Talc Surface Research Articles

Synthesis and characterization of silver/talc nanocomposites using the wet chemical reduction method

In this study, silver nanoparticles (Ag-NPs) were synthesized using the wet chemical reduction method on the external surface layer of talc mineral as a solid support. Silver nitrate and sodium borohydride were used as the silver precursor and reducing agent in talc. The talc was suspended in aqueous AgNO3 solution. After the absorption of Ag+ on the surface, the ions were reduced with NaBH4. The interlamellar space limits were without many changes (ds = 9.34–9.19 Aº); therefore, Ag-NPs formed on the exterior surface of talc, with dave = 7.60–13.11 nm in diameter. The properties of Ag/talc nanocomposites (Ag/talc-NCs) and the diameters of the Ag-NPs prepared in this way depended on the primary AgNO3 concentration. The prepared Ag-NPs were characterized by ultraviolet-visible spectroscopy, powder X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and Fourier transform infrared. These Ag/talc-NCs may have potential applications in the chemical and biological industries.

Effect of Adsorbed Polymers on Bubble−Particle Attachment

The influence of adsorbed dextrin-based polymers on the attachment of a rising air bubble to a talc surface has been investigated. Liquid film rupture and dynamic contact angle studies have highlighted the major role that adsorbed polymers can play in bubble-particle attachment. No direct link was established between the equilibrium contact angle of polymer-treated talc surfaces and talc flotation recovery. However, clear correlations were observed between the flotation recovery of polymer-treated talc and the measured wetting film rupture time and rate of dewetting for a bubble attaching to a talc basal plane surface treated with the polymers. The retardation of the three-phase contact line expansion caused by the adsorbed polymers was found to have the largest influence on the bubble-particle attachment. The effect of the morphology (coverage, distribution, and shape) of the adsorbed layer on the wetting film rupture and the motion of the receding water front is discussed.

Influence of Wetting and Dispersing Agents on the Interaction between Talc and Hydrophobic Particles

The interactions between a natural talc surface and a model hydrophobic particle have been investigated in aqueous solutions by employing the atomic force microscopy (AFM) colloidal probe technique. The results demonstrate the presence of long-range attractive forces due to bridging via preadsorbed or induced bubbles/cavities. Due to the natural heterogeneity of talc, and the stochastic nature of the bubble bridging process, the variability in the range and magnitude of the attraction is larger than that for cases when other interactions predominate or than that when only model surfaces are used. Addition of poly(acrylic acid), a common dispersing agent, did not affect the measured forces. Thus, we conclude that poly(acrylic acid) does not adsorb to the basal plane of talc. In sharp contrast, addition of Pluronic PE6400, a nonionic triblock polymer used as wetting agent, resulted in complete removal of the bubble-induced attractive force. Instead, a short-range steric repulsion is the dominating feature. Clearly, Pluronic PE6400 is able to displace air bubbles from the surface and prevent their formation when the particles come into contact. These are suggested to be important features of efficient wetting agents.

In Situ Particle Film ATR FTIR Spectroscopy of Carboxymethyl Cellulose Adsorption on Talc: Binding Mechanism, pH Effects, and Adsorption Kinetics

Carboxymethyl cellulose (CMC), in solution and adsorbed on the surface of talc, has been studied with ATR FTIR spectroscopy as a function of the solution pH. The solution spectra enable the calculation of the extent of ionization of the polymer (due to protonation and deprotonation of the carboxyl group) at various pH values, yielding a value of 3.50 for the pK(app)(1/2) (pH at which half of all carboxyl groups are ionized) in a simple electrolyte solution and a value of 3.37 for the pK(app)(1/2) in solutions containing magnesium ions (3.33 x 10(-4) M). The spectra of the adsorbed layer reveal that CMC interacts with the talc surface through a chemical complexation mechanism, via the carboxyl groups substituted on the polymer backbone. The binding mechanism is active at all pH values down to pH 2 and up to pH 11. The adsorbed layer spectra reveal that protonation and deprotonation of the polymer are affected by adsorption, with an increase in the pK(app)(1/2) to a value of 4.80. Spectra of the adsorbed polymer were also acquired as a function of the adsorption time. Adsorption kinetic data reveal that the polymer most likely has two different interactions with the talc surface, with a stronger interaction with the talc edge through chemical complexation and a weaker interaction with the talc basal plane presumably through the hydrophobic interaction.

