Abstract
The vanadium occurrence in stone coal, water leaching, and acid leaching residue was investigated by energy dispersive spectrometer (EDS) mapping and point analysis, and the vanadium transitions during roasting-leaching of stone coal were revealed. In the roasting process, vanadium-bearing muscovite is converted to K-Na-feldspar, accompanying the liberation of vanadium. Most liberated vanadium reacts with sodium salt to generate water-soluble sodium vanadate, some reacts with calcite in stone coal to form water-insoluble calcium vanadate, and other liberated vanadium exists as free vanadium oxide. However, for coarse muscovite grains, the reaction of muscovite converted to K-Na-feldspar only occurs at the outer margin of muscovite grains, and the vanadium in the interior of muscovite grains is not liberated. During water leaching, the sodium vanadate is leached out. The calcium vanadate and free vanadium oxide are dissolved out in the process of acid leaching, and the vanadium, presenting in muscovite grains surrounded by K-Na-feldspar, still remains in the acid leaching residue. Two suggestions, including optimization of grinding-classification process and adopting microwave roasting, were proposed for improving vanadium recovery according to the vanadium transition rules.
Highlights
Vanadium is an important rare element that has been extensively applied in fields of steel industry, titanium-aluminum alloys, vanadium redox battery, and catalysts [1]
For the process of vanadium extraction from stone coal, the vanadium recovery by the roasting-leaching procedure is around 65–75%, while for other procedures, such as ion exchange, solvent extraction, and vanadium precipitation, the vanadium recoveries are more than 97% [9,10]
We investigate the vanadium occurrence, in stone coal and in the water leaching and acid leaching residues, to seek the root of the relatively inferior vanadium recovery during the roasting-leaching process
Summary
Vanadium is an important rare element that has been extensively applied in fields of steel industry, titanium-aluminum alloys, vanadium redox battery, and catalysts [1]. Most vanadium in stone coal exists as V(III) replacing Al(III) from dioctahedral structure as isomorphism in mica group minerals [3], which is generally recovered by roasting with sodium additive at a high temperature [4]. The vanadium is liberated from crystal structure and converted to water or acid soluble vanadate [5], which is subsequently recovered by water leaching and/or acid leaching, ion purification, vanadium precipitation, and calcination [6,7,8]. For the process of vanadium extraction from stone coal, the vanadium recovery by the roasting-leaching procedure is around 65–75%, while for other procedures, such as ion exchange, solvent extraction, and vanadium precipitation, the vanadium recoveries are more than 97% [9,10]. The total vanadium recovery depends on the vanadium recovery of the roasting-leaching step [11]. The researches on vanadium occurrence mostly focus on the raw ore Minerals 2018, 8, 63; doi:10.3390/min8020063 www.mdpi.com/journal/minerals
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