Coal mining and washing activities in South Africa often lead to the generation of
fine and ultra-fine coal which is in most cases discarded due to high handling and
transportation costs. Studies conducted revealed that a large quantity of these fines
have market acceptable calorific values and lower ash contents. In order to reduce
fines discarded, processes have been developed to re-mine and process the fine coal
discards with the aim of improving the calorific value, adding them to coarse washed
coal to increase the yield as well as pelletizing the fines so as to meet the market
specifications in terms of size.
The goal of this study was to evaluate the efficiency of fine coal washing using
gravity separation methods and comparing the products thereof to the market
specifications with regards to the calorific value and the ash content. Coal fines from
the No.4 lower seam of the Witbank coalfield in South Africa resulting from a dry
coal sorting plant were subjected to a double-stage spiral test work, heavy liquid
separation and reflux classifier test work respectively.
The reflux classifier achieved products with low ash content and an increased
calorific value, at high mass yields. At higher fluidization water flowrate, the reflux
classifier performance was superior to that of the spirals with products of lower ash
content and higher calorific value. At low cut point densities, heavy liquid separation
yielded the cleanest products with very low ash content but at much lower mass
yields. As the density increased, the mass yields increased with the ash content while
the calorific value decreased. Most of the products from the different processes met
most of the local industries’ specifications but none of them met the export market
as well as the gold and uranium industry specifications due to the high ash content.
A Feasibility Study Evaluating the Efficiency of Fine Coal Washing Using Gravity Separation Methods
