Coagulation of colloidal particles with ferrate(vi). Issue 5 (5th April 2018)

• Record Type: Journal Article
• Authors: Lv, Dongyu; Zheng, Lei; Zhang, Huiqin; Deng, Yang
• Is Part Of: Environmental science. Volume 4:Issue 5(2018)
• Page Start: 701
• Page End: 710
• Publication Date: 2018-04-05
• Subjects: Water-supply -- Periodicals; Water security -- Periodicals; Water resources development -- Periodicals; Water chemistry -- Periodicals; 553.705
• DOI: 10.1039/c8ew00048d
• Languages: English
• ISSNs: 2053-1400

Abstract

Abstract : Coagulation and chemical oxidation have long been recognized as two major mechanisms of ferrate(vi ) ( i.e. FeO4 2−, an oxyanion containing Fe(vi )) in its environmental applications. Abstract : Coagulation and chemical oxidation have long been recognized as two major mechanisms of ferrate(vi ) ( i.e. FeO4 2−, an oxyanion containing Fe(vi )) in its environmental applications. Although ferrate(vi ) oxidation of various contaminants has been extensively studied, few efforts were made to appreciate the mechanisms and behaviors of ferrate(vi )-driven coagulation in water. In this study, coagulation of colloidal kaolin particles with ferrate(vi ) in simulated natural water was investigated under the conditions related to drinking water treatment (initial turbidity 25.00 NTU, 0.0–9.0 mg L −1 Fe(vi ), pH 7.5, and 0.50–10.00 mg L −1 DOC). Fe(iii ) produced from Fe(vi ) reduction initiated in situ coagulation. Lower minimum effective iron doses (MEIDs) were observed for Fe(vi ) coagulation than for direct Fe(iii ) coagulation at pH 6.5 and 7.5 (DOC = 2.00 mg L −1 ), at which the colloids were captured by iron precipitates principally via sweep coagulation. A citrate–ascorbate iron extraction method was used to reveal that Fe(vi ) resultant flocs were composed of both amorphous and crystalline iron with an amorphous to crystalline Fe ratio of approximately 2.3 : 1.0 (pH 7.5, 3.0 mg L −1 Fe(vi ), and 2.00 mg L −1 DOC). Ferrate(vi ) oxidation transformed natural organic matter (NOM) preferentially into more hydrophilic compounds, which have lower affinity with colloids and thus are less adsorbed on colloids to produce a less negatively charged surface. Therefore, ferrate(vi ) oxidation potentially promoted the aggregation of colloids through the alleviation of electrostatic repulsion. However, NOM at a high concentration (8.00–10.00 mg L −1 DOC in this study) could prevent the agglomeration of small iron oxide particles through the formation of a negatively charged NOM coating via adsorption, thereby preventing the growth of flocs. Ferrate(vi ) coagulation, when combined with ferrate(vi ) oxidation, provides a more viable treatment option to address multiple water pollution in raw water, e.g. the presence of colloidal algal cells and dissolved algal toxins in water during a harmful algal bloom. The dual treatment mechanisms enable a very effective treatment design with an economical physical footprint for supporting a sustainable municipal drinking water supply.