Calcium Dioleate Research Articles

New insights into the role of calcium dioleate in selectively separating fluorite from calcite during cleaning process

Research on fluorite and calcite cleaning process have been ignoring the effects of calcium dioleate in pulp on flotation. In this study, flotation tests showed that flotation separation of fluorite and calcite could be achieved by the cleaning process under acidic conditions. Solution chemistry equilibrium calculations revealed that large amounts of calcium dioleate formed, and this compound was the main component in the cleaning solutions of fluorite and calcite under acidic conditions. Desorption and adsorption tests, contact angle measurements and atomic force microscopy (AFM) revealed the mechanism of selective separation of fluorite and calcite during the cleaning process under acidic conditions. Flotation tests showed that under acidic conditions, calcite flotation was strongly inhibited but fluorite flotation was less affected. Desorption and adsorption measurements and mineral surface contact angle analysis revealed that under acidic conditions, the calcium dioleate on the surface of calcite rough concentrate was desorbed into the solution, whereas the calcium dioleate in the solution did not readily absorb on calcite surface. The calcium dioleate on the surface of fluorite rough concentrate was hardly desorbed, whereas the calcium dioleate in the solution continued to adsorb on the surface. AFM intuitively confirmed the desorption of calcium dioleate from calcite surface and the adsorption of this compound on fluorite surface under acidic conditions. The selective adsorption of calcium dioleate on fluorite rough concentrate is an important factor that promotes the selective separation of fluorite and calcite during the cleaning process.

Novel insights into the role of colloidal calcium dioleate in the flotation of calcium minerals

Previous studies on oleic acid systems have shown that calcium dioleate formed during the flotation process plays an important role. Calcium dioleate has been extensively studied as an important intermediate product in sodium oleate flotation of calcium-containing minerals sodium oleate, but its use as a collector to separate calcium-containing minerals remains unverified. The effect of calcium dioleate on fluorite, calcite and scheelite flotation and the adsorption mechanism on the mineral surface were examined using solution chemical analysis, flotation test, adsorption measurement, atomic force microscopy (AFM) and transmission electron microscopy (TEM) in this study. Solution chemical calculations prove that stable calcium dioleate colloid will be the dominant species at certain pH, calcium ion and oleate concentrations. Flotation experiments showed that the calcium dioleate plays an important role in the flotation process using sodium oleate. Calcium dioleate has better flotation effect for fluorite and scheelite but weaker effect for calcite than sodium oleate. Adsorption measurement showed that calcium dioleate is more easily adsorbed on the surface of scheelite and fluorite. AFM and TEM measurements exhibited that the formation of micelle adsorption on the surface of scheelite and fluorite caused by calcium dioleate clearly affects the surface roughness. Calcium dioleate colloids can likely enhance the surface roughness of scheelite and fluorite via selectively adsorption to improve the flotation of scheelite and fluorite.

Flotation features of fluorapatite with ricinoleic acid: the role of hydrogen bonds between collectors

Improving the collecting ability of a collector is a crucial issue in phosphate flotation. In this work, ricinoleic acid (RA) was used as a collector for fluorapatite (FA, Ca5(PO4)3F) flotation. There is an OH group in the middle of the RA molecule, and thus, hydrogen bonds (H-bonds) can be formed between RA species. The role of the H-bond between RA molecules in FA flotation was revealed by experimental and theoretical calculation methods. The flotation results suggested that RA was more efficient than oleic acid for FA flotation at pH 9. The RA− anion was chemisorbed onto the negative FA surface, forming calcium ricinoleate (Ca(RA)2) precipitates. The crystallization of Ca(RA)2 on the FA surface was aided by the H-bonds between RA species. On the other hand, the results of quantum chemistry calculations showed that the H-bond in Ca(RA)2 resulted in the close packing of RA− anions. Such a packing structure may occur on the FA surface, which favors the formation of Ca(RA)2 on the surface and FA flotation. Moreover, Ca(RA)2 was more stable than calcium dioleate in solution, also contributing to the better flotation efficiency of RA. These theoretical calculation results clarified the beneficial effect of the H-bond between RA species on FA flotation at the atomic level.

