Zeta Potential Curves Research Articles

Correlation between zeta potential and electron paramagnetic resonance of thulium, europium co-doped yttria based suspensions

The formation of advanced ceramic components with homogeneous microstructure and functional characteristics demands a suitable control of particle dispersion. Thus, the characterization of particle stability as immersed in a liquid medium is important. The present paper reports an approach to evaluate the stability of europium, thulium co-doped yttria (YET) nanoparticles by a correlation between zeta potential and Electron Paramagnetic Resonance (EPR) techniques. Based on results, YET suspensions exhibited high stability apart from pH 10, while their isoelectric point presented a slight variation from pHIEP 8.5 to 9.2 according to thulium content 0 and 2 at.%, respectively. The peak-to-peak amplitude of EPR spectra of the YET suspensions increased as pH shifted toward alkaline condition, following zeta potential curves features. The present achievements are very useful parameters to form stable suspensions based on rare-earth oxides and to advance toward new materials for radiation dosimetry.

Comparative Analysis of Electrokinetic Properties of Periodate- and TEMPO-Oxidized Regenerated Cellulose Fabric Functionalized with Chitosan

The electrokinetic properties of materials give useful insight into the behavior of surfaces in contact with liquids and other compounds and their quantification is a powerful tool to predict their behavior during further processing and application, especially in textile materials. In this work, we perform a comparative analysis of influence of the two most common selective oxidative protocols for viscose (regenerated cellulose) fabrics on subsequent functionalization with chitosan, and cellulose fabrics’ electrokinetic properties, zeta potential in a pH range of approx. 3–10, and isoelectric point (IEP). For oxidation before deposition of chitosan, sodium periodate and 2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPO) were used. The content of functional groups in oxidized cellulose fabric (carboxyl and carbonyl groups) was determined by titration methods, while amino functional groups’ availability in samples with chitosan was determined using the CI acid orange 7 dye absorption method. This study reveals that the periodate oxidation (PO) of cellulose is more effective for binding chitosan onto material, which gave rise to higher availability of amino groups onto cellulose/chitosan material, which also influenced the shift in zeta potential curve towards positive values at a pH below 5. Analysis of a relationship between zeta potential increase at pH 4.4 and amino groups’ amount measured using absorption of CI acid orange 7 dye at pH 4.4 revealed dependency that can be fitted linearly or exponentially, with the latter providing the better fit (R2 = 0.75).

Electrokinetic study of pyrochlore in the presence of calcium and magnesium electrolytes in the context of water reuse

This paper aims to present an adequate methodology for pyrochlore from flotation process sample to be used in fundamentals surface properties studies based on zeta potential measurements under Ca and Mg electrolytes in chlorides and sulfate media. A niobium ore concentrate with small amount of fine particles (−38 µm < 2.5%), composed by 61.8% (Nb2O5), 16.5% (CaO), 7.19% (TiO2), and 6.30% (Na2O), being pyrochlore (92.8%) the Nb-bearing mineral was used. The association of acid leaching (HCl 0.1 mol/L, 70 °C, 120 min, 20 g/L and 300 rpm) and heat treatment (300 °C, 120 min and 5 g/crucible) reduced the sample's flotability by 94% which was suitable for fundamental studies. Ca and Mg ions modified the zeta potential curve of the pyrochlore without causing any changes in the pHPIE, which occurs at pH 3.1. Ca(OH)2 precipitation was not evidenced in the system containing calcium ions. Thermodynamic simulation predicted its precipitation above pH 12.3 which is outside of the range of pH studied (2.0 to 12.0). However, Mg(OH)2 precipitation associated to the formation of metal hydroxy complexes predicted by PHREEQC (version 3.7.3, llnl.dat database) contributed to the reversal in the zeta potential of the sample. The anion supporting the metallic cations also contributed to the zeta potential alteration mainly due to the ionic strength modification associated to sulfate and chloride anion charges. The alternation of chloride and sulfate sources for [Ca + Mg] system did not affect the zeta potential curves.

