Apatite Surface Research Articles

Activation mechanisms of apatite by purifying reagent polyacrylamide for backwater from mineral processing in flotation of rare earths

This study revealed activation mechanisms of apatite by polyacrylamide (PAM) during flotation of rare earth minerals in Bayan Obo Ore. This activation leads to high phosphorus content in rare earth concentrate. Ultraviolet (UV) absorption measurements show that adsorption of PAM on the surfaces of apatite and rare earths follows a pseudo-second-order reaction kinetic model. The isothermal adsorption process follows the Freundlich adsorption model, indicating that the adsorption of PAM on apatite is a multi-layer, non-uniform process, that is, physical and chemical adsorption occurs simultaneously. The measured zeta potential shows that under weakly alkaline conditions, amide groups with a negative charge are adsorbed on the surface of apatite, increasing the electronegativity, so that the potential is shifted negatively; however, the negative shift of the potential on the surface of rare earths is insignificant. Fourier transform infrared (FT-IR) test and X-ray photoelectron spectroscopy (XPS) results imply that PAM is chemically adsorbed on the surface of apatite, while 506E undergoes stronger chemical adsorption than PAM on the surface of rare earth minerals. It is found that multi-layer, non-uniform adsorption of PAM combining physical and chemical adsorption occurs on the surface of apatite and the process is dominated by physical adsorption: the adsorption of PAM on surfaces of apatite is stronger than that on the surface of rare earth minerals. Such adsorption activates the apatite, causing it to float during the flotation of rare earths, which is the reason for the high phosphorus content in the rare earth concentrate.

Flotation separation of apatite and calcite using gum arabic as a depressant

Flotation separation of apatite and calcite has always been difficult because of their similar physiochemical properties. To realize the flotation separation of the two minerals, many inorganic depressants are usually used, which contaminate the environment. In this study, the behavior of the polymer molecule gum arabic (GA) as a depressant of calcite in the apatite flotation was investigated by the pure mineral flotation experiments, and the mechanism was discussed by the contact angle measurement, adsorption tests, Fourier transform infrared (FTIR) spectroscopy and X–ray photoelectron spectroscopy (XPS). The flotation results showed that GA had a significant depressive effect on calcite but not on apatite. The separation of apatite from calcite was realized by adding 50 mg/L of the depressant GA followed by 0.5 × 10−4 mol/L of the collector sodium oleate (NaOl) at pH 7–11. The contact angle measurements showed that GA considerably enhanced the hydrophilicity of the calcite surface but had no significant effect on that of the apatite surface. The adsorption tests showed that the amount of GA adsorbed on the calcite surface was obviously greater than that on the apatite surface, indicating that calcite had a stronger affinity for GA. The FTIR and XPS analysis indicated that GA was adsorbed weakly on the apatite surface, but strongly adsorbed on the calcite surface. After GA was strongly adsorbed on the calcite surface, the abundant free –OH and –COOH groups in the GA molecule made the calcite surface more hydrophilic. Subsequently, it was hard for NaOl to be adsorbed on the calcite surface due to the reduction of active site calcium as well as the steric hindrance and electrostatic repulsion effect of GA on the NaOl molecule, which resulted in the selective depression of calcite in the apatite flotation.

Influence of surface dissolution on reagents’ adsorption on low-grade phosphate ore and its flotation selectivity

