The Fate of Trace Elements During MTE and HTD Dewatering of Latrobe Valley Brown Coals

Abstract

ABSTRACT The nonevaporative brown coal dewatering technologies, Mechanical Thermal Expression (MTE) and Hydrothermal Dewatering (HTD), are being evaluated in an attempt to increase the efficiency of coal drying compared with current evaporative methods. Product waters from each of the three major Latrobe Valley mines were prepared under both MTE (200°C and 15 MPa mechanical pressure) and HTD (300°C and 12 MPa) conditions. Comparison of the relative abundance of individual inorganic components across the two processes generally reflected their form (dissolved, exchanged, or mineral) in the parent coals. For MTE the data were complicated by leaching of rig components (principally bronze). MTE-derived waters contained greater amounts of Ag, As, Cd, Cr, Cu, Hg, Mo, Ni, Sn, and Zn. HTD waters had greater amounts of Al, B, Ba, Ca, Fe, K, Mg, Mn, Na, Pb, Se, Sr, Tl, and V. Dissolved organic carbon was five times higher in the HTD products as a result of the higher processing temperature employed. Many species (Al, Ag, As, Cd, Cr, Cu, Hg, Mo, Ni, Pb, V, Se, and Zn) were found to be above acceptable guidelines for discharge to the environment.