Colloidal processing, sintering and properties of aluminum borate Al18B4O33 porous ceramics

Aluminum borate (Al18B4O33) is one of the mixed oxides with extensive applications as due to its good thermomechanical properties. Its application requires of accessible processing techniques to provide controlled microstructures and shapes. This work presents an aqueous colloidal route to manufacture porous aluminum borate ceramics from micrometric Al18B4O33 powder (∼2.0 μm) obtained by high temperature reaction of alumina and boric acid. Zeta potential measurements determine that isoelectric point of the Al18B4O33 powders suspended in water happens at pH = 8.5 achieving a maximum positive value of 60 mV for pH < 4. Rheological characterization of concentrated slurries showed a pseudoplastic flowing behavior with a thixotropic cycle, being the yield point and the thixotropy value strongly dependents on the solid content. Shear thinning curves were fitted to a Windhab model that confirmed a face-edge interactions of the particles in the suspension.Porous ceramic with a green density of 50 % and a narrow micronic (1–2 μm) porosity are obtained by slip-casting of the optimal concentrated suspension (33 vol%). Sintering above the formation temperature showed a decrease in the density of the compacts as a consequence of the acicular grain growth. Four sintering conditions were tested to follow the structural and compositional evolution. It has been observed that thermal treatments up to 1300 °C do not affect the composition but the microstructure. At 1400 °C presence of alumina is detected indicating the initial decomposition of Al18B4O33 and evaporation of boron. At 1500 °C decomposition and evaporation phenomena are massive. The porous compacts sintered below the decomposition temperature are characterized by scanning electron microscopy, mercury intrusion porosimetry and mechanical strength, indicating that at 1300 °C Al18B4O33 achieves the more uniform microstructure and the better mechanical response.It should be noted that for the first time the Zeta potential curve for aluminum borate powder is reported. The processing methodology employed in this study, has potential application to the manufacture of porous materials with insulating applications to replace traditional ceramic materials working in harsh conditions, especially in nuclear energy systems with complex geometry by casting techniques and even by 3D printing.

The effect of dephosphorylation on the properties of αS1-casein enriched protein

αS1-Casein was dephosphorylated using alkaline phosphatase without the interference from proteolysis. The progressive dephosphorylation was monitored by alkaline urea polyacrylamide gel electrophoresis and mass spectrometry techniques. Little change was observed in the SDS-polyacrylamide gel patterns for the native and dephosphorylated αS1-casein. Dephosphorylation modified the zeta-potential of the αS1-casein, shifting the pH versus zeta potential curves to higher pH as dephosphorylation increased. The isoelectric pH of the dephosphorylated αS1-casein increased by about 0.55 pH units when compared with the native protein. Dephosphorylation increased the surface hydrophobicity of αS1-casein and a negative linear correlation was observed between the surface hydrophobicity and the isoelectric pH of αS1-casein. Dephosphorylation did not affect the secondary structure of the αS1-casein.

Investigation of dye removal ability and reusability of green and sustainable silica and carbon-silica hybrid aerogels prepared from paddy waste ash

