Thermochemical regeneration of bleaching earth waste with zinc chloride

In the present study, thermochemical regeneration with ZnCl2 has been carried out on bleaching earth waste at heating rate of 10 degreesC/min up to 570 degreesC under nitrogen atmosphere for 1 h. Various acid solutions and ultrasonic cleanings further washed the resulting solids after regeneration. The variations of pore space as well as the change of sorption properties in the resulting solids have been studied. Results showed that, once treated samples are of type IV with hysteresis loops corresponding to type H3 from nitrogen adsorption-desorption isotherms, indicating slit-shaped mesoporous characteristics. However, the surface areas (7392 m(2)/g) of regenerated clays were obviously smaller than those of the fresh bleaching earth (245 m(2)/g). The true density and porosity of the samples created with ultrasonic washing were larger than those of acid-washed samples, possibly because of the cleaning and opening of intraparticle pores. Further, the regenerated samples exhibited a selective sorption of paraquat (herbicide). Thus, the regeneration of this industrial waste enhanced the sorption properties linked with the mesoporous clay minerals. This might open new ways for other applications, such as drinking water processing and waste water treatment. (C) 2002 Elsevier Science B.V. All rights reserved.