“Can Coal Have a Place in the 21st Century Environment? YES, It Can”
Project Title: Sustainable Utilization Of Coal Combustion
Byproducts Through Production Of High Grade Minerals And Cement-less
Background and Problem Definition
During 2009, about 122 million tons of Coal Combustion by Products (CCBs) were generated in the US by electric utilities and non-utilities. However approximately 41 percent of the total CCBs were used in various applications and the remaining products are disposed off in landfills and ash ponds (ACAA, 2009).This project aims to sustainably utilize 100% of coal combustion byproducts (CCBs), a solid waste directly related to the Solid Waste Disposal Act – Section 8001.
The main objectives of the proposed study
To develop a novel flowsheet for extracting
valuable minerals like Iron oxide, Aluminum and Titanium from the
waste products of coal
combustion/electricity generation process.
To develop a suitable process to utilize
the coal combustion residues as a useful product in the form of a
geopolymer-based concrete to reduce or eliminate the use of any
Data, Findings, and Discussion
1. Sample Collection and characterization
Two coal fly ash samples were collected from two Illinois high sulfur coal burning utilities (named SIPC and CWLP) and brought to the Coal Development Park in Carterville, IL. Table 1 shows the XRF and ICP analysis results on these two samples. Davis Tube tests showed that the magnetite content of CWLP and SIPC fly ash samples are about 17% to 10%, respectively.
2. Mineral Extraction Flowsheet Design
In the first step, a classifying cyclone was used to pre-concentrate magnetite in the fly ash. For the SIPC sample, the magnetite was enriched from 10% to 26.7% in the underflow stream with 92.7% recovery. A water-only-cyclone will be used to further enrich the magnetite preconcentration to about 35%.
Preliminary leaching tests were conducted on SIPC fly ash sample for extracting Al, Ti and the remaining Fe, from the non-magnetic tailing obtained from Step 1 (Figure 1). The results gave an Al, Ti and Fe extraction efficiency of 82.7%, 86.2% and 89.6%, respectively.
3.Cement-less Green Concrete Testing
Illinois coal fly ash is known to be a Si-Al rich material making it a very suitable feed material for geopolymerization process and production of cement-less concrete technically named “geopolymer concrete”. In this study, tests were done to make geopolymer concrete using both SIPC and CWLP fly ash samples. The results of compressive strength tests indicated that the geopolymer concrete samples made from the SIPC fly ash can compete with the Portland cement concrete in terms of compressive strength (Figures 2 and 3).
Conclusions & Recommendations
This study so far has envisioned a two-step processing scheme to extract high-grade (> 96%) magnetite from fly ash generated from burning high sulfur coal.
The exploratory leaching tests done on the non-magnetite part of SIPC fly ash samples showed that the leaching process can effectively extract Al, Ti and Fe from the non-magnetite part of Illinois fly ash. It may also be possible to leach and
recover other valuable elements like Germanium, Gallium and Vanadium.
The results exhibited that the geopolymer concrete samples made from the SIPC fly ash sample can compete with the Portland cement concrete in terms of compressive strength. This preliminary finding supports our original hypothesis of suitability of Illinois coal fly ash to serve as a good raw material for its
wide-scale utilization as a feed stock for geopolymer-based concrete.