A preliminary study was conducted on the Hallimond tube to find routes for the direct flotation of fluorapatite. Carboxymethylcellulose-sodium oleate and sodium alginate-sodium oleate were the most promising depressant-collector combinations. Apatite recovery exceeded 95%. Conversely, replication of these findings in the mechanical flotation cell proved to be different. The results show a flotation of the calcite, while the fluorapatite remains in the tailings. Grades of 27.63% P2O5 with a recovery of 69.9% and 28.22% P2O5 with a recovery of 73.93% were obtained in the non-floated fraction using 1500 g/t of sodium oleate and 25 g/t of sodium alginate and carboxymethylcellulose as depressants, respectively.The effects of metal ions on the flotation behavior of fluorapatite, calcite, and quartz were investigated through micro-flotation tests and bench-scale flotation experiments. The findings were further elucidated by dissolution study, zeta potential measurements, and FTIR analyses. The results demonstrated that pulp water containing large amounts of Ca2+, Mg2+, and Fe3+ directly influences the performance of apatite flotation. Fluorapatite recovery substantially dropped from 97.27% in deionized water, reaching values below 11.11% at alkaline pH. These ionic species interfere in the interfacial processes and perturb selective adsorption. Ca2+ ions favor the precipitation of CaCO3, hence forms a coating on the apatite surface, rendering it unavailable for NaOL chemisorption. Ca2+, Mg2+, and Fe3+ complex with the reagents and the precipitates adsorb onto the minerals’ surfaces, impairing their floatability. Also, their presence activates the quartz surface, increasing its recovery. Zeta potential curves overlap, implying a similar build-up of negative charge on the three mineral surfaces. The most intense peaks in FTIR spectra indicated more adsorption, suggesting that the detrimental species Ca2+, Mg2+, Fe3+ must be involved in adsorption mechanisms and explain flotation trend change.

Effect of Al3+ and Mg2+ on the flotation of fluorapatite using fatty- and hydroxamic-acid collectors – A multiscale investigation

Fluorapatite flotation is influenced by the dissolved lattice metal ions. Al3+ and Mg2+ from the associating gangue minerals influence the adsorption of collector molecules onto the fluorapatite surface during flotation. Hence, unveiling new insights on such interactions in the context of froth flotation at an atomic level paves the way for improving flotation selectivity. An original multiscale approach has been developed involving flotation experiments, electro-kinetic and adsorption density measurements, X-ray photoelectron spectroscopy studies, and density functional theory simulations. Fatty acid establishes an enhanced interaction with the bare apatite surface compared to the hydroxamates. Na+ counter-ion contributes to the adsorption of fatty acid on bare apatite. Both Al3+ and Mg2+ ions are beneficial for the adsorption of fatty acid, thereby the fluorapatite flotation. For octanohydroxamic acid, the presence of Al3+ results in a stronger collector-apatite interaction, and therefore an enhanced flotation. For fatty acid and hydroxamates, adsorption of Mg2+ leads to an improved collector-apatite interaction. Benzohydroxamic acid is more vigorously adsorbed than octanohydroxamic acid in the presence of Mg2+. Fatty acid establishes a stronger interaction with bare and Al3+/Mg2+-treated fluorapatite, as opposed to hydroxamates. Mg2+ is more favorable than Al3+ in fluorapatite flotation using both fatty acid and hydroxamates.

Double roles of sodium hexametaphosphate in the flotation of dolomite from apatite

Sodium hexametaphosphate (SHMP), as a common flotation agent, is widely used in various mineral processing. In this study, effects of SHMP on the flotation of fine apatite and dolomite were investigated. It was proved to play a role as depressant for both of the minerals by single and artificially mixed minerals flotation, while the effective improvement of apatite concentrates under low amount SHMP addition demonstrated that it worked as another unknown role. Solution chemistry analyses, zeta potential measurements, X-ray photoelectron spectroscopy (XPS) and DLVO calculation were carried out to systematically investigate the corresponding mechanism of SHMP effect in the flotation process. DLVO theory calculation verified the dispersion function of SHMP for mineral particles. Hence, SHMP played double roles in the flotation process. On the one hand, it worked as a depressant by increasing the hydrophilicity of apatite, through promoting the formation of CaHPO4 and Ca(H2PO4)2 on the apatite surface. On the other hand, it acted as a dispersant by increasing the total interaction energy between apatite and dolomite mineral particles, enhancing the dispersion of dolomite and adhesion of agents and bubbles to the minerals. Both roles were favorable for the separation of mixed minerals in flotation.

Adhesion evaluation of the Rhodococcus opacus strain on an apatite surface

Adsorption of microorganisms and/or their different components onto a mineral surface would modify the surface characteristics of the mineral. Thus, this investigation evaluated the adsorption capacity of the Rhodococcus opacus strain onto an apatite surface. Zeta potential and contact angle measurements of the mineral showed dislocations of the values after interaction with the microorganism. The maximum adsorption density reached was 24.10 mg of bacterial cells per gram of mineral using a biomass concentration of 400 mg/L. The experimental data were linearly fitted by the Freundlich model and the adsorption density as a function of time was linearly fitted by the pseudo-second order kinetic equation. The results showed that the bacterial strain has affinity for the apatite surface and ability to make it hydrophobic.

