The Application of Fluidized-Bed Crystallization Technology in Nickel-containing Wastewater Treatment

• Main Authors: Tsai , Yue -Ju, 蔡月珠
• Other Authors: Shiau , Lie -Ding
• Format: Others
• Language: zh-TW
• Published: 2000
• Online Access: http://ndltd.ncl.edu.tw/handle/87061896531996709551

碩士 === 長庚大學 === 化學工程研究所 === 88 === In recent years fluidized bed pellet reactors (FBPRs) have been extensively applied in the removal of heavy metals from wastewater. In the traditional unseeded precipitation treatment of wastewater where a dissolved component has to be removed, the addition of precipitating chemicals results in the formation of sludge. Then the sludge produced must be transported to and disposed off in a waste landfill. On the contrary, a major advantage of the FBPRs is the production of a small amount of water-free, reusable pellets, without extra surplus sludge production. In this research, the crystallization process of a fluidized bed pellet reactor was studied in the treatment of the nickel-containing wastewater. Sodium carbonate was added as the reagent solution to form nickel carbonate and nickel hydroxide on the surface of the pellets in a fluidized pellet reactor. We investigated the effects of some important factors, including pH, CT/Ni feeding ratio, recirculation ratio and Ni-loading, on the performance of the fluidized bed crystallization technique. The results showed that pH had a great effect on the crystallization efficiency of nickel and the optimal pH was about 9.0. At this pH value, the crystallization efficiency could be achieved about 80﹪at Ni-loading of 274g Ni per m2 of reactor cross-section per hour, upflow superficial velocity of 103.23 m/hr and feeding ratio CT/Ni of 0.125 mol/mol. A higher rate of upflow superficial velocity (i.e. higher recirculation ratio) would lead to a decrease in the degree of supersaturation. Therefore, the spontaneous nucleation of nickel carbonate and nickel hydroxide were inhibited and the crystallization efficiency of nickel carbonate and nickel hydroxide were increased. When the upflow superficial velocity was varied from 69.28 m/hr to 103.23 m/hr, the crystallization efficiency increased from 50﹪to 79﹪at Ni-loading of 274 g/m2hr and pH = 9. High upflow superficial velocity (e.q. 111.72 m/hr) would lead to carry-over of the pellets in the fluidized bed. When Ni-loading was varied from 274 to 550 g/m2hr at pH = 9, CT/Ni ratio of 0.125 mol/mol and upflow superficial velocity of 103.23 m/hr, the crystallization efficiency of nickel decreased from 80﹪to 60﹪. In operation of the Ni-loading of 550 g/m2hr ( high degree of supersaturation ), the distributor was often clogged by the fines of nickel carbonate due to the spontaneous nucleation. The crystallization material on the pellets consists mainly of nickel carbonate and nickel hydroxide. The analysis indicated that nickel hydroxide percentage increased in the crystallization of the pellets at higher value of pH. When CT/Ni feeding ratio was greater than 0.5, the crystallization material on the pellets was almost composed of nickel hydroxide.