Rebellious Tin Ore Processing with New Agents for Nonferrous and Noble Metal Recovery

The occurrence form of sodium dibutyl dithiocarbamate on chalcopyrite is defined by IR spectroscopy. A stable compound of lead dibutyl dithiocarbamate forms on galenite. Fat acids of tall oil are adsorbed at the surface of cassiterite as chemically adsorbed oleate and physically adsorbed calcium dioleate. Sodium oleate adsorption at quartz surface is unfound in the mineral spectra after contact with fat acids, which proves selectivity of this agent relative to cassiterite. Applicability of 1,3,5-triazine-2,4,6-triamine agent to flotation of silver-bearing minerals is studied. The output of ultrasonic treatment aimed to remove slime material which deteriorates gravity separation of tin tailings at Solnechny Mining and Processing Plant is described.

Role of calcium dioleate in the flotation of powellite particles using oleate

Micro-flotation, zeta potential, fluorescence emission, interface topography and XPS tests were carried out to investigate the flotation and adsorption of sodium oleate (NaOl) on powellite. Micro-flotation results show that the flotation recovery varies with different Ca2+ concentrations in pulps. The greater negative charge on the washed powellite (W-M) surface with both Ca2+ and Ol− compared to that with only Ol− could be explained by the additional adsorption of Ol− on the surface, along with calcium dioleate precipitation through hydrophobic interactions between hydrocarbon chains in the Ol− ion and Ca(Ol)2, as indicated by the results from zeta potential measurements. The most nonpolar powellite surface were obtained from raw powellite (R-M) with Ol− and washed powellite with both Ca2+ and Ol−, which is in good accordance with flotation and zeta potential test results. When the powellite crystal was equilibrated with a mixed solution of calcium chloride and sodium oleate, the surface roughness average increased greatly from 4.503 nm to 16.327 nm, revealing the formation of non-uniform clusters of Ca(Ol)2 precipitates. XPS analysis further demonstrates the release of Ca ions into powellite pulp and the removal of them by ultrasonic treatment. The adsorption of Ca(Ol)2 and oleate anions are responsible for the flotation of powellite using NaOl, and the former is more predominant. A suggested comparative model are given through molecular dynamics simulation analysis.

Effect of calcium minerals reactivity on fatty acids adsorption and flotation

The separation between calcium minerals such as apatite and calcite by flotation relies on the use of long chain fatty acid collectors. Oleic acid, and its salt, is the main fatty acid collector and many studies have reported on the mechanisms of its interaction with calcium at the mineral surface and in solution, and on the oleic acid species present at the mineral surface. Although collector adsorption and mineral flotation depend mainly on solution pH and collector concentration, other factors such as mineral crystallinity and impurity affect mineral dissolution, influence collector adsorption and may explain the different flotation results reported in the literature on the same minerals. In this study the flotation of two calcites, with different degrees of purity, and one apatite was compared and related to the amount and type of collector adsorbed on the mineral surface, and to the reactivity of these minerals (acid-base interaction and dissolution). The results obtained in this study indicate that calcium dioleate (or dilinoléate) is the species present on the minerals surface at pH 9 and its amount increases with collector addition and calcium mineral dissolution, which results in a higher flotation of the calcium minerals. The influence of calcium site density and impurity in the minerals on flotation was also discussed.

