Application of lipase to reduce ONP flotation rejects. Part 2. Reduction of flotation rejects

Lipase hydrolysis of ester linkages on the surface of hydrophobic fines was suggested in a previous paper as a new method to promote hydration of the fines and to prevent the unwanted loss of these fines during froth flotation. Lipase was added before the secondary flotation stage of old newspapers (ONP) such that concentrated hydrophobic fine components were subjected to selective lipase hydrolysis. As a result, secondary flotation rejects were reduced, while the brightness and the effective residual ink concentration (ERIC) of secondary flotation accepts were maintained at the same level as the nontreated case. The application of lipase in secondary stage flotation results in fewer rejects from the low alkaline or neutral deinking of ONP by the enhancement of flotation deink-ing selectivity.