General Aspects of Calcium Carbonate Production

The production of valuable carbonate products implies in practice the production of a valuable (precipitated) calcium carbonate. When producing these from calcium-containing waste materials, several process parameters have a direct influence on product quantity and quality. Many test results and product analyses have been reported, mainly for low-value feedstock materials such a cement waste, ashes and slags from iron- and steel production, and the carbonation processes are practically all based on aqueous systems operating at conditions up to 473 K, 20 MPa. 

Based on the required product purity and quality, processes can be divided into  

While the apparently single-step process partly involves gas-solid carbonation chemistry, the two-step process implies carbonation of dissolved calcium only, and is primarily a crystallization process. In order to achieve a valuable carbonate product, the single-step conversion is generally followed by a product improvement step, for example a recrystallization. Therefore, this is referred to here as an apparent single step. 

Based on reports in the open literature (e.g., Refs [19, 26, 44—49]), the following can be concluded with regards to product amounts and properties  

The pressure of C02 will affect the pH of the solutions, with one outcome that higher pH levels will result in smaller particles. Likewise, also mixing and stirring will affect particle size (distribution), to a large extent following general experiences with crystallization. Strong relationships between the product particle size (distribution) and the process conditions do not exist, however. 

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