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Fluid Extraction of Metals from Coal Fly Ash: Geochemical Simulation of Natural leaching

Kim, Ann Gallagher (2002) Fluid Extraction of Metals from Coal Fly Ash: Geochemical Simulation of Natural leaching. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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The objective of this study was to develop data that are broadly applicable to the release of trace metals from fly ash, and to quantify the rate of release as a function of the composition of the ash. Thirty-two samples of Class F fly ash from pulverized coal combustion boilers were leached with seven leaching solutions simulating natural fluids. The leachate was analyzed for 21 cations that were major, minor, or trace constituents of the ash. The rate at which metal ions are released from fly ash is a complex function of the alkalinity of the ash, the distribution of elements in various chemical compounds or minerals, and characteristics of the leachant solution, particularly its pH. In this experiment, the release of cations is defined as a solubility function with respect to the volume of leachant solution. During the first leaching interval, the ashes alkalinity is neutralized, and the release of metal ions, except for Ca, is relatively low. At some point, the release of metal ions increases by one or more orders of magnitude, and remains at that level, until the readily soluble ions are released. Then the elemental release decreases, again by one or more orders of magnitude. The solubility of an element is defined by the three volumetric functions and the median volumes for those functions. The N LF (neutralization leaching function) is describes the release of cations until the sample is neutralized (dMN/dVN, meq/L). The RLF (rapid leaching function) rate is the average slope of cumulative curve between inflection points (dML/dVL, meq/L). The TLF (terminal leaching function) is the average slope of cumulative curve after 2nd inflection point (dMT/dVT, meq/L). In a natural setting, if the infiltration rate is known (L/d), the time dependent release of the elements can be estimated. The results of this study show that most cations in fly ash are only slightly soluble, that elements, other than arsenic, tend to be most soluble in acid solutions, and that non-silicates tend to be more soluble than silicates.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Kim, Ann,akim@netl.doe.govAGKST5
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairStewart, Brian
Committee MemberRollins, Harold
Committee MemberBikerman, Michael
Committee MemberNeufeld, Ronald
Committee MemberCapo, Rosemary
Date: 6 August 2002
Date Type: Completion
Defense Date: 26 April 2002
Approval Date: 6 August 2002
Submission Date: 8 May 2002
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Institution: University of Pittsburgh
Schools and Programs: Dietrich School of Arts and Sciences > Geology and Planetary Science
Degree: PhD - Doctor of Philosophy
Thesis Type: Doctoral Dissertation
Refereed: Yes
Uncontrolled Keywords: coal combustion by-products; coal utilization by-products; fly ash; trace elements
Other ID:, etd-05082002-093040
Date Deposited: 10 Nov 2011 19:44
Last Modified: 15 Nov 2016 13:43


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