Hydrodynamic Cavitation-Assisted Synthesis of Nanocalcite

A systematic study was made on the synthesis of nanocalcite using a hydrodynamic cavitation reactor. The effects of various parameters such as diameter and geometry of orifice, flow rate, and concentration were investigated. It was observed that the orifice diameter and its geometry had significant effect on the carbonation process. The reaction rate was significantly faster than that observed in a conventional carbonation process. The particle size was significantly affected by the reactor geometry. The results showed that an orifice with 5 holes of 1？mm size resulted in the particle size reduction to 37？nm. The experimental investigation reveals that hydrodynamic cavitation may be more energy efficient. 1. Introduction The effect of acoustic cavitation on different chemical reactions is well established. Gedanken [1] has reviewed the use of sonochemistry for fabrication of inorganic nanomaterials of various shapes, size, structure, and phases. Acoustic cavitation in liquids leads to two of major effects: physical (streaming, turbulence, microjet, shear, etc.) and chemical (radical production). While acoustic cavitation-induced chemical reactions have been successfully achieved, hydrodynamic cavitation is found to be efficient for applications involving continuous processing such as industrial carbonation operation. It is expected that hydrodynamic cavitation would increase the rate of carbonization reaction by lowering the mass transfer resistance. Hydrodynamic cavitation, in which a liquid is passed through constrictions, such as orifice plate or Venturi, has been found useful in specific chemical reactions. Hydrodynamic cavitation occurs due to the changes in the pressure of liquid flow in a pipe fitted with orifice or Venturi. A liquid experiences a sudden drop in pressure at downstream resulting in the collapse of formed cavities. The collapse of the cavities generates highly reactive radicals, which are responsible for specific chemical reactions. In gas-solid reactions, the dissolution of solids is enhanced due to the turbulent mixing generated by hydrodynamic cavitation. The vigorous mixing enhances the transport of gas solutes to the solid surface that results in an increase in the mass transfer and hence the overall reaction rate [2–4]. Hydrodynamic cavitation has been found useful in the hydrolysis of fatty oils [5] and polymer solutions [6] and in the formation of styrene butadiene rubber nanosuspensions [7]. Morison and Hutchinson [8] have shown the limitations of the Weissler reaction as a model reaction for measuring efficiency of