Air nanobubbles retard calcite crystal growth

Demands for "green" additives that control the crystal growth and inhibit the scale formation in industrial processes are growing as never before. Nanobubbles can be the green additive for inhibiting and/or promoting the crystal growth of calcium carbonate, given their well-known unique physicochemical properties. This paper reports for the first time the changes in the crystal growth rate of calcite in liquid in the presence of air nanobubbles. We injected the air nanobubbles into the solution and studied the calcite crystal growth for the first 4 h in a static condition at 20 degrees C and 88 degrees C. We found that air nanobubbles retarded the growth rate of calcite crystal by up to 53 % and 33 % at 20 degrees C and 88 degrees C, respectively. The retardation of calcite crystal growth could differ with different number densities of air nanobubbles added to the solution. A higher number density of nanobubbles generally showed slightly greater retardation throughout the tested 4 h. Air nanobubbles may influence the crystal growth either by changing solid-liquid interfacial tension on the crystal surface, reducing the free growth sites, adsorbing Ca2+ ions, playing roles in bubble mattress and thermal buffering on the crystal surface, or combinations of them. Our findings suggest that air nanobubbles can be utilized as a green inhibitor of calcite crystal growth and calcium carbonate scale in broad industrial areas.