Bleaching paper without chlorine.

A new process for making white paper without chlorine has been developed by Craig Hill of Emory University in collaboration with the Forest Products Laboratory at the U.S. Department of Agriculture's Forest Service. It substitutes polyoxometalate (POM) salts and oxygen for chlorine and creates only carbon dioxide and water as byproducts.

Paper mills traditionally have been a potential source of pollution, particularly when making white paper. The chlorine commonly used to bleach out the brown lignin in the pulp can form dioxin and other chlorinated aromatic compounds that can end up in runoff streams.

The new process has four steps: anaerobic (no oxygen) bleaching; pulp washing; concentration of wash water; and removal of dissolved organic materials, primarily lignin-derived materials, with simultaneous regeneration of the POM to its active form for reuse.

Removal of lignin from the wood pulp is the purpose of bleaching because that is what makes paper brown. In the bleaching step, mixtures of water, pulp, and fully oxidized POM are heated anaerobically. During this reaction, the POM seeks out and selectively degrades the...