EVALUATION OF MINERAL FILLER INTERACTION WITH WOOD EXTRACTIVE COLLOIDS IN PULP AND PAPER MILL PROCESS WATERS USING FLOW CYTOMETRY

The use of mineral adsorbents to passivate and control paper machine deposits arising from wood extractives and recycled fibre stickies is widespread in the paper industry. A range of techniques have been used to evaluate and choose minerals such as bentonite and talc to control these deposits. Flow cytometry has been used to study the interaction between wood extractive colloids present in mechanical pulp process waters and various fillers. Mineral adsorbents such as bentonite can be observed in flow cytometry density plots as small particles with low hydrophobicity. As extractive-laden process white water was progressively added to the mineral adsorbent, a population of particles separate from both the adsorbent and the hydrophobic extractive colloids appeared in the density plots. The characteristics of this new population (number and fluorescence intensity) were used as a means to measure and compare the adsorbents' ability to interact with extractive colloids. The formation of this new particle population was attributed to the adsorption of very small dissolved and colloidal material (DCS<0.2 mu m) present in the white water and was observed with the adsorbents bentonite, calcined clay, zeolite, and precipitated calcium carbonate (PCC), but not with talc. Adsorption of DCS<0.2 mu m onto bentonite appeared to approach a plateau once the extractives: bentonite ratio rose above similar to 1.0-1.5 kg extractives per kg of bentonite. Bentonite took up the DCS<0.2 mu m material more effectively than calcined clay, PCC, or zeolite, while talc did not do so to any significant extent. The hydrophobicity of the larger colloids normally visible to the flow cytometer was also reduced to varying degrees by the addition of bentonite, calcined clay, zeolite, and PCC, but not by talc. Bentonite samples from four different manufacturers all interacted to a similar degree, but bentonite was superior to the other adsorbents in both adsorption of DCS<0.2 mu m material and reduction in hydrophobicity. Bentonite was able to achieve an 80% reduction in hydrophobicity, with no significant further reduction beyond an addition rate of approximately 5kg kg(-1) of extractives.