Study On Extracting Scandium With Microcapsule

Microcapsule is a novel composite biomimetic membrane. Core material of microcapsule is isolated from environments because of its encapsulation. Thus, properties of core material are remained perfectly. Microcapsule have been investigated for the application in the fields of medicine, foodstuff, pesticide, cosmetic. Besides, it can be used for extraction as separation systems. Compared to common Liquid-Liquid extraction, The use of microcapsules containing extractant P507 for extraction exhibits semipermeability and has the advantage that a large specific interfacial area is obtained and internal phase is separated from external phase by microcapsule. Thus, emulsion and the formation of the third-phase could be avoided and separation of the microcapsules can be achieved easily.Two microcapsules were prepared using calcium alginate and EC as wall material, using extractant P507 as core material. In the process of molding of calcium alginate microcapsule, piercing-solidifying incubation method was applied. The optimum operation conditions were as following: the concentration of sodium alginate, the concentration of calcium chloride, stirred velocity, drop velocity, drop height is 1.5wt%~2.0wt%, 2.0wt%~4.0wt%, 300rmin-1, 60~90d/min, 8~12cm,respectively. The mean diameter of this microcapsule is 3millimeter measured by microscope. For the preparation of ethyl cellulose microcapsule, drying in water method was adopted. Accordingly, the mean diameter of this particle is 0.4 millimeter. On the premise that wall material content, glutin content, tween-60 content and the volume ratio of wall phase to core phase is3.0wt%~4.0wt%,1.0wt%~1.5wt%,0.9wt%~l.lwt%and 1: 0.5 respectively, high productivity of ethyl cellulose microcapsule was obtained.As ethyl cellulose microcapsule was used to extract scandium, some impact factors such as stirred velocity, the amount of microcapsule, pH value, extraction time were analyzed by orthogonal experiments. Optimum operation conditions were obtained. Stirred velocity, pH value, extraction time and the ratio of microcapsule mass to the feed volume were 250rmin-1,4.5 , 35 min and 0.5g/50mL, respectively.In addition, the dependence of extraction ratio on preparation conditions was studied. The maximum extraction ratio was 99.9%, and extraction equilibrium time was 20min. When 5mol/L HC1 was used for backward extraction, backward extraction ratio was 98%.In comparison, when sodium alginate microcapsule was used to extract Sc3+, extraction ratio was merely 34.4%.Extraction equation with ethyl cellulose microcapsule was also deduced in this paper. The experimental results indicated that the osmosis rate well accord with first order reaction equation.Based on above research, calcium alginate microcapsule used as wall material was bigger in size than that using ethyl cellulose. Accordingly, ethyl cellulose microcapsule exhibited larger mass transfer surface area. As a result, high extraction ratio was easy to be achieved with ethyl cellulose microcapsule. So, ethyl cellulose microcapsule is a primary choose for extracting scandium.