In this study, the paddy waste ash (PA) was utilized for producing carbon-silica hybrid (PCS) and silica (PS) aerogels. X-ray fluorescence (XRF) spectrometer analysis revealed a high silica content in PA. Crystalline SiO2-cristobalite structure was observed in the X-ray diffraction (XRD) patterns of PA. As expected, the PCS and PS samples exhibited an amorphous SiO2 phase. The pore enlargement and structural improvement after aerogel synthesis were determined using a N2 adsorption-desorption analysis. The specific surface area of the PCS and PS samples were found to be 519 and 652 m2/g, respectively. From the zeta potential results, the points of zero charge (pHPZC) of the samples were found below “2” except for the PCS sample (pHPZC = 2.08). In the first stage of the Remazol Turquoise GN (RTGN) adsorption experiments, the effect of initial pH (2–8) was examined for PA, PCS, and PS sorbents. The highest dye removal value of the PCS sorbent was 61% at pH = 2, while this value was 17.9% and 21.4% for PS and PA sorbents, respectively. The removal percentage curve exhibited a similar trend to the zeta potential curve of the samples. In the experiments conducted with different amounts of sorbents, the dye removal percentage increased with increasing amounts of sorbents. The experimental results and thermodynamic calculations showed that the RTGN adsorption onto PCS was an endothermic process. Pseudo-first order, pseudo-second order and intra-particle diffusion equations were applied to determine the adsorption kinetics of RTGN onto PCS, and it was found that the experimental data was well-fitted to the pseudo-second order kinetic model. The Langmuir, Freundlich, Temkin and Dubinin-Radushkevich (D-R) adsorption isotherm models were used to define the adsorption mechanism of RTGN onto PCS. The Freundlich and Langmuir isotherm models were in agreement with our experimental data and it was concluded that RTGN adsorption on PCS surface occurred both as single layer and multi-layer, as well as took place on heterogeneous and homogeneous surfaces. Characterization analyses were conducted for the PCS sorbent after use to understand the structural changes after dye removal. The regeneration and reusability of the PCS sorbent were investigated and it was found that it preserved its initial removal ability by about 95% after four cycles. The dye removal percentage of PCS decreased by 28% after five cycles.

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

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

ADSORPTION BEHAVIOUR OF IONIC AND NON-IONIC SURFACTANTS ONTO TALC A NATURALLY HYDROPHOBIC MINERAL-A COMPARATIVE STUDY

In present study, the adsorption behaviour of surfactants which are cationic (hexadecyltrimethylammonium bromide, HTAB), anionic (sodium dodecyl sulphate, SDS) and non-ionic (Triton X-100, TX-100) onto naturally hydrophobic talc were investigated. In this scope, a series of batch adsorption tests at natural pH were performed to determine adsorption isotherms and zeta potential (ZP) measurements of the ionic and non-ionic surfactants onto talc surfaces were measured using electrophoresis technique. To understand the mechanism of the adsorption process, the adsorption of ionic and non-ionic surfactants was studied as a function equilibrium concentration (mol/L). The amount of maximum adsorption of the surfactants onto talc are ordered as in the following: TX-100 (9.0x10-5 mol/m2)&gt;HTAB (8.5x10-5 mol/m2) &gt; SDS (5.32x10-5 mol/m2). Even though both the SDS and talc have negative surface charge, SDS can adsorb onto talc. Moreover, a good correlation was seen between the adsorption isotherms and the zeta potential curves. Considering their adsorption isotherms, the ionic surfactants were showed different adsorption behaviour concerning the non-ionic surfactant molecules. The adsorption isotherms of TX-100 and SDS increase rapidly in a narrow concentration range until the plateau region, while such a sharp increase does not appear for HTAB. The maximum adsorption amount of TX-100 and HTAB is greater than SDS. The results indicate that hydrophobic interaction and hydrogen bonding play a decisive role on the adsorption of non-ionic and anionic surfactants onto talc a naturally hydrophobic mineral, whereas electrostatic interaction becomes more important in the adsorption of cationic surfactant.

Interaction of Polyoxometalates and Nanoparticles with Collector Surfaces—Focus on the Use of Streaming Current Measurements at Flat Surfaces

