Mineralogical and geochemical compositions of the coal in the Guanbanwusu Mine, Inner Mongolia, China: Further evidence for the existence of an Al (Ga and REE) ore deposit in the Jungar Coalfield

Aluminum-hydroxide (boehmite and diaspore)-, Ga-, REY (rare earth elements and Y)-, and Al-rich Pennsylvanian Taiyuan Formation coals have previously been found in the Jungar and Daqingshan Coalfields, Inner Mongolia, China. Gallium, REY, and Al are potentially extractable and usable elements in combustion residues derived from these coals. This paper reports new results on 50 bench samples of the No. 6 coal from the Guanbanwusu Mine, Jungar Coalfield, Inner Mongolia, and provides new data and evidence for the existence of an Al (Ga, REY) ore deposit in the unique Jungar Coalfield. The No. 6 coal in the Guanbanwusu Mine has a low rank (R-o,R-ran = 0.56%) and a low-sulfur content (S-t,S-d = 058%). The proportion of inertinite in the coal (56.7%; mineral-free basis) is higher than that of vitrinite (31%). The minerals in the coal are mainly represented by kaolinite, boehmite, and chlorite, along with variable proportions in some samples of calcite, ankerite, siderite, and goyazite. Boehmite, goyazite, and part of the kaolinite were derived from bauxite in the weathered surface of the sediment-source region. Ankerite, calcite, and siderite in the coal are of authigenic origin. The chlorite in the Guanbanwusu coals appears to have a chemical composition intermediate between cookeite and chamosite. This mineral mainly occurs as cell-fillings, also indicating an authigenic origin, and was probably derived from hydrothermal fluids. A new mineral phase mainly composed of Ti, Cl, and Fe is probably a Ti-bearing oxychloride or hydroxychloride. Compared to other Chinese coals and to world hard coals, the coal from the Guanbanwusu Mine is enriched in Al2O3 (9.34%), P2O5 (0.126%), Li (175 mu g/g), F (434 mu g/g), Cl (1542 mu g/g), Ga (12.9 mu g/g), Sr (703 mu g/g), and Th (12.9 mu g/g), but has a lower SiO2/Al2O3 ratio (0.74) due to the higher proportions of boehmite and goyazite in the coal. The major carrier of P2O5 and Sr is goyazite. Lithium mainly occurs in the chlorite (cf. cookeite), kaolinite. and possibly, to a lesser extent, illite. Fluorine in the coal has a major boehmite affinity, but a small proportion may also occur in the organic matter and chlorite. Gallium in the coal largely occurs in goyazite. Chlorine is independent of other elements in the coal, associated neither with moisture nor with organic matter, but possibly occurring in molecular form (Cl-2) and in the Ti-bearing oxychloride or hydroxychloride. Thorium in the coal occurs in the clay and accessory minerals, and was mainly derived from detrital materials of the source region. Rare earth elements and Y have a mixed (organic and inorganic) affinity, largely occurring in goyazite-group minerals and, to a lesser extent, boehmite and organic matter. Most coal benches and partings have either an L-type or H-type of REY enrichment, owing respectively to the weathered bauxite source region and groundwater effects. The Al2O3, Ga, REV and possibly Li in the Guanbanwusu coals, like those in coals from the Jungar and adjacent Daqingshan Coalfields, are industrially useful metals that could potentially be recovered from the relevant coal combustion residues. It is suggested that, if Ga in ash > 50 mu g/g, REY > 800-900 mu g/g, SiO2/Al2O3 < 1 (or Al2O3 > 40% in ash), and coal thickness > 5 m, the coal combustion residues would be expected to be suitably enriched in Al2O3 and can be considered for Al2O3, Ga, and REV recovery. (C) 2012 Elsevier B.V. All rights reserved.