Nanoparticle flotation collectors II: the role of nanoparticle hydrophobicity

The ability of polystyrene nanoparticles to facilitate the froth flotation of glass beads was correlated to the hydrophobicity of the nanoparticles. Contact angle measurements were used to probe the hydrophobicity of hydrophilic glass surfaces decorated with hydrophobic nanoparticles. Both sessile water drop advancing angles, θ(a), and attached air bubble receding angle measurements, θ(r), were performed. For glass surfaces saturated with adsorbed nanoparticles, flotation recovery, a measure of flotation efficiency, increased with increasing values of each type of contact angle. As expected, the advancing water contact angle on nanoparticle-decorated, dry glass surfaces increased with surface coverage, the area fraction of glass covered with nanoparticles. However, the nanoparticles were far more effective at raising the contact angle than the Cassie-Baxter prediction, suggesting that with higher nanoparticle coverages the water did not completely wet the glass surfaces between the nanoparticles. A series of polystyrene nanoparticles was prepared to cover a range of surface energies. Water contact angle measurements, θ(np), on smooth polymer films formed from organic solutions of dissolved nanoparticles were used to rank the nanoparticles in terms of hydrophobicity. Glass spheres were saturated with adsorbed nanoparticles and were isolated by flotation. The minimum nanoparticle water contact angle to give high flotation recovery was in the range of 51° < θ(np(min)) ≤ 85°.     

Separation and determination of the sulph-hydryl flotation collectors using ion-interaction chromatography

Summary This paper discusses simple and practical methods for the separation and determination of various sulph-hydryl flotation reagents by ion-interaction chromatography. Physical and chemical parameters such as column length, the support, and the constituents of the mobile phase and their respective concentrations were considered. A set of capacity factors, determined for a given set of conditions, is used to assist in the design of separation methods. The developed methodology enables the determination of various sulph-hydryl compounds in a given mixture of flotation reagents, distinction between compounds with the same functionality, and the separation of structural isomers of a particular compound. The applicability of the methods was demonstrated by the analysis of some commercial flotation reagents, as well as samples generated in an investigation of synergism of the sulp-hydryl collectors.     

QSAR modeling of flotation collectors using principal components extracted from topological indices

Several topological indices were calculated for substituted-cupferrons that were tested as collectors for the froth flotation of uranium. The principal component analysis (PCA) was used for data reduction. Seven principal components (PC) were found to account for 98.6% of the variance among the computed indices. The principal components thus extracted were used in stepwise regression analyses to construct regression models for the prediction of separation efficiencies (Es) of the collectors. A two-parameter model with a correlation coefficient of 0.889 and a three-parameter model with a correlation coefficient of 0.913 were formed. PCs were found to be better than partition coefficient to form regression equations, and inclusion of an electronic parameter such as Hammett sigma or quantum mechanically derived electronic charges on the chelating atoms did not improve the correlation coefficient significantly. The method was extended to model the separation efficiencies of mercaptobenzothiazoles (MBT) and aminothiophenols (ATP) used in the flotation of lead and zinc ores, respectively. Five principal components were found to explain 99% of the data variability in each series. A three-parameter equation with correlation coefficient of 0.985 and a two-parameter equation with correlation coefficient of 0.926 were obtained for MBT and ATP, respectively. The amenability of separation efficiencies of chelating collectors to QSAR modeling using PCs based on topological indices might lead to the selection of collectors for synthesis and testing from a virtual database.     

