title: Removal of fluoride from semiconductor wastewater by electrocoagulation-flotation.
abstract: This work employs an anodic surfactant, sodium dodecyl sulfate (SDS), to improve the flotation performance of the electrocoagulation-flotation (ECF) process to treated fluoride containing semiconductor wastewater following calcium precipitation. The dissolved fluoride ions and CaF(2) particles in the wastewater after calcium precipitation were effectively removed in the ECF process simultaneously. The dosage of SDS required for ECF was much less than those for dispersed air flotation (DiAF) or dissolved air flotation (DAF) processes because the CaF(2) particles can be collected by hydro-fluoro-aluminum flocs in ECF. Thus, SDS only served as a frother to make the bubbles tiny and stable in the ECF defluoridation process. The interference of co-existing anions can be overcome by increasing the dosage of calcium ions and SDS. The optimum initial acidity for ECF is close to the initial fluoride concentration after calcium precipitation; the amount of SS removed dropped rapidly if the initial acidity exceeded the optimal value because the surface charge of the hydro-fluoro-aluminum particles increased. The initial acidity of the wastewater after calcium precipitation can be modified by changing the [Ca(OH)(2)]/[Ca(2+)](T) ratio and the appropriate ratio is approximately given by the acid dissociation constant of hydrofluoric acid and the initial pH of the wastewater before calcium precipitation.
authors.affiliation: Research Center for Environmental Pollution Prevention and Control Technology, Graduate Institute of Environmental Engineering, National Taiwan University, Taipei 106, Taiwan.
authors.forename: C Y
authors.initials: CY
authors.lastname: Hu
authors.forename: S L
authors.initials: SL
authors.lastname: Lo
authors.forename: W H
authors.initials: WH
authors.lastname: Kuan
authors.forename: Y D
authors.initials: YD
authors.lastname: Lee
mesh_terms: D002118:Calcium / Q000737:chemistry; D011232:Chemical Precipitation; D004563:Electrochemistry / Q000379:methods*; D004566:Electrodes; D005459:Fluorides / Q000737:chemistry / Q000302:isolation & purification*; D006863:Hydrogen-Ion Concentration; D012666:Semiconductors; D012967:Sodium Dodecyl Sulfate / Q000737:chemistry; D013501:Surface-Active Agents / Q000737:chemistry; D014865:Waste Disposal, Fluid / Q000379:methods*; D014874:Water Pollutants, Chemical / Q000302:isolation & purification; D018508:Water Purification / Q000379:methods*
chemical_list: D013501:Surface-Active Agents; D014874:Water Pollutants, Chemical; D012967:Sodium Dodecyl Sulfate; D005459:Fluorides; D002118:Calcium