A procedure performed to make recovered fiber usable for the manufacturing of recycled paper that is to be used for printing and writing papers. Deinking is the first phase of the "repulping" process for recycled papers. Mesh screens filter out large particles, and centrifugal cleaners remove other non-fibrous particles. Particles that float to the surface of the cleaning tank are skimmed off. In wash deinking, chemical dispersents and physical collision remove ink particles from the wastepaper, allowing them to be washed away. Further chemical treatment keeps the separated ink from returning to the fibers. The fibers are strained out of the solution, and the ink particles remain behind. This process also removes fines and particles of filler from the previous papermaking process, which helps produce a stronger, brighter pulp. Wash deinking, however, tends not to be a very cost-effective procedure, requiring large amounts of water.
Flotation deinking treats wastepaper with chemicals such as calcium soaps that render the ink particles hydrophobic, or tending to avoid water. The suspended ink particles are collected by air bubbles injected into the flotation tank, and they are carried to the surface where they can be skimmed off. Flotation deinking uses less water than wash deinking, but often both procedures must be used to make the recovered fibers suitable for writing and printing papers.