A study on the effect of grinding-liberation of coking coal middlings in vertical spiral agitating grinding mill

Grinding-liberation of coking coal middlings is a basic precondition for realizing efficient utilization of coking coal resources. Test is made on the grinding of the > 300, 300~74 and < 74 μm coking coal middling products using the spiral agitating grinding mill, and the effects of liberation of the middlings in different sizes are assessed with the use of scanning electron microscope (SEM), energy spectrometer and laser particle size analyzer. Test result shows that of all the 3 sizes of middlings, the disseminated minerals are predominately scattered fine-grained kaolinite with some kaolinite distributed in aggregated form mainly in the 300~74 μm size fraction; the best liberation effect can be obtained through grinding of the 300~74 μm size fraction; through grinding of this size fraction, the yield of clean coal with a cumulative ash of 10% is increased by 20 percentage points became of the much higher ratio of size reduction, and there can be seen a rise of the yield of the < 45 μm size coal in the ground product by 35.57 percentage points, an increase noticeably greater than those in the case of grinding the other two size fractions; and the mean particle grain-size ratio of either high-density or low-density material before and after grinding of the 300~74 μm middling is likewise higher as compared with the grinding of the other two size fractions.