Dechlorination of pentachlorophenol by grinding at low rotation speed in short time

In order to apply grinding method for degradation of pentachlorophenol (PCP) to an industrial scale, the proportion of different materials [CaO, SiO2 and CO(NH2)2] and the size of grinding balls were examined. For saving energy and increasing dechlorination efficiency, the rotation speed and grinding time were maintained at relatively low values. At a mass ratio of grinding balls to materials (40:1), PCP was added into a big steel jar (300 ml) with other materials to grind at 300 r·min− 1 for 5 h. The results indicated that when PCP was mixed with CaO and SiO2 in a molar ratio of 1:60:60, the best dechlorination of 58.4% was achieved. CO(NH2)2 could not be used as hydrogen donor in the dehalogenation by mechanochemical reaction, since it restrained the dechlorination process. The size of grinding balls has significant effect on the reaction. The experiment with 5 mm steel balls indicates that the weight is too light to provide appropriate energy for the reaction, while steel balls of 10 and 15 mm could give better dechlorination reaction. It indicates that dechlorination depends on the mass of balls and fill rate.

Graphical AbstractIn this paper, the proportion of different materials (CaO, SiO2 and CO(NH2)2) and the size of grinding balls were examined to get the optimal dechlorination. As the results show the best dechlorination is 58.4% when molar ratio of PCP, CaO and SiO2 is 1:60:60. Free electron is an important factor which could attack chlorine atom of benzene ring. SiO2 can enhance the dechlorination rate significantly. The chloridion which chlorine atom changed to is detected in water. The reductive degradation with 15 mm grinding balls is better than 5, 10 mm and mixing sizes, so two parameters, the mass of grinding balls and filling rate of grinding jar, should be considered.Figure optionsDownload as PowerPoint slide