Streaming current measurements were used to study the interaction of polyoxometalates (POMs) and nanoparticles (NPs) with flat surfaces as an alternative, innovative approach to infer POM and NP properties of potential sparse material in terms of charge and magnitude. With respect to POMs, the approach was able to reveal subtle details of charging properties of +7 vs. +8 charge at very low POM concentrations. For NPs, the sign of charge and even the zeta-potential curve was retrieved. Concerning NPs, mutual interaction between TiO2 and SiO2 surfaces was studied in some detail via macroscopic measurements. Post-mortem analysis of samples from electrokinetic studies and separate investigations via AFM and HRTEM verified the interactions between TiO2 NPs and SiO2 collector surfaces. The interactions in the SiO2/TiO2 system depend to some extent on NP morphology, but in all our systems, irreversible interactions were observed, which would make the studied types of NPs immobile in natural environments. Overall, we conclude that the measurement of streaming currents at flat surfaces is valuable (i) to study NP and POM collector surface interactions and (ii) to simultaneously collect NPs or POM (or other small mobile clusters) for further (structural, morphological or release) investigations.

Laboratory results and mathematical modeling of spore surface interactions in stormwater runoff

Development of numerical models to predict stormwater-mediated transport of pathogenic spores in the environment depends on an understanding of adhesion forces that dictate detachment after rain events. Zeta potential values were measured in the laboratory for Bacillus globigii and Bacillus thuringiensis kurstaki, two common surrogates used to represent Bacillus anthracis, in synthetic baseline ultrapure water and laboratory prepared stormwater. Zeta potential curves were also determined for materials representative of urban infrastructure (concrete and asphalt). These data were used to predict the interaction energy between the spores and urban materials using Derjaguin-Landau-Verwey-Overbeek (DLVO) modeling. B. globigii and B. thuringiensis kurstaki sourced from Yakibou Inc., were found to have similar zeta potential curves, whereas spores sourced from the U.S. military's Dugway laboratory were found to diverge. In the ultrapure water, the modeling results use the laboratory data to demonstrate that the energy barriers between the spores and the urban materials were tunable through compression of the electrical double layer of the spores via changes of ionic strength and pH of the water. In the runoff water, charge neutralization dominated surface processes. The cations, metals, and natural organic matter (NOM) in the runoff water contributed to equalizing the zeta potential values for Dugway B. globigii and B. thuringiensis kurstaki, and drastically modified the surface of the concrete and asphalt. All DLVO energy curves using the runoff water were repulsive. The highest energy barrier predicted in this study was for Dugway B. globigii spores interacting with a concrete surface in runoff water, suggesting that this would be the most challenging combination to detach through water-based decontamination.

Surface fluorinated hematite for uranium removal from radioactive effluent

Facile and robust technologies for efficient removal of uranium from effluent and groundwater is important for sustainability and environmental protection. Herein, we describe engineered surface fluorinated nano-hematite nanoparticles (F-α-Fe2O3) for the effective removal of uranium from aqueous media. The sorption of U(VI) from aqueous solution is investigated as a function of pH, contact time and concentration using batch technique. The adsorption capacity (qm) is found to be 79 mg/g using Langmuir adsorption isotherm within 60 min at pH 5. The isothermal data shows better fit with Langmuir than Freundlich equations and follow the pseudo-second-order kinetic model. The interactions between adsorbents and adsorbates are accounted for by the Temkin isotherm model. The surface charge of F-α-Fe2O3 is evaluated by the zeta potential curve. The results are best in terms of adsorption capacity and kinetics for hematite/modified hematite material. The results are significant for the application of surface fluorinated hematite in U(VI) removal from drinking water.

Enhancement of heavy metals removal by microbial flocculant produced by Paenibacillus polymyxa combined with an insufficient hydroxide precipitation

