Method for Extracting Calcium Ions and Manufacturing Nano-Sized Calcium Carbonate Using Cement Kiln Dust

Manufacturing Nano-Calcium Carbonate from Cement Kiln Dust Using pH-Swing Indirect Carbonation

This technology is an indirect carbonation process that extracts calcium ions by dissolving cement kiln dust—a byproduct of the cement industry—in a strong acid. The pH is then adjusted in stages to precipitate and remove impurities, and carbon dioxide is injected into the remaining high-purity calcium solution to produce nano-sized calcium carbonate. The average particle size of the final calcium carbonate can be controlled within the 10–100 nm range.

Due to a shortage of natural minerals for carbonation, such as wollastonite and serpentine, utilizing industrial byproducts as raw materials for mineral carbonation has been considered a practical alternative. However, existing direct carbonation processes, which involve reacting carbon dioxide directly with cement kiln dust, suffer from low efficiency, slow reaction rates, and the contamination of the resulting calcium carbonate with impurities.

This technology uses a three-stage pH adjustment (3.0–3.5, 11.0–11.5, and 12.5–13.0) to sequentially filter out non-calcium metal components. The alkaline supernatant from the final stage is recycled as a CO2 absorption solvent and pH buffer, which increases reaction rates and reduces wastewater treatment burdens. Applicable to carbon capture and storage (CCS) facilities in cement plants and production lines for paper, plastic, and paint, this process simultaneously achieves industrial waste management, greenhouse gas reduction, and the production of high-value materials.

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Key Features:

• Adding cement kiln dust to a strong acid solvent, raising the pH to 3.0–3.5, and removing the resulting first precipitate
• Raising the pH of the first supernatant to 11.0–11.5 to remove the second precipitate, then further raising the pH to 12.5–13.0 to separate the third supernatant and third precipitate
• Injecting gaseous carbon dioxide into the third precipitate and third supernatant to adjust the pH to 6.5–12.5, producing calcium carbonate with an average particle size of 10–100 nm
• Using 0.8M–1.2M hydrochloric acid as the strong acid solvent, 4.5M–5.0M sodium hydroxide as the base, and stirring all stages at 380–420 rpm

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This invention was developed with support from the Ministry of Environment for the synthesis and commercialization of high-quality light calcium carbonate using active ingredients from shells.

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