Production of precipitated calcium carbonate (PCC) from steelmaking slag for fixation of CO_2

摘要

Producing precipitated calcium carbonate (PCC) from steelmaking slag is a technology that contributes to the reduction of carbon dioxide emissions from iron and steel industries. While the carbon dioxide emissions from the sector are large, it could benefit from this option by utilizing its own by-products, i.e. steelmaking slags for fixation of CO_2. Since the calcium content of the steelmaking slag is high, a calcium carbonate precipitate can be produced with the method which we have recently developed, and, if fulfilling the requirements (e.g. purity and crystal shape), it can be utilized as PCC. Therefore, the objective of this study is to further evaluate the feasibility of this method. Calcium was extracted selectively from the slag with aqueous solution of ammonium salt (NH_4NO_3, CH_3COONH_4 or NH_4Cl) in an extraction reactor. After removal of the residual slag, the calcium-rich solution reacted with CO_2 in a carbonation reactor producing PCC. Based on the experimental results, the slag's grain size has a clear effect on the calcium extraction efficiency; the smaller the steel converter slag's grain size, the larger the surface area, and the better the mass transfer rate which in turn results in a higher extraction efficiency. Grinding to smaller sizes is therefore one strategy towards improved efficiencies and chemical conversion rates. Solid to liquid ratio is another important parameter for improving extraction efficiency. The smallest solid to liquid ratio 5 g/1 resulted in the maximum calcium extraction efficiency (73%) while the highest solid to liquid ratio 100 g/1 resulted in the lowest extraction efficiency (6%). Consequently this option will be operationally expensive because of larger reactor volumes. The PCC produced from the calcium rich solution is comparable to the PCC produced with conventional methods.