Michael J. Matteson

Electrocoagulation and separation of aqueous suspensions of ultrafine particles

Abstract Conventional methods for the removal of suspended ultrafine particulates in industrial effluents and wastewater treatment frequently involve the bulk addition of inorganic coagulants (e.g. aluminum or ferric salts). This electrolytic dosing is followed by sedimentation to obtain a clarified supernatant liquid. The increased size of the coagulated material facilitates subsequent solid-liquid separation processes such as filtration. An alternative separation treatment for ultrafine particles is electrocoagulation, which involves the in situ formation of ions by electrolysis. This generation of ions is succeeded by the electrophoretic concentration of the particulates in the immediate region surrounding the electrode. The addition of the electrochemically generated reagent can be controlled by adjusting the supplied power, thereby enabling optimization of the process. The effective performance of the electrocoagulation technique was evaluated with kaolinite suspensions, using a batch, stirred cell system, and a continuously flowing suspension through a series of stirred cells. Particular attention was focused on determining the rate constants for the kinetics of the particulate coagulation process. The parameters examined were electrode voltage, residence time, particle concentration, and suspension flow rate. The results showed that the electrocoagulation rate follows a second order relationship, accounting for the electrophoretic movement of the particles toward the anode.

Adsorption of gases at evaporating and condensing water surfaces

Abstract Single water droplets 0.23 cm in diameter were suspended and allowed to evaporate partially in a nitrogen stream (velocity, 50 cm s −1 ) containing various concentrations of SO 2 ((1 — 3) × 10 −3 atm) and water vapor (6.8–16.9 Torr). In a separate series of tests the SO 2 was replaced by oxygen in the 21% – 80% range. The droplets were exposed for fixed time intervals and then removed and analyzed for total sulfur oxide or oxygen content. The temperature of the droplet was monitored during the exposure time. The water vapor concentration in the bulk gas phase as well as the SO 2 or oxygen concentration determined the equilibrium saturation concentration of gas transferred to the water which was always less than at thermal equilibrium. The rate of mass transfer was controlled by heat transfer to the droplets. In the second part of this study, water vapor in various concentrations was passed through a tubular furnace and condensed at various temperatures (0 – 27 °C) to form a cloud in the presence of SO 2 (10 −5 - 10 −2 atm). The sizes of the condensed droplets were in the range 1 – 2 μm. Cloud droplets were separated from the gas stream electrostatically and analyzed for sulfur content. The concentrations of SO 2 in the aqueous phase were supersaturated compared with those at equilibrium, were relatively independent of gas phase SO 2 concentrations of less than 10 −3 atm and were strongly dependent on the amount of water condensed. A mechanism is proposed whereby hydrate formation at the water surface explains the results observed. ft*]|Present address: Corning Glass Works, Wilmington NC 28403, U.S.A.

The separation of charge at the gas-liquid interface by dispersion of various electrolyte solutions

Abstract The electrostatic charge separation associated with the pneumatic dispersion of various electrolyte solutions was investigated by measuring the current flow between the bulk phase reservoir and ground. By varying ionic concentrations, pH, types of ions, solvent, and hydrodynamic conditions, current profiles were generated to determine the influence of these parameters on the mechanism of the spray electrification process. Previous explanations for charge separation based on a shearing of the electrical double layer are discarded in favor of an approach which takes into account the liquid phase ion-pair separation arising from an imbalance of force fields responding to a bulk phase attraction for ions at a suddenly created surface.

Penetration of a multistage diffusion battery at various temperatures

Abstract A six stage miniature diffusion battery with “Collimated Hole Structure” plates is described. Its penetration is measured at temperatures between +25°C and −75°C using monodispersed sodium chloride aerosols of known size distribution with spherical particles of mean diameters between 0.2–0.6 μm and relative standard deviations of about 7%. Deposition by diffusion, impaction and interception is considered; measurements are compared to various theoretical models for the deposition mechanisms and their combinations. Agreement was found to be within about 2% at all temperatures for a model combining only diffusion and impaction as independent effects.

Oxygen absorption in evaporating and condensing water droplets

The amount of oxygen absorbed by individual drops of water suspended in a gas stream was measured. The water vapor content in the gas was regulated so that oxygen mass transfer could be observed under evaporation or condensation conditions. Other variables studied were oxygen concentration and exposure time. The rate of mass transfer of oxygen increased significantly with increasing water vapor and oxygen content in the gas. The relevance of mass transfer in growing aerosol systems to industrial hygiene is discussed.

