Solution Chemistry Analysis Research Articles

Structural modification of hydroxamic acid collectors to enhance the flotation performance of malachite and associated mechanism

A series of N-hydroxy-N-aryl amide collectors, including N-hydroxy-N-benzyl acetamide (NHNBA), N-hydroxy-N-benzyl butyramide (NHNBB), N-hydroxy-N-phenyl acetamide (NHNPA) and N-hydroxy-N-phenyl butyramide (NHNPB), was designed in this study and employed for the first time in malachite flotation. Flotation tests conducted in the absence of frothers and activators revealed that the N-hydroxy-N-aryl amide collectors realized effective separation of malachite from calcite and quartz, which could not be readily achieved with benzohydroxamic acid (BHA). NHNBB exhibited optimal collection ability and selectivity for malachite over calcite and quartz. Quantum chemistry calculations, solution chemistry analysis and FTIR spectroscopy and XPS analyses revealed that in addition to electrostatic attraction, NHNBB possibly interacted with the malachite surface via chemisorption by forming five-membered-ring complexes, resulting in an efficient collection capacity for malachite.

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.

New insights for improving ilmenite flotation via surface modification with lead ions

In order to further investigate the mechanism of lead ions in activation ilmenite flotation, the adsorption behaviour of lead ions on ilmenite surface was deeply illustrated using the combination of adsorption amount, zeta potential, inductively coupled plasma mass spectrometry (ICP), energy-dispersive X-ray spectroscopy Mapping (EDS-Mapping), and X-ray photoelectron spectroscopy (XPS) in this study. The results revealed that lead ions activated the ilmenite flotation by promoting the adsorption of sodium oleate. This promotion impact could be attributed to the positive shift of surface charge and the increase in surface active sites after lead adsorption. The changes transferred the adsorption mode of sodium oleate on ilmenite surface into electrostatic adsorption and chemisorption involving double active site (Pb, Fe). The Pb(OH)+ was certified as the main active species on activating ilmenite flotation through the analysis of lead adsorption amounts and solution chemistry. Furthermore, the EDS-Mapping and XPS high-resolution spectra analysis evidenced that the Pb(OH)+ adsorbed onto the surface sites of O, Fe, and Ti on ilmenite surface by resorting the bridging action of the O atom.

Surface chemistry considerations of gangue dissolved species in the bastnaesite flotation system

Inefficient flotation of bastnaesite remains a challenge in the production of rare earth elements. This study aimed to investigate the dissolution and adsorption behaviour of species that are commonly released into bastnaesite flotation pulp from Ca/Ba-bearing gangue minerals. The influence and corresponding mechanisms on the bastnaesite mineral surface and collectors, namely sodium oleate (NaOL), were evaluated experimentally based on micro-flotation, zeta potentials, in situ attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), and X-Ray photoelectron spectroscopy (XPS) analyses. The flotation recovery of bastnaesite significantly decreased from ∼95% to ∼25%, ∼15%, ∼80%, ∼25% when exposed to calcite, fluorite, barite, and mixed dissolved species, respectively. The zeta potential of bastnaesite was pH sensitive, indicating that H+ and OH- determine the surface potential of bastnaesite. Solution chemistry analyses revealed that the presence of the dissolved species differed at various pH values. In situ ATR-FTIR demonstrated the different effects of the dissolved species from calcite, fluorite, and barite on collector adsorption. The former two dissolved species mainly depressed the chemisorption of the NaOL monomers (RCOO‒), whereas calcite also affected the physical adsorption of the oleic acid molecular dimer (RCOOH·RCOO‒). Moreover, the barite dissolved species only affected the physical adsorption of the NaOL species. The results of XPS analysis revealed that dissolved species from these three gangues could pre-adsorbed onto bastnaesite and affected the interaction with the collector. Density functional theory calculations were employed to provide further theoretical insights into the interactions between the dissolved species from calcite, fluorite, and barite and NaOL.

