Dynamic Drainage of Froth with Wood Fibers

Understanding froth drainage with fibers (or simply called fiber drainage in froth) is important for improving fiber yield in the flotation deinking operation. In this study, the data of water and fiber mass in foams collected at different froth heights were used to reconstruct the time-dependent and spatially resolved froth density and fiber volumetric concentration in the froth. The results revealed that fiber drainage is caused by water carryover. However, fiber drainage stopped in the upper part of the froth and at longer draining time because of decreased draining water flux, as indicated by a critical water flux of about 5 mg s^-1 cm^-2. As a result, some fibers were permanently trapped in the froth and were unrecoverable. These findings indicate that only the upper part of a froth should be removed in flotation deinking operations to reduce fiber yield loss.