In situ particle film ATR-FTIR studies of CMC adsorption on talc: The effect of ionic strength and multivalent metal ions

The adsorption of carboxymethyl cellulose (CMC) onto talc has been studied using particle film ATR FTIR. This approach allows for the in situ acquisition of vibrational spectra, i.e., acquired as the polymer is adsorbing from solution, enabling adsorption to be studied as a function of varying solution conditions. In this work, adsorption has been studied in the absence and presence of calcium ions, as well as under conditions of increased ionic strength of a simple electrolyte. Calcium ions have been implicated in the enhancement of adsorption of CMC on talc and an increase in the effectiveness of CMC as a talc depressant. The in situ spectra of the adsorbed polymer indicate clearly that CMC interacts chemically with the talc surface. In addition, the effects of ionic strength and the presence of Ca ions on the adsorption of the polymer were seen to be similar: they increased the adsorbed amount and altered the polymer conformation at the surface.

Stabilizing Effect of Chitosan on Curcumin from the Damaging Action of Alkaline pH and Ultraviolet Light

The naturally available biopolymer, chitosan (MW = 10 kD) binds to yellow herbal spice, curcumin with high affinity (K a ~ 400 μM) and moderate capacity (n∼20 Mole/Mole of Chitosan) at considerably high pH (pH∼10.5, 0.1 M NaBO 3 ). Binding is pH sensitive and reduces nearly to zero at the acidic range (pH∼5.0). The presence of high salt (0.1 M-2.0 M NaCl) does not alter the binding affinity (K a ) rather increases the capacity ∼12 %. Interestingly, the affinity (K a ) remains unaltered even when the chitosan was coated on powdered Talc surface causing ∼ 40% reduction in binding capacity (n). The chitosan-curcumin complex formed at high pH shows remarkable stability at pH 7.0 - 10.5 and in high salt concentrations (1.0 M - 4.0 M NaCl) showing least dissociation effect. Lowering the pH (<7.0) enables the complex to dissociate efficiently. The bound curcumin remains chemically unaltered when analyzed by high-pressure liquid chromatography (HPLC). As per logical expectation, the glucosamine unit within chitosan molecule participates in the binding process as evidenced by dose-dependent enhancement of optical density (O.D.) (λ = 440 nm) of curcumin in the presence of glucosamine at pH - 8.5. The thin layer chromatography (TLC) of glucosamine-curcumin complex confirms the chemically unaltered state of curcumin within the complex. The enhancement of O.D. in basic environment by glucosamine was unnoticed in acidic condition, pH ∼ 4.8. Perhaps, protonation (-NH 3 + ) of the - NH 2 (s) within sugar moiety in acidic environment hinders curcumin to interact. As for interest, the complexed curcumin molecule in chitosan or glucosamine acquires substantial stability from the alkaline pH (∼10.5) or UV damage (λ∼240 nm).

The influence of metal cations on the behaviour of carboxymethyl celluloses as talc depressants

