INFLUENCE OF MIXING CHARACTERISTICS ON THE QUALITY AND SIZE OF PRECIPITATED CALCIUM-OXALATE IN A PILOT-SCALE REACTOR

Evidence is presented of mixing effects on the precipitation of calciu m oxalate from aqueous solutions of calcium chloride dihydrate and sod ium oxalate in both MSMPR and single-feed semi-batch precipitators. Ex periments of precipitation were carried out in a pilot tank of 20 dm(3 ) volume stirred by three different impellers. The influence of stirri ng speed, stirrer type and reagent feed tube location on the product s ize and morphology was studied. Whereas weak effects of these operatin g parameters were noticed in the continuous operation mode, the semi-b atch single-feed mode was shown to be more sensitive to mixing effects . Experimental results on crystal mean size during single-reed semi-ba tch experiments could be related to the temporal variance of the conce ntration field of a fluorescent inert tracer injected into the same fe ed location and tube in the tank which was then continuously operated. These variances were measured by laser sheet visualization and image processing techniques.