New flotation flowsheet for recovering combustible matter from fine waste coking coal

Abstract

Fine waste coking coal (FWCC) is a high-ash-content by-product produced in large quantities during separation of raw coking coal and deposited in open air without treatment, causing environmental hazards and energy waste. The main objective of this study was to recover clean coal with ash content less than 12.5% by reprocessing FWCC at KaiLuan (Group) Limited Liability Corporation (KLLC) via spiral separation, grinding, and flotation processes. First, the physical characteristics of FWCC were investigated using particle-size analyses, washability analyses, and polarizing microscopy. Then, a spiral separator was used to remove materials with high ash content from the FWCC. Subsequently, spiral clean coal was ground in a roll mill for different grinding durations. Finally, flotation separated the products of grinding from the clean coal. Analyses of the physical characteristics showed that the FWCC could be pretreated using gravity in a spiral separator because it had a large amount of high-density materials. 46.28% spiral clean coal with 26.50% ash content was obtained and 53.72% of spiral tailings with 68.94% ash content were removed with a spiral separator under optimal conditions. The following flotation theoretical yield of clean coal increases with the grinding time. However, flotation experiments show that the maximum actual yield of clean coal first increases and then decreases on increasing the grinding time from 3.5 min to 15 min. Approximately 50% clean coal was obtained at grinding times between 3.5 and 5 min. This can be used for metallurgical plants and has economic value. A novel gravity-grinding-flotation separation flowsheet was developed and nearly 24% of the FWCC could be translated into qualified clean coal to realize comprehensive utilization of this waste resource. Engineering practice further confirm that deep processing of FWCC could generate an extra profit of $11.846 million per year for KLLC. These results indicate that deep processing of FWCC is reliable, economical, and promising for the coking coal industry, and therefore, cleaner production of coking coal is feasible.