Effect of power ultrasound on crystallization characteristics of magnesium ammonium phosphate

Magnesium ammonium phosphate (MAP) crystallization could be utilized for the recovery of phosphorus from wastewater. However, the effectiveness of the recovery is largely determined by the crystallization process, which is very hard to be directly observed. As a result, a specific ultrasonic device was designed to investigate the crystallization characteristics of MAP under various ultrasonic conditions. The results demonstrated that the metastable zone width (MZW) narrowed along with the rising of the ultrasonic power. Similarly, for the 6mM MAP solution, with the ultrasonic power gradually enhanced from 0W to 400W, the induction time was shortened from 340s to 38s. Meanwhile, the crystallization rate was accelerated till the power reached 350W, and then remained a constant value. It can be observed from the scanning electron microscopy (SEM), the MAP crystal became bigger in size as well as the crystal size distribution (CSD) became broad and uneven, with the increase of ultrasonic power. The results indicate that the crystallization process enhanced by power ultrasound could be used as an effective method to eliminate and recover the phosphorus from wastewater.

Effect of ultrasound and stabilizers on nucleation kinetics of curcumin during liquid antisolvent precipitation

Nucleation kinetics of liquid antisolvent precipitation of a poorly water soluble drug curcumin in presence of ultrasound and surfactants have been estimated. Ultrasound and stabilizers were found to have opposing effects on induction time (τ ind), metastable zone width (MSZW) and nucleation rates (J) of curcumin during antisolvent precipitation. The use of ultrasound (in presence or absence of stabilizers) was found to decrease τ ind and MSZW drastically while the values of nucleation rates were found to increase. In contrast to these observations, use of stabilizers (in presence or absence of ultrasound) were found to increase MSZW, increase τ ind and lower the nucleation rates (J) of curcumin. The solid-liquid interfacial energies (γSL) for curcumin in aqueous ethanolic solutions (with and without stabilizers) have also been calculated using experimentally estimated induction time (τ ind) and supersaturation data. The values of solid-liquid interfacial energies were found to be in the range of 1.5-3.5 mJ/m(2). In comparison to these values, the values of γSL predicted by Mersmann equation and equation proposed by Bennema and Sohnel were found to be significantly higher and were in the range of 10-30 mJ/m(2).