Effects ofpH and salt concentration on particle capture in co-filtration of papermaking slurry

Much research has been carried out to correlate the surface charges to particle capture in papermaking and filtration industries. Most of the previous attempts modeled the co-filtration process of simultaneous fibrous mat formation and filler particle capture as a combination of cake and depth filtration. Very few works have quantified the surface charge and related it to the filtration behavior, except for some pure experimental studies. This work is to model the co-filtration process through multiphase transport theory, coupled with the postulated constitutive equations and experimental data, to determine the effect of surface charges on filtration efficiency and to explain the dominant particle capture mechanism under different water chemistry conditions.; The model was examined by the specified co-filtration process of raw paper formation using cellulose fibers, TiO₂ particles as the fillers, and alum as the salt additive. The zeta potentials, effective surface charges, of cellulose fibers from bleached southern pine pulp and TiO₂ particles under different conditions were measured prior to filtration experiments. The experimental variables were pH, salt and particle concentrations. The results of filtration experiments show a significant effect of material surface charges on particle capture efficiency.; The developed model with constitutive equations were numerically solved and the capture and release coefficients were optimized using genetic algorithm to ‘best’ fit into experimental data. The capture coefficient that accounts for the different capture and release mechanisms was correlated to zeta potentials and sufficiently explains the changes in capture efficiency. By correctly incorporating the lower-scale electrostatic mechanism, the developed model is able to describe the macro-scale capture quantities.; The uniqueness of this work has two parts. The first is that a quantity relating the zeta potentials of both materials is incorporated in the model. Hence the postulated constitutive equation that was verified by experiments is able to separate the particle capture due to electrostatic-attraction from the other mechanisms. Second, it develops a FORTRAN code to handle the moving boundary problem for co-filtration process. This gives it the future potential in modeling effective surface area and pressure profiles for co-filtration process.