Binding mechanism and binding free energy of amino acids and citrate to hydroxyapatite surfaces as a function of crystallographic facet, pH, and electrolytes

Hydroxyapatite (HAP) is the major mineral phase in bone and teeth. The interaction of individual amino acids and citrate ions with different crystallographic HAP surfaces has remained uncertain for decades, creating a knowledge gap to rationally design interactions with peptides, proteins, and drugs. In this contribution, we quantify the binding mechanisms and binding free energies of the 20 end-capped natural amino acids and citrate ions on the basal (001) and prismatic (010)/(020) planes of hydroxyapatite at pH values of 7 and 5 for the first time at the molecular scale. We utilized over 1500 steered molecular dynamics simulations with highly accurate potentials that reproduce surface and hydration energies of (hkl) hydroxyapatite surfaces at different pH values. Charged residues demonstrate a much higher affinity to HAP than charge-neutral species due to the formation of superficial ion pairs and ease of penetration into layers of water molecules on the mineral surface. Binding free energies range from 0 to −60 kJ/mol and were determined with ∼ 10% uncertainty. The highest affinity was found for citrate, followed by Asp(-) and Glu(-), and followed after a gap by Arg(+), Lys(+), as well as by His(+) at pH 5. The (hkl)-specific area density of calcium ions, the protonation state of phosphate ions, and subsurface directional order of the ions in HAP lead to surface-specific binding patterns. Amino acids without ionic side groups exhibit weak binding, between −3 and 0 kJ/mol, due to difficulties to penetrate the first layer of water molecules on the apatite surfaces. We explain recognition processes that remained elusive in experiments, in prior simulations, discuss agreement with available data, and reconcile conflicting interpretations. The findings can serve as useful input for the design of peptides, proteins, and drug molecules for the modification of bone and teeth-related materials, as well as control of apatite mineralization.

The adsorption mechanism of synergic reagents and its effect on apatite flotation in oleamide-sodium dodecyl benzene sulfonate (SDBS) system

The usage of synergic reagents plays vital role in the effective flotation of phosphate ore. In this paper, the adsorption mechanism of synergic reagents and its effect on apatite flotation in oleamide-sodium dodecyl benzene sulfonate (SDBS) system were investigated via micro-flotation experiment, Zeta-potential determination, X-ray photo-electron spectroscopy (XPS), and Time-of-flight secondary ion mass spectrometry (ToF-SIMS). Experimental research represented that a highest recovery rate of 97.09% could be obtained when a mixed collector dosage of 4 × 10−4 mol/L was used with a molar ratio of oleamide to SDBS of 2:1 at pH = 9.0, and the recovery could be improved by ~4.87% comparing with the theoretical recovery rate of single collector. Results of Zeta potential and XPS indicated that the chemisorptions of C17H33CONH−, (C17H33CONH2)m and sulfonate species originated from the mixed collector onto apatite surfaces occurred. More importantly, the adsorption of amide could be reinforced in the presence of SDBS, and the N atomic concentration increased from 1.23% to 1.66%. The results of ToF-SIMS further confirmed that the normalized peak intensities of C4H5+ and C4H7+ for apatite-oleamide-SDBS sample showed a statistically increase comparing with corresponding results of apatite-oleamide sample, while the normalized peak intensities of C6H4+ presented an opposite trend comparing with that of apatite-SDBS sample. The whole thickness of the formed hydrophobic species on the apatite surfaces was approximately 40.29 nm. The synergistic effects of mixed collector were mainly attributed to the improvement of solubility and dispersion and the decrease in critical micelle concentration of oleamide in the presence of SDBS, which provided easy access to the interaction between C17H33CONH−, (C17H33CONH2)m and apatite surfaces. The results provided a new path for apatite flotation, and reinforced the theoretical basis for flotation technique of phosphate ore.

