The carbon dioxide removal potential of cement and lime kiln dust via ocean alkalinity enhancement

Abstract. Ocean alkalinity enhancement (OAE) is a proposed method for atmospheric carbon dioxide removal (CDR), and involves the addition of alkaline minerals to surface waters to elevate seawater alkalinity and enhance atmospheric CO₂ storage. Cement kiln dust (CKD) and lime kiln dust (LKD) are alkaline side streams from the cement and lime industry that have OAE potential due to their widespread availability and fine particle size. Here, we evaluated the dissolution kinetics, CO₂ sequestration potential, and ecological risks of CKD and LKD by means of laboratory dissolution experiments. A reactive fraction (~25 % in LKD and ~29 % in CKD) dissolved rapidly within 24 hours, with most dissolution occurring within the first hour. Dissolution provided a concomitant alkalinity release that was higher for LKD (up to 8.0 ± 0.5 mmol alkalinity per g) than CKD (2.4 ± 0.2 mmol g^-1), thus providing a sizeable CO₂ sequestration capacity for LKD (297 ± 20 g CO₂ per g) and CKD (88 ± 6 g CO₂ per g). Based on current industrial production rates, this translates into global CDR potentials of up to 8.7 ± 0.6 Mt CO₂ yr⁻¹ for LKD and 25 ± 2 Mt CO₂ yr⁻¹ for CKD, suggesting that both materials could serve as viable OAE feedstocks. Furthermore, we hypothesize that the substantial residual calcite content of LKD (~54 %) and CKD (~37 %) may provide additional sequestration via metabolic dissolution in marine sediments. However, kiln dust deployment will generate elevated turbidity levels that may exceed environmental thresholds, underscoring the need for carefully designed application strategies to minimize local ecological impacts.