The Effect of Electrohydraulic Discharge on Flotation Deinking Efficiency
Carleton, James Richard
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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.