Bentonite polymer composite for water purification

A polyethylene glycol (PEG)-bentonite (BT) composite was prepared by direct polymerization of PEG in suspensions of BT. Based on detailed analyses using field-effect scanning electron microscopy, X-ray diffraction, surface area measurements and chemical methods, the obtained product was mainly composed of Ca-BT with a specific surface area of 4.13 m² g^-1. The optimal conditions for adsorption of Pb²⁺ and Cd²⁺ ions were found to be a PEG content of 0.1% and a contact time of 60 min. The sorption experiments were performed under various operating variables, including polymer concentration, pH and temperature. For both Pb²⁺ and Cd²⁺, the adsorption equilibrium was described by the Freundlich model, which confirmed the presence of a heterogeneous system with irregular filling of the active centres. The maximum sorption capacities of BT-PEG for removal of Pb²⁺ and Cd²⁺ were found to be 22 and 18 mg g^-1, respectively. The rate constants calculated for the sorption of Pb²⁺ and Cd²⁺ were 6.29 and 6.67 g mg^-1 min^-1, respectively, at 25°C. This study shows that the obtained sorbents based on BT may be used for treatment of waste water and could help resolve environmental protection issues.