The adsorption of oleate on powellite and fluorapatite: A joint experimental and theoretical simulation study

Flotation and adsorption performance of sodium oleate(NaOl)on powellite and fluorapatite were investigated in this work through micro-flotation tests, work of adhesion calculations, molecular dynamics simulation, micro-topography studies and FTIR measurements. The micro-flotation results show a similar flotation behaviors of powellite and fluorapatite under alkaline conditions, but a considerable difference in mineral recoveries in the pH range 2–7, which demonstrates the possibilities for separating powillite from fluorapatite under acidic conditions. The great difference in mineral recovery displays a good accordance with the obvious difference in the work of adhesion of powellite and fluorapatite at NaOl dosage range of 40–80mg/L, obtained from flotation and contact angle measurements, respectively. The more negative interaction energy (ΔE) between NaOl and powellite/water interface from molecular dynamics simulation reveals a more easily adsorption of NaOl onto powellite than onto fluorapatite, which excellently matches with the results of flotation and work of adhesion. The results of micro-topography study shows that the adsorption of NaOl on powellite is mainly ascribed to the chemisorption of oleate ions with Ca2+ on powellite lattice or the precipitation of calcium dioleate agglomerates on powellite surface when it was in the solution without or with Ca2+, respectively. The FTIR measurements further confirm the chemisorption of oleate ions with Ca2+ active sites on powellite surface.

Investigation into the surface modification of aragonite whiskers

Aragonite whiskers (AWs) were treated with several fatty acid surfactants and silane coupling agent in order to determine the optimal modifier by using contact angle measurements. The results revealed that the AWs modified by fatty acids showed more remarkable increase in the contact angle than by silane, suggesting the former were preferentially applied in modifying AWs. While the samples coated with fatty acids exhibited hydrophobicity with contact angles ranging from 104.08° to 137.87° with increasing of carbon chain length. Therefore, the highest contact angle of AWs treated by oleic acid was discussed in detail as an example, which was characterized by field emission scanning electron microscope (FESEM), transmission electron microscopy (TEM), thermo‐gravimetry analyses (TGA), X‐ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR). FESEM and TEM results showed a thin layer coated on the modified sample surface. Both the results of TGA and XPS confirmed organic groups existed in the sample of AWs treated by oleic acid. FTIR demonstrated that calcium dioleate was formed in the modification process. Further, modification mechanism was proposed based on the obtained results. Copyright © 2016 John Wiley & Sons, Ltd.

Electrokinetic Behavior of Fluorite

The electrokinetic behavior of fluorite mineral was studied under various partical sizes and different concentrations of oleic acid at constant pH. The particle size has been reduced with an increase in activation time. The surface energies of milled fluorite minerals were calculated theoretically and experimentally. The zeta potential of the fluorite/water system has shifted to lower side with an increase in particle size. The isoelectric point (iep) of fluorite minerals has been shifted to lower side with increase in oleic acid concentration. This indicates the chemisorbed oleate formation on fluorite. A sharp decrease in zeta potential in the pH range of 6.5–8.4 and the decrease in calculated free energy of adsorption shows the formation of calcium dioleate precipitate on fluorite.

In situ AFM study of potassium oleate adsorption and calcium precipitate formation on an apatite surface

This study investigates the effect of ionic strength on the adsorption of potassium oleate in apatite surfaces in situ by atomic force microscopy (AFM). Natural apatite crystals were equilibrated with calcium nitrate solutions in the presence and absence of potassium oleate (4×10−3M). AFM images for each experiment along with their histograms were recorded. The contact AFM mode allowed visualizing the topography of the surfaces with the formation of adsorbed layers and calcium dioleate colloids. The presence of calcium ions in aqueous solution (2×10−4M) led to the formation of precipitated calcium carbonate/hydroxide, as evidenced in the histogram. Oleate adsorption, in the presence of high ionic strength, occurs through the formation of clusters of calcium dioleate, observed in both 2D and 3D micro-topography. The presence of these clusters makes the apatite surface heterogeneous and rough, thus influencing its flotability.

Interaction of calcium dioleate collector colloids with calcite and fluorite surfaces as revealed by AFM force measurements and molecular dynamics simulation

Spherical calcium dioleate particles (∼ 10 μm in diameter) were used as AFM (atomic force microscope) probes to measure interaction forces of the collector colloid with calcite and fluorite surfaces. The attractive AFM force between the calcium dioleate sphere and the fluorite surface is strong and has a longer range than the DLVO (Derjaguin–Landau–Verwey–Overbeek) prediction. The repulsive AFM force between the calcium dioleate sphere and the fluorite surface does not agree with the DLVO prediction. Consideration of non-DLVO forces, including the attractive hydrophobic force, was necessary to explain the experimental results. The non-DLVO interactions considered were justified by the different interfacial water structures at fluorite– and calcite–water interfaces as revealed by the numerical computation experiments using molecular dynamics simulation. The density of interfacial water at the fluorite surface is low and the fluorite surface is not strongly wetted by water molecules. In contrast to the water at the fluorite surface, water molecules at the calcite surface form tightly packed monolayer structures and the calcite surface is extensively hydrated by water molecules. The interfacial water structure agrees with the AFM force measurements and the flotation recovery data. The strong attraction between the calcium dioleate colloid and the fluorite surface, and the moderately wetted fluorite surface by water molecules explain the better flotation response of fluorite with the oleate collector colloid.

Hydrophobic Attraction As Revealed by AFM Force Measurements and Molecular Dynamics Simulation

Spherical calcium dioleate particles ( approximately 10 mum in diameter) were used as AFM (atomic force microscope) probes to measure interaction forces of the collector colloid with calcite and fluorite surfaces. The attractive AFM force between the calcium dioleate sphere and the fluorite surface is strong and has a longer range than the DLVO (Derjaguin-Landau-Verwey-Overbeek) prediction. The AFM force between the calcium dioleate sphere and the mineral surfaces does not agree with the DLVO prediction. Consideration of non-DLVO forces, including the attractive hydrophobic force and the repulsive hydration force, was necessary to explain the experimental results. The non-DLVO interactions considered were justified by the different interfacial water structures at calcite- and fluorite-water interfaces as revealed by the numerical computation experiments with molecular dynamics simulation.

Calcium activation of silica surfaces with sodium oleate collector

In the Florida phosphate industry, fatty acid collectors are used to separate phosphate ore from silica during the rougher flotation stage. However, the presence of multivalent ions (in particular Ca++) in the processing water has been reported to result in the activation of silica with respect to oleate adsorption, rendering it floatable. Hence, adequate separation may not be achieved during the rougher flotation stage. In this study, the direct measurement of surface interaction forces via atomic force microscopy was used to delineate possible mechanisms for calcium activation under phosphate flotation conditions at oleate/calcium concentrations both above and below the calcium dioleate precipitation limit.

Interaction Forces between a Calcium Dioleate Sphere and Calcite/Fluorite Surfaces and Their Significance in Flotation

Spherical particles of calcium dioleate were successfully prepared to measure the interaction force of a calcium dioleate collector colloid at calcite and fluorite surfaces. Scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectroscopy, and electrophoretic mobility measurements were used to characterize the specially prepared calcium dioleate spheres. FTIR spectra show that the spheres have the same spectral properties as untreated (freshly precipitated) calcium dioleate. SEM imaging of the sphere surface and AFM roughness measurements indicate that these spheres can be used as colloidal probes for interaction force measurements. AFM interaction force measurements between calcium dioleate spheres and mineral surfaces were conducted at selected pH values from pH 5.2 to pH 10.0. The attractive force and adhesion force between the calcium dioleate sphere and the fluorite surface were found to be much stronger and longer-range than those measured between the calcium dioleate sphere and the calcite surface. The range and magnitude of these attractive forces were found to be pH dependent in the case of fluorite. These results are discussed in conjunction with streaming potential measurements, contact angle measurements, and the flotation behavior of calcite and fluorite with oleate as the collector.

