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

Facile Fabrication of Recyclable, Superhydrophobic, and Oleophilic Sorbent from Waste Cigarette Filters for the Sequestration of Oil Pollutants from an Aqueous Environment

The oil industry is plagued with regular incidences of spills into the environment, causing environmental damage to flora and fauna, especially in marine environments where spills easily travel long distances from their sources. This study was carried out to investigate a simple two-step process for the conversion of waste cigarette filters into a superhydrophobic and oleophilic sorbent for application in oil/water separation and spill clean-up. Ultrasonically cleaned filters were surface modified by chemical vapour deposition using methyltrichlorosilane. The results show that the functionalised waste filters achieved superhydrophobic properties with a water contact angle of 154 ± 3.5°, adsorbing 16 to 26 times their weights in various oils, which is a better oil sorption performance than those of commercially available non-woven polypropylene adsorbents. Also, the sorption capacity did not significantly deteriorate after 20 cycles of reuse, with up to 75% sorption capacity retained. The surface modified filters demonstrated excellent water repellency, oil sorption, and recyclability showing their potential application for full scale oil spill clean-up

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

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

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

In vitro characterization of HIV type 1 biological clones from asymptomatic and symptomatic pediatric patients

To investigate the mechanisms of HIV-1 cytopathogenicity, functional biological HIV-1 clones were isolated from two infected children with high viral loads in vivo. Clone HC4 was isolated from a symptomatic child and clone GC6 8-4 was isolated from an asymptomatic child. These clones were characterized for their ability to induce syncytia, and to replicate and induce single-cell death in peripheral blood-derived normal CD4 T cell cultures containing anti-CD4 antibody. Despite similar viral loads as determined by p24 antigen production or viral RNA expression, GC6 8-4 was noncytopathogenic and HC4 was cytopathogenic. Since we had demonstrated that mitochondrial dysfunction correlated with HIV-1-induced cell death, we determined whether the cytopathogenic HC4 clone decreased mitochondrial viability using a mitochondrial-specific dye, rhodamine-123. Following infection, mitochondrial viability decreased in cells infected with HC4 by day 4 and continued to decline through day 7 when compared to uninfected cells. By day 7 postinfection, greater than 80% of the cells in culture were dead. Similar analyses on CD4 T cells infected with the noncytopathogenic GC6 8-4 demonstrated that mitochondria remained functionally viable and \u3e 90% of the cells excluded trypan blue. These studies describe a cell culture system to study single-cell death in the absence of syncytia and secondary infection. Results with two patient-derived HIV-1 biological clones suggest that loss of mitochondrial viability may play a role in HIV-1-induced cytopathogenicity

Poly(4-vinylpyridine) as a platform for robust CO2 electroreduction

The development of efficient and robust catalysts is critical for the viability of the electrocatalytic conversion of CO2 into useful chemicals. Herein, we discover a new class of metal-polymer electrocatalysts with incorporated mechanisms of their stabilization which is based on a poly(4-vinyl pyridine). We attribute the outstanding catalytic properties of the new hybrid material to new intrinsic mechanisms of the metal stabilization offered by the N-heteroaromatic polymer. More generally, our study offers a new simple strategy to design and prepare robust CO2 reduction electrocatalyst