M.A. Cabrerizo

Flotation properties of celestite in aqueous solutions of ionic surfactants

Abstract An experimental study is reported on the flotation behaviour of celestite (SrSO 4 ) in solutions of n-alkylammonium chlorides (with 10, 12 and 14 carbon atoms), sodium n-alkylsulfonates (with 12, 14 and 16 carbon atoms) and sodium dodecylsulfate. Previous experiments showed that pH determines the sign and magnitude of the net surface charge of the mineral. Hence, the effect of pH on the flotation recovery is given special attention. The increase in flotation with pH when alkylammonium chlorides are used as collectors (up to a given pH value in which an important decrease takes place) is explained on the basis of (mainly) electrostatic interactions between the mineral and the alkylammonium ion, as well as of the hydrolysis of the latter. The results with sulfonates and sulfate can be qualitatively explained assuming an important contribution of chemical interactions to the net adsorbate-adsorbent interaction. The effect of chain length on the flotation recovery is well determined when cationic collectors are used. The (slight) solubility of celestite can be given as an explanation for the fact that no such clear dependence appears when alkylsulfonate solutions are used.

A study of the electrophoretic properties of montmorillonite particles in aqueous electrolyte solutions

Abstract Experimental results on the electrophoretic velocity and mobility on Ca- and Na-montmorillonite in water and aqueous electrolyte solutions are reported. The effects of particle concentration, electric field strength and, particularly, pH and concentration and type of the electrolyte present in the dispersion medium are considered. The very weak variation of the mobility with the volume fraction of solids is discussed in the light of the predictions of three theoretical models of collective electrophoresis. The null effect of the variations of the applied field strength is considered on a qualitative basis assumming a simple double layer model. Finally, the general trends of the interesting behaviour of montmorillonite in different conditions of electrolyte concentration and valency are discussed taking into account the structural characteristics of the clay.

The zeta potential of celestite in aqueous electrolyte and surfactant solutions

Determination du potentiel electrocinetique des solutions aqueuses de SrSO 4 et de chlorure de dodecylammonium

Comparative electrophoretic mobility and streaming current study for ζ-potential determination

Abstract The main purpose of this work is to compare the ζ -potential obtained from streaming current and electrophoretic mobility measurements. The electrokinetic experiments were performed using two anionic polystyrene latexes whose surface charge density and average particle diameter were −9.8 and −3.4 μC cm −2 and 0.65 and 1.2 μm, respectively. For the conversion two theories were used, the Levine et al. theory for the streaming current and O’Brien–White for the electrophoretic mobility measurements. This way most of the phenomena taking place at the interface are taken into consideration. The ζ -potentials obtained this way compare well for the largest latex with the lowest surface charge. However, there are substantial discrepancies for the smaller latex sample with the higher surface charge density. These discrepancies are discussed in terms of the effect of the surface conductance on the electrokinetic signal.

Adsorption-desorption in celestite (SrSO4) flotation with a cationic-type collector

Abstract A relationship between the flotation activity of celestite, the adsorbed amount of a cationic collector (dodecylammonium chloride, DDACl) and pH was studied by adsorption measurements and flotation tests. It was found that with this collector effecient flotation (90–95%) takes place in DDACl solutions at concentrations above 5·10 −5 mol dm −3 and pH below 9. This corresponds to, at most, 3–5 statistical DDACl monolayers adsorbed on the surface. However, the actual coverage with the collector is probably non-uniform.

A study of the primary electroviscous effect in pyrex glass suspensions

ABSTRACT An experimental investigation on the electrokinetic phenomenon known as primary electroviscous effect is described for suspensions of Pyrex glass, a highly charged and well known material. By means of an automatic method, the viscosity of the suspensions is measured for different volume fractions of solids, at various electrolyte concentrations and pH values. These measurements allow the estimation of the electroviscous coefficient, p. The electrophoretic mobility was determined for the same systems and zeta potential calculated from these experimental data in order to carry out the comparison between the measured values of p and different theoretical predictions. A qualitative agreement between theory and experiment was found in many cases, but the rigorous theories seem to systemmatically underestimate the experimental p values. The reasons for this disagreement are discussed in addition to the general trends of the electrokinetic behaviour of Pyrex glass.

Effect of the Solvent Composition on the Electrophoretic Coefficient of Polymer Model Colloids

An experimental investigation on electrophoresis of polystyrene beads in methanolwater and ethanol-water is described. The electrophoretic transport is considered from the point of view of Thermodynamics of Irreversible Processes. The electrophoretic phenomenological coefficient of model polymer colloids in both binary liquid mixtures has been measured. The influence of the composition of the mixture on the electrophoretic coefficient has been discussed on the basis of the variation of C-potential, viscosity, dielectric permittivity and density with the molar fraction of alcohol in binary mixtures. The concentration dependence of the electrophoretic coefficient is found to be non-linear in both cases studied. The ̂ -potential has been shown to play a significant role in the internal structure of the electrophoretic coefficient (/21) for the polystyrene/water-ethanol system only.

On the bulk and surface electric conductivity in montmorillonite suspensions

Abstract Experimental results on the electrical conductivity of Na-montmorillonite suspensions in solutions of different electrolyte concentrations and pH values are used for the determination of the relative conductivity increment, ΔK, and the surface conductivity, κσ, of such suspensions. A previous estimation of the conductivity, K∞, of the liquid media employed is required. Hence, different methods for the evaluation of K∞ are discussed. Best results are obtained when K∞ is computed theoretically, a good qualitative agreement being found with the general physical principles of the phenomenon of electrical conductivity in suspensions. A comparison is carried out between the experimental values of ΔK and those deduced from a detailed theoretical analysis; again, the qualitative agreement is, generally speaking, good, but theory seems to underestimate the results. Reasonable values of κσ are obtained only if the clay particles are idealized as oblate spheroids, worse results being found if they are considered spherical in shape. The experimental conductivity data allow the estimation of the axial ratio of the spheroids.

A device for the automatic determination of the surface tension of surfactant solutions

An experimental device and procedure are described for the fully automatic determination of the surface tension of liquids and (particularly) surfactant solutions. The computer-controlled system is capable of yielding precise and reproducible values of that quantity. The possibilities of equilibration times selected by the user, cleaning the surface by suction, and adding fresh solution prior to each measurement are emphasised among other capabilities. As an example, a solution of sodium dodecylsulphate (10-3 mol dm-3) plus sodium chloride (10-2 mol dm-3) is extensively studied.