Physico-Chemical Aspects of Adsorption of Surface Active Agents on Minerals

Basic principles and some special aspects of adsorption on minerals are discussed. Electrostatic forces, lateral interaction between surfactants, chemical and other forces are discussed in more detail as well as the role of the chemical state of surfactants. It is pointed out the importance of pretreatment of mineral systems which can affect their electrokinetic behaviour as well as the presence of other charged particles in solution if electrostatic forces play a major role. The sharp increase in electrophoretic mobility at a given adsorbtion density for certain conditions and appearance of maximum flotation of certain minerals with hydrolyzable sur- . factants a t the point of zero charge are attributed to micellisation and covalent bonding respectively with possible polymer formation. Other factors such as hydrogen bonding, solvation or desolvation of species and hydrophobic bonding are mentioned. Special attention is paid to the adsorption in micellar solutions and adsorption kinetics

Bio-Based Surfactants for Benign Cosmetic Products: Principles and Applications

Bio-based surfactants offer a unique opportunity alone as well as mixed with traditional surfactants to meet the increasing demand for benign cosmetic actives in this era of concern for toxicity of chemicals. Our overall aim is to understand interactions of typical bio-based surfactants with biosurfaces. Sugar based alkyl glucosides, sophorolipids and protein based surfactants show high surface activity and salt tolerance. Importantly, when mixed with conventional surfactants the systems exhibited synergistic interactions that are useful for reducing the dosage requirements and thus the resultant chemical foot print. The unique surface activity and biodegradability make this group of surfactants potential candidates for future cosmetic agents. The interfacial and colloidal properties of these reagents play critical role in determining their performance in many other industrial applications, such as detergency, enhanced oil recovery and water treatment. We are now exploring the next generation greener and microbial (genetically engineered) and plant-derived based surfactants which show robust emulsification properties and self-assembly behavior of systems involving oil. We also explore role of these surface active agents in the design of novel nano-systems as active drug carriers and disease diagnosis

Adsorption of Surfactants on Mineral Solids

Factors influendng 1he adsorption of ionic surfactants on solids are outlined. Emphasis is placed on the role of electrostatic forces and of lateral association within adsorbed layers. MechanLsms leading to charge gene.ration on solids are descdbed, and the dependence of adsorption on charge effects i\u27s mustrated by reference to published data on a number of different solid surfactan:t systems. It is shown how the electrostatic factor can be strongly modified · by the presence of inorganic salts. The importance of chain-chain interactions is illustrated by the influence of chains length and composition on adsorption, and also by the pH dependence of the adsorption of long chain, weak electrolytes. This leads to a discussion of the possible role of highly surface active long chain complexes. Lastly, the influence of polymers on the adsorption of surfactants is discussed

A population balance model for flocculation of colloidal suspensions by polymer bridging

A detailed population balance model for flocculation of colloidal suspensions by polymer bridging under quiescent flow conditions is presented. The collision efficiency factor is estimated as a function of interaction forces between polymer coated particles. The total interaction energy is computed as a sum of van der Waals attraction, electrical double layer repulsion and bridging attraction or steric repulsion due to adsorbed polymer. The scaling theory is used to compute the forces due to adsorbed polymer and the van der Waals attraction is modified to account for presence of polymer layer around a particle. The irregular structure of flocs is taken into account by incorporating the mass fractal dimension of flocs. When tested with experimental floc size distribution data published in the literature, the model predicts the experimental behavior adequately. This is the first attempt towards incorporating theories of polymer-induced surface forces into a flocculation model, and as such the model presented here is more general than those proposed previously

Impact of pulp rheology on selective recovery of value minerals from ores

Rheological behavior of mineral pulps plays a critical role in almost all mineral processing unit operations. Although the impact of rheology in unit operations such as grinding and slurry transport has received much attention in the past, this is not the case for flotation. The pathway by which the pulp rheology influences the flotation performance is not well understood. The aim of this paper is to explore how physical (shape, size and morphology) and surface chemical properties of minerals contribute to pulp rheology and pathways by which rheology can influence selective value mineral recovery and/or concentrate grade. Systematic studies involving spiking experiments (deliberate addition of fibrous minerals and other solids), measurement of pulp viscosity and yield stress, flotation tests, SEM, EDX and XRD were conducted on a Ni ore and a Cu ore. A phenomenological model was developed. The key components of the model are the formation of a macro-network comprising micro-aggregates of fibrous minerals which significantly increases pulp viscosity, and as a result impedes gas dispersion and bubble-particle attachment and influence froth phase properties. Additionally, the role of various reagent types in regulating pulp rheological behavior was explored