Adsorption mechanism of mixed cationic/anionic collectors in feldspar-quartz flotation system

The adsorption mechanism of mixed cationic alkyl diamine and anionic sulfonate/oleate collectors at acidic pH values was investigated on microcline and quartz minerals through Hallimond flotation, electrokinetic and diffuse reflectance FTIR studies. In the presence of anionic collectors, neither of the minerals responded to flotation but the diamine flotation of the minerals was observed to be pH and concentration dependent. The presence of sulfonate enhanced the diamine flotation of the minerals by its co-adsorption. The difference in surface charge between the minerals at pH 2 was found to be the basis for preferential feldspar flotation from quartz in mixed diamine/sulfonate collectors. The infrared spectra revealed no adsorption of sulfonate collector when used alone but displayed its co-adsorption as diamine-sulfonate complex when used with diamine. The presence of sulfonate increased the diamine adsorption due to a decrease in the electrostatic head-head repulsion between the adjacent surface ammonium ions and thereby increasing the lateral tail-tail hydrophobic bonds. The mole ratio of diamine/sulfonate was found to be an important factor in the orientation of alkyl chains and thus the flotation response of minerals. The increase in sulfonate concentration beyond diamine concentration leads to the formation of soluble 1:2 diamine-sulfonate complex or precipitate and the adsorption of these species decreased the flotation since the alkyl chains are in chaotical orientation with a conceivable number of head groups directing towards the solution phase.     

Differential pulse polarographic determination of thiol flotation collectors and sulphide in waters

Thiol collectors and sulphide can be determined together by differential pulse polarography. Ethyl xanthate, diethyl dithiophosphate, and diphenyl dithiophosphate have been determined in concentrations from 10 muM to 2 mM, and sulphide from 1 muM to 0.5 mM. The method is reliable and rapid; however, the exact behaviour of the thiol collectors must be known since the pattern of current peaks changes as the concentration increases. This method has been used in the study of sulphide mineral flotation and could be utilized at full-scale flotation plants.     

HPLC determination of collectors used for the flotation of heavy metal minerals

 A reversed-phase HPLC-method for the separation of mixtures of collectors for the flotation of heavy metal minerals is described. It is based on a Nucleosil 5C18 column, isocratic elution and UV-detection at 238 nm. The mobile phase is methanol-water-5% phosphoric acid (40:60:4, v/v). The method is applied to the determination of six collectors in aqueous solutions from flotation processes. The relative standard deviations are 1.6–3.2% in the concentration range 2–10 mg/L. The detection limits are 1 μg/L for 8-hydroxyquinoline, dimethylglyoxime and salicylic acid, 2 μg/L for salicylhydroxamic acid and 5 μg/L for benzenetriazol and salicylaldoxime, respectively. Received: 19 April 1996/Revised: 14 August 1996/Accepted: 23 August 1996     

Increase in flotation activity of salts of higher aliphatic amines, potassium chloride collectors

For increasing the flotation activity of potassium chloride collector, salts of higher aliphatic amines, effects of a temperature of collector solutions, mixtures of homologues of different chain length, a solubilization of organic oleophilic compounds in the colloidal solutions of amine salts were examined on their micellar structure and ion-molecular composition.     

Combination collectors in adsorption colloid flotation for multielement determination in waters by neutron activation

A method is described for the collection of small amounts of both anions and cations in water samples by adsorption colloid flotation with a combination collector, prior to quantitation by neutron activation. In the presence of 20 mg of iron(III) and 2 ml of 0.1 M ammonium pyrrolidinedithiocarbamate, As(V), Cd(II), Co(II), Cu(II), Hg(II), Mo(VI), Sn(IV), Sb(III), Te(VI), Ti(IV), U(VI), V(V) and W(VI) are quantitatively collected from 1 -l samples at a pH 5.8 ± 0.1; sodium dodecyl sulfate and sodium oleate are used as surfactant. Recoveries for all the elements tested are greater than 90%. Results for a number of elements in sea waer and an NBS water standard, SRM 1643a, are given.     

Understanding the role of ion interactions in soluble salt flotation with alkylammonium and alkylsulfate collectors

There is anecdotal evidence for the significant effects of salt ions on the flotation separation of minerals using process water of high salt content. Examples include flotation of soluble salt minerals such as potash, trona and borax in brine solutions using alkylammonium and alkylsulfate collectors such as dodecylamine hydrochloride and sodium dodecylsulfate. Although some of the effects are expected, some do not seem to be encompassed by classical theories of colloid science. Several experimental and modeling techniques for determining solution viscosity, surface tension, bubble-particle attachment time, contact angle, and molecular dynamics simulation have been used to provide further information on air–solution and solid–solution interfacial phenomena, especially with respect to the interfacial water structure due to the presence of dissolved ions. In addition atomic force microscopy, and sum frequency generation vibrational spectroscopy have been used to provide further information on surface states. These studies indicate that the ion specificity effect is the most significant factor influencing flotation in brine solutions.     

