title: Effect of AlCl3 concentration on nanoparticle removal by coagulation.
abstract: In recent years, engineered nanoparticles, as a new group of contaminants emerging in natural water, have been given more attention. In order to understand the behavior of nanoparticles in the conventional water treatment process, three kinds of nanoparticle suspensions, namely multi-walled carbon nanotube-humic acid (MWCNT-HA), multi-walled carbon nanotube-N,N-dimethylformamide (MWCNT-DMF) and nanoTiO2-humic acid (TiO2-HA) were employed to investigate their coagulation removal efficiencies with varying aluminum chloride (AlCl3) concentrations. Results showed that nanoparticle removal rate curves had a reverse "U" shape with increasing concentration of aluminum ion (Al(3+)). More than 90% of nanoparticles could be effectively removed by an appropriate Al(3+) concentration. At higher Al(3+) concentration, nanoparticles would be restabilized. The hydrodynamic particle size of nanoparticles was found to be the crucial factor influencing the effective concentration range (ECR) of Al(3+) for nanoparticle removal. The ECR of Al(3+) followed the order MWCNT-DMF>MWCNT-HA>TiO2-HA, which is the reverse of the nanoparticle size trend. At a given concentration, smaller nanoparticles carry more surface charges, and thus consume more coagulants for neutralization. Therefore, over-saturation occurred at relatively higher Al(3+) concentration and a wider ECR was obtained. The ECR became broader with increasing pH because of the smaller hydrodynamic particle size of nanoparticles at higher pH values. A high ionic strength of NaCl can also widen the ECR due to its strong potential to compress the electric double layer. It was concluded that it is important to adjust the dose of Al(3+) in the ECR for nanoparticle removal in water treatment.
authors.affiliation: Chemistry Department of Science School, Harbin Institute of Technology, Harbin 150090, China. Electronic address: zlz4513@sina.com.
authors.forename: Lizhu
authors.initials: L
authors.lastname: Zhang
authors.affiliation: Chemistry Department of Science School, Harbin Institute of Technology, Harbin 150090, China.
authors.forename: Jingchun
authors.initials: J
authors.lastname: Mao
authors.affiliation: Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, China. Electronic address: zhaoqing@iae.ac.cn.
authors.forename: Qing
authors.initials: Q
authors.lastname: Zhao
authors.affiliation: Chemistry Department of Science School, Harbin Institute of Technology, Harbin 150090, China.
authors.forename: Shaobo
authors.initials: S
authors.lastname: He
authors.affiliation: School of Municipal and Environmental Engineering, Harbin Institute of Technology, Harbin 150090, China. Electronic address: majun@hit.edu.cn.
authors.forename: Jun
authors.initials: J
authors.lastname: Ma
mesh_terms: D000077410:Aluminum Chloride; D017607:Aluminum Compounds / Q000737:chemistry*; D000536:Aluminum Hydroxide / Q000737:chemistry; D002712:Chlorides / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D053758:Nanoparticles / Q000737:chemistry*; D037742:Nanotubes, Carbon / Q000737:chemistry; D014025:Titanium / Q000737:chemistry
chemical_list: D017607:Aluminum Compounds; D002712:Chlorides; D037742:Nanotubes, Carbon; C009495:titanium dioxide; D000077410:Aluminum Chloride; D000536:Aluminum Hydroxide; D014025:Titanium
keywords: Al(3+); Coagulation; Effective coagulation concentration; Nanoparticles