Conformation of chemisorbed oleate at a calcite surface

The surface chemistry of the calcite/oleate flotation system was examined by in situ FT-NIR/IRS. Spectra of combination and overtone bands of aliphatic stretching vibrations revealed gauche/trans conformational changes that occurred solely as a function of temperature. The conformational changes were attributed to the simple “melting” behavior associated with phase transitions. It was concluded that chemisorbed oleate at calcite surfaces is gel-like at temperatures below 22°C, resembles a coagel between 22°C and 31°C, and becomes micelle-like at temperatures above 31°C. By comparison, chemisorbed oleate at fluorite surfaces also undergoes these phase transitions but is additionally dependent on adsorption density. The conformational changes were observed at high chemisorption densities (> 2.0×10−10 mol/cm2) and attributed to molecular forces, primarily van der Waal’s interactive forces, among neighboring chemisorbed oleate molecules. Similar analysis of in situ FT-NIR/IRS spectra of surface-precipitated calcium dioleate at calcite surfaces did not exhibit this behavior thereby confirming that surface-precipitated calcium dioleate remains in an all-trans conformation. The results help explain why surface polymerization is not observed at calcite surfaces but is observed at fluorite surfaces.

Effect of temperature on oleate adsorption at a calcite surface: an FT-NIR/IRS study and review

In-situ Fourier transform infrared/internal reflection spectroscopy (FT-IR/IRS) with reactive internal reflection elements (IREs) has been extended to study oleate adsorption at a calcite surface. Birefringent and transmission limitations of calcite were overcome with appropriate optics and a near-infrared (NIR) spectrometer. Adsorption isotherms were determined at pH 9.2 for temperatures of 20°C and 60°C and found to agree with data reported in the literature. The in-situ FT-NIR/IRS results indicate that chemisorption occurs at low oleate concentrations since the extent of adsorption increases at the higher temperature. At higher oleate concentrations, surface precipitation of calcium dioleate predominates but, in this case, the adsorption densities decrease with increasing temperature. This effect was related to surface-passivation due to increased chemisorption and to the increased solubility of calcium dioleate at 60°C. A thorough review of the literature substantiates this position. Finally, ex-situ FT-IR/IRS spectra of the chemisorbed and surface precipitated states were obtained in the mid-infrared (MIR) region and were found to support the in-situ FT-NIR/IRS results. Previous attempts with other infrared sampling methods were not successful in obtaining such MIR spectra due to the highly absorbing nature of carbonate vibrations.

Oleate Adsorption at an Apatite Surface Studied by Ex-Situ FTIR Internal Reflection Spectroscopy

Oleate adsorption at an apatite surface was investigated by ex-situ Fourier transform infrared internal reflection spectroscopy (FTIR/IRS). Adsorption isotherms have been determined using an apatite internal reflection element (IRE) and it has been found that pH has a significant influence on oleate adsorption by apatite. At pH 8.0 and 20°C, oleate adsorption density increases monotonically as equilibrium oleate concentration increases from 5 × 10−6to 1 × 10−3M. These results are in contrast to the results at pH 9.5 and 20°C in which case the adsorption density is limited to that corresponding to approximately monolayer coverage. Oleate adsorption by apatite was compared to oleate adsorption by fluorite and calcite and the different adsorption behavior at these three mineral surfaces is attributed to the differences in the densities of surface calcium sites and to the differences in the solubilities of these minerals.The spectral results at pH 8.0 and 20°C, suggest that the dominant adsorbed species at the apatite surface is oleic acid as indicated by the appearance of a strong IR absorbance peak at about 1710 cm−1for the whole oleate concentration range investigated from 5 × 10−6to 1 × 10−3M. On the other hand at pH 9.5, 20°C, and low surface coverage, it appears that oleate is chemisorbed as indicated by a peak at 1554 cm−1and an increased adsoption density at higher temperatures. Above what corresponds to monolayer coverage, surface precipitation of calcium dioleate salt is suggested by the doublet at 1575 and 1540 cm−1. At pH 9.5 and elevated temperature, 65°C, both chemisorption of oleate and surface precipitation of calcium dioleate at the apatite surface are enhanced. These FTIR/IRS spectra are compared with those obtained by the diffuse reflection technique, and the difference between the spectra are discussed.Finally, contact angles have been measured at the apatite IRE surface and it has been demonstrated that both the amount and the nature of the adsorbed species influence the hydrophobic state of the surface.

