Lime Kiln Dust and Cement Kiln Dust

Nontraditional Soil Amendments

LIME KILN DUST AND CEMENT KILN DUST

Lime kiln dust (LKD) and cement kiln dust (CKD) are very fine particulates trapped in air pollution control systems of rotary kilns used to manufacture lime and portland cement. LKD and CKD are mixtures of dust from finely ground limestone fed into the kilns and fly ash from the fuel (coal, fuel oil, natural gas) used to heat the kilns. In the kilns, limestone (CaCO₃) is converted to quick lime (CaO). Depending on the amount of lime-derived material in the dust, LKD and CKD can have a high CCE and can be an effective soil liming material. As with slags, the CCE of these materials can vary widely depending on the source and composition. Farmers considering using LKD or CKD should obtain several analyses of the CCE of the material. Because these materials contain CaO, their pH often is around 12, compared to the pH of limestone at about 8.2. Application of LKD or CKD in excess of soil liming requirements could increase soil pH to levels above 8.2, the maximum pH obtainable with conventional limestone (CaCO₃). High soil pH can lead to problems with crop nutrition and herbicide efficacy and carryover.

Kiln dusts are extremely fine materials. This can make handling and spreading more challenging than conventional ground ag-limestone. Generation of excessive dust can be a problem, as can bridging and uneven flow in some spreading equipment. As with slags, LKD and CKD may contain significant amounts of some trace elements, mainly due to the fly ash they contain. Again, it is important to obtain analyses of total metal concentrations in the kiln dust. Some kilns double as waste incinerators and may include materials such as old tires and municipal solid waste in their fuel source. Incineration of these wastes could result in dusts contaminated with any number of organic and inorganic constituents. Dusts from waste incinerator kilns should not be used for liming soils.