Flotation separation of scheelite and apatite by polysaccharide depressant xanthan gum

Tungsten is a crucial rare metal with extensive application in modern industries and scheelite is the major resource for tungsten production. In this work, xanthan gum (XG), a non-toxic, environmentally friendly polysaccharide, was explored as a depressant of apatite during the scheelite flotation. The results of single mineral flotation and artificial mixed minerals flotation showed that XG exhibited efficient selective depressive effect on apatite rather than on scheelite. The Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) analysis indicated that the chelation action between the –COO– groups and the Ca on apatite surface was responsible for XG chelating adsorption. The firm XG chemisorption on apatite surface hindered subsequent sodium oleate (NaOl) chemisorption. Due to fewer available surface Ca sites and intenser anions group electronegativity on scheelite, the XG adsorption on scheelite surface was weak and it exhibited little effect on following NaOl chemisorption. As a result, the flotation separation of scheelite from apatite was achieved using XG as depressant and NaOl as collector.

Metadynamics Simulations of the pH-Dependent Adsorption of Phosphoserine and Citrate on Disordered Apatite Surfaces: What Interactions Govern the Molecular Binding?

Both citrate ions and proteins with phosphorylated side chains are believed to play central roles in bone mineralization. Using metadynamics simulations, we elucidated the pH-dependent surface bind ...

Synergetic effect of cottonseed fatty acid salt and nonionic surfactant NP-4 in the froth flotation of siliceous-calcareous phosphate rock

Fatty acid is constricted when used in phosphate flotation alone as a collector due to its high reagent consumption and low separation efficiency. When fatty acids are mixed with other surfactants, the flotation performance can be greatly enhanced because of the synergetic effect, and therefore, widely adopted in industry. The cottonseed fatty acid salt (CSFA) and nonionic surfactant of NP-4 mixture was used in the upgrading of phosphate ores in this study. Batch flotation tests, droplet size distribution of CSFA, zeta potential measurements and X-ray photoelectron spectroscopy were conducted to elucidate the synergistic mechanism between the two surfactants. It was found that NP-4 improved the emulsification of CSFA and can reduce the adverse effect of calcium ion concentrations, which may otherwise be detrimental to CSFA. When mix CSFA with 10 wt% NP-4, an optimum separation between apatite and dolomite or quartz and lower reagent consumption were observed in flotation of siliceous-calcareous phosphate ore. With the aid of zeta potential measurement and XPS analysis, the adsorption behaviors of CSFA and NP-4 on the surfaces of apatite, dolomite and quartz was revealed. NP-4 enhanced the adsorption of CSFA on the surface of apatite and dolomite but decreased its adsorption on quartz, indicating that CSFA and NP-4 were co-adsorbed on surfaces of apatite and dolomite whereas in a competitive adsorption on the quartz surfaces.

Application of a fungal cellulase as a green depressant of hematite in the reverse anionic flotation of a high-phosphorus iron ore

In this study, a fungal cellulase enzyme was applied to improve the selective separation of apatite from hematite during the reverse anionic flotation of a high-phosphorus iron ore. Bench-scale flotation tests were conducted on pure hematite and apatite minerals, their artificial mixture, and a high-phosphorus iron ore sample, using oleic acid as a collector. Flotation tests on single minerals showed that cellulase was a good depressant of hematite, but had no depressing effect on apatite at pH 10. The phosphorus content in the concentrate product of the flotation of artificially mixed pure minerals was reduced from 1.96% to 0.03%, with iron grade and recovery of 64.15% and 94.74%, respectively, using 4x10−5 mol/L oleate and 0.02% cellulase at pH 10. By applying the optimum separation conditions to the flotation of a natural high-phosphorus iron ore, the phosphorus content in the concentrate was reduced from 0.84% to 0.19% at an iron recovery of 67.85%. The mechanism of the cellulase depressing effect was investigated through Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) analyses. The results showed that cellulase enzyme was adsorbed on the surfaces of both minerals; however, the depressing effect was significant in case of hematite but not apatite. This might be attributed to the coverage of apatite surface with a close-packed layer of oleate molecules, which made the surface of apatite hydrophobic enough to counter the polarity induced upon cellulase adsorption.

