Control strategies for the selective precipitation of CaCO3 from multi-ion solutions

With rising atmospheric CO2 levels, carbon dioxide capture through calcium carbonate (CaCO3) precipitation offers a viable pathway for permanent CO2 storage and the production of useful industrial materials. This study presents the experimental implementation of selective CaCO3 precipitation from multi-ion solutions in a semi-batch operation. The objective is to develop and further implement an autonomous control strategy for the selective precipitation using mine wastes. Two distinct pH control strategies were developed and evaluated: a pH swing approach and a pH constant approach. Both methods prove effective for the precipitation of CaCO3 selectively from different multi-ion solutions rich in Mg2+. The two strategies, however, differ in their precipitation mechanisms. The pH swing method induced rapid nucleation under high supersaturation, producing fine particles predominantly with Calcite morphology. In contrast, the constant-pH method allowed for a slower, controlled growth following initial nucleation, resulting in larger particles with a well-defined bimodal particle size distribution (PSD). Initial development of the strategies done using model solutions that mimics real mine tailing extraction solutions and later validated with actual tailing extraction solutions. Depending on the target particle size, morphology, and process control requirements, either approach can be tailored for specific applications.