Adsorption Of Oleate Research Articles

An atomic scale investigation of the adsorption of sodium oleate on Ca2+ activated quartz surface

An atomic scale investigation of the adsorption of sodium oleate on Ca2+ activated quartz surface

Encapsulation of oils and fragrances by core-in-shell structures from silica particles, polymers and surfactants: The brick-and-mortar concept

Colloidosomes provide a possibility to encapsulate oily substances in water in the form of core-in-shell structures. In this study, we produced microcapsules with shell from colloidal particles, where the interparticle openings are blocked by mixed layers from polymer and surfactant that prevent the leakage of cargo molecules. In other words, the particles and polymer play the role of bricks and mortar. For this goal, we used hydrophilic silica particles, which were partially hydrophobized by the adsorption of potassium oleate to enable them to stabilize Pickering emulsions. Various polymers were tested to select the most appropriate one. The procedure of encapsulation is simple and includes single homogenization by ultrasound. The produced capsules are pH responsive. They are stable in aqueous phase of pH in the range 3–6, but at pH > 6 they are destabilized and their cargo is released. With the optimized formulation of silica particles, polymer, oleate and NaCl, we were able to encapsulate various oils and fragrances, such as tetradecane, limonene, benzyl salicylate and citronellol. All of them have a limited and not too high solubility in water. In contrast, no stable microcapsules were obtained with oils that either have zero water solubility (mineral and silicone oil) or higher water solubility (phenoxyethanol and benzyl alcohol). By analysis of results from additional interfacial-tension and thin-film experiments, we concluded that a key factor for obtaining stable capsules is the irreversible adsorption of the polymer at the oil/water interface. The hydrophobization of the particles by surfactant adsorption (instead of silanization) plays an important role for the pH responsiveness of the produced capsules. The obtained information about the role of various factors for the stabilization of microcapsules, which are based on the brick-and-mortar concept, can be further used to achieve better stability; selection of polymers that are appropriate for different classes of oils, as well as for the production of smaller capsules stabilized by nanoparticles.

States of coadsorption for oleate and dodecylamine at selected spodumene surfaces

In our latest study, it was reported that the effective flotation separation of spodumene from feldspar could be achieved using a mixture of the anionic collector, sodium oleate (NaOL) and the cationic collector, dodecylamine hydrochloride (DDA). This study is an extension of the previous work to provide further details of the coadsorption and association states for the NaOL/DDA collector mixture at selected spodumene and feldspar surfaces using Fourier transform infrared spectroscopy (FTIR), sum frequency vibrational spectroscopy (SFVS), density functional theory (DFT) calculations, contact angle measurements, and micro-flotation experiments. An important finding from the results was significantly improved collector adsorption at the spodumene (001) surface with small addition of DDA which was responsible for improved spodumene flotation using NaOL as the dominating collector. In the absence of DDA, oleate adsorbed as a well packed monolayer at the spodumene (110) surface, while poor adsorption of oleate with gauche defects was observed at the spodumene and feldspar (001) surfaces. A certain amount of DDA significantly enhanced the collector adsorption at the spodumene (001) surface, but had little or no effect on adsorption at the spodumene (110) surface and the feldspar (001) surface. Under these circumstances, an excellent separation of spodumene from feldspar can be achieved, as confirmed by contact angle and micro-flotation results. On the other hand, good adsorption and ordered structures of DDA and its dominative mixtures were observed at all selected surfaces. DFT calculation indicates that the association of DDA ion with oleate is preferred and accounts for the variations in collector adsorption states at these selected surfaces.

Effect of Sodium Pyrophosphate on the Reverse Flotation of Dolomite from Apatite

In this study, the effect of sodium pyrophosphate (NaPP) on the separation of apatite from dolomite by flotation was systematically investigated. Flotation results revealed that NaPP could selectively depress the flotation of apatite, thus realizing the separation of apatite from dolomite. Further, the selective depression mechanism of NaPP was studied through zeta potential measurements, contact angle measurements, and X-ray photoelectron spectroscopy (XPS) analysis. The results demonstrated that the adsorption of sodium oleate (NaOL) onto apatite surface was depressed by the preferential interaction of NaPP with active Ca sites. For dolomite, while the presence of NaPP hindered the interaction of NaOL with active Ca sites, it appeared to enhance the reactivity with active Mg sites. Thus, the adsorption of NaOL onto dolomite surface was hardly influenced. In this way, the separation of apatite from dolomite was achieved.

