Year

1992

Degree Name

Master of Science

Department

Department of Geology

Abstract

This work investigates the ultrafine component of the reject stream from West Cliff Colliery, near Appin, on the NSW South Coast. The tailings studied were less than 118|im in size. The tailings were characterised mineralogically and elementally, using analytical techniques such as XRD, SEM, Y-Spectrometry and ICP. A series of standard and modified leaching tests, based on the BEOP-31 standard, was used on the tailings to determine the release of four of the primary elements, and ten heavy metal elements, under different leaching conditions. The tailings were found to consist mainly of kaolinite, siderite, including a magnesium-bearing siderite, calcite and quartz, with lesser amounts of illite and magnetite. Kaolinite was considered to be the primary source for aluminium in the leachates, siderite for iron, calcite for calcium, and the magnesium-bearing siderite for magnesium. The release of calcium and magnesium was relatively high, saturating the leachates, and accounting for the alkalinity. The pH of the leachates increased rapidly from 4 of the initial leaching solution to 9. The release of the heavy metals was very low. The leaching of manganese differed from the other heavy metal elements, and appeared to parallel that of magnesium and calcium for at least some of the leaching time. The release of the heavy metals from the tailings was generally much less than the concentrations recommended for potable water by the SPCC. Geochemical modelling of the leaching system was able to predict pH and magnesium and calcium concentrations in the leachates reasonably well. Modelling of the dissolution of siderite and kaolinite was not successful probably due to the complex behaviour of these minerals in aqueous systems.

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