Bench-Scale Operation of a Concrete Sludge Recycling Plant

A bench-scale plant for waste concrete sludge recycling was designed, constructed, and operated. Real concrete sludge generated from a pile and pole production plant and groundwater were used for the experiments. The process mainly consists of the extraction of calcium ions from the concrete sludge into the aqueous phase and the crystallization of calcium carbonate from the solution with CO2. The CO2 was supplied from boilers installed in the plant, where heavy oil is combusted. High-purity calcium carbonate (>99%) was obtained in the process, with particle sizes distributed in the range of 3–30 μm (volume-based), peaking at about 10 μm. A net reduction in CO2 emissions can be achieved based on the process power consumption and the amount of product. The effects of operating conditions on process performance data such as calcium extraction rate and calcium carbonate crystallization rate were examined, which can lead to scaling-up of the plant.