Firing an underwater spark discharge generates an expanding plasma which causes a spherical shockwave to propagate through the surrounding water. The shockwave can have many effects, including resonance effects on bubbles, mechanical destructive effects on solid surfaces and living organisms, and sonochemical oxidative effects on particles and chemical species present in the water. This phenomenon has been shown to improve the efficiency of ink removal in a laboratory flotation deinking cell, while simultaneously decreasing fiber loss. These process improvements are attributed to the sonochemical oxidation of ink particle surfaces, caused by shockwave-induced cavitation. This finding is supported by zeta potential measurements. Sparking was found to reduce the zeta potential of ink particles by up to 20 mV. When sparking was performed during deinking, no effect was found on either ink removal or solids loss. However, when the pulp was pretreated with sparking before flotation, a significant improvement was seen in the brightness gain. Further, fiber loss was decreased by up to 25% in a single flotation stage. The economics of this process are attractive; payback is on the order of three months based on fiber savings alone. Also, at about 1.5 kJ per spark, the power requirements are minimal with respect to the benefit derived.

La tesi realitza un estudi detallat dels principals processos que tenen lloc durant l'eliminació de tinta tòner per flotació.L'estudi del procés d'adhesió de tinta a la superfície de bombolles d'aire s'ha realitzat mitjançant visió artificial. Els resultats obtinguts han mostrat que un excés de tensioactiu provoca una disminució de la quantitat de tinta unida a la bombolla d'aire i per tant una disminució de l'eficàcia del procés de flotació. La caracterització de les bombolles d'aire presents en una cel·la de flotació ha posat de manifest que tant el cabal d'aire com la velocitat de l'agitador configuren la distribució de diàmetres final. L'estudi del procés d'eliminació de tinta per flotació en absència de fibres cel·lulòsiques ha mostrat que les variables físico-químiques estudiades són les que tenen una major influència en el procés d'eliminació de tinta tòner per flotació.Finalment s'han addicionat fibres cel·lulòsiques a la suspensió. S'ha pogut comprovar que s'aconsegueix una bona eliminació de tinta sempre i quan les condicions hidrodinàmiques siguin les adequades. / First of all the adhesion of ink particles to air bubbles surface was studied by means of artificial vision. Results obtained showed that an excess of surfactant decreases ink adsorption decreasing flotation efficiency. Air bubbles created in a lab-scale flotation cell were characterized by means of artificial vision. Results showed that air flow and agitation rate configure the final air bubble distribution.Ink removal from a flotation cell was studied without the presence of cellulose fibers. Results obtained showed that the physico-chemical variables studied had a major influence on ink removal than hydrodynamic variables studied.Finally, cellulose fibers were added to the suspension. Results obtained showed that it was possible to obtain good flotation results provided that the hydrodynamic conditions were carefully adjusted.