An Integration of dense medium cycloning and froth flotation for fine coal cleaning

Magnetite is used to prepare the heavy medium in heavy medium cyclones in coal cleaning. Recovering the magnetite from the products of the heavy medium cyclones is of great importance in terms of cost of cleaning. Traditionally, cyclone products are passed through a set of sieve bend-wash screens. The screen oversize is recovered as the clean coal and refuse. The screen undersize, however is sent directly to the medium preparation tank for the sieve bend while the undersize of the wash screens is directed to a magnetic separator for magnetite recovery. The efficiency of magnetite recovery depends inversely on the amount of non-magnetics. In this study, the undersize products of the wash screens for the cyclone over and under flows were subjected to froth flotation to ¦ decrease the amount of non-magnetics in the feed to the magnetic separator, - recover the fine coal as a clean product from the wash screen underflows. For this purpose samples from the various points on the cyclone circuit of the Tunçbilek Coal Preparation Plant were obtained. These samples were subjected to froth flotation to determine the feasibility of the process. Also, flotation tests were carried out with raw coal samples and coal-magnetite mixtures to determine the best conditions for flotation. Upon determining the best conditions for flotation, the proposed heavy medium cyclone-flotation circuit was compared technically and economically with the current heavy medium cyclone circuit in the plant. The results show that floating the undersize products of the wash screens of the heavy medium cyclone circuit produces an extremely clean coal product with 6.7% ash, having a calorific value of about 6300 kcal/kg. In addition, the non- magnetics content of the material which would go to the magnetic separators decreases to 7.8% from 18%. This should decrease the magnetite losses in the magnetic separation circuit substantially. However, the economics of the proposed heavy medium cyclone-flotation circuit depends heavily on the cost of the oil and the frother used for the flotation process.