Research on Desulfurization and Ash Reduction of Zichang Coal from Northern Shaanxi Province through Three Inorganic Inhibitors by Flotation

Desulfurization and ash reduction are the key to clean utilization of medium and high sulfur coal, and flotation plays an important role in fine coal desulfurization. In order to improve the desulfurization and ash reduction effect of medium and high sulfur coal by flotation, taking Zichang coal from northern Shaanxi as the research object, the particle characteristics of raw coal were investigated by screening and float-sink test, and the distribution changes of pyrite in coal before and after flotation were investigated by coal petrography. The desulfurization and ash reduction effects of three non-toxic inorganic corrosion inhibitors: calcium oxide (CaO), ammonium sulfate (NH₄)₂SO₄, sodium pyrophosphate decahydrate (Na₄P₂O₇·10H₂O) and their combination inhibitors were compared. The results show that the distribution density of pyrite decreases effectively after flotation, CaO has the best desulfurization and ash reduction effect, which is similar to (NH₄)₂SO₄, followed by Na₄P₂O₇·10H₂O, but Na₄P₂O₇·10H₂O has almost no desulfurization effect. When the dosage of CaO and (NH₄)₂SO₄ is 4 000 g·t^-1 and 1 000 g·t^-1, respectively, the sulfur content of cleaned coal is the lowest 1.83%. The highest desulfurization efficiency of CaO and (NH₄)₂SO₄ is 18.28% and 12.35%, respectively. The desulfurization and deashing effect of CaO and (NH₄)₂SO₄ is not as good as the three single inhibitors, but it can improve the desulfurization and deashing effect of fine coal to a certain extent. CaO and (NH₄)₂SO₄ can be used as pyrite inhibitors to improve the desulfurization and the deashing efficiency of flotation.