Effect Of Ultrasound On Crystallization Process Of Calcium Sulfite And Its Crystal Morphology

The neutralization reaction of calcium hydroxide and sulfur dioxide is the main reaction of cane juice clarification process in cane sugar mill which sulfurous acid methods are applied. According to the industrial need, in order to obtain White sugar with high quality,all the following should match: calcium hydroxide and sulfur dioxide should react fast and completely, therefore the remains of Ca2+ and SO32- in the sugar juice are little; the calcium sulfite crystals formed should be uniform and possess high specific surface area, therefore the crystals have strong adsorption capacity in absorbing non-sugar impurities. But the present technology has some disadvantages, the remains of SO32- in white sugar are often high, which reduces the quality of the products and depresses the competitiveness of sugar factory. For that reason, finding a method which has great efficiency and simple process is the hotspot in sugar-making industry. Lately, ultrasound as a clean,effective means is studied to enhance the cane juice clarification process. As the basic research of cane juice clarification process enhanced by ultrasonic treatment, based on previous works, the influence of ultrasonic treatment on the neutralization reaction of calcium hydroxide and sulfur dioxide is studied. The main contents of studies were as follow:1. The influences of ultrasonic parameters such as ultrasonic power,ultrasonic treatment time and horn immersion depth on the reaction of calcium hydroxide and sulfur dioxide were analyzed. The results showed that compared with magnetic stirring, the residuals of Ca2+ and SO32- was decreased significantly and all of the ultrasound parameters affected the results. The optimum conditions were as follows:ultrasound power 97.5W,ultrasonic treatment time 1min,horn immersion depth 1.4cm.2. The influences of ultrasonic parameters such as ultrasonic power,ultrasonic treatment time and horn immersion depth on the morphology of calcium sulfite formed were analyzed. The results showed that the crystal morphology changes with ultrasonic treatment. Compared with natural reaction and reaction with magnetic stirring, the calcium sulfite crystals obtained by ultrasound treatment was smaller in size and more uniform in shape and possessed higher specific surface area. In addition, to the calcium sulfite already formed, the bigger the crystals were, the more influence ultrasonic treatment had.3. The influence of ultrasonic treatment on primary nucleation of calcium sulfite was studied. The results showed that ultrasonic treatment decreased the induction period significantly, and based on the classical theory of nucleation, ultrasonic treatment could decrease surface tension and enhance diffusion of particles in the solution.4. The influence of ultrasonic treatment on the properties of calcium hydroxide solution and sulfurous acid solution with different concentrations was investigated. The result showed that ultrasonic treatment reduced surface tension and increased electrical conductivity of these solutions, therefore the result obtained by the classical theory was verified.5. The change of cavitation effect was study by adding nitrogen,and the influence of ultrasonic treatment that had different cavitation intensity on the crystallization process was investigated. The results showed that adding nitrogen enhanced the ultrasonic cavitation effect, and ultrasonic cavitation effect accelerated the crystallization process of calcium sulfite.