Recovering fibers from fine-prescreening reject at deinking mills

The yield of recycled paper production can be as low as 75%. The reject losses at deinked pulp mills are high compared to the small amount of ink applied to paper during printing. Thus, plenty of sufficiently clean fibers, fiber fines, and fillers are also rejected. This study provided proof of concept for recovery of long fibers from fine-prescreening rejects that contain a considerable amount of contaminants, such as stickies and dirt specks. The recovery of long fibers was studied by means of laboratory flotation experiments for untreated (fine-prescreening reject without dispersing) and dispersed (fine-prescreening reject after low-consistency dispersing) rejects. The pos¬sibility of recycling dispersed fine-prescreening rejects directly back into the preflotation feed also was considered; however, this technique was found to be unworkable. Instead, these results showed that low-consistency dispersion before flotation enabled a high level of contaminant removal at the separate flotation unit. Thus, there seems to be an opportunity to purify fine-prescreening rejects to a level that enabled reuse of the long-fiber fraction without degrading the quality of the end product.