A Method for Recovery of High-Purity CaCO3 during Carbon Sequestration Using Municipal Solid Waste Incineration Fly Ash

The effective utilization of municipal-solid-waste-incineration fly ash (FA) is the bottleneck of incineration. Previous reports has carried out sufficient works on carbon sequestration using pure Ca source. Carbon sequestration of FA only generally results in pure CaCO3 by leaching Ca first. This work proposes a slow-crystallization-after-fast-carbonation method to separate CaCO3 from FA during carbon sequestration. In brief, CaCO3 is formed and separated after FA is removed from a monoethanolamine (MEA) carbonation solution. As a result, 290 kg of CaCO3 per ton of FA is separated, i.e., reaching a carbonation rate of 44 wt % Ca in FA. Impurity content (such as Cl and S) is less than 1 wt %, i.e., the purity of CaCO3 is bigger than 99 wt %. At the same time, leaching of the carbonation products meets the limits of GB 5085.3-2007. Furthermore, crystal phase of the CaCO3 is regulable. Bigger concentrations of MEA and Ca2+ are in favor of forming more vaterite, resulting in as high as 96% in this work. A crystal temperature of 60 °C helps to form 66% of aragonite in the separated CaCO3. The put-forward method is repeatable using the filtrate after carbon sequestration. Therefore, this work obtains relatively pure CaCO3 without acid leaching from FA, which is in favor of high-value-added utilization of FA.