Selective depression of arsenopyrite with in situ generated nanoparticles in pyrite flotation

In this study, the selective depression of arsenopyrite in pyrite flotation with in-situ generated nanoparticles was studied. Scanning electron microscope and energy dispersive X-ray spectroscopy (SEM/EDS) detection, solution chemistry analysis, fourier transform infrared spectroscopy (FTIR), adsorption tests and contact angle measurement were used to reveal the corresponding mechanism. Flotation results showed that arsenopyrite were selectively depressed and pyrite had a better flotability at pH 8.7. SEM/EDS results showed that Zn-containing nanoparticles are largely produced on arsenopyrite but rarely on the pyrite surface. Solution chemistry calculations showed that ZnCO3 nanoparticles were the major hydrophilic species at pH 7–9. This consists with the pH range where arsenopyrite was depressed. The selective generation of ZnCO3 nanoparticles on arsenopyrite surface was further confirmed by FTIR analysis. The ZnCO3 nanoparticles inhibited the adsorption of the collector onto arsenopyrite surface and made it more hydrophilic, which was suggested by the adsorption and contact angle measurement results. A model showing the selective depression mechanism of ZnSO4 on pyrite/arsenopyrite flotation system in Na2CO3 solution was also proposed. The comminution process is worth further study to clarify that whether the selective formation of ZnCO3 nanoparticles on pyrite and arsenopyrite surface is due to the difference in surface roughness.

Electrolyte solutions design for lithium-sulfur batteries

<h2>Summary</h2> Lithium-sulfur (Li-S) batteries promise high energy density for next-generation energy storage systems, yet many challenges remain. Li-S batteries follow a conversion chemistry, which radically differs from intercalation-based lithium-ion batteries. Recently, it has become clear that the chemistry of electrolyte solutions and their ability to stabilize polysulfide Li₂S_x species formed by sulfur reduction have a critical effect on energy density and cycling performance. This review evaluates the key role of solution properties and polysulfide solvation. Factors that determine the solvation are discussed, including the solvent, salt, concentration, and interaction with Li-polysulfide species. Three fundamental types of electrolyte solution—moderately (conventional), sparingly, and highly solvating—are presented along with a multi-dimensional analysis of solution chemistry, polysulfide solubility, sulfur reaction pathway, Li₂S deposition, and solution quantity. The stability of lithium metal anodes with these solutions is discussed with respect to side reactions, protective surface film formation, and dendritic Li deposition. Emphasis is placed on options to reduce the electrolyte solution/sulfur ratio and prolong battery cycle life. The advantages and disadvantages of the three systems are compared in accordance with the multifaceted requirements. In conclusion, we offer our perspective for future development of Li-S batteries.

Adsorption mode of sodium citrate for achieving effective flotation separation of ilmenite from titanaugite

Sodium citrate was introduced as a depressant for ilmenite flotation, and its effect on the activation of ilmenite and depressing titanaugite was investigated. The flotation results showed that ilmenite was effectively separated from titanaugite as a concentrate with a TiO2 grade of 43.62% and recovery of 87.42%. The contact angle analysis revealed that sodium citrate further increased the hydrophobicity of ilmenite and decreased it in the case of titanaugite. The zeta potential results indicated that the adsorbed sodium citrate accelerated the adsorption of sodium oleate on the ilmenite surface, but weakened the adsorption on titanaugite. Inductively coupled plasma mass spectrometry (ICP) and solution chemistry analyses illustrated that sodium citrate improved the flotation of ilmenite and depressed the flotation of titanaugite. Furthermore, X-ray photoelectron spectroscopy (XPS) analysis demonstrated that sodium citrate adsorbed onto ilmenite through Fe3+ and onto titanaugite through the active sites of Ca and Mg.

Investigating the performance of oxalic acid for separating bastnaesite from calcium-bearing gangue minerals based on experiment and theoretical calculation

Bastnaesite is a major light rare earth resource in the earth, which is difficult to separate from calcium-bearing gangue minerals in flotation because of their similar flotation characteristics as the semisoluble salt minerals. To address this problem, in 3-hydroxy-2-naphthyl hydroxamic acid (H205) system, the selective inhibition mechanism of oxalic acid on common calcium-bearing gangue minerals (calcite and fluorite) in bastnaesite flotation was studied by flotation tests, solution chemistry analysis, zeta potential measurements, and X-ray photoelectron spectroscopy (XPS) measurements, combined with thermodynamics and density functional theory (DFT) calculation. After the analysis of those tests and calculation results, it can be known that the hydrophilic oxalic acid can selectively compete with H205 for the active site (Ca2+) on the surface of the calcium-bearing gangue minerals, thus reducing its surface hydrophobicity and inhibiting its floating, while bastnaesite is not susceptible. In this process, fluorite is more inhibited than calcite.