Novel biocomposite based on functionalized poorly crystalline apatite and chitosan: A physicochemical evaluation

The lack of the required mechanical strength and adequate biodegradation rate of calcium phosphate materials constitutes the most relevant drawback prohibiting their use for orthopaedic applications. One of the promising strategies to overcome this intrinsic limitation is the functionalization of these materials through the combination with specific functional groups. In this study, we investigated APTES (3-aminopropyl-triethoxy-silane) functionalization of a poorly crystalline apatite (PCA) and its further combination for the first time to chitosan (CS) to elaborate PCA-APTES-CS functionalized composite material. XRD patterns of the elaborated materials exhibit broad peaks typical of poorly crystalline apatite. FTIR spectroscopy showed, in addition to the PCA characteristic bands, bands assigned to silane alkyl groups and evidenced the success of functionalization process. The TGA analysis confirmed the attachment of 8 wt% of APTES and 3 wt% of chitosan within the composite. SEM microscopy and EDX silicon mapping demonstrated a homogeneous silane presence on functionalized apatite surface and showed that chitosan enveloped the functionalized apatite particles surface. The elaborated PCA-APTES-CS functionalized composites exhibited compressive strength similar to the spongy bone. The functionalized biocomposite will be investigated as potential biomaterial for orthopedic application.

The selective adsorption of xanthan gum on dolomite and its implication in the flotation separation of dolomite from apatite

In this work, xanthan gum (XG) was exploited as a novel dolomite depressant in the flotation separation of apatite from dolomite in sodium oleate system. The flotation performances and adsorption mechanism of XG towards apatite and dolomite were studied through flotation tests, adsorption capacity measurements, micro-heat tests, atoms density calculations and surface characterizations. Flotation results revealed that XG exhibited strong depression effect on dolomite but barely influenced the flotation of apatite. The results of zeta potential, infrared spectroscopy analysis, adsorption capacity measurements and micro-heat tests proved that XG trended to adsorb on dolomite other than apatite, which hindered the adsorption of NaOL on dolomite and rendered the surface hydrophilic. Atom density calculations indicated that the preferential adsorption of XG on dolomite was due to much more dense and active Ca sites on dolomite surface than that of apatite. XPS results suggested that XG was strongly adsorbed on dolomite surface by means of chelation between COOH or OH groups within XG and Ca sites on dolomite, while it was weakly adsorbed on apatite by hydrogen bonding between OH groups within XG and F atoms on apatite surface.

Bioactive glasses and electrospun composites that release cobalt to stimulate the HIF pathway for wound healing applications

BackgroundBioactive glasses are traditionally associated with bonding to bone through a hydroxycarbonate apatite (HCA) surface layer but the release of active ions is more important for bone regeneration. They are now being used to deliver ions for soft tissue applications, particularly wound healing. Cobalt is known to simulate hypoxia and provoke angiogenesis. The aim here was to develop new bioactive glass compositions designed to be scaffold materials to locally deliver pro-angiogenic cobalt ions, at a controlled rate, without forming an HCA layer, for wound healing applications.MethodsNew melt-derived bioactive glass compositions were designed that had the same network connectivity (mean number of bridging covalent bonds between silica tetrahedra), and therefore similar biodegradation rate, as the original 45S5 Bioglass. The amount of magnesium and cobalt in the glass was varied, with the aim of reducing or removing calcium and phosphate from the compositions. Electrospun poly(ε-caprolactone)/bioactive glass composites were also produced. Glasses were tested for ion release in dissolution studies and their influence on Hypoxia-Inducible Factor 1-alpha (HIF-1α) and expression of Vascular Endothelial Growth Factor (VEGF) from fibroblast cells was investigated.ResultsDissolution tests showed the silica rich layer differed depending on the amount of MgO in the glass, which influenced the delivery of cobalt. The electrospun composites delivered a more sustained ion release relative to glass particles alone. Exposing fibroblasts to conditioned media from these composites did not cause a detrimental effect on metabolic activity but glasses containing cobalt did stabilise HIF-1α and provoked a significantly higher expression of VEGF (not seen in Co-free controls).ConclusionsThe composite fibres containing new bioactive glass compositions delivered cobalt ions at a sustained rate, which could be mediated by the magnesium content of the glass. The dissolution products stabilised HIF-1α and provoked a significantly higher expression of VEGF, suggesting the composites activated the HIF pathway to stimulate angiogenesis.

