Removal of heavy metal ions from water by an combined sorption–crystallization process using activated clays

Abstract

The degree of comminution of materials in an ultrasonic field has been theoretically estimated by calculating the maximum and minimum energy inputs necessary for this process (upper and lower estimates have been obtained). The degree of comminution of kaolin in an ultrasonic bath determined by light and electron microscopy is in satisfactory agreement with the theoretical estimates. The efficiencies of heavy metal ion (Cu²⁺, Ni²⁺) removal from aqueous solutions in the following processes have been compared: adsorption on natural materials (kaolin and bentonite), chemical precipitation in homogeneous crystallization, and integrated sorption–crystallization process using activated clays. The highest purification efficiency has been attained in the integrated process preceded by ultrasonication of the clay slurry and alkaline reagent. Use of these sonochemically activated additives has shortened the duration of the integrated process and has increased the degree of removal of toxic metals to 10²–10³. Clays have been demonstrated to act as a sorbent, a heterogeneous crystallization stimulator, and a coagulant accelerating the sedimentation of the solid phase.