SORPTION PROCESSES OF NATURAL IRANIAN BENTONITE EXCHANGED WITH CD²⁺, CU²⁺, NI²⁺, AND PB²⁺ CATIONS

Abstract

Experimental studies on the retention of cadmium (Cd²⁺), copper (Cu²⁺), nickel (Ni²⁺), and lead (Pb²⁺) by bentonite samples from Iran were conducted using single- and multiple-component solutions. Based on the sorption capacity of bentonite the following order was obtained for single- and multiple-component solutions: Pb²⁺ > Cd²⁺ > Ni²⁺ > Cu²⁺. The maximum adsorption capacities of bentonite with metals in single- and multiple-component solutions were 29.5%, 22.5%, 19.2%, and 17.1% and 13.5%, 13.4%, 12.1%, and 9.1% for Pb²⁺, Cd²⁺, Ni²⁺, and Cu²⁺, respectively. Desorption isotherms of Cd²⁺, Cu²⁺, Ni²⁺, and Pb²⁺ deviated significantly from the sorption isotherms, thereby indicating irreversible or very slowly reversible sorption. Finally, soil solution saturation indices and metal speciation were assessed using the Visual MINTEQ 2.6 program and the probability of mineral precipitation was supported by scanning electron microscopy.

Keywords:

• Desorption
• Heavy metals removal
• Natural bentonite
• Sorption

Acknowledgment

Four anonymous reviewers made valuable comments on the manuscript. The authors express their gratitude for their thoughtful and thorough reviews.

Notes

^a Measured in 5:1 liquid, solid solution (dS m⁻¹). The contact time was 24 h.