Abstract
The fly ashes derived from three giant coal-hosted Ge deposits, Lincang (Yunnan of southwestern China), Wulantuga (Inner Mongolia of northern China), and Spetzugli (Primorye, Russian Far East), are unique because they are highly enriched in elements, including up to (on an organic-free basis): 4.66% Ge, 2.12% As, 1.56% F, 1.22% Sb, 0.56% W, 0.56% Zn, 0.55% Pb, 0.13% Sn, 0.12% Ga, 0.056% Bi, 0.04% Be, 0.028% Cs, 0.017% Tl, and 0.016% Hg. These high element concentrations in the fly ashes are due both to their high levels in the raw coals from which they were derived and their high volatility during the coal combustion process.Rare earth elements and yttrium (REY) were fractionated during coal combustion. They are more enriched in fly ashes than in slag from the respective coals. Maximum REY enrichment may occur either in fine-grained fly ash from baghouse filters or in coarse-grained fly ash from electrostatic precipitators. Cerium and Eu are more enriched in the fly ashes than other REY, and yttrium is relatively depleted in the fly ashes in comparison with the slag.Three types of unburnt carbon can be identified in the fly ashes: (1) carbon with well-preserved initial maceral structures (fusinite and secretinite), (2) isotropic and anisotropic carbon, and (3) secondary fine-grained carbon. The last type of unburnt carbon is characterized by embedded fine-grained Ge-bearing and other mineral phases.Ge oxides (e.g., GeO2) are the major Ge carrier in the fly ashes. Other Ge-bearing mineral phases, however, were also identified, including glass, Ca ferrites, solid solutions of Ge in SiO2, and probably elemental Ge or Ge (Ge-W) carbide, as well as previously-unknown complex oxides including (Ge,As)Ox, (Ge,As,Sb)Ox, (Ge,As,W)Ox, and (Ge,W)Ox. Some portion of the Ge occurs as adsorbed species in different types of unburnt carbon (Types 1 and 2) in the ash particles.
Original language | English |
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Pages (from-to) | 79-97 |
Number of pages | 19 |
Journal | International Journal of Coal Geology |
Volume | 121 |
DOIs | |
State | Published - Jan 1 2014 |
Bibliographical note
Funding Information:This research was supported by the National Key Basic Research Program of China (No. 2014CB238902 ), the National Natural Science Foundation of China (Nos. 41272182 and 40930420 ), and the Fundamental Research Funds for the Central Universities (No. 2011YM02 ), and the Program for Changjiang Scholars and Innovative Research Team in University ( IRT13099 ). Special thanks are given to Professor M. Shpirt and Dr. P. Kudryavtsev for their valuable advice and comments on the manuscript.
Keywords
- Ge-rich fly ash
- Minerals in fly ash
- Toxic trace elements
- Valuable trace elements
ASJC Scopus subject areas
- Fuel Technology
- Geology
- Economic Geology
- Stratigraphy