Pulp Waste Could Be Useful In Cement Production

Reports of the death of the newspaper and book industries are greatly exaggerated, if the growing volumes of pulp and paper wastes are anything to go by. This waste, which include grits and dregs as well various inorganic and organic materials, represents a major management concern.

Now, Fernando Castro and Candida Vilarinho of the University of Minho, Portugal, and colleagues have looked at the paper-making process and found a way to use the waste as raw materials in the production of clinker, a base material for Portland cement.

Chemical processing of wood to make pulp for paper manufacture usually involves a chemical treatment with sodium hydroxide and sodium sulfide, which produces good quality pulp but also releases large volumes of waste materials. Incorporated into construction materials, however, would not represent a health or environmental risk and prevents the need to send millions of tonnes of dregs and grits from the world's paper mills to landfill without a major energy penalty for the process.

The Portucel paper plant at Viana do Castelo, in Northern Portugal produces almost 300,000 tonnes of paper per year from pine and eucalyptus trees and generates more than 3,000 tonnes of wet dregs and grits.

The researchers have now carried out industrial trials with conventional raw clinker and clinker to which they added grits and dregs at 0.25% and 0.13%. They processed the materials as they would normally be treated for cement production and then tested their chemical composition and leaching behaviour. The resulting products are just as robust as conventional cement and do not degrade to release toxic components. During the trials at the Secil clinker plant in Maceira - Leiria the quality of the gaseous emissions were measured and no significant effect has been detected as a consequence of waste incorporation.

"Our results show that such incorporation could be an effective process for waste management from both the environmental and economic points of view," the researchers conclude.