Low-Temperature Water Electrolysis Under a Sustained pH-Gradient for Electrochemically-Induced Decarbonation of Limestone into Hydrated Lime

Abstract

Lime holds considerable potential in diverse environmental applications. However, its current production remains highly carbon-intensive, emitting more than one ton of CO2 per ton of lime. To address this issue, recent studies have explored the concept of electrifying the decarbonation of limestone to produce hydrated lime. In this work, a two-compartment electrolysis cell capable of producing Ca(OH)2 has been tested at different currents. Precise pH and Ca2+ concentration measurements demonstrate that the electrolysis setup is able to dissolve CaCO3 and precipitate Ca(OH)2 with near-perfect efficiencies. Notably, it highlights that Faraday’s law and the concept of transport number can be applied to predict both the equilibrium and kinetic behavior of each step of the process in each of the two cell compartments. Moreover, the use of controlled batch additions of CaCO3 in the system, as opposed to one-time excess addition, was assessed to mitigate the fouling of the cationic exchange membrane used to separate the compartments. Finally, based on the experimental findings, key guidelines are proposed to achieve a perfect reaction stoichiometry for each step. These findings pave the way for a more sustainable and environmentally friendly approach to lime production.