Interaction mechanism of magnesium ions with cassiterite and quartz surfaces and its response to flotation separation

• The interaction mechanism of magnesium ions with cassiterite and quartz surfaces was proposed. • Magnesium ions suppressed the floatation of cassiterite and activated the flotation of quartz, and it was related to pH. • Magnesium ions considerably affected the adsorption of oleate species onto cassiterite and quartz surfaces. • Magnesium ions interacted with the mineral surfaces via specific adsorption of hydrated Mg(OH) + and Mg(OH) 2 . The interaction behavior and mechanism of magnesium ions with cassiterite and quartz surfaces and their effects on flotation separation of cassiterite from quartz were investigated by micro-flotation tests, surface adsorption experiments, zeta potential measurements, solution chemistry calculation, and X-ray photoelectron spectroscopy (XPS) analysis. The micro-flotation tests showed that solution pH significantly affected the floatability of cassiterite and quartz in the absence and presence of magnesium ions, and the preferred flotation separation of cassiterite from quartz was obtained at pH 6.8–8.2. Adsorption experiments and zeta potential measurements indicated that magnesium ions significantly affected the adsorption of sodium oleate on the mineral surface. The effect gradually aggravated with increasing pH due to the specific adsorption of hydrated Mg(OH) + and Mg(OH) 2 on the mineral surface. The adsorption mechanism of magnesium species onto the mineral surface was ascertained by XPS measurement. Magnesium species were adsorbed onto the mineral surface through interaction with the O sites of cassiterite and quartz particles, and a strong interaction occurred in the solution with high pH.

Flotation separation of scheelite from calcite using carboxyl methyl cellulose as depressant

The effect of carboxyl methyl cellulose (CMC) on the flotation separation of scheelite from calcite using sodium oleate as collector was studied in this work. The results of flotation tests indicated that CMC could selectively depress the flotation of calcite. However, the addition of calcite strongly strengthened the depressing effect of CMC on scheelite flotation. The addition of sodium carbonate could eliminate the adverse impact of calcite on the performance of CMC in scheelite flotation, and a concentrate with both high grade of WO3 and scheelite recovery could be achieved under CMC in the presence of sodium carbonate. Zeta potential results indicated that CMC adsorbed more strongly on calcite surface than that on scheelite surface, and the addition of CMC prevented the adsorption of the sodium oleate on the calcite surface.

Effects of crystal chemistry on sodium oleate adsorption on fluorite surface investigated by molecular dynamics simulation

The surface properties of minerals are governed by the crystal chemistry of their cleaved and exposed surfaces, which will vary with the reduction of particle size under mechanical crushing or grinding. Molecular dynamics (MD) simulations were used to study the adsorption conformations and interaction energies of sodium oleate (NaOL) on different fluorite (CaF2) surfaces in an explicit solution system. Three fluorite crystal planes, namely, the (1 1 1) surface, the (1 1 0) surface and the (3 1 1) surface, were considered. Anisotropic surface energies and broken bond densities were calculated based on density function theory (DFT) to confirm the cleavage plane of fluorite and to investigate the crystal-chemical characteristics of fluorite crystal planes. It was demonstrated that NaOL preferentially combined in a bridged ring complex configuration with the most stable plane of fluorite, the (1 1 1) surface, which bears a Ca┄F broken bond density of 100%. The exposure of the (1 1 0) surface of fluorite limited its flotation response to NaOL collectors, as this surface exhibited a lower affinity for NaOL, agreeing well with the results of the fluorite flotation experiments performed with different size distributions. The anisotropy of fluorite with different size fractions was further verified by X-ray diffraction (XRD) analyses. The findings in this work suggest that the flotability of fluorite could be further improved if a selective grinding process is applied to favour the exposure of the (1 1 1) surface.

Utilization of sodium humate as selective depressants for calcite on the flotation of scheelite

ABSTRACTThe flotation separation of scheelite from calcite using sodium humate (SH) as a potential depressant has been studied through micro-flotation experiments, zeta potential and Fourier transform infrared (FT-IR) spectra measurements. The flotation results indicate SH exhibited selective depression effect on calcite in the presence of sodium oleate, achieving the flotation separation of scheelite from calcite. Zeta potential results indicate that SH strongly absorbed on calcite surface but negligibly on scheelite surface, which prevents the adsorption of sodium oleate on calcite surface. The FT-IR results also show that SH can be adsorb on the surface of calcite. Results shown a higher Ca density on the calcite than on scheelite surface, and that calcite can accommodate the interaction of SH.

