Effect Of Fiber Properties On Flotation Deinking Of Old Newsprint

In recent years, although flotation deinking of waste paper has been more and more matured, there are still some problems have not been satisfactorily resolved in the actual production process. Hence study the related factors in flotation deinking and analyze their mechanisms of action, may recommend guiding suggestions on production, thereby improving the effect of flotation deinking.In this paper, old newsprint(ONP) was chosen as raw materials. Firstly, the effects of fiber length on the fiber loss in flotation process were studied. Then the effects of residual ink concentration, surfactants and electrolytes on the fiber surface chemistry were discussed, and their influences on flotation deinking were also analyzed.The component of ONP which has a larger value of fiber length got a higher flotation yield. Higher content of residual ink on fiber surface caused higher fiber hydrophobicity, which improved fiber loss. But its effect on fiber loss was less than the fiber length, further more, these two properties were not affected by the types of surfactants used in flotation deinking. Colloid chemical properties of deinking system could be significantly improved by Mg2+ ions, which increased removal rate of free ink particles, so that the pulp brightness enhanced significantly. However, the free ink particles also could be adsorbed by Mg2+ ions to form hydrophobic composite which adhered to the fiber surface, thus improving the fiber hydrophobicity and making fiber loss increased.Equilibrium adsorption isotherms of sodium dodecyl benzene sulfonate(SDBS) onto ONP fiber surface could be subdivided into four regions and have a maximum in the Region IV. For Triton X-100(TX-100), equilibrium adsorption isotherms showed Langmuir-type and could be described with Langmuir model. The adsorption kinetics of SDBS and TX-100 could be approximated by the pseudo-second-order model. The effects of the initial surfactant concentration, Mg2+ ions and temperature on the rate of adsorption were found to be of considerable significant. SDBS and TX-100 were mainly adsorbed to the hydrophobic sites of the secondary fiber as a tail-down, head-out monolayer, which obviously reduced the fiber hydrophobicity and decreased the fiber loss. When the concentration of Mg2+ ions was high, majority of SDBS molecules adsorbed on the negative charged sites as a head-down, tail-out monolayer due to the bridging action of Mg2+ ions, which increased the fiber hydrophobicity and enhanced the fiber loss. In a conventional flotation temperature range(35 ?C-55 ?C), the adsorption of SDBS and TX-100 on ONP fiber surface was a typically diffusion-controlled process and an associative mechanism, which attributed to physical adsorption. The molecules of SDBS and TX-100 at activated state on ONP fiber surface ware always more organized than those in the bulk solution phase. The adsorption processes of both surfactants were endothermic. Heating was favorable for surfactant molecules to overcome the steric hindrance, and can accelerate the adsorption process. The adsorption process required external energy to react.Flotation strength could be enhanced by increasing surfactant concentration, which improved the removal of ink particles. Meanwhile surfactant concentration increased, the number of bubbles rised, and the bubble stability was enhanced, so that the ability of physical entrainment was improved. Physical entrainment was the main influence on fiber loss in flotation deinking process.