Surface distribution of heterogenous clathrin assemblies in resorbing osteoclasts

Osteoclasts seeded on either glass coverslips or apatite pellets have at least two morphologically distinct substrate adhesion sites: actin-based adhesion structures including podosome belts and sealing zones, and adjacent clathrin sheets. Clathrin-coated structures are exclusively localized at the podosome belts and sealing zone, in both of which the plasma membrane forms a tight attachment to the substrate surface. When cultured on apatite osteoclasts can degrade the apatite leading to the formation of resorption lacunae. The sealing zone divides the ventral membrane into different domains, outside and inside of the sealing zones. The former facing the smooth-surfaced intact apatite contains relatively solitary or networks of larger flat clathrin structures; and the latter, facing the rough-surfaced degraded apatite in the resorption lacunae contain clathrin in various shapes and sizes. Clathrin assemblies on the membrane domain facing not only a resorption lacuna, or trails but also intact apatite indeed were observed to be heterogeneous in size and intensity, suggesting that they appeared to follow variations in the surface topography of the apatite surface. These results provide a detailed insight into the flat clathrin sheets that have been suggested to be the sites of adhesion and mechanosensing in co-operation with podosomes.

Studies on rhenium (Re) solubility and heat capacity measurements onCa10-xRex(PO4)6(OH)2±δ, x= 0 to 0.7for radwaste immobilization

Rhenium substituted Ca-hydroxy apatite (Ca10-xRex(PO4)6(OH)2±δ, x = 0−0.7) was synthesized by solid state reaction and characterized by XRD, Raman and TG-DTA analysis.Results show that the solubility limit of Re is below 5 mol %; above whichCa3(PO4)2 phase was separated out. In this study, Re is used as surrogate for technetium (Tc) which does not occur in nature. The incorporation and distribution of Re in Ca-hydroxy apatite surface was investigated by scanning electron microscopy (SEM) EDX. The prevalence of constituent elements was further examined by energy dispersive X-ray analysis (EDX) and neutron activation analysis (NAA). The heat capacity (Cp) of the compositions was measured by differential scanning calorimetry (DSC) at 298−800 K for the first time. The Cpvalue of Re substituted compositions (0.84-1.07 JK-1 g−1) was found to be higher than the pristine Ca-hydroxyapatite (0.77-1.02 JK−1 g−1).Thermodynamic functions of the compositions were derived by using the measured Cp values.

Employing sulfur–phosphorus mixed acid as a depressant: a novel investigation in flotation of collophanite

ABSTRACT Inorganic acids (sulfuric acid (H2SO4) or phosphoric acid (H3PO4)) are generally employed as depressants in the reverse flotation of collophanite to separate apatite from dolomite. In this study, the flotation performance of a collophanite ore was studied, employing H2SO4, H3PO4, and a sulfur–phosphorus mixed acid as the depressants. The flotation tests revealed that the sulfur–phosphorus mixed acid could depress the apatite effectively. A high-quality concentrate with P2O5 content of 28.4 wt% and MgO content of 0.95 wt% was obtained, the corresponding P2O5 recovery of which was 85.0%. Furthermore, the separation mechanism of apatite and dolomite was clarified by zeta potential measurements, solution chemistry analysis and X-ray photoelectron spectroscopy (XPS). Within the pH range of 4.0–7.0, the zeta potentials of apatite were negative while those of dolomite were positive in the presence of all the three acid-depressants. The addition of sodium oleate made the potentials of both minerals to a more negative position. However, the potential shifts of dolomite were much more significantly negative than apatite when H2SO4 or H3PO4 was used. It indicated a greater absorption of sodium oleate on the surface of dolomite than apatite, which contributed to a more widen hydrophobicity gap between the surfaces of apatite and dolomite. SO4 2− and H2PO4 −, not H+ or Cl−, were founded to be the pivotal ions for depressing. XPS analyses illustrated that the simultaneous additions of H2SO4 and H3PO4 as depressants were beneficial to the formation of CaHPO4 and CaSO4 on the surface of the apatite, which were harmful for the adsorption of sodium oleate, making the depressing effect more remarkable and result in a better separation of dolomite from apatite. It performed much more efficiently in collophane ore flotation when H3PO4 and H2SO4 were used corporately as a combined depressant than when they were used separately.

