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Title: Novel applications for paper sludge ash
Author: Spathi, Charikleia
ISNI:       0000 0004 5920 7970
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2016
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The disposal of paper sludge ash (PSA) generated by the UK paper industry has caused environmental concerns and there is a need to provide more sustainable management options as an alternative to landfill. This study investigated and developed viable technologies for the production of waste-derived lightweight filler (LWF) particles with high strength-to-density ratios and hydrophobic materials. Two types of PSA, supplied by Aylesford Newsprint and UPM-Shotton recycled paper mills, were processed into LWFs and hydrophobic powders. They were both composed of gehlenite (Ca2Al2SiO7), calcite (CaCO3), calcium silicate (a'-Ca2SiO4), lime (CaO) and quartz (SiO2). Given that PSA exhibited low sintering reactivity at temperatures up to 1200 °C, recycled soda-lime glass was used to promote sintering while minimising the energy intensity of the proposed thermal treatment. Wet-milling of glass with PSA addition up to 20 wt. % produced foamed lightweight materials (~1 g·cm⁻³) after rapid sintering at 800 °C. This was shown to be because of extensive growth of pores caused by gas evolution from the decomposition of, primarily, calcium carbonate present in PSA. Thermodynamic considerations for the 80/20 glass/PSA system also showed that the amount of gas evolved and entrapped within the sintered body determined the extent of closed-cell porosity for mixes of given viscosity and particle size characteristics. This was found to be a time-sensitive mechanism on a minutes scale. Incorporation of such low water permeability LWFs in cement mortars corroborated their use as structural, thermal-insulating materials. Dry milling of PSA particles with stearic acid led to unexpected surface functionalization inducing super-hydrophobicity. Both PSA samples exhibited water contact angles in the region of 150° when treated with 4 wt. % of stearic acid under optimised process conditions. This was due to the formation of calcium stearate self-assembling layers physically and chemically adsorbed on fracture PSA surfaces. PSA particles exhibited higher hydrophobicity when treated with stearic acid compared to other inorganic substrates and organic acids investigated. Research findings indicate that manufacturing of glass/PSA LWFs and PSA-based hydrophobic materials was technically feasible at laboratory scale. Economic and environmental benefits could drive commercial exploitation of research outputs.
Supervisor: Cheeseman, Chris ; Vandeperre, Luc Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral