Optimisation of MX7, SX7, SX10, and SX4 coal spirals on South African coal to produce data that can be used to generate a predictive model for spiral performance

Spirals are used in the South African coal industry for the beneficiation of coal in the 0.1 mm to 2 mm range. While some fine coal in the range <1mm and O.lmmcan be treated using dense medium systems, spirals remain the preferred method in many local operations due to their lower operating costs and simplified design. Multotec coal spirals have been able to produce good product quality with a high calorific value (CV) recovery, while demonstrating high ash and sulphur rejection. These can be used to clean coals that are difficult to wash while providing an enhanced and efficient coal-washing experience due to their compact modular design. Coal washing efficiency, however, is dependent on the spiral operating parameters and there exists optimum operating conditions at which the highest separation efficiency is achieved. The effect of feed solid throughput and solid concentration on mass yield, CV recovery, and ash rejection were studied on four spirals for the purpose of selecting optimal operating conditions. Test work was conducted using coal sample sourced from Emalahleni region on the four xxx spiral concentrators (MX7, SX10, SX7 and SX4 models). For each spiral, sensitivity analyses were conducted by varying solid concentration between 25% and 35%, and feed throughput was between 2 tph and 3.2 tph. Thereafter, the results were compared, and in each case, the optimal operating conditions were selected. While a predictive model is not yet developed, the data and insights generated here form the foundation for future modelling efforts aimed at supporting accurate spiral selection and performance estimation.