The microbial flocculants (MBFs) hold the potential of biosorption to removal the heavy metals. However, it remains unclear what the relationship between biosorption and bioflocculation. Here, during the hydroxide precipitation of Cu, Zn, Pb and Cd, besides the commonly used pH, a three-phase division of zeta potential curves provided an orientation for the addition of MBFs. The plateau phase of zeta potential, indicating an insufficient hydroxide precipitation, was appropriate for introducing MBFGA1, a polysaccharide-based MBF. Its removal capacities on Cu, Zn, Pb and Cd reached the highest of 250 mg/g, 96.7 mg/g, 551.1 mg/g and 233.3 mg/g, respectively. A sufficiently suspended hydroxide precipitates of Pb could receive a higher dosage of MBFGA1, ensure their thorough separation, and finally improve the removal efficiency. In order to further control the residual risk of MBFGA1, the response surface methodology (RSM) was employed to optimize this process. The compromised results improved the Pb removal rate to 98% in a weak acidic solution at pH 6.2. The precipitates composition and crystallinity, the functional groups and the molecular morphology were characterized by the X-ray diffraction (XRD), fourier transform-infrared spectra (FTIRs) and atomic force microscopy (AFM), respectively. The results indicated that the negatively-charged hydroxyl, carbonyl, amino and phosphoryl played the significant roles on fixing the molecular of MBFGA1 on the precipitates, providing the points for the aggregation of flocs, and capturing the residual Pb ions. The insufficient hydroxide precipitation laid the foundation for these multiple functions of MBFGA1, and promoted the synergistic effects between biosorption and bioflocculation.

Interrelations of structure, electric surface charge, and hydrophobicity of organo-mica and –montmorillonite, tailored with quaternary or primary amine cations. Preliminary study of pyrimethanil adsorption

Abstract In this work, organo-montmorillonite (organo-Mt) and organo-synthetic mica (organo-mica), obtained by quaternary or primary amine cations (octadecyltrimethylammonium (ODTMA) or octadecyl-amine (ODA), respectively) exchanged at 50% and 100% of their respective CEC, were thoroughly characterized and tested for pyrimethanil uptake. The interlayer entrance of both surfactants for Mt loaded at 50% and 100% CEC indicated a close basal space (of around 1.5 and 1.8 nm, respectively). However, for synthetic mica (Na-Mica-4) the basal space shifted to higher values (3.5 and 3.9 nm and 4.7 and 5.0 nm, for ODTMA and ODA at 50% and 100% CEC, respectively) than those of organo-Mts, keeping the interlayer surface partially free for ODTMA-Mica-4 samples. Tg analysis revealed that the actual ODA loadings were around 40% and 80% for both clays and for ODTMA exchanged Mts, while the actual ODTMA loading for organo-mica samples did not exceed 10.6%. The decrease of negative zeta potential evidenced the presence of ODA or ODTMA at the external surfaces of organo-Mt, while the zeta potential curves for organo-mica samples described the system as a mixture of individual surfactants and Na-Mica-4 sample. Total specific surface area (TSSA) and contact angle (CA) measurements revealed a general hydrophobicity increment with the presence of both surfactants. Interrelations of these parameters point out the different affinity and steric hindrance of the polar head of both surfactants with the solid surfaces, which also conditioned pyrimethanil adsorption.

Surface characterization of microwave-treated chalcopyrite

The application of microwave radiation as an assisted grinding technique has shown great potential to improve comminution. Besides fracturing, the treatment also leads to phase transformations at the grain boundaries of the minerals, changing their surface properties and affecting downstream processes, such as flotation. Therefore, the study of the effects of microwave treatment on a mineral’s surface properties is important for the industrial application of microwave assisted grinding. In this work, the surface properties of untreated and microwave-treated chalcopyrite were investigated by XRD, XPS, ATR-FTIR, SEM, BET/BJH, IGC, ELS (zeta potential) and microflotation. While short exposure times were found to favor the formation of copper polysulphides (CuxFeySn) at the mineral surface, longer treatments converted CuFeS2 into iron oxides/ hydroxides/oxyhydroxides and sulfate at the surface and, enriched CuxFeySn underneath the oxidation layer. A shift in the zeta potential curves to less negative values was observed after treatment, reaching an IEP around pH 4.5. The collectorless floatability of chalcopyrite initially improved after exposure as its surface energy decreased. However, the samples’ surface became energetically more active after longer treatment times, and the flotation recovery decreased. Microwave treatment also increased the mineral’s specific surface area (SSA) and porosity; and changed the pore size distribution.