Abstract Metal cations have been shown to depress the floatability of siliceous minerals indicating an interaction with the mineral surface. In this work, the effect of metal cations on the interaction of sodium carboxymethyl cellulose (CMC) depressants and talc has been studied. Equilibrium adsorption and microflotation studies were conducted on pure talc with a range of ions (Ca 2+ , Mg 2+ , K + ) and ionic strengths, using CMCs of two different degrees of substitution (DS). In order to probe the effect of the ions on the polymer molecules themselves, intrinsic viscosity measurements were made where the ionic strength (IS), pH and type of ion were varied. The results of the adsorption studies showed that the divalent cations Ca 2+ and Mg 2+ were far more efficient at promoting adsorption on to the talc surface than the monovalent K + ion. The higher DS CMC had a much more stringent requirement than the low DS CMC for the presence of high ionic strength electrolyte in order to achieve good adsorption. The microflotation studies complemented these results and showed that talc was more efficiently depressed by CMCs when Ca 2+ and Mg 2+ ions were present than when only K + was present and that the high DS CMC was less efficient at the ionic strength used than the lower DS CMC. Intrinsic viscosity measurements of a CMC in different ionic strength solutions of K + and Ca 2+ ions showed that over a wide pH range, Ca 2+ ions caused the CMC molecule to coil more than the K + ions. This is in keeping with the observed increase in adsorption density on the talc surface with Ca 2+ ions and subsequent improvement in the depressant activity. These results were complemented by those from size exclusion chromatography with triple detection where the light scattering data revealed that for a solution of CMC of DS 0.78 in 10 −2 IS Ca(NO 3 ) 2 the radius of gyration was 28% smaller than in 10 −2 IS KNO 3. The adsorption studies show however, that at high ionic strength (10 −1 ), when the CMCs are fully coiled, the enhancement of bonding due to Ca 2+ and Mg 2+ ions is still significantly greater than for K + ions, which implies that there is also an interaction between the CMCs and the divalent ions on the talc surface which increases CMC adsorption and facilitates depression.

Anisotropic Character of Talc Surfaces as Revealed by Streaming Potential Measurements, Atomic Force Microscopy, Molecular Dynamics Simulations and Contact Angle Measurements

A study of the interfacial properties of the basal plane and the edge surfaces of talc is described in this paper. The isoelectric points measured at two different crystallographic surfaces by the streaming potential method were found to be similar and exist at about pH 3.0. In the case of the edge surface, the zeta potential increases at higher pH values which can be attributed to the hydration of surface magnesium ions. The forces between the edge of a 20 μm talc particle and the two different crystallographic surfaces of talc were measured at various pH values using atomic force microscopy (AFM). These measurements show differences between the properties of the basal plane and edge of the talc. Finally, the differences in the hydration of the basal plane and the edge of talc are revealed from molecular dynamics (MD) simulations. The basal plane of talc is much less hydrated than the edge as can be seen from the water density distribution functions which correlate quite well with the contact angle measurements at the basal plane surface and the edge surface. Improved quality of the edge surface was achieved by sandblasting (erosion with alumina) and research regarding the characteristics of this edge surface is in progress.

Anisotropic Character of Talc Surfaces as Revealed by Streaming Potential Measurements, Atomic Force Microscopy, Molecular Dynamics Simulations and Contact Angle Measurements

A study of the interfacial properties of the basal plane and the edge surfaces of talc is described in this paper. The isoelectric points measured at two different crystallographic surfaces by the streaming potential method were found to be similar and exist at about pH 3.0. In the case of the edge surface, the zeta potential increases at higher pH values which can be attributed to the hydration of surface magnesium ions. The forces between the edge of a 20 μm talc particle and the two different crystallographic surfaces of talc were measured at various pH values using atomic force microscopy (AFM). These measurements show differences between the properties of the basal plane and edge of the talc. Finally, the differences in the hydration of the basal plane and the edge of talc are revealed from molecular dynamics (MD) simulations. The basal plane of talc is much less hydrated than the edge as can be seen from the water density distribution functions which correlate quite well with the contact angle measurements at the basal plane surface and the edge surface. Improved quality of the edge surface was achieved by sandblasting (erosion with alumina) and research regarding the characteristics of this edge surface is in progress.

The effect of lignosulfonates on the floatability of talc

The floatability of talc in the presence of six lignosulfonates was studied in a series of Hallimond tube flotation experiments in the alkaline pH range from about 7 to 11.2. The strongest depression of talc was observed at higher pH values (pH ∼ 11) when lime was used for pH adjustments. The depressing power of lignosulfonates correlated very well with the adsorption density of the polyelectrolytes on the talc surfaces. As the adsorption of lignosulfonates increased, their depressing action was also enhanced. The adsorption data strongly suggest that electrostatic repulsion between the negatively charged talc surfaces and the strongly anionic polyelectrolytes prevents lignosulfonates from adsorbing onto the talc surfaces and depressing the flotation of the mineral. The results demonstrate an “activating” role of calcium ions in the depression of talc by lignosulfonates. Calcium species on the talc surface appear to act as adsorption sites for the anionic polyelectrolytes, particularly at higher pH values adjusted with lime when increasing amounts of specifically-adsorbing calcium hydroxy-cations start appearing in solution.

