Environmental management and potential use of heavy oil fly ash

Mofarrah, Abdullah (2014) Environmental management and potential use of heavy oil fly ash. Doctoral (PhD) thesis, Memorial University of Newfoundland.

[English] PDF (Migrated (PDF/A Conversion) from original format: (application/pdf)) - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (50MB) [English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. (Original Version)

Abstract

Heavy oil fly ash (HOFA) is a by-product generated in power plants by the burning of heavy fuel oil. The main constituent of HOFA is unburned carbon; it also contains other elements such as arsenic (As), cadmium (Cd), cobalt (Co), chromium (Cr), mercury (Hg), nickel (Ni), lead (Pb), copper (Cu), zinc (Zn), selenium (Se), calcium (Ca), magnesium (Mg), sodium (Na), silicon (Si), aluminium (Al), iron (Fe), and vanadium (V) in different forms of oxides or sulfates. Due to insufficient knowledge of the physical and chemical properties and related applications of this by-product, it is usually disposed off into landfills. In order to explore the beneficial utilization of HOFA, this research study analyzes the physical, chemical, and morphological characteristics of HOFA. It also includes an in-depth investigation on its reuse as (i) a natural absorbent such as activated carbon (AC), (ii) fill material for construction use, and (iii) a colour ingredient in ornamental concrete. Chemical and physical activation techniques were used to produce fly ash activated carbon (FAC). Before activation, the minerals and other metals present in the HOFA were removed by standard leaching procedures. The performances of the produced FAC were tested for the removal of selected pollutants such as dyes, naphthalene, and metals from aqueous solutions. The results from the laboratory batch experiments indicated that the developed FAC has the potential to remove organic and inorganic (e.g., 85% to 90%) pollutants from wastewater. Soil stabilizer or fill material for construction use was prepared by mixing HOFA with Portland cement at different ratios. The leaching behaviour of the trace elements and compounds within HOFA and fill materials was studied by standard laboratory batch and column leaching tests. The results of the study showed that the toxic elements in HOFA are easily leachable and can be toxic to the environment. However, the addition of 40% Portland cement with HOFA significantly decreased the leaching concentration of most elements below the permissible level. To explore the possible use of HOFA as a black pigment or admixture in ornamental concrete, it was mixed with cement mortar at different percentages. The standard compressive strength test with 50 mm cement mortar cubes showed that the addition of 2% to 5% HOFA in cement mortar does not affect its compressive strength. The leaching behaviour of trace elements within HOFA mixed concrete material was also investigated through laboratory batch leaching experiments. The findings confirmed that HOFA can be used as a black pigment in ornamental concrete, which is environmentally safe, and provides a good balance between colour and concrete quality. In the final phase of this research, a human health risk assessment methodology was developed in order to assess the potential health risk to people living in the area surrounding the HOFA dumping site. This study also explores environmental concerns and the importance of HOFA management practices.

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