Treatment of Ferric Ion Containing Wastewater Using Crystal Growth and Cake Filtration

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This paper presents an experimental study on the growth of particles by crystallization in the reactor which has a cake filtration unit. The wastewater sample that contains ferric ion is poured into the reactor and crystallized by mixing under various pH conditions, pH 3, 3.5, 4, 7.8, and 12. The results are summarized as follows.<BR>There is a close relation between the mean particle size and pH value. The mean particle size becomes larger with a decrease in pH in the range of pH 3.5 to pH 12.0. The mean particle size at steady state was 8.42 μm at pH 3.5. From the observation with SEM, and the measurements with X-ray diffraction meter and X-ray fluorescence spectrometer, the produced material was determined to be FeOOH.<BR>The growth of particles reduced the specific resistance of cake by two orders, which meant there was a significant improvement of the cake dewaterability. The moisture content of dewatered cake was 2527% at pH 4.0, while 77-80% in the conventional treatment method.<BR>In addition, the capacity of solid-liquid separation of this wastewater treatment is high enough for a practical industrial plant, if the scale up of this system is made. It was also found that there is the possibility that we can get a low moisture cake without using a sedimentation plant.
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