Development of a technology for sulfuric acid breakdown of a bertrandite-phenacite-fluorite flotation concentrate

The possibility of direct sulfuric acid breakdown of the bertrandite-phenacite-fluorite concentrate from the Ermakovskoe deposit was studied experimentally using samples taken from 23 different batches of the concentrate over the period from 1997 to 2004.     

Preconcentration and determination of trace metals in synthetic sea water by flotation with inert organic collectors

The preconcentration and separation of copper, cadmium, cobalt and nickel 8-quinolinolates in solutions of high salinity including synthetic sea water is studied with phenolphthalein or 2-naphthol as collector and octadecylamine as surfactant. A simplex optimization is applied. Yields > 90% are achieved for Ni, Co and Cd with both collectors, but the copper yield is low. Flame atomic absorption spectrometry is used for the final measurements.     

Quantitative property-property relationship (QPPR) approach in predicting flotation efficiency of chelating agents as mineral collectors

The QPPR approach has been used to model cupferrons as mineral collectors. Separation efficiencies (Es) of these chelating agents have been correlated with property parameters namely, log P, log Koc, substituent-constant sigma, Mullikan and ESP derived charges using multiple regression analysis. Es of substituted-cupferrons in the flotation of a uranium ore could be predicted within experimental error either by log P or log Koc and an electronic parameter. However, when a halo, methoxy or phenyl substituent was in para to the chelating group, experimental Es was greater than the predicted values. Inclusion of a Boolean type indicative parameter improved significantly the predictability power. This approach has been extended to 2-aminothiophenols that were used to float a zinc ore and the correlations were found to be reasonably good.     

Quantitative property-property relationship (QPPR) approach in predicting flotation efficiency of chelating agents as mineral collectors

The QPPR approach has been used to model cupferrons as mineral collectors. Separation efficiencies (Es) of these chelating agents have been correlated with property parameters namely, log P , log K oc , substituent-constant σ , Mullikan and ESP derived charges using multiple regression analysis. Es of substituted-cupferrons in the flotation of a uranium ore could be predicted within experimental error either by log P or log K oc and an electronic parameter. However, when a halo , methoxy or phenyl substituent was in para to the chelating group, experimental Es was greater than the predicted values. Inclusion of a Boolean type indicative parameter improved significantly the predictability power. This approach has been extended to 2-aminothiophenols that were used to float a zinc ore and the correlations were found to be reasonably good.     

Metamaterials: a new frontier of science and technology

Metamaterials, artificial composite structures with exotic material properties, have emerged as a new frontier of science involving physics, material science, engineering and chemistry. This critical review focuses on the fundamentals, recent progresses and future directions in the research of electromagnetic metamaterials. An introduction to metamaterials followed by a detailed elaboration on how to design unprecedented electromagnetic properties of metamaterials is presented. A number of intriguing phenomena and applications associated with metamaterials are discussed, including negative refraction, sub-diffraction-limited imaging, strong optical activities in chiral metamaterials, interaction of meta-atoms and transformation optics. Finally, we offer an outlook on future directions of metamaterials research including but not limited to three-dimensional optical metamaterials, nonlinear metamaterials and "quantum" perspectives of metamaterials (142 references).     

