A new method and in-house device for treating secondary fiber were developed. The method is based on the fluid-jet cavitation technique. In this apparatus, pulp suspension was injected into the reacting vessel by using a high-speed jet that produced cavitation bubbles around the jet. The impact of the collapse of cavitation bubbles detached ink, binder, and other contaminants from fiber surfaces. The effects of the cavitating jet (CV-jet) treatment on deinking of the pulp from mixed office waste (MOW) and old newsprint/old magazines (ONP/OMG) mixture were studied. The basic experiments on cavitation control showed that the intensity and region of cavitation were controlled by the jet velocity and the pressure difference in the reacting vessel. The CV-jet generated broad ultrasound waves; the conventional ultrasonic apparatus generated an intrinsic frequency. The MOW test results showed that CV-jet, even without chemicals and high temperature, decreased dirt speckles and reached almost the same dirt reduction level as the mill kneader. Moreover, the CV-jet minimized fiber damage during the process. This yielded pulp handsheets giving much higher paper strength compared with pulp from the kneader. The ONP/OMG test revealed that CV-jet was superior to mill disperser in terms of ink detachment and stickies dispersion.
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