Review of recycling alternatives for paper pulp wastes

Abstract

The demand for products derived from the pulp and paper industry has been increasing over the past years and is projected to further increase over the coming decades. Although being one of Portugal’s most relevant industrial activities, contributing to nearly 2.3% of the GDP, this sector is known to generate a variety of wastes including fly ashes, exhausted bed sands, green liquor dregs, grits, lime muds, biological and pulp and paper mill sludges, which have been mostly disposed of in landfills. This strategy is not aligned with the circular economy vision, and therefore it is imperative to develop new recycling routes for the different waste streams. This scenario has driven a significant research effort in the attempt to design sustainable recycling alternatives for the distinct wastes. This study summarizes the investigations focusing on the valorisation of these wastes in a wide range of applications, including the production of low carbon footprint binders or mortars for the construction sector, but also the production of novel materials for high added-value applications such as wastewater treatment and pH regulation. The present work also highlights the main bottlenecks and future prospects for the studied wastes.

Development of Eco-Mortars with the Incorporation of Municipal Solid Wastes Incineration Ash

“…When analyzing the effect of adding BA as aggregate, it was possible to verify that its incorporation caused a decrease in the density of the samples. This is due to the lower density of BA (1.30 g/cm 3 ) compared to sand (1.81 g/cm 3 ).…”

“…The difference in density between the A 0 and A 100 is notorious and also justifies the differences observed in the mechanical strength values. After 28 days of curing, the standard mortar (A 0 ) has a density of 1.9 g/cm 3 and the A 100 1.7 g/cm 3 . This decrease is in line with that reported in the literature, where studies whose focus was the replacement of aggregate by BA led to a decrease in density in samples with higher incorporation levels [38].…”

“…It can be seen that for both curing times, the geometric density of the samples decreased with the rise in the replacement level of OPC with BA. For example, after 28 days of curing, the standard mortar, B 0 , has a density of 1.9 g/cm 3 , while the sample B 30 has a lower value, 1.8 g/cm 3 . This decrease can be attributed to the density difference between OPC and BA, 1.36 g/cm 3 and 0.92 g/cm 3 , respectively.…”

“…For example, after 28 days of curing, the standard mortar, B 0 , has a density of 1.9 g/cm 3 , while the sample B 30 has a lower value, 1.8 g/cm 3 . This decrease can be attributed to the density difference between OPC and BA, 1.36 g/cm 3 and 0.92 g/cm 3 , respectively. It can also result from the lower reactivity of the BA, producing less compact samples.…”

“…Several scientific developments have been made to replace clinker/cement with other materials, such as calcinated clay and residues/by-products from other industries, i.e., paper pulp wastes [3]. One residue/by-product that has gained interest in recent years is the ashes resulting from municipal solid waste incineration (MSWI) [4][5][6][7][8].…”