Clean and Feasible Utilization of High Silica Fluorspar Powder via Reverse Flotation: A Pilot Study

Fluorite is a nonrenewable mineral used to produce anhydrous hydrofluoric acid (AHF) and aluminum fluoride. The demand for low-grade fluorite powder (CaF2 &lt; 97%) has fallen sharply owing to the current market conditions. Therefore, a large number of fluorite concentrates have been improved by acid leaching. While this approach can efficiently remove CaCO3 from fluorite concentrate, the SiO2 content, which significantly affects AHF consumption during the production of HF or aluminum fluoride, cannot be completely removed. To solve this problem, in this study, we used reverse flotation before leaching the fluorite concentrates. Subsequently, the feasibility of reverse flotation desilication was determined. The obtained results of the ZP (zeta potential) measurements, solution chemistry analysis, FTIR (Fourier transform infrared spectroscopy) analysis, and micro-flotation tests indicated that employing dodecylamine as the collector and citric acid as the depressor could effectively separate sericite from fluorite. The batch flotation experiment and the pilot test were conducted in Chenzhou (Hunan, China) followed by their operation in Xinyuan Mining Co. Ltd., which produces monolithic fluorite ore on the large scale in Asia. Notably, we found that the contents of both SiO2 and Al2O3 were from 2.82%, 1.17% reduced to 1.28%, 0.74% in the batch flotation experiment. The results of the pilot test showed that the new reverse flotation + leaching technology could dramatically reduce the potential environmental impact and costs, thereby significantly improving the economic benefits by satisfying the requirements of the market.

Improving the flotation efficiency of Pb–BHA complexes using an electron-donating group

Lead complexes of benzohydroxamic acid (Pb–BHA) are metal-organic complex collectors having excellent selectivity. However, the flotation efficiency of Pb–BHA needs improvement. In this research, we report the introduction of an electron-donating group into the BHA ligand to improve the performance of Pb–BHA in mineral flotation; p-methyl-benzohydroxamic acid (MBHA) was synthesized and used as a new ligand to form the Pb–MBHA complex. The flotation behavior of Pb–MBHA in scheelite flotation was investigated using micro-flotation experiments. The adsorption mechanism of collectors at the solid–liquid interface was investigated via solution chemistry analysis, Fourier-transform infrared spectroscopy (FTIR), zeta potential, X-ray photoelectron spectroscopy (XPS), and contact angle measurements. Froth stability tests were used to study the adsorption behavior of the collectors at the gas–liquid interface. Pb–MBHA had stronger collecting ability and pH adaptability than Pb–BHA. The Pb(MBHA)+, Pb(MBHA)2, and Pb(OH)MBHA were the main species of Pb–MBHA in solution. For oxygen atoms on the scheelite surface, Pb–MBHA has stronger chemical adsorption ability than Pb–BHA, and its adsorption made the scheelite surface more hydrophobic. The foaming ability and foam stability of Pb–MBHA were stronger than those of Pb–BHA in solution, and stable foam was more likely to form at the gas–liquid interface.

Chemical Change Induced by CO &lt;sub&gt;2&lt;/sub&gt; Leakage through Wellbore Cement and Casing Interfaces

Damaged wellbores pose some of the greatest risks for CO2 leakage from underground storage reservoirs. If CO2 is injected into the subsurface, leakage may occur through fractures and cracks formed at the cement-casing interface due to deficient well completion, poor mud displacement, or damage during operation or abandonment. A review of the literature has shown that a range of cement fractures can be sealed through calcium carbonate precipitation, given appropriate fluid residence time and initial fracture aperture. In the presence of steel casing, studies have observed that iron carbonate precipitation may also play a key role in fracture sealing. Here we discuss results of cement-steel, cement-cement, and steel-steel core-flood experiments simulating CO2-brine leakage in these systems. The aim of this study is to quantify the chemical changes in the cement and steel materials upon exposure to CO2-equilibrated brine. Using a combination of surface profilometry measurements, X-ray tomography (XRCT) and solution chemistry analyses, we quantified the chemical changes within both the cement and steel phases. These new experimental data are needed to extend chemical degradation models and predict the long-term behavior of the casing-cement interface in the wellbore environment.

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.

Adsorption of ferric ions on the surface of bastnaesite and its significance in flotation

In the system of 3-hydroxy-2-naphthyl hydroxamic acid (H205) collector, the adsorption of ferric ions on the surface of bastnaesite and its significance in flotation was investigated by micro-flotation tests, zeta potential measurements, adsorption experiments, solution chemistry analysis, X-ray photoelectron spectroscopy (XPS) measurements and density functional theory (DFT) calculations. From the results of our experiments, it can be known that ferric ions species (Fe(OH)3(s)) can absorb on the surface of bastnaesite by interacting with RE(OH)x3−x (x = 1, 2) (RE = Ce, La and Nd) to form RE-O-Fe-OH. And in this process, Fe(OH)3(s) is bound to RE(OH)x3−x (x = 1, 2) mainly by bidentate adsorption. By bidentate adsorption with RE(OH)x3−x (x = 1, 2), the addition of ferric ions decreases adsorption sites for H205, impedes the adsorption of H205 on the surface of bastnaesite, and then depresses bastnaesite flotation.

