3.8 Characterization of crystal product
The shape and morphology images of the crystals in the slurry were obtained by optical microscope (Motic (Xiamen) Electric Group Co., Ltd., Motic SMZ-168), and then the crystal size distribution (CSD) was analyzed by Nano Measurer software. The results of each experiment were repeated more than three times and the average value was reported. Purity of the thiourea crystal is measured by the analytical laboratory of the Shandong Jingbo Co., Ltd. In alkaline condition, thiourea and iodine have quantitative reaction, while excess iodine solution was titrated with standard sodium thiosulfate, to obtain the content of thiourea.