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Ultrasonication has proved to be a highly advantageous method for depolymerizing macromolecules because it reduces their molecular weight simply by splitting the most susceptible chemical bond without causing any changes in the chemical nature of the polymer. Most of the effects involved in controlling molecular weight can be attributed to the large shear gradients and shock waves generated around collapsing cavitation bubbles. In general, for any polymer degradation process to become acceptable to industry, it is necessary to be able to specify the sonication conditions which lead to a particular relative molar mass distribution. This necessitates the identification of the appropriate irradiation power, temperature, concentration and irradiation time. According to the results of this study the reactors constructed worked well in depolymerization and it was possible to degrade aqueous polyvinyl alcohol (PVA) polymer with ultrasound. The most extensive degradation took place at the lowest frequency used in this study, i.e. 23 kHz, when the input power was above the cavitation threshold and at the lowest test concentration of PVA, i.e. 1% (w/w). Thus this study confirms the general assumption that the shear forces generated by the rapid motion of the solvent following cavitational collapse are responsible for the breakage of the chemical bonds within the polymer. The effect of polymer concentration can be interpreted in terms of the increase in viscosity with concentration, causing the molecules to become less mobile in solution and the velocity gradients around the collapsing bubbles to therefore become smaller.

During iron ore sintering, material coalescence in the bed determines the physical properties of the agglomerated product. Sinter density and structural quantification by 2D image analysis were used to elucidate the degree of coalescence and densification achieved during sintering. In the first program, samples -representing increasing temperatures -were obtained from three locations down a sintered bed. Sinter density, determined by liquid pycnometry, was found to be strongly dependent on green granulated bed bulk density. Image analysis results indicated a strong dependence between sinter density and porosity. Results also show that more coalescence occurs for blends containing porous ores at increasing sintering temperatures. When sinter basicity and/or coke rate is low the effect of temperature on coalescence is less pronounced for all blends. The second program compared coalescence using 19 to 21 mm sinter from eight different pot tests and blends containing significant porous ores. For the same ore blend sintered under different conditions, measured trends in sinter density and porosity were in line with expectations but the changes were not large because the material in sinter has a high specific gravity of over four and changes in porosity were less than 5%. It was concluded that small increases in coke level could decrease sinter porosity by 5%, resulting in increased sinter tumble strength. Both programs show that when melt volume is high, small increases in temperature have a significant effect on coalescence in the flame front.

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Chemical, physical and biological technologies for removal of sulphate from mine tailings pond water (8 g SO/L) were investigated. Sulphate concentrations of approximately 1,400, 700, 350 and 20 mg/L were obtained using gypsum precipitation, and ettringite precipitation, biological sulphate reduction or reverse osmosis (RO) after gypsum pre-treatment, respectively. Gypsum precipitation can be widely utilized as a pre-treatment method, as was shown in this study. Clearly the lowest sulphate concentrations were obtained using RO. However, RO cannot be the only water purification technology, because the concentrate needs to be treated. There would be advantages using biological sulphate reduction, when elemental sulphur could be produced as a sellable end product. Reagent and energy costs for 200 m/h tailings pond water feed based on laboratory studies and process modelling were 1.1, 3.1, 1.2 and 2.7 MEur/year for gypsum precipitation, ettringite precipitation, RO and biological treatment after gypsum precipitation, respectively. The most appropriate technology or combination of technologies should be selected for every industrial site case by case.