The effect of citric acid in the flotation separation of bastnaesite from fluorite and calcite using mixed collectors

Bastnaesite is a chief natural source of light rare earth elements (LREEs). The effective depression of Ca-containing minerals such as fluorite and calcite in bastnaesite flotation system is normally difficult, and it is imperative to exploit more environmentally-friendly depressants which can inhibit these gangue minerals simultaneously. Hence, we employ citric acid (H3Cit), a green, cheap and commonly available organic acid, to selectively depress the flotation of fluorite and calcite, and use octanohydroxamic acid (OHA) and sodium oleate (NaOL) with a molar ratio of 2:1 as mixed collectors. Micro-flotation results show that H3Cit decreases the recoveries of fluorite, calcite, and bastnaesite by 84.73%, 62.96%, and 9.23%, respectively at pH 8–9. The depression mechanism of H3Cit was investigated through zeta potential measurements, microcalorimetry measurements, solution chemistry and reaction thermodynamic analyses, and X-ray photoelectron spectroscopy (XPS) analyses. These further analyses at the minerals/water interfaces indicate that H3Cit preferentially adsorbs on the gangue mineral surfaces due to the positively charged fluorite and calcite surfaces which interact more easily with citrate ions (Cit3-), and the spontaneous interaction between Cit3- and Ca2+ on the surfaces. Accordingly, H3Cit is supposed to be a potential depressant for Ca-containing minerals in the flotation separation of bastnaesite.

A novel surfactant 2-(benzylthio)-acetohydroxamic acid: Synthesis, flotation performance and adsorption mechanism to cassiterite, calcite and quartz

In order to improve the floatability of cassiterite, a novel surfactant 2-(benzylthio)-acetohydroxamic acid (BTHA) was synthesized and first used as flotation collector to selectively separate cassiterite from calcite and quartz. The flotation performance and adsorption mechanism of BTHA to cassiterite were studied by micro-flotation tests, zeta potential measurements, solution chemistry analysis, XPS and DFT calculations. The results of micro-flotation tests showed that BTHA possessed not only stronger collecting ability than either octanohydroxamic acid (OHA) or benzohydroxamic acid (BHA) under weak alkaline conditions, but also better selectivity to cassiterite against calcite and quartz. The results of zeta potential and solution chemistry analysis suggested that BTHA could produce co-adsorption between molecules and ions on the surface of cassiterite. The results of XPS spectra demonstrated that Sn-BTHA complexes were formed on cassiterite surfaces while no chemical bond or new chemical state emerged on calcite or quartz surfaces after BTHA treatment. DFT calculations provided further evidence that the BTHA interacted with cassiterite mainly through CO and OH in hydroxamate groups and S atoms in BTHA had certain electronic supply abilities which would promote the flotation of cassiterite.

Bastnaesite, Barite, and Calcite Flotation Behaviors with Salicylhydroxamic Acid as the Collector

The flotation of bastnaesite, as a major mineral source of rare earth elements, attracting much attention in the mineral processing field, is challenging owing to the natural flotability of calcium-bearing minerals. To promote the application of flotation, we systematically investigated the flotation behavior of bastnaesite, barite, and calcite, with salicylhydroxamic acid (SHA) as the collector through micro-flotation experiments, zeta-potential measurements, Fourier transform infrared (FT-IR) analyses, X-ray photoelectron spectroscopy (XPS) analyses, and solution chemistry analyses. Micro-flotation experiments confirm that the flotability of bastnaesite is high at pH 6.5–8.5, while calcite floats at pH 8.0–9.5, and barite has little flotation response. The results of FT-IR, XPS, and zeta-potential measurements indicate that there is chemical adsorption of SHA on the bastnaesite surface, and physical adsorption also occurs. However, as for barite and calcite, there is only physical adsorption of SHA on the surfaces. The solution chemistry results show that SHA anions can interact with RE3+, REOH2+, and RE(OH)2+ on bastnaesite surfaces in aqueous suspensions, resulting in bastnaesite flotation.