Effect of calcium ions on adsorption of sodium oleate onto cassiterite and quartz surfaces and implications for their flotation separation

Abstract The effect of calcium ions on the adsorption of sodium oleate on the mineral surfaces and flotation separation of cassiterite from quartz were studied in this work through micro-flotation tests, zeta potential measurements, solution chemistry calculation, surface adsorption experiments, and X-ray photoelectron spectroscopy (XPS) analysis. The micro-flotation tests showed that calcium species had little effect on the floatability of cassiterite and quartz at acidic pH, but the effect significantly changed at pH higher than 9.1. Cassiterite had good floatability at pH 8.2 and was less affected by calcium species. Quartz exhibited poor floatability in the absence and presence of calcium ions around pH 8.2, which facilitated its flotation separation from cassiterite. Zeta potential and surface adsorption results indicated that the adsorption of sodium oleate on the mineral surface was minimally influenced by calcium ions at acidic pH but was greatly affected at strong alkaline pH because of the specific adsorption of hydrated Ca(OH)+ and Ca(OH)2 on the mineral surface. The adsorption mechanism was identified by XPS analysis, demonstrating that calcium species were adsorbed onto the mineral surface through the interaction with O sites of cassiterite and quartz particles.

Direct measurement of oleate adsorption on hematite and its consequences for flotation

The direct measurement of adsorbed oleate onto hematite removes the uncertainty of depletion of oleate onto non-hematite surfaces. Direct measurement of oleate onto hematite at pH 4 and as a function of pH at constant oleate addition was made using Differential Scanning Calorimetry. Oleate adsorption measurements were conducted on conditioned, concentrate and tailing samples, corrected for their surface areas. Adsorption measurements were complemented by flotation tests. At pH 4, oleate adsorption on conditioned samples reached a complete monolayer by vertical orientation at the critical micelle concentration (CMC) of the oleate. The onset of multilayer adsorption by vertical orientation on the concentrate samples was determined at the CMC, and monolayer coverage on the non-floated material was always less than one monolayer under two-point and vertical oleate orientation. Flotation recovery of hematite at pH 4 remained high under equilibrium oleate concentrations above the critical hemi-micelle concentration of oleate. Oleate adsorption on hematite as a function of pH showed maxima at pH 4 and 9, suggesting co-adsorption of molecular and ionic oleate species at pH 4. Hematite flotation with 10−4 molar oleate addition was high for pH values above 4.

Density Functional Theory and Atomic Force Microscopy Study of Oleate Functioned on Siderite Surface

Efficiently discovering the interaction of the collector oleate and siderite is of great significance for understanding the inherent function of siderite weakening hematite reverse flotation. For this purpose, investigation of the adsorption behavior of oleate on siderite surface was performed by density functional theory (DFT) calculations associating with atomic force microscopy (AFM) imaging. The siderite crystal geometry was computationally optimized via convergence tests. Calculated results of the interaction energy and the Mulliken population verified that the collector oleate adsorbed on siderite surface and the covalent bond was established as a result of electrons transferring from O1 atoms (in oleate molecule) to Fe1 atoms (in siderite lattice). Therefore, valence-electrons’ configurations of Fe1 and O1 changed into 3d6.514s0.37 and 2s1.832p4.73 from 3d6.214s0.31 and 2s1.83p4.88 correspondingly. Siderite surfaces with or without oleate functioned were examined with the aid of AFM imaging in PeakForce Tapping mode, and the functioned siderite surface was found to be covered by vesicular membrane matters with the average roughness of 16.4 nm assuring the oleate adsorption. These results contributed to comprehending the interaction of oleate and siderite.

New Insights into the Adsorption of Oleate on Cassiterite: A DFT Study

A new understanding of the adsorption mechanism of oleate on cassiterite surfaces is presented by density functional theory (DFT) calculations. Various convergence tests were conducted to optimize the parameter settings for the rational simulation of cassiterite bulk unit cell and surface slabs. The calculated surface energies of four low-index cassiterite cleavage planes form an increasing sequence of (110) < (100) < (101) < (001), demonstrating (110) is the most thermodynamically stable surface of cassiterite. The interaction strengths of the oleate ion (OL−), OH−, and H2O on the SnO2 (110) face are in the order of H2O < OH− < OL−, which reveals that the OL− is able to replace the adsorbed H2O and OH− on the mineral surfaces. Mulliken population calculations and electron density difference analysis show that electrons transfer from the Sn atoms on the cassiterite (110) surface to the O atoms offered by carboxyl groups of oleate during the interaction. The populations of newly formed O1–Sn1 and O2–Sn2 bonds are 0.30 and 0.29, respectively, indicating that these two bonds are of a very low covalency. Density of states analysis reveals that the formation of an O1–Sn1 bond mainly results from the 5s and 5p orbitals of the Sn1 atom and the 2p orbital of the O1 atom.

