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Calcium-based materials represent a critical industrial resource, particularly for the cement and steel manufacturing sectors, as well as for the development of various functional materials. The primary constituents of these resources are calcium oxide and calcium hydroxide—collectively referred to as lime— which are conventionally produced through the thermal decomposition of limestone (calcium carbonate). This calcination process typically requires temperatures around 1000 °C and relies heavily on fossil fuels such as heavy oil, resulting in substantial carbon dioxide (CO₂) emissions. In the context of advancing toward a low-carbon society—a key objective for sustainable development—the environmental impact of lime production has emerged as a significant challenge. Our investigation into the carbon footprint (CFP) of lime production at a small-scale industrial facility in Japan revealed that approximately 1.2 metric tons of CO₂ are emitted per ton of lime produced. Notably, 60% of these emissions originate from the decomposition of the limestone itself. These findings underscore the necessity of reducing reliance on natural limestone to mitigate carbon emissions in the lime industry. To address this issue, we have explored innovative technologies aimed at producing lime with reduced carbon emissions. One such approach involves mechanochemical reactions, which utilize frictional energy generated between milling media and the vessel wall in a rotating system. This high-energy environment enables chemical transformations at ambient temperature. Our research has focused on converting underutilized calcium-containing waste materials into valuable lime products. For instance, we successfully transformed calcium scale—obtained from water softening processes—into calcium hydroxide (Ca(OH)₂). Another promising strategy involves leveraging water treatment processes for low-carbon lime production. Specifically, we examined wastewater from the cleaning of returnable glass bottles, which contains a few percent sodium hydroxide (NaOH). As a calcium source, we selected gypsum (calcium sulfate dihydrate) recovered from building demolition waste. Our experiments demonstrated that gypsum can be effectively converted into Ca(OH)₂ in aqueous solutions with low NaOH concentrations. Our research integrates both academic inquiry and industrial collaboration, with the goal of scaling up the production of low-carbon lime. We anticipate that these technologies will contribute to the commercial availability of environmentally sustainable lime products in the near future.