Chemical analysis by X-ray spectroscopy near phase transitions in the solid state

The methods discussed in this work show that the types of changes which may be observed, by precise XAS measurements of Absorbance A versus temperature, across a phase transition are: the changes in the relaxation time of the final states due to fluctuations near a phase transition; the detection of the anomalous Bragg condition coupled to phonon modes XAS enhancement that identifies the temperature interval where the phonon modes are active, the symmetry changes which introduce new allowed transitions to finite states below an element edge, near Tc indicate what symmetry changes occur, and the method of XTDAFST0 = XAFS(T) - XAFS(T0), allows the precise measurement of the progressive changes in the Debye-Waller factor versus T near a phase transition, and identify (when no other structural changes occur, except in the vibrational modes of a specific bond) the bond responsible for the transition. The methods have been applied to the superconducting transition in layer cuprates and the metal to insulator transition in NiS2-xSex

BEHAVIOR OF SURFACTANT MIXTURE AT SOLID/LIQUID AND OIL/LIQUID INTERFACE IN CHEMICAL FLOODING SYSTEMS

The aim of the project is to develop and evaluate efficient novel surfactant mixtures for enhanced oil recovery. Preliminary ultra-filtration tests suggest that two kinds of micelles may exist in binary surfactant mixtures at different concentrations. Due to the important role played in interfacial processes by micelles as determined by their structures, focus of the current work is on the delineation of the relationship between such aggregate structures and chemical compositions of the surfactants. A novel analytical centrifuge application is explored to generate information on structures of different surfactants aggregates. In this report, optical systems, typical output of the analytical ultracentrifuge results and four basic experiments are discussed. Initial sedimentation velocity investigations were conducted using nonyl phenol ethoxylated decyl ether (NP-10) to choose the best analytical protocol, calculate the partial specific volume and obtain information on sedimentation coefficient, aggregation mass of micelles. The partial specific volume was calculated to be 0.920. Four softwares: Optima{trademark} XL-A/XL-I data analysis software, DCDT+, Svedberg and SEDFIT, were compared for the analysis of sedimentation velocity experimental data. The sedimentation coefficient and aggregation number of NP-10 micelles obtained using the first three softwares at 25 C are 209, 127, and 111, respectively. The last one is closest to the result from Light Scattering. The reason for the differences in numbers obtained using the three softwares is discussed. Based on these tests, Svedberg and SEDFIT analysis are chosen for further studies. This approach using the analytical ultracentrifugation offers an unprecedented opportunity now to obtain important information on mixed micelles and their role in interfacial processes

Study of properties of modified silicones at solid-liquid interface: Fabric-silicone interactions

Abstract Silicones are special reagents that impart desired surface properties such as softness, bounciness and antiwrinkle properties to fabrics and related materials. Although these finishing processes have been practiced routinely, very little is known about the mechanisms involved in modification so that they could be improved. The current study was undertaken to develop basic understanding of the mechanisms responsible for surface modification of fibers using silicones. PDMS based amino silicone emulsions, quaternized to various degrees using dimethyl sulphate, were used in the present study. The electrokinetic properties of the modified silicones were studied as a function of pH. It was expected that the silicone emulsions would show a steady positive zeta potential throughout the pH range due to the quaternization by dimethyl sulphate. Surprisingly, a sudden drop in the zeta potential was observed around pH 8 with the samples turning hazy in the pH range of 8-10. Turbidimetric studies also showed a sudden increase in the turbidity in the pH range 8-10 where commercial processes also encounter problems. It was concluded that the emulsions were destabilized at pH 8-10 thus rendering them ineffective for surface treatment. In order to identify reason for the improvement in fabric properties, fiber structure was monitored using atomic force microscopy. It was observed that the treated fibers were far smoother, relaxed and uniform as compared to the untreated fibers. Thus the morphology of the fabric is modified in a specific way by treatment with specialty silicones

Highly Ordered Microstructure of Flocculated Aggregates

RACT By contrast to recent descriptions of fractal aggregates, we report the stroct.ure of non-fractal I(IJ'egates of silica spheres made by polymeric flocculation. Using small angle neutron scattering, -measure a highly unifonn distance on the order of 1-2 particle diameters between particles in .&c. Thus there is a distinct short range order in the Roc slrocture which is not apparent from macroscopic meaaurement& of t.he system. Conversely, t.he stnICture of aggregates resulting from lation by t.he addition of an inorganic electrolyte (CaC~) shows no preferred distance beparticles. The application of SANS to the study of aggregation by Rocculation and coagu--tion is discussed