Solution chemistry of carbonate minerals and its effects on the flotation of hematite with sodium oleate

The effects of carbonate minerals (dolomite and siderite) on the flotation of hematite using sodium oleate as a collector were investigated through flotation tests, supplemented by dissolution measurements, solution chemistry calculations, zeta-potential measurements, Fourier transform infrared (FTIR) spectroscopic studies, and X-ray photoelectron spectroscopy (XPS) analyses. The results of flotation tests show that the presence of siderite or dolomite reduced the recovery of hematite and that the inhibiting effects of dolomite were stronger. Dissolution measurements, solution chemistry calculations, and flotation tests confirmed that both the cations (Ca2+ and Mg2+) and CO3 2− ions dissolved from dolomite depressed hematite flotation, whereas only the CO3 2− ions dissolved from siderite were responsible for hematite depression. The zeta-potential, FTIR spectroscopic, and XPS analyses indicated that Ca2+, Mg2+, and CO3 2− (HCO3 −) could adsorb onto the hematite surface, thereby hindering the adsorption of sodium oleate, which was the main reason for the inhibiting effects of carbonate minerals on hematite flotation.

New insights into the oleate flotation response of feldspar particles of different sizes: Anisotropic adsorption model

The anisotropic adsorption of sodium oleate (NaOL) on feldspar surfaces was investigated to elucidate the different flotation properties of feldspar particles of four different size ranges. Microflotation experiments showed that the feldspar flotation recovery of particles with sizes spanning different ranges decreased in the order 0–19>19–38>45–75>38–45μm. Zeta potential and FTIR measurements showed that NaOL was chemically adsorbed on the Al sites of the feldspar surface. The anisotropic surface energies and broken bond densities estimated by density functional theory calculations showed that, although feldspar mostly exposed (010) and (001) surfaces, only the (001) surfaces contained the Al sites needed for NaOL adsorption. The interaction energies calculated by molecular dynamics simulations confirmed the more favorable NaOL adsorption on (001) than (010) surfaces, which may represent the main cause for the anisotropic NaOL adsorption on feldspar particles of different sizes. SEM measurements showed that the main exposed surfaces on coarse and fine feldspar particles were the side (010) and basal (001) ones, respectively. A higher fraction of Al-rich (001) surfaces is exposed on fine feldspar particles, resulting in better floatability compared with coarse particles. XPS and adsorption measurements confirmed that the Al content on the feldspar surface varied with the particle size, explaining the different NaOL flotation of feldspar particles of different sizes. Therefore, the present results suggest that coarsely ground ore should be used for the separation of feldspar gangue minerals. Further improvements in the flotation separation of feldspar from associated valuable minerals can be achieved through selective comminution or grinding processes favoring the exposure of (010) surfaces.

Synergetic Effect of the Mixed Anionic/Non-Ionic Collectors in Low Temperature Flotation of Scheelite

The synergetic effect of four octaphenyl polyoxyethyienes (TX) on low temperature flotation of scheelite at 9–11 °C was investigated through flotation experiments, and the adsorption mechanism was studied by way of surface tension, zeta potential, and adsorption measurement. The results show that the presence of the four octaphenyl polyoxyethyienes can improve scheelite flotation in a low concentration range, and their synergetic effects increase with the increase of the oxyethyl group (EO) number in their molecular structure, the mixed sodium oleate/TX-15 collector exhibits the best collecting performance for scheelite. Compared with sodium oleate alone, a larger reduced value of zeta potential is seen in the presence of the mixed collectors, and the adsorption of sodium oleate on the scheelite surface is enhanced for a constant sodium oleate concentration. Moreover, the synergetic effect of TX-15 can be well demonstrated through surface tension measurement, a lower critical micelle concentration (CMC) value of the mixed sodium oleate/TX-15 surfactant is obtained, indicating a higher surface property. Therefore, the mixed sodium oleate/TX-15 collector is suitable for low temperature flotation of scheelite.

Molecular dynamics simulation of siderite-hematite-quartz flotation with sodium oleate

Models of sodium oleate adsorption on siderite, hematite and quartz were investigated by molecular dynamic simulation, respectively. Surface energy was calculated to confirm the cleavage plan of hematite and quartz. Both natural cleavage plane of siderite and calculated plane were used to investigate the flotation of the three minerals. Based on the molecular simulation in solution with water as medium, adsorption quantity and interaction capability of oleate ions on the three minerals indicated that siderite could be collected efficiently by sodium oleate at neutral pH. Results of flotation experiments were further demonstrated by analysis of relative concentration of carbon atoms and oxygen atoms.

