Recycling of Waste Paper Sludge in Cements: Characterization and Behavior of New Eco-Efficient Matrices

Abstract

The pulp and paper industry, in Europe, generates 11 million tons of solid waste each year (Monte et al., 2009). Paper waste covers a diverse range of non-hazardous waste streams, prominent among which are different types of sludge, boiler ash, combustion furnace ash and organic and inorganic rejects. Manufacturing processes to produce new paper from the deinking of recycled paper account for 70% of these waste products. Following its reception, sorting and storage, the recycled paper is transformed into an aqueous suspension of fibers, while inappropriate materials are eliminated in different cleaning processes. Following this initial treatment, the resultant paper sludge is subjected to deinking in a froth flotation process, which produces waste known as de-inked sludge. This waste sludge is fundamentally composed of water, fiber, ink and a mineral load. In addition, various paper manufacturing processes have water treatment plants that generate sludges with high humidity contents. The deinked paper sludge and the sludge from the water treatment process have a high humidity content (≈ 50%), and are roughly composed of organic material with their origin in paper fibers (≈ 25%) and mineral loads such as calcium carbonate, kaolin, talc and titanium oxide (≈ 25%). A similar composition highlights the wealth of energetic and mineral resources saturating the paper sludge. Thus, the most advanced techniques for the use of paper sludge are intended to take full advantage of the saturated biomass and the recovery of the mineral constituents in the inorganic fraction. The most common options for the processing of paper industry sludge range from their exploitation for agricultural purposes, composting, or use as a primary material in the manufacture of ceramics and cement (Moo-Young & Zimmie, 1997; Ahmadi & Al-Khaja, 2001; Lima & Dal Molin, 2005; Conesa et al., 2008), to energy recovery in biomass boilers or fluidized bed systems. Thus, the Dutch CDEM process (International Patent, 2006) represents a pioneering recovery system, where the paper sludge is treated at temperatures of around 730oC, in a fluidized bed combustion system, so as to activate the latent