Column flotation, widely used in the mineral processing industry, has recently been suggested for waste paper deinking to take advantage of its low capital cost and excellent separation performance. Bubble generation in flotation columns is achieved through a variety of air sparging systems, broadly divided into two types: internal and external. Internal spargers, such as porous metal or ceramic tubes, have been used in deinking, but they are prone to plugging and must be frequently removed and cleaned. This is costly because it requires the column be removed from service. In external air sparging systems, pulp and gas are contacted outside of the column to generate a bubble dispersion which is directed into the column. In this work, an external air sparging technique, based on an in-line static mixer, was tested as an alternative to a porous metal sparger. The spargers were compared in an industrial deinking facility using a laboratory scale flotation column. Operating conditions for the static mixer were defined and the effect of gas rate, retention time, wash water rate, and froth height on deinking was investigated. Both spargers gave similar results in terms of ink recovery versus bubble surface area flux. However, the static mixer gave stable operation while the porous sparger showed evidence of plugging over a period of 6 hours. Combined with some ability to control bubble size, overall the in-line static mixer gave superior performance.
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