Microwave irradiation consequences on chemical reagent consumption in ilmenite flotation

ABSTRACTThe effect of microwave irradiation on chemical reagent consumptions in the ilmenite flotation process was investigated. The flotation tests have been carried out in two stages of micro and mechanical agitation cells. The microwave irradiation increased the contact angle about 25% within 4 minutes of flotation. The adsorption results after irradiation indicated that in the presence of the activator (lead II nitrate), the collector (sodium oleate) adsorption on the ilmenite surface is increased, whereas in the presence of depressant (acidified sodium silicate), the collector adsorption on the olivine-pyroxene surface is decreased. The microflotation results showed that despite the decreasing in the collector dosage up to 50%, the recovery increased about 3.17% after irradiation. In this condition, the consumption of depressant and activator decreased 50%. The results of mechanical agitation flotation after irradiation showed that not only the dosages of collector, activator and depressant are decreased 25%, 50% and 50%, respectively, but also the recovery and separation efficiency of ilmenite flotation are increased 6.29% and 2.63%, respectively. These results confirmed the microflotation results. Microwave pretreatment improved the time of ilmenite hydrophobicity, collector adsorption is confirmed by contact angle and adsorption analysis and had a good corresponding to the flotation recovery.

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.

Foamability of fatty acid solutions and surfactant transfer between foam and solution phases

The foaming properties of aqueous solutions of fatty acids with different hydrocarbon chain lengths - hexanoate, laurate, and oleate - were assessed through measurements of foam volume and growth rate under continuous aeration. Simultaneous measurements of the partition of each surfactant between the bulk solution and foam phases were also carried out. Although bubble size measurements in bulk solution pointed towards quite similar gas dispersing abilities of the tested surfactants, their foamabilities under the same conditions were remarkably enhanced with increasing chain length of the hydrocarbon tail. Shorter chain surfactants - hexanoate and laurate - generated wet foams and the accumulation of these surfactants in the foam phase was very low, indicative of a low adsorption density of the reagents at the gas-liquid interface. In contrast, sodium oleate produced stable dry foams, and the amount of oleate transferred to the foam was much higher. The formation of these different types of foam was attributed to the higher adsorption of oleate at the gas-liquid interface compared to the lower adsorption of hexanoate or laurate, and to different mechanisms of foam stabilization. Regardless of the interfacial mechanism of the foaming action of the tested surfactants, it was generally found that strong foaming was possible only from surfactant solutions whose bulk concentration was higher than the critical coalescence concentration of a given surfactant. It was concluded that bubbles entering the foam phase from the bulk solution phase must already be stable against coalescence to induce foam formation and impart stability to the entire foam column. Foaming was observed only in true solutions of the tested surfactants, while precipitation of colloidal acid species completely depressed foam formation.

Interactions Between Sodium Oleate and Polyoxyethylene Ether and the Application in the Low‐Temperature Flotation of Scheelite at 283 K

AbstractThe poor collecting performance of fatty acids at low temperatures is a problem in mineral flotation. In this study, the floatability of scheelite at 283 K was studied using sodium oleate and binary mixtures of sodium oleate and lauryl alcohol polyoxyethylene ether (MOA‐9) as the collector, and interactions between the two surfactants at 283 K were investigated by the means of surface tension and steady state fluorescence measurements. The flotation experiment results show that the collecting performance of the mixed anonic/nonionic collector is stronger than that of single surfactant, and the best molar ratio of sodium oleate to MOA‐9 is 10:1 at pH 10. The surface tension results show that the critical micelle concentration value of sodium oleate, MOA‐9 and the binary solution is about 2 × 10−4, 2.5 × 10−4, and 1.2 × 10−4 mol/l, respectively. Compared with single surfactants, the mixture exhibits better surface activities since it is more efficient at decreasing the air–water surface tension. The steady state fluorescence results indicate that the hydrophobic parts of MOA‐9 molecules insert into the hydrophobic region of sodium oleate micelles to form larger and less compact mixed micelles. The decrease in zeta potential of scheelite treated with the mixed collector indicates the presence of MOA‐9 can enhance the chemical adsorption of sodium oleate on the scheelite surface. Therefore, the mixed anonic/nonionic collector can enhance the flotation behavior of scheelite at 283 K.