Environmentally responsible production of lime from recycled gypsum and weakly alkaline wastewater

• Published in: New journal of chemistry 2024-06, Vol.48 (23), p.1384-139
• Main Authors: Tafu, Masamoto, Suzuki, Asumi, Nakamura, Juna, Fukumura, Takuya, Tobe, Tomofumi, Tobe, Noboru
• Format: Article
• Language: English
• Subjects: Aqueous solutions; Calcium carbonate; Calcium oxide; Calcium sulfate dihydrate; Carbon dioxide; Gypsum; Limestone; Resource recovery; Slaked lime; Sodium hydroxide; Wastewater treatment
• ISSN: 1144-0546; 1369-9261
• DOI: 10.1039/d3nj06003a

Lime (which exists as calcium oxide and calcium hydroxide) is typically obtained by calcinating limestone, which consists of calcium carbonate. The process releases large amounts of carbon dioxide (CO 2 ) into the atmosphere. Calcium hydroxide (Ca(OH) 2 ) may also be obtained by treating calcium carbonate or calcium sulphate with an alkaline aqueous solution. These processes generate Ca(OH) 2 without calcinating limestone, thereby avoiding the emission of CO 2 . However, the use of alkaline chemicals may still be accompanied by a carbon footprint associated with the manufacturing process (for example, using electricity generated through the combustion of fossil fuels). In this study, we produced Ca(OH) 2 using gypsum (calcium sulphate dihydrate) powder and wastewater containing a small amount of sodium hydroxide (NaOH). Our method constitutes an environmentally responsible process for producing lime, using resources harvested from demolishing buildings and returnable bottle-washing processes. Our results demonstrate that a small amount of NaOH in an aqueous solution can effectively transform gypsum into Ca(OH) 2 and that the composition of Ca(OH) 2 and gypsum can affect the NaOH content and reaction time. We establish a process for transforming wastewater treatment into resource recovery, producing lime in an environmentally responsible manner and augmenting the construction of a carbon-neutral society. Benefits associated the treatment of wastewater from a returnable glass bottle-washing process as applied in this study. Our result transforms wastewater treatment into resource recovery, producing lime in an environmentally responsible manner.