Abstract
Spherical vaterite particles were produced by carbonation of calcium chloride solution with addition of ammonia to facilitate CO2 absorption. Synthesis of calcium carbonate was carried out in a bubble column or gas-lift reactor. The course of the reaction was monitored by pH measurements. Precipitated solids were analyzed by Fourier-transformed infrared spectroscopy, x-ray powder diffraction and scanning electron microscopy, and the particle size distribution was determined by a laser diffraction method. Synthesized calcium carbonate products were mainly vaterite. The calcium chloride concentration and carbon dioxide volume fraction in a gas phase had the main impact on the size of the produced particles in both reactors. A slight decrease in the mean particle size was observed for the highest mixing intensity. Both tested reactors can be applied to produce vaterite particles, although formation of homogeneous non-agglomerated spherical particles in a gas-lift reactor required careful selection of the process parameters.
Highlights
Calcium carbonate is a compound that occurs extensively in nature, and it is produced on a large scale by the chemical industry
Spherical vaterite particles have been proposed as a delivery carrier for drugs and bioactive proteins.[5,6,7]
Changes of pH over time during CaCO3 precipitation in both reactors to compare the influence of the calcium chloride concentration and of the CO2 volume fraction in a gas phase are shown in supplementary materials Fig. S-1 and Fig. S-2
Summary
Calcium carbonate is a compound that occurs extensively in nature, and it is produced on a large scale by the chemical industry. It can crystallize as three anhydrous polymorphs: calcite, aragonite and vaterite. The least stable polymorph is vaterite, which relatively transforms into more stable forms, i.e., calcite (the most stable polymorph), at temperatures< 40°C or aragonite at higher temperatures.[1,2] Vaterite has a hexagonal crystal system, and all vaterite structures belong to the order–disorder (OD) family.[3] This means that the occurrence of multiple polytypes on the micro- to macroscopic scale and considerable stacking disorder are both to be expected. Spherical vaterite particles have been proposed as a delivery carrier for drugs and bioactive proteins.[5,6,7]
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