Separation and Recovery of Potassium Chloride from Sintering Dust of Ironmaking Works

Sintering plant in iron and steel making company generates very fine metal-containing dusts which can present major environmental problems. This paper describes experimental work on a relatively simple and inexpensive process for recovering the potassium chloride and upgrading the iron level of dust from a Chinese plant, to produce saleable potassium chloride product and environmentally safe waste products for reuse. The dust contained about 10-20% potassium as potassium chloride, 20% iron as iron oxides, plus small quantities of lead, copper, cadmium, zinc and other materials. Individual particles of the dust were commonly aggregates of various shapes. Multi-stage countercurrent leaching was taken to completely remove potassium chloride in the ESP dust, but leave iron in the leach residual. With the help of sodium sulfide precipitation, the leached heavy metals were removed from the leaching solutions and a mixture solution which can be perceived as system KCl-NaCl-CaCl2-H2O was left. Then potassium chloride in the system can be separated and recovered by fractional crystallization. At last the mother liquor was returned to the leaching process as leaching agent together with new tap water. This proposed flow sheet was proved feasible through construction of the demonstration unit in the lab, and KCl product with a purity of 96.5% was obtained.