Depth Dewatering of Kaolinite Cake by SDBS/PEI Synergy and a Mesoscopic Mechanism Study

The objective of this study was to elucidate the synergistic dewatering mechanism of mixed sodium dodecylbenzene sulfonate (SDBS) and polyethyleneimine (PEI) on kaolinite filter cakes and to test the dewatering effectiveness of a custom-built pressure dewatering device. The dewatering experiments showed that while the reagent dose was reduced by 50%, the dewatering rate decreased to 19.78%, surpassing the optimal dose of a single reagent. During the natural compression stage of the filter cake, the deformation reached its maximum under the same pressure difference. During the transitional period, the closure of the filter cake pores occurred at a slower rate, facilitating better moisture drainage. Under strong compression, the ultimate deformation reached its maximum. PEI acted as a bridging agent for kaolin flocculation and served as a medium for SDBS on the kaolin surface. A small amount of PEI reduced the electrostatic repulsion of SDBS, increasing its adsorption capacity. PEI adsorbed on the kaolin surface through electrostatic and hydrogen bonding, while SDBS could adsorb onto the PEI reagent layer through electrostatic and polar interactions, exposing its alkyl chains on the surface and thereby facilitating flocculation and generating a hydrophobic reagent layer. This study could provide a new method and insights for the efficient pressurized dewatering of kaolin.