Experimental Results for the Settling Behaviour of Particle‐Fiber Mixtures

Markus Feist,Hermann Nirschl,Jörg Wagner,Samuel Schabel,Georg Hirsch

doi:10.1155/2007/91740

Markus Feist, Hermann Nirschl + Show 3 more

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https://doi.org/10.1155/2007/91740

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Abstract

Sedimentation of organic fibres and inorganic particles can be observed in several industrial applications. Fibres are involved not only in wastewater treatment but also in other separation applications. In the paper industry, the separation of inorganic filler and coating particles from short cellulose fibres is still a challenge in the recycling process. During that process, particles have to be removed to obtain a purified fibre suspension. These fibres can be used again to produce new paper. With the currently applied techniques, like screening and flotation, the efficiency of short fibre separation is very poor. Moreover, also separation by sedimentation fails due to similar settling velocities of heavy‐small particles and the light and larger fibres. This paper concentrates on the sedimentation of organic fibres and inorganic particles in water. The investigated suspensions are made by resolving two different and specially produced papers a coated and an uncoated one, as well as the single components used for its production. We observe a different sedimentation behaviour according to the concentration of fibres and particles in the suspension and the pH‐value of it. The main result is that, according to the fibre rate, the sedimentation behaviour is particle dominant or fibre dominant.

Highlights

Knowledge about the sedimentation behaviour of fibres and particles is necessary for many applications
It can be seen that the CaCO3 has nearly the same sedimentation velocity distribution for 3 wt% and 5 wt%
The average velocity of the suspension with a concentration of 10 wt% and 20 wt% is again slightly faster than of 5 wt%. This is caused by the effect of cluster and swarm sedimentation as described in Beiser [3]

Summary

Introduction

Knowledge about the sedimentation behaviour of fibres and particles is necessary for many applications. Flotation processes are employed in paper recycling, where a separation of inorganic and organic fine material is rather frequently required. These three examples show that it is worth discussing the effects and differences between the sedimentation of fibr suspensions, particle suspensions, and fibre-particle suspensions. Experiments concerning the sedimentation behaviour were made by Beiser [3], Beiser et al [4], and Bickert [5] They investigated the sedimentation velocity and particle distribution with the help of a long-arm centrifuge. The result is an average velocity much smaller than the Stokes velocity This regime is used for separation purposes while swarm sedimentation gives the preferred process conditions for classification. The experiments have been performed under the assumption that particles do not agglomerate during the sedimentation process

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Results

Conclusion