Design And Study On Capacitive Deionization Module

Electrosorption technology is electrochemcial method for removing ions from aqueous solutions. The capacitive deionization (CDI) modules have an excellent adsorptive capacity, which is due to high specific surface areas of the electrodes of CDI modules. The ions in the solution are adsorbed in the double electrical layers at electrode-solution interface to achieve the desalination, when the solution flows through the CDI modules that have been connected with external power sources. Electrosorption is considered as an effective and economical method to realize the desalination because of many outstanding properties such as small pressure drop, low consumption, no secondary pollution, low cost, long recycling life (more than one hundred thousand times) and regeneration.In this paper, the effects of different influence factors on electrosorption were studied, such as voltage, initial concentration and flow rate. And it was found that the best work voltage was 1.2V and the adsorption amount increased as the initial concentration increased. Meanwhile, with the increase of flow rate, adsorption amount increased first and then decreased. Furthermore, the adsorption law of various ions was studied. It was shown that the adsorption depended on the atomic number and hydrated ionic radius, i.e., the adsorption rate decreased with the atomic number increasing and adsorption amount was inversely proportional to hydrated ionic radius, which was probably caused by the PH value rise that would make the heavy metal ions into precipitation during the adsorption. For this reason, PH value should be assured to a specific range to avoid the precipitation which could contaminate the surface of electrodes.In addition, a new type of CDI modules was introduced in this paper, and several CDI modules of this type were prepared to study the effects of some factors on adsorption, such as different numbers of CDI module electrodes, various voltages between electrodes, adsorption and desorption cycle process, different adsorption materials and adsorption laws of ions. The experimental results showed that the optimum number of the CDI modules in one unit was six in cycle process of adsorption and desorption. The relationship between physical adsorption amount and total adsorption amount was also studied, and it showed that physical adsorption amount account for about 47% in the total adsorption amount. The adsorption amount of active carbon is 1.6 times bigger than that of carbon aerogel, at the same time, the adsorption time and work current of active carbon are twice bigger than that of carbon aerogel. Furthermore, the adsorption rate of ions was inversely proportional to mass-to-charge ratio, and the adsorption amount of ions is also inversely proportional to hydrated ionic radius.