Antti Grönroos

Ultrasonic depolymerization of aqueous polyvinyl alcohol

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.

Ultrasound assisted cleaning of ceramic capillary filter

Research in the fields of filtration and dewatering connected with the use of ultrasound (US) has been carried out mainly with small laboratory-scale batch or continuously operating devices. So far the only large scale industrial cake filtration applications have been developed and manufactured by Larox Oyj for mining industry. These applications apply ultrasound for cleaning of ceramic capillary action elements having at maximum total filtration area of approximately 150 m(2). Several hundreds of filter units have been delivered worldwide during the past two decades.

Experimental Aspects of Scaling Control in Membrane Filtration of Mine Water

This study focused on membrane filtration of neutralized pond water, which may be necessary when good quality water is required for hydrometallurgical processes. Neutralized mine water can still have fairly high metal and sulphate levels, which can hinder discharge and reuse possibilities. Both nanofiltration and reverse osmosis are effective in removing metals and sulphate, but scaling can be a severe problem. Microfiltration as a pre-treatment method, although meant for particle removal, seemed to decrease the amount of scalants, thus delayed scaling on the membrane surface and increasing water recovery for both nanofiltration and reverse osmosis. It is possible that the presence of particles in the feed water promoted crystal growth in the turbulent flow and caused the removal of dissolved constituents. Alternatively, supersaturation could have occurred, allowing microfiltration to remove the scalants as particles. The Liqum sensor indicated that redox values started to increase again just before scaling began due to precipitation in the supersaturated membrane concentrate solution. Thus, the sensor seemed to provide real time, in-situ, early-stage scaling warning.ZusammenfassungDiese Studie untersucht die Membranfiltration von neutralisiertem Wasser, welche notwendig ist, um eine gute Wasserqualität für hydrometallurgische Prozesse zur Verfügung zu stellen. Auch neutralisiertes Grubenwasser kann hohe Metall- und Sulfatkonzentrationen enthalten, welche die Ausleitung und Wiederverwendungsmöglichkeiten einschränken. Sowohl die Nanofiltration als auch die Umkehrosmose sind effektive Verfahren zur Entfernung von Metallen und Sulfat. Aber die Krustenbildung stellt dabei ein ernstes Problem dar. Mikrofiltration als eine Vorreinigungsstufe, eigentlich zur Partikelentfernung gedacht, scheint die Menge der Krustenbildner zu verringern und somit die Krustenbildung an der Membranoberfläche, sowohl bei der Nanofiltration als auch beider Umkehrosmose, zu verzögern. Es ist möglich, dass das Vorhandensein von Partikeln im Zuflusswasser das Kristallwachstum in den turbulenten Strömen fördert und die Entfernung gelöster Bestandteile verursacht. Alternativ könnte bei der Mikrofiltration eine Übersättigung aufgetreten sein, welche die Entfernung von Krustenbildnern als Partikel zur Folge hat. Der Liqum Sensor zeigte an, dass kurz vor der Krustenbildung, die Redoxwerte durch die Ausfällung in der übersättigten Membranlösung stiegen. Somit scheint der Sensor eine in-situ-Echtzeitwarnung zu liefern.ResumenEste estudio se enfocó sobre la filtración por membrana de agua neutralizada que podría ser necesario cuando se requiere agua de buena calidad para procesos hidrometalúrgicos. El agua de mina neutralizada aún puede contener relativamente altos niveles de metales y sulfatos que pueden complicar su descarga y sus posibilidades de uso. La nanofiltración y la ósmosis inversa son efectivas en remover metales y sulfatos pero la precipitación de especies inorgánicas puede ser un serio problema. La microfiltración como un método de pretratamiento, aunque es válido para la remoción de partículas, parece disminuir la cantidad de incrustaciones, postergando así la precipitación de especies inorgánicas sobre la superficie de la membrana e incrementando la recuperación de agua tanto en nanofiltración como en ósmosis inversa. Es posible que la presencia de partículas en el agua de alimentación promueva el crecimiento de cristales en el flujo turbulento y cause la precipitación de los constituyentes disueltos. Alternativamente, podría haber ocurrido una supersaturación que remueva a los incrustantes como partículas. El sensor Liqum indicó que los valores redox comenzaban a crecer de nuevo justo antes que la incrustación comenzara debido a la precipitación en la solución supersaturada. Así, el sensor parece proveer una alarma temprana, in situ y en tiempo real, de generación de incrustaciones.水泥窑粉尘去除酸性废水金属离子机理