Aspects Flotation Clarification Mixed Juice

The influence of several parameters on removal of various impurities during vacuum flotation clarification of mixed juice has been investigated, and possible ways of dealing with the secondary precipitate obtained in this clarification process have been examined. Dispersed a~ir flotation clarification is described and the experience gained with this separation technique is recorded. Introduction The vacuurn flotation process of juice clarification was introduced to South Africa in 1966 by Rabel. The efficiency of this process for starch removal was immediately recognised but there were, at the-same time, several aspects of the process, both operational and fundamental, which required further investigation. A literature survey revealed that a clarification process using phosphoric acid and lime, with the removal of phosphate precipitate b y air flotation, was patented by Williamson in 1918'. Instead of vacuum, heat was used in this process for release of dissolved air. 'The Williamson clarifier and particularly various modifications of it introduced by Jacobs" and IBulkley-Dunton and Sveen Peterson4 became firmly established in sugar refineries for treatment of raw sugar melt. A thorough study of various parameters influencing performance of one of these c1arifil:rs has been made by Saranins. In raw sugar mills the application of a flotation technique to the treatment of cloudy filtrate obtained from rotary vacuum filters was described by Higginbotham" and Foster et a17 studied the application of this technique to syrup. A preliminary report by Sloane8 appears to be the only publication dealing with the application of flotation to the clarification of mixed juice. The additional information required in connection with the Rabe process was therefore not available. In an attempt to fill this gap the S.M.R.I. investigated several aspects of the flotation process and a part of this work, to various stages of which E. J. Buchanan, A. Jullienne, R. M. Morris and A. J. MacRitchie, particularly contributed, is summarised in this paper. Influence of pH, flocculant level and freshness of juice on removal of impurities Normally, the operating conditions during vacuum clarification are as follows: mixed juice is heated to 60°C and limed to pH 8.1 or slightly higher. The juice is then treated with mono-calcium phosphate or phosphoric acids to reduce pH to 7.4 and, after the addition of a coagulant, introduced into the vacuum clarifier8. It was of some interest to investigate other pH levels at which precipitate could be floated and the influence of these pH levels on removal of various impurities. A series of experiments were carried out with juices obtained from several mills. In each run one litre aliquots of juice were heated to 60°C and the required amount of calcium saccharate (about 20 mg CaO per rnl) was added in order to obtain the desired pH. After the addition of 10 ppm of flocculant (0.05% solution of Nc 1273 Dow Chemical) the juice was transferred to a conical vacuum flask and the precipitate floated at 15" vacuum. From the heating stage to flocculant addition the juice was stirred at constant speed. For comparison purposes a portion of the same juice was defecated at pH 7.5. The clear juice thus obtained was analysed for starch, P,O,, SiO,, protein and Ca + Mg using standard S.M.R.I. methods. Although absolute values varied with the origin of the juice, the trend was always the same and a set of typical results is reproduced in Table 1.