Portuguese researchers use waste products from the paper industry to produce greener cement

Builders pouring cement

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The disposal of waste products from the paper industry is an enormous environmental issue and sending them to landfill is not a sustainable option. Now Portuguese researchers have shown that this unwanted material could be used as a raw material for cement production and so provide a green, recycled construction material.

The chemical processing of wood to make pulp for paper manufacture usually involves chemical treatment with sodium hydroxide and sodium sulfide. This produces high-quality pulp for making good paper but also releases waste materials from the wood. These include so-called grits and dregs, which are composed of a wide variety of inorganic and organic materials. A typical paper plant, such as the Portucel 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 waste each year, which no one has yet found a viable use for. However, Fernando Castro and Candida Vilarinho of the University of Minho, in Portugal, and their colleagues have found a way to use this waste as a raw material in the production of 'clinker', ie lumps of sintered limestone and clay which are ground to make Portland cement. 

Castro and Vilarinho trialled the manufacture of their greener cement at the Secil clinker plant in Maceira, Leiria. They compared cement made from conventional raw clinker and clinker to which they added paper industry grits and dregs at quantities of just 0.25 per cent and 0.13 per cent. The materials were put through a normal cement production process and the chemical composition and leaching behaviour of the cement products were tested. 

The trials showed that the resulting products are just as robust as conventional cement and do not degrade to release toxic components. During the trials the team also recorded the gaseous emissions of the manufacturing process and found them to be the same as for conventional cement production. 

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