Apatite fission-track dating by LA-Q-ICP-MS imaging

Obtaining accurate and precise apatite fission-track (AFT) ages depends on the availability of high-quality apatite grains from a sample, ideally with high spontaneous fission-track densities (c. >1.105 tracks.cm−2). However, many natural samples, such as bedrock samples from young orogenic belts or low-grade metamorphic samples with low U contents yield low spontaneous fission-track densities. Such apatites must be counted to avoid biasing the resultant FT age. AFT dating employing LA-Q-ICP-MS spot ablation works very well for grains with high spontaneous fission-track densities. This approach allows detection of potential U zoning, while also removing the need for an irradiation step and facilitating simultaneous acquisition of U-Pb and trace element data. The LA-Q-ICP-MS spot ablation thus offers several advantages compared to the External Detector Method (EDM). However, the spot ablation approach requires the counted area to mimic exactly the site and size of the laser spot, which for grains with low spontaneous fission-track densities (<105 tracks.cm−2), implies fewer track counts and impairs the precision of the resultant AFT age. Here we present an alternative approach to LA-Q-ICP-MS spot analysis of low fission-tracks density grains by generating a U distribution (238U/43Ca) map of the entire apatite surface by LA-Q-ICP-MS elemental mapping, which enables characterization of U zonation. The Monocle plugin for the Iolite LA-ICP-MS data reduction software is used to display elemental maps and extract mean 238U/43Ca values of the same area counted for the fission-tracks. A typical grain-mapping session takes <5 h to map 80 grains. The method was employed on the Durango and Fish Canyon Tuff apatite reference materials, six bedrock apatite samples with low fission-track densities (≤1.105 track.cm−2), and one bedrock apatite sample with high fission-track density (>1.106 track.cm−2) to assess the precision and accuracy of our approach. Most apatite samples investigated here were previously dated by the EDM or the LA-Q-ICP-MS ablation spot method. The AFT grain-mapping ages agree with previously published EDM or LA-Q-ICP-MS spot ablation ages at the 2σ level. For each apatite sample, we simultaneously acquired U-Pb age and trace element data (Mn, Sr, La, Ce, Sm, Eu, Gd, Lu); here again the data agree with literature constraints (when available) within uncertainties. The mapping approach is therefore a practical solution to low-temperature thermochronology studies facing apatite grains with low spontaneous fission-track densities, while also facilitating investigation of the spatial relationships between thermo- and geochronometric ages and grain chemistry.

Differential adsorption of hydrolytic polymaleic anhydride as an eco-friendly depressant for the selective flotation of apatite from dolomite

Differential adsorption of surfactants (e.g., collectors and depressants) on the minerals plays a key role in mineral flotation through selectively altering the surface wettability of minerals. In this study, to improve the removal efficiency of dolomite from apatite by direct flotation, hydrolytic polymaleic anhydride (HPMA) was introduced as an eco-friendly depressant for dolomite. The depressing performance and adsorption mechanism of HPMA on the dolomite and apatite surfaces were studied through flotation tests and surface analyses. Flotation results demonstrated that HPMA displayed an intense depressing impact on the dolomite flotation while affected slightly the apatite flotation. Surface wettability analysis indicated that the selective adsorption of HPMA at the dolomite/water interface declined significantly the dolomite hydrophobicity even in the case of sodium oleate (NaOl). Surface adsorption detection and zeta-potential results demonstrated that HPMA had a much stronger interaction with dolomite than apatite, resulting in the intense adsorption of HPMA onto dolomite. Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) further evidenced that compared with apatite, the strong interaction between HPMA and magnesium sites of dolomite enhanced the chemisorption of HPMA onto dolomite surface, which prevented strongly NaOl adsorption onto dolomite. As a result, dolomite was strongly depressed by HPMA to achieve the effective recovery of apatite. Based on these findings, HPMA can be potentially utilized as an eco-friendly and high-selectivity depressant for removing dolomite from apatite.