanoparticles of PS-b-PVDPA were prepared by solvent displacement methods. All the nanoparticle suspensions had a narrow size distribution (0.014 ≤ PDI ≤ 0.144) with zeta potential in the range −27 mV to −38 mV indicating electrostatic repulsions due to carboxylate anions and therefore high colloidal stability. DLS was used to determine nanoparticle size, with SEM and TEM used to determine and confirm both size and spherical shape. All three methods found the size for these nanoparticles to be in the range 75–120 nm. Using fluorimetry and DLS methods, Critical Aggregation Concentration (CAC) for each type of nanoparticle was determined to be within the range of 33–69 mg/L. Micelles were pH-responsive with stability in aqueous conditions for pH > 3.5. Micelles were stable at pH 5.5 for up to 40 days and at temperature up to 60 °C.

Understanding the role of water quality in separation of rare earth minerals from iron oxide minerals in a flotation circuit

In many mineral processing plants, using saline water has become necessary to improve water efficiency. However, the dissolved ions in the water such as Ca2+ and Mg2+ may have a significant negative impact on the flotation of RE (rare earth) minerals due to the chemical reaction with flotation reagents used in RE flotation. Although some researchers investigated flotation performance of pure rare earth minerals, there is no study investigating the role of water quality in the separation of rare earth minerals from iron oxide minerals in a flotation circuit. This study focused on investigating the effect of divalent cations like Ca2+ and Mg2+ on the flotation of RE minerals using a fatty acid collector and Na2SiO3 depressant. The results showed that the presence of Ca2+ and Mg2+ decreased the selectivity and recovery of RE minerals due to the formation of insoluble calcium and magnesium carboxylate, leading to the reduced residual collector concentration. Furthermore, the divalent cations acted as a bridge between the oxygen atoms of the adsorbed SiO32− and carboxylate ions, resulting in increased adsorption of fatty acid collector ions and higher recovery of FeO. Rheological measurements also revealed that the presence of Ca2+ and Mg2+ significantly increased the flotation pulp viscosity, which could be attributed to the reduced repulsive forces between particles due to the compression of electrical double layer. This study provides valuable insights into the mechanisms underlying the effects of Ca2+ and Mg2+ on RE mineral flotation.