|摘要: ||處理含氟廢水以添加鈣鹽如氯化鈣、氫氧化鈣或石灰之傳統沉澱程序為主。雖然添加鈣離子以生成氟化鈣沉澱的處理效率良好，可達到氟離子放流水標準，但沉澱過程使操作時間較長以及產生大量的氟化鈣造成污泥脫水、掩埋等，後續的處理問題。本研究以流體化結晶床添加硝酸鋁與實廠含氟廢水，在調整至pH 5環境下使鋁鈉氟比足以產生無機化合物冰晶石。過程探討液相中氟離子的去除率以及在晶體成核過程中矽酸鹽之變化，晶相中表面結構與粒徑大小，以及出流水濁度在連續操作維持一定出流水品質。 |
結果顯示，在pH 5條件下以0.5/6、0.8/6、1.0/6、1.2/6鋁氟莫爾比作為進流條件，氟離子去除率約85%。出流水中矽酸鹽濃度約800~1000 mg/L之間，與進流濃度相當，可判斷水相中矽酸鹽對冰晶石成核不影響，因此純度問題影響不高，有利於後續利用。在槽體內部連續運作過程中連續產生晶體，濃度過高時，使上方出流口濃度升高；於槽體下端加入晶體排除管線後，使上端出流水濁度維持在1 NTU以下，並且可穩定由槽底取得晶體；槽體不同層面、鋁氟莫爾比、時間條件下可觀察，其粒徑隨著操作時間成長10倍；冰晶石含水率也控制在20~30%；晶體由XRD分析，與冰晶石特性波峰圖譜比對後，可證實與冰晶石特性波峰相當吻合。SEM、EDX可再次確認外觀表徵以及得知樣品中固體物元素組成。
The traditional procedure for fluoride-containing wastewater treatment by adding calcium such as CaCl2, Ca(OH)2 or CaCO3 is called chemical precipitation. Although the treatment efficiency of chemical precipitation is excellent and the process is capable of reducing the concentration of fluoride to reach the effluent discharge standard, the amount of calcium fluoride produced poses the huge burden to the treatment time and the treatment facilities. The follow-up treatment of the sludge such as dewatering and disposal will cause bigger problems as well. This research was based on fluidized bed crystallization with addition of aluminum nitrate and at the condition of pH 5 and the Al / Na / F molar ratio sufficient to produce cryolite. This work investigated residual fluoride ion and silicate in the treated effluent, the structure and the size of the formed particle, and the turbidity of treated effluent.
Experiments were conducted at pH of 5 and various Al/F molar ratios (0.5/6, 0.8/6, 1.0/6, 1.2/6). The test results show the removal efficiency of fluoride at different molar ratios were greater than 85%. Since the silicate concentration of effluent was same as that in the influent, the cryolite nucleation should not be inhibited by silicate in the liquid phase. Thus, the purity problem of formed cryolite is not the issue, and it is in favor of the continuing use. Besides, during the continuous test to make cryolite crystals, the turbidity of treated outflow increases when the concentration was too high; however, with the installation of cryolite crystals removing mechanism at the bottom of the reactor to remove crystals steadily, the turbidity of treated effluent is able to maintain under 1 NTU. In different levels of the reactor and under various Al/F molar ratios and HRT, we could observed the growth of particles which can grow to 10 times of the initial size with the operating time, and water content of the cryolite could be controlled at 20~30%. Finally, XRD analysis of the crystals shows the diffraction peaks match well with the characteristic peaks of cryolite. SEM and EDX, respectively, reconfirms the surface features and reveals elemental composition of particles produced.