CO2-fixing and Recovery of High-Purity Vaterite CaCO3 from Recycled Concrete Fines

Recycled concrete fines (RCF) are by-product of waste concrete recycling, and are commonly disposed in landfills. With global warming and natural resource depletion, it is imperative to identify novel upcycling technology to turn RCF into value-added products. This research proposes a two-step process to produce vaterite CaCO3 (rare earth carbonate) through extraction of calcium from RCF using ammonium chloride (NH4Cl) and leachate carbonation. The effect of operating conditions on leaching-carbonation of RCF in maximizing Ca2+ extraction and CO2 sequestration is investigated. Under the optimized conditions, the leaching rate of Ca2+ is 65.7%, and solid residue is amorphous gel with minor phase of brownmillerite. Vaterite (-1-10 mu m) with purity of 97.8% can be successfully produced. The formation of more stable carbonates is favored with higher aqua -ammonia dosage. The proposed strategy addresses issues such as upcycling RCF, extracting vaterite (615 g /1 kg RCF) and sequestrating CO2 (270 g/1 kg of RCF).