Manufacture of potassium chloride from cement kiln bypass dust: An industrial implementation case for transforming waste into valuable resources

Abstract

The recirculation of chlorine within the kiln presents a major hurdle in co-processing domestic waste in cement kilns. This chlorine enrichment not only adversely affects the quality of cement, but also pose a serious challenge to the subsequent eco-friendly disposal of kiln dust. To solve this problem, a proper bypass system has been implemented in this study on a 4000 t/d new dry process cement rotary kiln, and the collection of chlorine-rich bypass dust outside the kiln (30 t/d) has been achieved. In addition, a comprehensive and innovative system has been developed, including water washing and subsequent triple-effect salt extraction, to achieve leaching of K+ and Cl from the bypass dust in the water rinsing liquid, while effectively removing harmful metal ions such as Pb2+. Finally, the extraction of high-purity KCl salt (6 tons/day, purity of 90 %) has been successfully achieved. It is worth noting that high-temperature flue gas rich in CO2 has been used to precipitate certain heavy metal ions, while steam from the waste-heat power generation system has been employed as a heat source for the potassium salt evaporation process. More importantly, all the materials, except for the KCl salt product, are returned to the cement kiln system without causing any secondary pollution. This study not only effectively addresses the negative impacts of chlorine element circulation within cement kilns during domestic waste co-processing, but also achieves a highly innovative engineering practice of transforming waste into valuable resources from kiln dust to high-purity KCl products. In brief, this work provides a reference example for future approaches to clean production, carbon reduction and resource utilization in the cement industry.