Comparison of Internal and External Mixer Spargers in a Laboratory De‐inking Flotation Column

Abstract

Paper recycling is assuming increased importance in response to growing concerns over waste disposal and conservation of natural resources. The paper recycling process aims to remove contaminants while retaining the valuable fi bers. This is accomplished through a variety of separation processes including screening, cycloning, fl otation and washing.Today, fl otation dominates the removal of printing inks from recycled paper. A typical composition of a feed pulp is given in Table 1. De-inking is a reverse fl otation process where the fl oat product is the waste rejects and the non-fl oat is the valuable accepts. The increasing volume of recycled paper and the rising quality requirements of de-inked fi bers drive development of fl otation technologies. This has led to trials using column fl otation.Column fl otation in mineral processing has been introduced over the last two decades. Columns offer advantages in terms of reduced fl oor space, reduced operating and capital costs, simplifi ed circuits and greater selectivity (Luttrell et al., 1993). Unfortunately, these advantages are not always fully realized in practice, frequently due to defi ciencies in the design, scale-up and operation of the bubble generating system.The air sparging system should be capable of producing small (ca. 0.5 -2.5 mm), relatively uniform sized bubbles at the required aeration rate (Huls et al., 1991). Small bubbles enhance the capture of fi ne particles (Yoon and Miller, 1982;Dobby and Finch, 1986) and increase the fl otation rate and carrying capacity by increasing the bubble surface area rate (or fl ux) (Finch and Dobby, 1990;Gorain et al., 1996). Too small a bubble (e.g., < 0.2 mm) should be avoided as when loaded they can be swept in to the underfl ow stream (Uribe-Salas, et al., 2003). Many bubble-generating systems are available (Al Taweel, 1989;Dobby and Finch, 1991;Rubinstein, 1995); they can be broadly divided into two types, internal and external.* Author to whom correspondence may be addressed. E-mail address: jim.fi nch@mcgill.ca jim.fi nch@mcgill.ca Column fl otation has been introduced for waste paper de-inking to take advantage of low capital cost and excellent separation performance. Bubble generation employs a variety of systems, broadly divided into two types: internal and external. An external in-line static mixer sparger was tested against an internal porous stainless steel sparger. They were compared in an industrial de-inking facility using a 10 cm diameter column. Operating conditions were defi ned and the effect of gas rate, retention time, wash water rate, and froth height on de-inking was investigated. Both spargers gave similar ink recovery and fi ber loss as a function of bubble surface area fl ux. However, the static mixer gave stable operation while the porous sparger showed evidence of plugging over a 6h test. Combined with some ability to control bubble size, overall the in-line static mixer gave superior performance.La fl ottation en colonne a été adaptée pour le désencrage du papier recyclé afi n de ...

Recovery of ink particles in a concurrent column flotation

“…For instance, the operation of a flotation column with two phases (water–gas) has resulted in the clarification of many unknown factors regarding the individual phases . Column flotation reactors in countercurrent mode have been introduced into a number of deinking operations . Column trials indicated that, at a few minutes retention time, over 70% of macrostickies and wax from rejects of a typical pulp deinking plant could be removed .…”

Simulation of Surfactant Contribution to Ink Removal Selectivity in Flotation Deinking Lines

“…Despite its versatility and apparent simplicity, froth flotation is governed by complex physicochemical and hydrodynamic phenomena which depend on pulp slurry/process chemicals composition [6,14,15] and on gas sparger [16,17] and flotation cell design [18,19].…”