The significance of collector colloid adsorption phenomena in the fluorite/oleate flotation system as revealed by FTIR/IRS and solution chemistry analysis

Abstract Previous spectroscopic studies of the fluorite/oleate flotation system have shown that under certain conditions calcium dioleate is formed at or transported to the fluorite surface, leading to multilayer formation in the, so-called, surface precipitation region of the adsorption isotherm. Most studies show that the adsorbed calcium dioleate compound becomes significant at equilibrium oleate concentrations of between 4 × 10 −6 M and 4 × 10 −5 M, yet little explanation regarding the nature of this adsorption phenomenon is provided. In this study both ex-situ and in-situ FTIR/IRS experiments have been utilized in connection with a thermodynamic solution chemistry analysis to better understand the oleate adsorption mechanism as well as the factors which control precipitate formation and adsorption. Results show that contol of calcium ion concentration and pH in solution are crucial in determining both the form and quantity of the adsorbate. Also, results suggest that the predominant mechanism of calcium dioleate adsorption is formation of calcium dioleate in solution, followed by transportation to the surface rather than nucleation and growth at the surface as a surface precipitate.

Intraperitoneal free fatty acids induce severe hypocalcemia in rats: A model for the hypocalcemia of pancreatitis

Indirect evidence suggests a causative role for intraperitoneal free fatty acids (FFA) in hypocalcemia associated with pancreatitis. We examined the effects of intraperitoneal injection of four naturally occurring FFAs on serum calcium in rats. Two saturated FFAs, stearate and palmitate, induced little or no hypocalcemia. Two unsaturated FFAs, oleate and linoleate, caused dramatic hypocalcemia in treated versus control rats (6.3 +/- 1.4 and 5.3 +/- 0.7 mg/dl, respectively, versus 10.1 +/- 0.6). Dose-response studies demonstrated that minute quantities of oleate (100 microliters per 250 g rat) caused marked hypocalcemia (7.2 +/- 0.3 mg/dl). Treated versus control rats also revealed a decrease in ionized calcium (3.15 +/- 0.2 versus 5.6 +/- 0.05 mg/dl) and magnesium (1.4 +/- 0.15 versus 2.0 +/- 0.10), an appropriate increase in PTH levels (1670 +/- 451 versus 396 +/- 235 pg/ml), and a fall in calcitonin levels (70.4 +/- 21.3 versus 47.5 +/- 16.4 pg/ml) but no change in albumin or phosphate levels. In vitro, the Ksp of calcium dioleate was shown to be 5.3 x 10(-8) m3/liter3; thus under physiologic conditions 100 microliters oleate binds 7.2 mg calcium, or approximately twice the total ECF ionized calcium in the rat. The amounts of intraperitoneal FFA that can easily be achieved in pancreatitis complex pathophysiologically significant amounts of calcium and may lead to severe hypocalcemia.

Adsorption Density Calculations from in Situ FT-IR/IRS Data at Dilute Surfactant Concentrations

Adsorption densities of the surfactant oleate at the surface of a fluorite crystal have been calculated from in situ FT-IR internal reflection spectroscopic (1RS) data at very low surfactant concentrations. For the first time, a complete adsorption isotherm (5 × 10−7 to 5 × 10−4 M) has been calculated from the in situ spectral data with the use of internal reflection theory. It was found that monolayer coverage occurred at very low surfactant concentrations (<10−5 M), while at higher bulk concentrations, adsorption consists of multilayers of what appears to be surface-precipitated calcium dioleate. Calculated absorption densities by this in situ method agree quite well with those found previously by more traditional experimental techniques. These results provide considerable confidence that quantitative in situ FT-IR/IRS analysis of surfactant adsorption at the surface of reactive internal reflection elements is possible.