Determination of silver in fresh water by atomic absorption spectrometry following flotation preconcentration by iron(III) collectors

Colloid precipitate flotation of silver from fresh water is applied for preconcentration and separation. Optimal conditions using hydrated iron(III) oxide and iron(III) tetramethylenedithiocarbamate as collectors were investigated. Various factors affecting the silver recovery, including collector mass, nature of the supporting electrolyte, pH of the working medium, electrokinetic potential of the collector particle surfaces, type of surfactant, induction time etc., were checked. Within the optimal pH range (5.5–6.5) silver was separated quantitatively (94.9– 100.0%) with 30 mg Fe(III) as collector. The content of silver was determined by electrothermal atomic absorption spectrometry and compared to that from inductively coupled plasma-atomic emission spectrometry. The detection limit of silver by the method described is 0.01 μg/L.     

Spectrophotometric determination of flotation collectors and organic reagents in ore treatment process liquors and effluents with an atomic absorption spectrometer

An atomic absorption spectrometer has been adapted to measure the absorbance of solutions of flotation reagents (e.g. xanthate, mercaptobenzothiazole, dithiophosphate, and Z-200) in the concentration range 0–10 mg l^-1 in aqueous and non-aqueous solvents in the u.v. and visible regions. The absorbance values obtained are similar to those from a u.v.—visible spectrophotometer and straight-line calibration graphs are obtained. Hollow-cathode lamps emitting the desired wavelengths can be selected from wavelength tables of atomic lines. This technique allows a metallurgical analytical laboratory to extend its range of determinations without additional cost by the use of an a.a.s. unit as a u.v.—visible spectrometer.     

The flotation separation of apatite from dolomite using a fatty acid-based collector and the mechanisms of adsorption

In this work, GJBW, a fatty acid-based agent, was used as an efficient collector to separate dolomite from apatite to achieve high-purity apatite. The flotation performance of dolomite and apatite in the phosphate (H₃PO₄) system treated with sodium oleate (NaOl) and GJBW, respectively, was studied and compared. Microheat tests, surface characterization, and flotation solution chemistry calculations were used to evaluate the adsorption mechanism of GJBW onto dolomite. The smoothness and flatness of dolomite treated and untreated with GJBW may be also detected via atomic force microscopy (AFM). Microflotation results illustrated that GJBW performed better than NaOl for separating apatite from dolomite under the H₃PO₄ system. The grade of P₂O₅ in concentrates treated with 10 mg/L GJBW was 31.49%, which was 4.98% higher than that of NaOl. The recovery rate of P₂O₅ was 87.05%, which was 4.71% higher than that of NaOl. Microheat tests demonstrated that GJBW generated a higher heat of adsorption onto dolomite than did the same concentration of NaOl, significantly enhancing the dolomite's hydrophobicity. Fourier transform infrared spectroscopy (FTIR), zeta potential, flotation solution chemistry calculations, and surface characterization further demonstrated that GJBW may ionize large amounts of RCOO⁻ and H (RCOO)²⁻ ions in solution, which can be significantly chemisorbed with numerous sites of Ca and Mg exposed to dolomite, forming dense point-like adsorption onto dolomite. These findings shed more light on the mechanism of interaction between GJBW and dolomite, which has profound implications for the study and use of fatty acid-based treatments in phosphate ores.     

Determination of trace amounts of the flotation collectors ethyl xanthate and diethyl dithiophosphate in aqueous solutions by cathodic stripping voltammetry

A cathodic stripping method has been devised for determination of low concentrations of the flotation collectors ethyl xanthate, diethyl dixanthogen and diethyl dithiophosphate. The limit of detection for ethyl xanthate was 1 x 10(-8)M by the differential pulse technique and with deposition for 2 min at -0.1 V. Three peaks were observed, each increasing in different concentration ranges of ethyl xanthate. A reaction mechanism is proposed. The detection limit for diethyl dithiophosphate was 1 x 10(-7)M by the differential pulse technique and with deposition for 3 min at -0.1 V. The analytical method was applied to determine ethyl xanthate in a sulphide mineral flotation plant and the amount of adsorbed ethyl xanthate and diethyl dithiophosphate on Cu(2)S. It was found that the adsorbed ethyl xanthate forms nearly a monolayer on Cu(2)S and that the amount of adsorbed diethyl dithiophosphate corresponds approximately to 0.4 monolayer.