Effect of Process Water System Closure on the Flotation Deinking Efficiecy of Newsprint, 1998 Recycling Symposium Proceedings

The intent of this research was to discover how the accumulation of dissolved solids found in deinking mill waters contributes to inefficient flotation deinking of old newsprint. In the first phase, water from laboratory flotation trials was reused several times to examine the rate at which dissolved solids reach a concentration which impacts deinking efficiency. Phase two was a contaminant study where dissolved solids arising from the deinking process were added to the flotation cell individually to determine the reaction of the system to the build up of each separate chemical. The final phase then examined the chemicals added together at different concentrations. In each phase, flotation deinking efficiency was evaluated by brightness tests, effective residual ink concentration (ERIC) values, and reject analysis. Tensile strength properties were also examined in the contaminant trials.

The results of this study have shown that flotation deinking can be quite resistant to upset by increased levels of dissolved solids. With simulated mill water system closure, dissolved solids will reach an equilibrium concentration at a level low enough to not significantly degrade pulp quality, barring repeated upsets to the system.

It was also shown that high levels of fatty acid flotation aid and oleic acid (a fatty acid) both significantly decreased ink removal efficiency. Additionally, high pH levels were shown to cause alkaline darkening of the newsprint furnish and increased levels of wash surfactant in the flotation cell greatly increased flotation reject volumes.