Time required for adhesion of flotation reagent drops to oxidized coal particles

Abstract

The time required for an air bubble to adhere firmly to a mineral particle surface, the so-called induction time, has been investigated tn [1][2][3]. During coal flotation, for a considerable number of particles adhesion of the air babble is preceded by attachment of a drop of an apotar reagent to the particle. To the best of our knowledge, the induction time for adhesion of reagent drops to the surfaces of minerals and coal has never been investigated.Attachment of a reagent drop to a coal surface is determined by its hydrophilicity [4]. It is known that flotation of hydrophilic coals, particularly oxidized types, by the reagents normally used for unoxidized coals is ineffective [4,5].Our paper deals with the time required for adhesion of drops of flotation reagents to the surfaces of coals wtth specific degrees of oxidation, the object being to find ways of speeding up flotation of oxidized coals.The contact time required for firm adhesion of reagent drops to coal particles was measured in a device similar in principle to the contact devices in [2,3], but differing from them by the fact that the contact time was recorded accurately in each experiment.A cell of optical glass or t~ansparent plastic was placed in a microthermostat, placed on the core of a solenoid. Graded, air-free coal was placed in the glass cell. A drop of the reagent was placed on the holder by means of fine-pointed pipet and was brought to a given height from the layer of coal by a three-coordinate manipulator. The diameter of the drop and the distance from the apex of the drop to the coal layer were measured by means of a horizontal microscope equipped with an ocular micrometer with a scale value of 0.01 ram. The cell was lit by an illuminator. A silver mirror, in contact with a needle, which closed an oscillator-counter circuit when the cell was raised, was attached rigidly to the cell. The distance between the silver mirror and the needle was made equal to that between the apex of the drop of reagent and the coal layer by a two-coordinate manipulator. The current was fed from the rectifier to the solenoid by a programmed relay. The cell temperature was kept constant (:~ 0.2"C) by a thermostat and a water-jet pump. The cell was returned to the initial position by a spring.At a normal current frequency of 10,000 Hz in the measuring circuit, the error of the measurement of the duration of contact of the reagent drops with the coal grains was At: 0,0001 + t(1-10;0o)c, where t is the number of pulses on the scale-of-ten counter, and ~e is the frequency of the oscillator at the moment of measurement.With the stabilized quartz oscillator the measurement error was determined largely by the remlving power of the scaler and was +0.0001 sec.The coal used for the experiments was from the Tomusinskii coalfield (Kuzbass). The coal samples, denoted by A, B, C, D, E, and F, were taken at different depths from the surface in order to obtain coals with a gradual * Deceased.KuzNIIUgleobogashchenie, Prokop'evsk.