A fast and facile microwave irradiation method for the synthesis of ZnO@ZrO2 core-shell nanocomposites and the investigation of their optical properties

ZnO@ZrO2 core-shell nanocomposites (NCs) were prepared by a novel and accessible path employing microwave (MW) irradiation to regulate photocatalytic property of ZnO. The synthesized ZnO@ZrO2 NCs were further examined to discern their optical and chemical properties by FT-IR, XPS, XRF, XRD, FE-SEM, EDX, TEM, UV–vis, and PL analysis. XPS data analysis confirmed the presence of zirconium and oxygen on the coated surface. An almost similar zeta potential curve was observed for the pure ZrO2 and ZrO2 coated ZnO NCs, predicting the presence of the ZrO2 layer on ZnO. Photoluminescence studies show the enhanced intensity of ZnO@ZrO2 nanostructure compared to uncoated ZnO. Photocatalytic activity of ZnO could be controlled by the amorphous ZrO2 layer, which was guaranteed by the photo mineralization of methylene blue under UV irradiation at room temperature.

Development of alkaline electrochemical characteristics demonstrates soil formation in bauxite residue undergoing natural rehabilitation

AbstractMining and mineral processing industries have generated a large amount of polymineral wastes, causing the destruction and degradation of huge areas of landscapes at extensive geographical locations. Rehabilitation of these mine waste landscapes is critical to social and economic sustainability of mining and metallurgy operations, such as alumina refineries. The Bayer process to refine alumina generates large amounts of highly alkaline bauxite residues that are hazardous to plant growth. Innovative methodologies are urgently needed to address this economic and environmental challenges, one of which is soil formation from bauxite residues. Mineral weathering appears the prerequisite to the initiation of soil formation and development of functional soil properties in bauxite residue disposal areas. The present study investigated natural changes of mineralogy, zeta potential, isoelectric point, surface protonation, active alkaline groups, and associated implications for rehabilitation of the bauxite residue disposal area. Alkaline calcite, hydrogarnet, and sodalite minerals were slowly transformed or dissolved with declining levels over weathering time. Amorphous and semiamorphous minerals also decreased with a corresponding decrease in specific surface area and sorption sites. Zeta potential curve of fresh residue had steeper slope than those of aged residues. The isoelectric point of fresh residue was significantly higher, but those of aged residues were significantly lower, with a significant decrease of isoelectric point with increasing time. These attributes in mineralogy and electrochemical characteristics such as transformation of alkaline minerals, and decreases of surface protonation and active alkaline groups, may be used to help the assessment of soil formation status in the bauxite residues of different age and associated rehabilitation requirements.

Synthesis of ZnO[sbnd]Al2O3 core-shell nanocomposite materials by fast and facile microwave irradiation method and investigation of their optical properties

Alumina (Al2O3) coated ZnO core-shell structures were synthesized by a novel, fast, and facile route utilizing microwave (MW) irradiation to control photocatalytic property of ZnO. The phase analysis and the core–shell structure development were corroborated by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), X-ray fluorescence (XRF), transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray (EDX) analysis and Fourier transform infrared spectroscopy (FT-IR). The XPS results affirmed that elements on the coated surface were Al and O. Zeta potential analysis predicted the presence of Al2O3 layer on ZnO due to almost similar zeta potential curve for pure Al2O3 and Al2O3 coated ZnO nanoparticles. There was no significant change in band gap energy of ZnO after amorphous Al2O3 coating as obtained from derived data of the reflectance spectra but gradual decreasing of reflectance in the visible range, measured by UV–vis spectroscopy, of the prepared core-shell nanoparticle may be due to the coating of amorphous Al2O3 on ZnO. The photocatalytic efficiency of ZnO was reduced after amorphous Al2O3 layer as confirmed by the photodegradation of methylene blue under UV irradiation.

