A lime kiln is an industrial furnace or reactor used to produce calcium oxide (CaO), commonly known as quicklime or burnt lime, by thermally decomposing calcium carbonate (limestone, CaCO₃) through a process called calcination. The calcination reaction requires temperatures in excess of 900°C and results in the release of carbon dioxide gas (CO₂) and the formation of highly reactive calcium oxide. In the mining industry, lime kilns are critical supporting infrastructure for operations that consume large quantities of lime as a process reagent, particularly in gold mining and bauxite processing.
There are several types of lime kilns used in industrial applications. Rotary kilns are large, rotating cylindrical furnaces that can process high volumes of limestone continuously and are commonly used in alumina refineries and large mineral processing operations. Vertical shaft kilns (also known as plug flow kilns) are vertical cylindrical reactors in which limestone is charged at the top and moves downward through preheating, calcination, and cooling zones. Parallel flow regenerative (PFR) kilns and annular shaft kilns offer higher energy efficiency and product quality for specialized applications.
In gold mining operations that consume significant quantities of lime for pH control in cyanide leach circuits, operating an on-site lime kiln using locally available limestone deposits can dramatically reduce operating costs compared to purchasing commercially produced lime. The feasibility of a lime kiln depends on the proximity and quality of limestone resources, fuel availability and cost, and the scale of lime consumption.
In alumina refineries operating the Bayer Process, large rotary lime kilns are used to regenerate lime from calcium carbonate recovered from the process, reducing purchased lime requirements. The energy consumption and carbon dioxide emissions of lime kilns are significant operational and environmental considerations, driving interest in alternative fuel sources and carbon capture technologies.