Diffusion of aerosols at various temperatures

Abstract The theory of diffusion of aerosols has previously been experimentally verified at room temperature using large diffusion batteries of either parallel plates or long circular tubes. In this study the diffusion of aerosols was tested at low temperatures where classical Brownian movement theory may not apply. Tests were performed with a more compact diffusion battery consisting of newly developed discs of collimated hole structures with pores of 15·5 μm mean dia. and an average length to dia. ratio of 32·7. Monodisperse NaCl aerosols of sizes in the range 0·3–0.5 μm produced in a LaMer-type furnace generator, were sampled with a particle mass monitor before and after penetration through four successive units of holes. At room temperature, the diffusion coefficient, calculated from experimentally observed penetrations, agreed with the theoretically predicted coefficients. However at -16 and -72°C, the experimentally determined coefficients were 150–500 per cent greater than the theoretically predicted values.

Surfactant-Enhanced Electroosmotic Dewatering of Mineral Ultrafines

Abstract The rate and extent of electroosmotic dewatering of mineral ultrafines are dependent on the surface charge density which is quantitatively measured by the zeta potential. This research tailors the surface electrical properties of a naturally uncharged ochre (iron oxide) mineral slurry by altering the concentration of potential determining hydroxide ions to facilitate electroosmotic dewatering. The adsorption of hydroxide ions (9 × 10−4 to 9 × 10−3 M) onto the iron oxide surface provides the necessary increase in zeta potential; however, the resulting electrostatic dispersion of the particles severely limits the hydraulic permeability. Subsequent addition of cetyl trimethyl ammonium bromide (5 × 10−4 to 5 × 10−3 M), a cationic surfacant, reflocculates the particles, while maintaining sufficient zeta potential to generate an electroosmotic effect. Hydraulic performance of the treated slurries is characterized by measurement of flow rate data and specific resistance determination. Further characteri...

Particle mixing and diffusion in the turbulent wake of a sphere

The mixing and diffusion of monodisperse aerosols from a turbulent free stream into the wake created by a solid sphere were studied experimentally and analytically. Experimental measurements with regard to wake velocity profiles and momentum transport were taken in a tubular flow system by hot-wire anemometry. Particle concentration profiles, measured in the wake by means of a screen collection technique, were used to calculate mixing and diffusion parameters for the aerosols used. Experimental results are presented for the mean velocity and particle concentration profiles, wake centerline velocity and particle concentration, wake velocity and concentration half widths, and momentum and particle diffusivities. It is shown that the experimental results may be reasonably described in terms of two phenomenological theories, i.e., Prandtls mixing length and constant diffusivity in the radial cross section of the wake. Certain departures from predicted concentration behavior are empirically analyzed resulting...

The Collection of Aerosols from Gas Streams by Impaction on Multiple Spherical Targets

The impaction of 10-micrometer aerosol droplets on arrays of one to six spheres of 6-mm diameter was measured. Collection efficiencies were determined for linear arrangements parallel to and at angles to the axis of flow, as a function of spacing between spheres and free-stream Reynolds numbers (2400 to 12,000). Where the targets were arranged parallel to the flow axis and at relatively close spacings of 2 to 5 diameters center-to-center, the capture efficiencies of the second and third spheres were only 20 to 30% that of the lead sphere. At spacings of 6 to 7 diameters, the capture efficiency of each sphere became relatively independent and approached that of the lead sphere. When the targets were arranged at angles to the axis of flow, the collection efficiencies of the second and third spheres were greater than that of the leading sphere and often displayed maxima. There appeared to be a concentration of aerosol particles at the wake boundary of the leading target.

Design theory and calibration of a field type aerosol spectrometer

Abstract A cylindrical-type aerosol spectrometer, of simple compact design has been constructed and tested. The aerosol particles are injected into a horizontal centrifugal field through two ports — a pin-hole orifice situated opposite a larger port. Aerosol moving through the larger port is removed in a cumulative size deposition on half of a foil on the outer wall, and serves as clean air for aerosol injected through the pin-hole and deposited according to discrete sizes on the other half of the foil. The instrument based on a modification of a device developed by Hochrainer and offers the advantage of confining the aerosol deposit to a narrow streak or dot in the case of monodisperse particles. The spectrometer was calibrated with monodispersed polystyrene latex particles and the results were compared with a theoretical expression developed for sedimentation distances appropriate to aerosols flowing in the plane of rotation.