Preliminary assessment of cement kiln dust in solidification and stabilization of mercury containing waste from a chlor-alkali unit

A low-level mercury containing hazardous waste with a mercury concentration of 22.0 ± 5.00 ppm generated at a chlor-alkali unit was solidified and stabilized using cement kiln dust (CKD) and other binding agents. Similar in many aspects to cement, CKD is a waste byproduct of cement manufacturing process and is considered a waste material although in some cases it is partially reused. Application of CKD as a binding agent in solidifying and stabilizing mercury in the waste was preliminarily examined. The results indicated that addition of about 36.0 % by dry mass of CKD to the waste led to reduction of mercury concentrations to less than the strict land disposal restriction (LDR) of 25.0 ppb in toxicity characteristic leaching procedure extracts set by the US Environmental Protection Agency. Using CKD for solidifying/stabilizing mercury can be advantageous as it can be partially consumed in this process rather than being discarded as a waste material. However, the volume of the resulting solidified/stabilized waste may not be favorable for land disposal or onsite storage. Addition of less than 1.00 % of other chemicals such as lime, soda ash, sulfur and sodium metasilicate individually to the mixture resulted in about 12.0 % reduction in CKD requirement.