Effects of sodium dodecylsulfate on fluoride-containing wastewater treated by electro-coagulation-flotation (ECF) process
Date Issued
2004
Date
2004
Author(s)
Li, Yung-Te
DOI
zh-TW
Abstract
Recently, the conventional defluoridation process of fluoride-containing wastewater of semiconductor manufactory is lime or other calcium precipitation. The calcium fluoride (CaF2) particles are usually so fine that they can only be removed effectively after coagulation of polymer or aluminum salt. However, CaF2 has still moderate solubility, so it usually has to add excess calcium salt. Therefore, over-dosing occurs frequently and increases the hardness in the effluent. The high level of hardness constrains the reuse of water .
In this study, fluoride-containing wastewater was treated by a electro-coagulation reactor with bipolar aluminum electrodes. A bench-scale and a continuous system were used to evaluate the treatment performance. First, stoichiometric amounts of calcium salt would be added to decrease the fluoride concentration in aqueous solution. Then, electrocoagulation process and sodium dodecylsulfate (SDS) would be combined to remove suspended solids (SS) and residual fluoride ions. The treatment process of the combination is called electrocoagulation-flotation (ECF).
The results indicated that the removal efficiency of SS with adding SDS (over 80%) is better than that without SDS (about 56.4%). When 500mg-F/L synthetic wastewater was treated, the optimal operating conditions of batch system were: the dosage of SDS= 5mg/L, the operating current= 0.6A, and the operating time= 4minutes. In this case, the concentration of residual fluoride ions and SS were 10.6mg/L and 40mg/L (removal efficiency about 95.2%), respectively. The optimal operating conditions of continuous system were: the dosage of SDS= 30mg/L, the operating current= 1.0A, the flow rate =300ml/min, and the operating time= 1minutes. In that, the concentration of residual fluoride ions and SS were 5.7mg/L and 44mg/L (removal efficiency about 94.7%), respectively.
The interference of co-existing anions (SO42-、HCO3-、H2PO4-) can be overcome by increasing the dosage of calcium ions and SDS. The optimum initial acidity required for fluoride and CaF2 particle removal is close to the initial fluoride concentration after calcium precipitation. Finally, when fluoride-containing wastewater from a semiconductor manufactory was treated, the added [Ca(OH)2]/[Ca2+]T ([Ca2+]T =Ca(OH)2+CaCl2•2H2O) ratio can be modified by altering the initial acidity of the wastewater to make the best treatment efficiency of fluoride ions and SS.
Subjects
鈣鹽沈澱法
十二烷基硫酸鈉
電聚浮除法
氟系廢水
Calcium precipitation
Electrocoagulation-flotation(ECF)
Sodium dodecylsulfate (SDS)
Fluoride-containing wastewater
Type
thesis
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