Effect of AlCl_3 concentration on nanoparticle removal by coagulation

In recent years,engineered nanoparticles,as a new group of contaminants emerging in natural water,have been given more attention AlCl3 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）,multiwalled carbon nanotube-N,N-dimethylformamide（MWCNT-DMF） and nano TiO2-humic acid（TiO2-HA） were employed to investigate their coagulation removal efficiencies with varying aluminum chloride（AlCl3） concentrations AlCl3 Results showed that nanoparticle removal rate curves had a reverse ＂U＂ shape with increasing concentration of aluminum ion（Al^（3＋） ）AlCl3 More than 90% of nanoparticles could be effectively removed by an appropriate Al^（3＋） concentration AlCl3 At higher Al^（3＋） concentration,nanoparticles would be restabilized AlCl3 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 AlCl3 The ECR of Al^（3＋） followed the order MWCNT-DMF 〉 MWCNT-HA 〉 TiO2-HA,which is the reverse of the nanoparticle size trend AlCl3 At a given concentration,smaller nanoparticles carry more surface charges,and thus consume more coagulants for neutralization AlCl3 Therefore,over-saturation occurred at relatively higher Al^（3＋） concentration and a wider ECR was obtained AlCl3 The ECR became broader with increasing p H because of the smaller hydrodynamic particle size of nanoparticles at higher p H values AlCl3 A high ionic strength of Na Cl can also widen the ECR due to its strong potential to compress the electric double layer AlCl3 It was concluded that it is important to adjust the dose of Al^（3＋） in the ECR for nanoparticle removal in water treatment.