Anthony Francis Collings

Effect of ultrasound on surface cleaning of silica particles

Abstract One substantial benefit of ultrasonics in mineral processing can be the removal of surface coatings of clay and iron oxides from mineral surfaces. This is mainly achieved through the large, but very localised, forces produced by cavitation. The application of sonication to the reduction of iron oxide in a silica sand from 0.025% to less than 0.012% Fe2O3 — the difference between material suitable for clear glass container ware and that suitable for table ware — is presented. The ultimate reduction in iron oxide contamination is dependent on the sonication power, whereas increasing the concentration of Na2CO3 in the suspension, up to 0.2%, shortens the sonication time to approach this limit.

The application of power ultrasound to the surface cleaning of silica and heavy mineral sands.

Power ultrasound may be used in the processing of minerals to clean their surfaces of oxidation products and fine coatings, mainly through the large, but very localised, forces produced by cavitation. Results of the application of power ultrasound to remove iron-rich coatings from the surfaces of silica sand used in glass making and to improve the electrostatic separation of mineral sand concentrates through lowering the resistivity of the conducting minerals (ilmenite and rutile) are presented. Parameters affecting ultrasonic cleaning, such as input power and levels of reagent addition, are discussed. In particular, we present data showing the relationship between power input and the particle size of surface coatings removed. This can be explained by the Derjaguin approximation for the energy of interaction between a sphere and a flat surface.

Ultrasonic absorption in polymer gel dosimeters.

Ultrasonic absorption in polymer gel dosimeters was investigated. An ultrasonic interferometer was used to study the frequency (f) dependence of the absorption coefficient (alpha) in a polyacrylamide gel dosimeter (PAG) in the frequency range 5-20 MHz. The frequency dependence of ultrasonic absorption deviated from that of an ideal viscous fluid. The presence of relaxation mechanisms was evidenced by the frequency dependence of alpha/f(2) and the dispersion in ultrasonic velocity. It was concluded that absorption in polymer gel dosimeters is due to a number of relaxation processes which may include polymer-solvent interactions as well as relaxation due to motion of polymer side groups. The dependence of ultrasonic absorption on absorbed dose and formulation was also investigated in polymer gel dosimeters as a function of pH and chemical composition. Changes in dosimeter pH and chemical composition resulted in a variation in ultrasonic dose response curves. The observed dependence on pH was considered to be due to pH induced modifications in the radiation yield while changes in chemical composition resulted in differences in polymerisation kinetics.

Ultrasonic destruction of pesticide contaminants in slurries

The use of high power ultrasound to destroy pesticide contaminants in sand slurries is reported. Small quantities of DDT, chlordane, atrazine, 2,4,5-T and endosulfan in solvent were added to washed, screened sand and deposited onto the sand by slow evaporation of the solvent. Fifty wt.% slurries for all five pesticides and 20 wt.% slurries of atrazine and 2,4,5-T were sonicated for periods up to 30 min and samples were withdrawn at various intervals and analysed to follow the kinetics of contaminant destruction. Seventy percent destruction of the contaminant was obtained for four of the 50 wt.% slurries with approximately 50% destruction of 2,4,5-T in 10 min of sonication whereas, in the 20 wt.% slurries of atrazine and 2,4,5-T, and 75% and 85% reduction, respectively, was obtained in 10 min. We postulate that better stirring of the slurry will improve these rates of contaminant destruction.

Large scale environmental applications of high power ultrasound

In the present work, the use of high power ultrasound as a process tool for the removal of persistent organic pollutants (POPs) from soil and the treatment of bauxite red mud waste from the Bayer process is discussed. Laboratory scale experiments have confirmed that the application of high power ultrasound to slurries of contaminated soil and of bauxite ore can treat two major environmental problems cost-effectively. Destruction rates of POPs in soil of 90% and higher have been achieved whereas 85% iron oxide has been extracted from red mud waste leaving a low-iron fraction of approximately 50% by weight which is more environmentally friendly. A 4x4 kW pilot plant capable of treating 2.5 tonnes of slurry per day has been commissioned to provide more accurate estimates of power and energy requirements to allow scale-up to industrial use.

Flow patterns in an ultrasonic liquid flow meter

Abstract Flow visualisation studies have been undertaken for the case of an in-line, ultrasonic transducer housing in a cylindrical cross-section metering duct by direct observation of injected dye and of particles illuminated by a laser sheet. Results are presented for single and three bluff-body strut attachment of the transducer housing to the duct wall at Reynolds numbers (based on mean velocity and meter duct diameter) of 750, 1900 and 7950. Transducer face and wall fillet recirculation zones were dependent on the number of attachment struts and on the flow rate. The results are discussed in terms of their consequences for the performance of an ultrasonic transit time flow meter.

Soil Remediation Using High‐Power Ultrasonics

Abstract The application of high power ultrasonics to concentrated slurries of soils and sediments is discussed and we show that very high destruction rates can be achieved for many of the more notorious chemical contaminants, including PCBs and organochloride pesticides. Results are presented which suggest that a convenient and cost‐effective technology is generally applicable. Experiments have been conducted at laboratory and pilot plant scales showing that reduction of contaminant concentration by 90% or more can be achieved with low energy budgets and without the generation of dangerous breakdown products.

Ultrasonic Metering of Gas Flows

The large acoustic impedance mismatch between gases and conventional ultrasonic transducers has precluded the commercial ultrasonic metering of gas flow. This hurdle has been overcome by the invention of a low-impedance transducer which is also reported at this conference. This paper describes the development of a sequential-pulse, transit-time, ultrasonic flowmeter based on the low-impedance transducer. The flowmeter offers significant advantages over current domestic gas meters in size, accuracy, turn-down ratio and compatibility with new meter reading technologies. Natural gas flowrates ranging from 0.013 to 8 m3/h have been measured accurately at temperatures ranging from -13 to 47°C.