The use of ToF-SIMS and microflotation to assess the reversibility of binding of CMC onto talc

Carboxymethyl cellulose (CMC) is commonly used as a depressant for talcaceous minerals. To assess whether CMC depressants are strongly, or weakly and reversibly bound to the surface of talc, desorption experiments were conducted on New York talc. The floatability was monitored through microflotation experiments, combined with the determination of the CMC coverage on talc by ToF-SIMS. CMC adsorption and desorption were carried out in distilled water and in electrolyte containing Ca 2+ ions. CMC adsorption levels were higher using Ca 2+ electrolyte, in line with the depression behavior in the microflotation tests. Washing did not affect the flotation behavior. ToF-SIMS showed that CMC coverage of the talc particles was good and the distribution homogeneous. Adsorption and subsequent desorption in distilled water however, showed a partially restored floatability after desorption, which could be related to an inhomogeneous CMC distribution on the talc surface as shown by ToF-SIMS. By additional exposure to Ca 2+ ions CMC redistribution occurs causing depression.

A molecular dynamics simulation study of water structure and adsorption states at talc surfaces

A preliminary molecular dynamics simulation (MDS) study regarding interfacial phenomena at talc surfaces is reported. The use of computer methodology in the development of mineral processing technology has long been of interest to Professor R. P. King and, in this regard, it is appropriate that such a computer study of flotation chemistry be included in this special IJMP volume. Simulation results show that due to the absence of hydrogen bonding sites, the hydrophobic talc basal plane is not in close contact with water molecules, thus leaving a 3 Å void space at the basal plane. As expected from the previous laboratory studies the hydrophobic chains of the cationic surfactant dodecyl trimethyl ammonium bromide (DTAB) preferentially adsorb at the talc basal plane surface through hydrophobic interactions. On the other hand, the breakage of Si–O and Mg–O bonds provides the talc edge surface with many hydrogen bonding sites which facilitates the formation of strong hydrogen bonds with water dipoles. Thus, water wets the hydrophilic edges, and, in contrast to the face surface, simulation results reveal that the DTAB cationic surfactant adsorbs at the talc edge surface through electrostatic interactions. Finally, when a model dextrin molecule is considered, the simulation results suggest that the hydrophobic interaction between the talc basal plane surface and the hydrophobic moieties in the dextrin molecule plays a significant role in dextrin adsorption at talc surfaces. Whereas, at the talc edge surface the dextrin molecule is not able to displace water molecules at the edge surface.

Influence of Addition of Polyethylene-block-polyacrylate Copolymer on the Impact Strength of PP/EPDM/talc Composites

The influence of addition of low density polyethylene-block-Polyacrylate copolymer (PE-diblock) on the impact strength of ternary phase polypropylene (PP) composites containing ethylene-propylene-diene terpolymer (EPDM) and talc was investigated. The surface of talc was treated with 3-glycidoxypropyltrimethoxysilane (GPMS) in order to enhance the interaction between talc surface and the functional group (carboxy group) of the additive copolymers. The composites were prepared by twin-screw extruder. The impact strength of PP/EPDM (5wt%)/talc (30wt%) increased markedly with the addition of PE-diblock content up to 3wt% and about 40% impact strength improvement was achieved for the composite by the addition of PE-diblock. Scanning electron micrograph observation of PP/EPDM/PE-diblock/GPMS-treated talc composite suggested that the edges of talc particles were included in elastomer phase on the basis of interaction between PE-diblock and elastomer.