Effect of dissolved fluorite and barite species on the flotation and adsorption behavior of bastnaesite

The flotation of rare earth minerals, which is of current interest in the mineral processing field, is challenging owing to the dissolution of gangue minerals. In this study, dissolved fluorite and barite species were found to significantly affect the flotation behavior of bastnaesite. The mechanism was investigated using microflotation tests, zeta potential measurements, Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and solution chemistry analysis. The microflotation results confirmed that the presence of gangue supernatants significantly reduces the recovery of bastnaesite during flotation with sodium oleate as a collector. The zeta potential and solution chemistry analyses showed that the supernatant species can adsorb onto the bastnaesite surface by forming hydroxy and carbonate compounds, thus affecting the zeta potential value and reducing the adsorption of oleate species. The FTIR analysis suggested that treatment with supernatants weakens the adsorption of oleate species, and that Ca/Ba-oleate complexes are adsorbed on the bastnaesite surface. The XPS analysis confirmed that lattice ions from the gangue minerals adsorb/precipitate on the bastnaesite surface, hindering the chemisorption of oleate species and thus decreasing the floatability of bastnaesite.

Iron removal from raw asbestos by siderophores-producing Pseudomonas

Asbestos, mineral present in soil, are highly toxic due to the presence of iron. Microbes-mineral interactions occur naturally through various processes leading to their alteration. We examined the effect of siderophore-producing Pseudomonas with a particular focus on the role of pyoverdine and pyochelin on raw asbestos fibers such as amosite, crocidolite and chrysotile. We compared the efficiency of pyoverdine to the iron chelating agent EDTA in the release of iron from raw asbestos fibers. Pyoverdine was able to extract iron from all the tested raw asbestos with the higher efficiency observed for chrysotile and crocidolite. When asbestos were grinded, the iron removal was more important for all types. We monitored the effect of bacterial growth and siderophores containing bacterial supernatant on raw asbestos dissolution by solution chemistry analysis and transmission electron microscopy. The siderophore-containing supernatant allowed a higher iron solubilisation than the one obtained after bacterial growth. Moreover, the iron dissolution was faster with pyoverdine-containing supernatant than pyochelin-containing supernatant, with approximately the same iron level for the maximum extraction with a delay of 48 h. Our study clearly showed the involvement of bacterial siderophores, pyoverdine and pyochelin on chrysotile, crocidolite and amosite fibers weathering.

Green flotation of polyethylene terephthalate and polyvinyl chloride assisted by surface modification of selective CaCO3 coating

Abstract Plastic flotation was a promising separation method for efficient recycling of waste plastics. Aiming to avoid the destruction of original surface and secondary pollution, a novel flotation process based on calcium carbonate (CaCO3) coating was proposed for separation of polyvinyl chloride (PVC) and polyethylene terephthalate (PET). The mechanism of CaCO3 coating was researched via scanning electron microscope (SEM), X–ray photoelectron spectroscopy (XPS), X–ray diffraction (XRD), zeta potential, Fourier transformed infrared spectroscopy (FT–IR), and solution chemistry analysis. High polarity of C–Cl on PVC surface resulted in selective adherence of Ca2+ on PVC surface, and Ca2+ was a bridge between plastic surface and CaCO3 particles. The separation of PVC and PET was optimized by response surface methodology (RSM) combining Box–Behnken design (BBD). Optimal pretreatment conditions for flotation separation of PVC and PET were 0.11 g CaCO3, temperature 50.6 °C, treatment time 20 min, and pH 10.1. The purity and recovery of PVC could be 100% and 99%, respectively.

Understanding the depression mechanism of citric acid in sodium oleate flotation of Ca2+-activated quartz: Experimental and DFT study

Quartz, a common gangue mineral, often coexists with the Ca-containing minerals in natural ore deposits, such as scheelite, apatite, fluorite and calcite. The depression of quartz in the flotation separation of these minerals is normally difficult, especially when the surface of the quartz is activated by Ca2+ ions dissolved from the calcium-bearing minerals. Thus, the search for an efficient depressant for Ca2+-activated quartz is urgent. In this study, citric acid (CA) was employed as a depressant for Ca2+-activated quartz. Microflotation results showed an improved depression efficiency of CA for the sodium oleate flotation of Ca2+-activated quartz. The depression mechanism of CA was evaluated through combined experimental and computational techniques, including zeta potential measurements, adsorption tests, Fourier transform infrared and X-ray photoelectron spectroscopy analysis, solution chemistry analysis, and density functional theory-based first principle calculations.