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

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 CO 2 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, CO 2 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 h, 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 CO 2 sequestration capacity for LKD (297 ± 20 g CO 2 per kg) and CKD (88 ± 6 g CO 2 per kg). Based on current industrial production rates, this translates into global CDR potentials of up to 8.7 ± 0.6 Mt CO 2 yr −1 for LKD and 25 ± 2 Mt CO 2 yr −1 for CKD. These estimates suggest that both materials could be viable OAE feedstocks, although further testing under conditions that more closely mimic natural coastal conditions is needed. 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.