Structure of the {001} talc surface as seen by atomic force microscopy: comparison with X-ray and electron diffraction results

In this study the surface structure of a centimetre sized crystal of talc from the Trimouns deposit (Ariege, France) was imaged by atomic force microscopy. The direct image shows detailed characteristics of clay tetrahedral surfaces. The unit-cell dimensions obtained 30 using atomic force microscopy (aor = 5.47±0.28 and bor = 9.48±0.28 A) are found to be slightly higher, with an increased uncertainty, than those obtained using X-ray diffraction (aor = 5.288±0.007 and bor = 9.159±0.010 A) and selected-area electron diffraction (aor = 5.32±0.03 and bor = 9.22±0.05 A). Talc has a quasi-ideal surface, clean of strong 34 structural distortion as compared to most of other clay minerals and unlikely surface 35 relaxation. The observation on the obtained image of apparent cell dimension enlargement is 36 then more likely attributed to instrumental artefacts, also responsible for scattered values of unit-cell parameters rather than related to any surface structural features.

The Influence of Polymer Structure and Morphology on Talc Wettability

Advancing water contact angles were measured on freshly cleaved talc faces as well as on talc particles. The intrinsic hydrophobicity of talc was shown to be due to the dominance of the apolar components of the work of adhesion. Polyacrylamides and polysaccharides adsorb onto the surface of talc, displaying strikingly different morphologies. Adsorbed amount, apparent layer thickness, and polymer structure control talc wettability.

Ab initio quantum-mechanical modeling of pyrophyllite [Al2Si4O10(OH)2] and talc [Mg3Si4O10(OH)2] surfaces

Bulk and slab geometry optimizations and calculations of the electrostatic potential at the surface of both pyrophyllite [Al2Si4O10(OH)2] and talc [Mg3Si4O10(OH)2] were performed at Hartree–Fock and DFT level. In both pyrophyllite and talc cases, a modest (001) surface relaxation was observed, and the surface preserves the structural features of the crystal: in the case of pyrophyllite the tetrahedral and octahedral sheets are strongly distorted with respect to the ideal hexagonal symmetry (and basal oxygen are located at different heights along the direction normal to the basal plane), whereas the structure of talc deviates slightly from the ideal hexagonal symmetry (almost co-planar basal oxygen). The calculated distortions are fully consistent with those experimentally observed. Although the potentials at the surface of pyrophyllite and talc are of the same order of magnitude, large topological differences were observed, which could possibly be ascribed to the differences between the surface structures of the two minerals. Negative values of the potential are located above the basal oxygen and at the center of the tetrahedral ring; above silicon the potential is always positive. The value of the potential minimum above the center of the tetrahedral ring of pyrophyllite is −0.05 V (at 2 A from the surface), whereas in the case of talc the minimum is −0.01 V, at 2.7 A. In the case of pyrophyllite the minimum of potential above the higher basal oxygen is located at 1.1 A and it has a value of −1.25 V, whereas above the lower oxygen the value of the potential at the minimum is −0.2 V, at 1.25 A; the talc exhibits a minimum of −0.75 V at 1.2 A, above the basal oxygen.

Interaction forces between talc and hydrophobic particles probed by AFM

The interaction between cleaved talc surfaces and hydrophobic probe particles, silanized silica and thiolized gold, has been investigated employing the atomic force microscopy (AFM) colloidal probe technique. These model systems have hydrophobicities similar to some of the talc-pitch combinations present during pulp and paper manufacture. The talc surfaces used in this study, in the [0 0 1] plane, show a micro-roughness with sharp peaks of up to 3 nm in height. The force profiles obtained demonstrate the predominance of a long-range attractive force. However, the range and magnitude of the attractive force show large variability. The variability of the attractive force, and the frequent observations of clear steps in the force curve demonstrate that it is caused by gas/vapor cavities bridging the surfaces once the surfaces are brought sufficiently close together. The results suggest that the same mechanism is of importance in applications where talc is used as a collector for pitch.

ＥＰＤＭブレンドポリプロピレン／タルク複合材料の耐衝撃性に及ぼすポリエチレン‐ポリアクリレートブロックコポリマーの添加効果

The influence of addition of low density polyethylene-block-Polyacrylate copolymer (PE-diblock) on the impact strength of ternary phase polypropylene (PP) composites containing ethylene-propylene-diene terpolymer (EPDM) and talc was investigated. The surface of talc was treated with 3-glycidoxypropyltrimethoxysilane (GPMS) in order to enhance the interaction between talc surface and the functional group (carboxy group) of the additive copolymers. The composites were prepared by twin-screw extruder. The impact strength of PP/EPDM (5wt%)/talc (30wt%) increased markedly with the addition of PE-diblock content up to 3wt% and about 40% impact strength improvement was achieved for the composite by the addition of PE-diblock. Scanning electron micrograph observation of PP/EPDM/PE-diblock/GPMS-treated talc composite suggested that the edges of talc particles were included in elastomer phase on the basis of interaction between PE-diblock and elastomer.

