Research On Emergency Treatment Technology Of The Carbon Nanotubes Sudden Pollution By Coagulation

The wide application of carbon nanotubes (CNTs) has a great impact on many fields of human activity. In the process of production and use, carbon nanotubes can easily discharge into water, soil and the atmosphere, and CNTs can shift among them along with the natural circulation. CNTs have potential toxicity and can cause damaged to biological cells, which poses threat to the environment and human being. Therefore, it is necessary to make an intensive study of emergent treatment technology of the CNTs from the water by the method of coagulation. Firstly, this dissertation studied the characteristics of CNTs in the water and simulated the sudden pollution of CNTs in water. It studied the mechanism of removal of CNTs by coagulation, and the main influence factors of coagulation removal of CNTs by aluminum sulfate. It defined the key parameters of emergency coagulation treatment of CNTs sudden pollution. This study provides an expedient for sudden CNTs pollution, which can help to ensure the safety of water and environment.Firstly, based on the suspension of CNTs in the practical application, the dispersion effect of surface active agent, time of ultrasonic and pH conditions to CNTs are studied. The dissertation simulated the sudden pollution of CNTs in water. The results show that the best dosage of the three types of surfactants (SDBS, Triton X-100, and CTAB) is0.1%,0.5%and0.5%respectively (M/MH2O). The surfactants disperse the CNTs by enhancing the electrostatic repulsion and space steric effect. Experiment results show that the best ultrasonic time to the suspension of CNTs is40minutes. The SDBS-CNTs, Triton X-100-CNTs suspension is unstable when pH ranges from0to4. When the pH is within10-14, CTAB-CNTs suspension is unstable. When the pH is within4to10, three kinds of surfactants all have good dispersion effects, and the average particle size of SDBS-CNTs、Triton X-100-CNTs、CTAB-CNTs is255.8nm,288.5nm and307.8nm.Secondly, the efficiency and mechanism of the coagulation removal of stabilized carbon nanotubes from water by aluminum sulfate, polyaluminium chloride, and ferric chloride are studied. The optimum dosing amount of coagulant of aluminium sulphate, polyaluminium chloride and ferric chloride are determined by experiment. Aluminum sulfate was selected as the optimal coagulant. The coagulations of SDBS-CNTs and Triton X-100are mostly by electric neutralization and compressed electric double layer effect, and simultaneously by bridging adsorption and sweep flocculation. The coagulation of CTAB-CNTs is mostly by sweep flocculation. The coagulation removal mechanism of CNTs is mainly related to the nature of the surfactant. Finally, the influences of pH condition, natural organic matter in water, sedimentation time and hydraulic conditions on coagulation of SDBS-CNTs, CTAB-CNTs and Triton X-100-CNTs are studied. It defines the key parameters of emergency coagulation treatment of CNTs sudden pollution. The conclusions from the experiments are as follows: pH condition influents the coagulation effect by changing the hydrolyzed form of aluminum sulfate and zeta potential of CNTs. Humic acid (HA) impedes the coagulation of SDBS-CNTs and Triton X-100-CNTs, while promotes the coagulation of CTAB-CNTs, the reason is related with the electrical properties and molecular structure of HA. The optimal hydraulic conditions are defined. Hydraulic conditions of mixing stage is200rpm,1min. Value G is99.7s-1and value GT is5982. Hydraulic conditions of flocculation stage is60rpm,40min. Value G is19.8s-1and value GT is53502. When the sedimentation time is30minutes, optimum removal can be achieved.