Ocean alkalinity enhancement is a carbon capture strategy that has gained interest over the past years. This strategy relies on the dissolution of alkaline minerals to increase the alkalinity of the ocean, among which iron and steel slags are potential candidates. However, their dissolution in seawater as well as the leaching of potentially toxic elements is unknown. These data were collected as part of a research article that assess the alkalinity generation potential of iron and steel slags in MilliQ and seawater, as well as the dissolution of potentially toxic elements. The dataset is composed of various sheets, each of them reporting data from a specific experiment. For each experiment, the analysis details (instrument used, parameters analysed etc) are provided on each individual sheet, and an overview one regroups the main aims of this research as well as the technical terms used throughout.