Heavy metal removal from water/wastewater using fly-ash derived zeolites

Ankrah, Archibald F. (2020) Heavy metal removal from water/wastewater using fly-ash derived zeolites. PhD thesis, University of Nottingham.

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Abstract

Heavy metal pollution in water has been a growing concern over the years and is under strict regulations from legislative bodies. Adsorption is an efficient and cost-effective way of metal removal from polluted water. Therefore, industries are seeking cheaper, environmentally friendly, easily accessible and efficient adsorbents for treating their effluents of heavy metals before disposal into surface waters. Activated carbon, the most popular commercial adsorbent, has become more expensive due to increasing demand, high cost of production and regeneration. Natural zeolites are not commercially available in most parts of the world while synthetic zeolites, produced from chemical precursors, are also expensive. Fly-ash derived zeolites provide a cheaper alternative as they can be synthesized from a waste product.

Initial research on fly-ash derived zeolite (Sodium P/ Gismondine) NaP1 has highlighted the potential for heavy metal removal from wastewater under different conditions without a clear understanding of the metal uptake mechanism and within industrial conditions (i.e. pelleting, multi-element adsorption with pellets and regeneration). Hence, there is limited information to adapt this material for industrial wastewater treatment. This research aims to provide a thorough understanding of the characteristics of fly-ash derived NaP1 to harness its potential use in industrial wastewater treatment.

Results from this study indicate metal uptake capacities of NaP1 for zinc (34 mg/g) and lead (192 mg/g) were higher than other fly-ash derived NaP1, commercial activated carbon and clinoptilolite. In competitive adsorption, the metal selectivity for NaP1 followed the order Pb2+>Cu2+>Zn2+, while multi-element removal efficiency was identified in the order NaP1 powder > NaP1 pellet > commercial 3A pellet.

Langmuir model and pseudo-second order kinetic model fitted best for all elements. The rate of metal uptake was fast and occurred in 15 min for all metals in contact with powder. The rate-determining step is controlled by diffusion of hydrated metals through microporous channels of NaP1. Copper regeneration from NaP1 was best achieved using Na and K salts at pH 5 and 22 ± 2 °C. NaCl and KCl solutions produced ~ 30% copper regeneration (representing 2.6 mg/g NaP1) while copper recovery with regeneration solutions was in the order K+>Na+>H+.

After pelleting without binder, adsorption experiments showed a type II isotherm with an H3 hysteresis loop, indicating the presence of unrestricted monolayer – multilayer adsorption. The mean pore diameter for NaP1 pellet was 14.3 ± 0.275 nm compared to 10.95 ± 0.069 nm for powder NaP1. However, BET area of NaP1 pellets was 28% lower than the powder form.

This research has demonstrated the viability of NaP1 for heavy metal removal from wastewater. Fly-ash waste from coal power plants could be sourced in creating zeolite NaP1 instead of dumping them into landfills and enhancing secondary pollution. Secondly, NaP1 can be converted into pellets without a binder for industrial use since it displays quick kinetics of 15 mins for metal uptake. Furthermore, NaP1 works efficiently at pH 5 and can be regenerated easily with eluents such as NaCl and KCl.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Snape, Colin
Tokay, Begum
Keywords: Zeolites, Coal fly-ash, NaP1, Pelleting, Regeneration, Single and Multi-element adsorption, Isotherm, Wastewater treatment.
Subjects: T Technology > TD Environmental technology. Sanitary engineering
Faculties/Schools: UK Campuses > Faculty of Engineering
Item ID: 63818
Depositing User: Ankrah, Frank
Date Deposited: 07 Jan 2021 11:48
Last Modified: 07 Jan 2021 12:00
URI: http://eprints.nottingham.ac.uk/id/eprint/63818

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