Potential utilization of coal gasification residues from entrained-flow gasification plants based on rare earth geochemical characteristics

Abstract

During coal processes, such as coal gasification and coal combustion, non-volatile trace elements (including rare earth elements and yttrium (REY)) tend to remain in the slag or ash. As REY are critical to modern society, it is important to evaluate gasification residues as potential sources of these elements. Ninety-eight samples, including residues and feed coals, were collected from two different commercial-scale gasification plants (GE and GSP) in Northwest China over one week to study their rare earth geochemical characteristics and to evaluate the economical extraction the rare earth elements and yttrium in the residues. A comprehensive evaluation of the REY in the gasification residues, based on four parameters (outlook coefficient (Coutl), REYdef, rel-Coutl graph, REO, and relative enrichment factor (EF)) indicate that the residues could be regarded as promising REY raw materials for economic exploitation, as the REO average contents in the GE-CR-A, GSP-CR and GSP-FR were relatively high. Compared to the GSP residues, REY in the GE residues are more enriched. The modes of occurrence of the REY in one subset of feed coals and corresponding residues were determined. However, considering the heterogeneous composition of gasification residues and calculated mass balance deviation (MBD) of the REY for chemical extraction, regression analyses of ∑REY and some selected major elements (Si, Al, Ca, Fe and Mn) were also performed. The results indicate that REY in the GE residues are associated with carbonates and Fe–Mn oxides, but with aluminosilicate as well. In the GSP residues, REY is primarily associated with aluminosilicates.