Synergistically effective flotation enrichment of vitrinite by Na removal for high-Na high-inertinite low-rank Zhundong coal

The highly effectively removing Na and enriching vitrinite for high-Na high-inertinite low-rank Zhundong coal is of great significance for its efficient and clean utilization. The effect of Na removal by low concentration HCl and AcOH on vitrinite enrichment before and during the flotation process of Zhundong coal are investigated. The vitrinite content in raw coal is only 48.67%, it can be increased to 61.85% and the yield of clean coal is only 26.44% by flotation for raw coal. However, if Na is nearly fully removed by HCl and AcOH before flotation, the vitrinite content can reach as high as 70.22% and the yield of clean coal can be significantly increased to 39.77% for AcOH-treated coal. The comprehensive efficiency is significantly improved to 57.38% from 33.60% for raw coal. When directly adding low concentration AcOH and HCl during flotation process of raw coal, the flotation effects are nearly the same to those of the above Na-removed coals in advance. The results clearly indicate that the effective removal of organic Na on surface and in macropores of coal plays a decisive role in synergistically enriching vitrinite by flotation. Further studies on vitrinite-rich coal (VC) and inertinite-rich coal (IC) and their Na-removed samples show the improvement of flotation effect can be attributed to the effective adjustment of the surface properties of Zhundong coal accompanying the Na removal, which not only improves the hydrophobicity of coal, but also promotes the hydrogen bonding interactions between collector and coal, especially vitrinite.