Influence of adsorbed polysaccharides and polyacrylamides on talc flotation

The adsorption and action of various polymers on talc has been investigated. Two families of polymers (starch-based polysaccharides and synthetic polyacrylamides) with specific molecular weights and functional group chemistry were studied. Adsorption isotherms, acoustophoresis, and contact angle studies enabled polymer adsorption behaviour, adsorbed layer thickness, and the hydrophilicity of the polymer-treated talc surface to be determined. Flotation testing on the treated talc revealed a hierarchy of effectiveness within the group of polymers studied. The observed trends in flotation performance are discussed with reference to the measured polymer layer properties. A 3D correlation plot of adsorbed layer thickness and contact angle against flotation recovery indicates that it may be feasible to predict an order of effectiveness for polymeric depressants based solely on measurements of the adsorbed layer properties, without recourse to flotation testing. This approach would be desirable when screening large numbers of potential depressants.

Effects of substrate structure and composition on the structure, dynamics, and energetics of water at mineral surfaces: A molecular dynamics modeling study

Molecular dynamics computer simulations of the molecular structure, diffusive dynamics and hydration energetics of water adsorbed on (0 0 1) surfaces of brucite Mg(OH) 2, gibbsite Al(OH) 3, hydrotalcite Mg 2Al(OH) 6Cl · 2H 2O, muscovite KAl 2(Si 3Al)O 10(OH) 2, and talc Mg 3Si 4O 10(OH) 2 provide new insight into the relationships between the substrate structure and composition and the molecular-scale structure and properties of the interfacial water. For the three hydroxide phases studied here, the differences in the structural charge on the octahedral sheet, cation occupancies and distributions, and the orientations of OH groups all affect the surface water structure. The density profiles of water molecules perpendicular to the surface are very similar, due to the prevalent importance of H-bonding between the surface and the water and to their similar layered crystal structures. However, the predominant orientations of the surface water molecules and the detailed two-dimensional near-surface structure are quite different. The atomic density profiles and other structural characteristics of water at the two sheet silicate surfaces are very different, because the talc (0 0 1) surface is hydrophobic whereas the muscovite (0 0 1) surface is hydrophilic. At the hydrophilic and electrostatically neutral brucite and gibbsite (0 0 1) surfaces, both donating and accepting H-bonds from the H 2O molecules are important for the development of a continuous hydrogen bonding network across the interfacial region. For the hydrophilic but charged hydrotalcite and muscovite (0 0 1) surfaces, only accepting or donating H-bonds from the water molecules contribute to the formation of the H-bonding network at the negatively and positively charged interfaces, respectively. For the hydrophobic talc (0 0 1) surface, H-bonds between water molecules and the surface sites are very weak, and the H-bonds among H 2O molecules dominate the interfacial H-bonding network. For all the systems studied, the orientation of the interfacial water molecules in the first few layers is influenced by both the substrate surface charge and the ability by the surfaces to facilitate H-bond formation. The first layer of water molecules at all surfaces is well ordered in the xy plane (parallel to the surface) and the atomic density distributions reflect the substrate crystal structure. The enhanced ordering of water molecules at the interfaces indicates reduced orientational and translational entropy. In thin films, water molecules are more mobile parallel to the surface than perpendicular to it due to spatial constraints. At neutral, hydrophilic substrates, single-monolayer surface coverage stabilizes the adsorbed water molecules and results in a minimum of the surface hydration energy. In contrast, at the charged and hydrophilic muscovite surface, the hydration energy increases monotonically with increasing water coverage over the range of coverages studied. At the neutral and hydrophobic talc surface, the adsorption of H 2O is unfavorable at all surface coverages, and the hydration energy decreases monotonically with increasing coverage.