Adding Value to Coal Cleaning Wastes
AUTHOR: Gordon R Couch
DATE: April 1998
Coal cleaning and preparation are essential to provide consistently high grades of coal from many mining operations and, worldwide, about half the output of higher rank coals is washed. It is estimated that over 600 Mt/y of such wastes are produced. Utilisation of some or all of the material is clearly a preferable option to disposal in most circumstances, and offers opportunities for adding value.
In most countries, the regulations governing the disposal of waste materials have become more stringent. There is sensitivity to the effects of dumps on ground water quality, to safety issues, and to the visual appearance of waste stacks. In addition, in connection with coal washing wastes, there are concerns about the risks of spontaneous combustion, and the emissions which arise.
As a result, more thought is being given to the possibilities of the use of wastes in preference to disposal. Ways of effectively adding value to the material include:
- incorporating course wastes as a construction material for dam walls and as a base for building roads;
- incorporating waste materials into cement;
- using the wastes as a low grade fuel. The possibility of burning the residual carbon present in waste material in a fluidised bed combustor, thus recovering usable energy, has the attraction that virtually all the mined carbonaceous material can be burned.
Some low grade (high ash content) washery wastes which were previously dumped are now being recovered from tips, and used in fluidised bed combustors. Experience in Australia, France, India, South Africa and the USA is described, and in some plants, the wastes are supplied directly from the preparation plant.
In both China and India, most coals currently used for power generation are not cleaned. However, new washeries are being planned and built to improve the coal quality, and these will give rise to substantial amounts of additional waste and reject. Finding appropriate methods of dealing with this material is an important issue.