Research On Mass Transfer of Metallic Ion Micromass From Phosphoric Acid to Organic Phase by Visualization

Abstract£º It is difficult for purification of phosphoric acid, and this is a hot topic in industry. Phosphate rock resources are non-renewable natural resources. Its use depends on its purity. However, phosphoric acid contains magnesium, sulfur, chlorine, fluorine, calcium, iron, aluminum and other impurities which affect its application. In China, some techniques on purification of phosphoric acid, such as solvent extraction, crystallization, ion exchange, electrodialysis, precipitation, sulfide precipitation, emulsion liquid membrane were developed. In 2002, our research group proposed emulsion liquid membrane to purify phosphoric acid which is an economical and feasible method. But an industrial scale application was not realized, due to lack of basical experimental data. In order to speed up the industrialization process, it is necessary to study on the mass-trasfer behaviors of metallic ions or metallic ion micromasses in liquid-liquid phase.

In our experiments, the mass-trasfer behaviors of metallic ion micromasses from phosphoric acid to organic phase were observed by in a CCD device with visualization technique and visible light-ultraviolet light. Experimental devices consist of an optical microscope, a long-distance lense, a miniature reactor, a camera, a video capture card, and the software for auto tracking image. Combined with infrared spectroscopy and visualization technology, the mass transfer of metallic ion micromasses in phosphoric acid were studied from the perspective of submicroscopic. Initially, the density and viscosity of phosphoric acid solution were measured. The organics were added carefully to phosphoric acid solution in the miniature reactor. Metallic ion micromasses in the phosphoric acid were moved upward to the organic phase in 3-5 min. It was observed that the mairomasses were of level movement and revolving movement. The images captured by CCD were analyzed to obtain the moving velocity of mairomasses using the software for auto tracking image. Application of equation Navier-Stokes, the mechanics of metallic ion mairomasses in phosphoric acid were analyzed. By setting the appropriate boundary conditions, the velocity distribution of metallic ion mairomasses in phosphoric acid were found as follows:

 

By calculation, the fluid pressure that acting on the surface of micro-particles was 0.2067V₀a, and the shear stress that acting on the surface of micro-particles was 0.413V₀a. The velocity and geometric diameter of metallic ion mairomasses in phosphoric acid were measured by particle velocity measurement software. According to the above equation, the theoritical velocity of metallic ion mairomasses were also calculated, and the result show that the calculated values agreed with the measured data very well. It explained that this equation is capable of simulating mciromass transfer. These data can provide a fundamental for emulsion liquid membrane to purify phosphoric acid.

Key word£ºphosphoric acid purification; emulsion liquid membrane; visualization; metallic ion micromass; N-S equation