The ionic strength dependent zeta potential at the surface of hexadecane droplets in water and the corresponding interfacial adsorption of surfactants.

An anomalous maximum in the ionic strength dependent electrophoretic mobility curves has been observed in previous reports from particles dispersed in colloids. This maximum has been considered anomalous because it is contradictory with the Gouy-Chapman model. The existence of such a maximum has been attributed to specific ionic adsorption, a hairy layer at the surface, or the effect of the anomalous change of surface conductivity in different studies. It was also pointed out that the O'Brien-White approach based on the Gouy-Chapman model could be used to understand this maximum in electrophoretic mobility curves and lead to understandable zeta potential curves. This implied that the observed maximum was actually not "anomalous". In this work we report our simulation of ionic strength dependent zeta potential curves based on the O'Brien-White approach and experimental studies of the ionic strength dependent electrophoretic mobility of the hexadecane droplets in the hexadecane-water emulsions at different pH or in the presence of sodium dodecyl sulphate at varied concentrations. In some cases, the simulation shows that the calculation with the O'Brien-White approach does change the trend in the concerned ionic strength dependent curves. However, the simulation in some other cases also leads to similar trends in the ionic strength dependent electrophoretic mobility curves and zeta potential curves. In the experiments, both the existence and non-existence of such a maximum were observed and demonstrated to be system dependent. The corresponding molecular structure of the oil-water interface was then discussed with the analyses of the zeta potential curves and second harmonic generation signals recorded at the hexadecane-water interface.

Evaluation of the mercaptobenzothiazole degradation by combined adsorption process and Fenton reaction using iron mining residue

ABSTRACT The present study investigated the degradation of mercaptobenzothiazole (MBT), evaluating homogeneous and heterogeneous systems. An iron mineral residue from the desliming step of iron mining was used as a source in the Fenton-like reaction (advanced oxidation process). A granulometric analysis of the residue was performed and yielded fractions with high hematite (Fe2O3) and low quartz content in sieves from 74 to below 44 mm. In this particle size range, the hematite content from 58.9% to 67.4% and the Brunauer-Emmett-Teller area from 0.1345 to 1.3137 m2 g−1 were obtained. The zeta potential curves as a function of pH were obtained for the residue, the MBT solution and mixtures thereof. The adsorption of MBT in the residue and its degradation through the Fenton-like reaction were investigated. Adsorption tests and the Fenton-like reaction were carried out, where the MBT species and the residue are oppositely charged, yielding, respectively, 10% MBT adsorption on the surface of the residue and 100% MBT degradation by the Fenton-like reaction at pH 3, hydrogen peroxide concentration of 25 mg L−1, residue concentration of 3 g L−1, 200 rpm and 25°C, from a 100 mg L−1 MBT solution. MBT degradation was found to occur mainly by the heterogeneous Fenton-like process.

The depression effect and mechanism of NSFC on dolomite in the flotation of phosphate ore

Abstract The flotation response of collophane and dolomite using β-naphthyl sulfonate formaldehyde condensate (NSFC) as depressant has been investigated through micro-flotation and batch flotation in this paper. Their adsorption mechanisms were studied by means of zeta potential, contact angle, adsorption measurements and thermodynamics calculation. The flotation results indicated that NSFC exhibited a straining influence on the depression of dolomite and had little effect on the flotation of collophane minerals. Compared with the results achieved without the NSFC, the NSFA increased the collophane/dolomite selectivity index significantly. The zeta potential results showed a change in the zeta potential measurements of the minerals after NSFC interaction. This change was more significant in the zeta potential curves of dolomite than that of collophane. This difference is also verified by the results of the contact angle and adsorption measurements. The results of thermodynamics calculation indicated that the adsorption of NSFC at collophane and dolomite was chemisorption and physisorption, respectively. This study provides new insights into the separation of collophane minerals.