Effects of Cr³⁺, Cu²⁺, and Pb²⁺ on Fly Ash based Geopolymer

Abstract

The effects of Cr³⁺, Cu²⁺, and Pb²⁺ on compressive strength, reaction products, and pore structures of fly ash based geopolymer were studied. In addition, the immobilization and bonding interaction between heavy metal and fly ash based geopolymers were investigated by X-ray photoelectron spectroscopic (XPS) and environmental scanning electron microscope (ESEM) techniques. The experimental results showed that the incorporation of Cr³⁺, Cu²⁺, and Pb²⁺ had a great effect on the later compressive strength and resulted in producing reinhardbraunsite in the solidified body. Moreover, the Pb²⁺ reduced the total pore volume of the solidified body, while Cr³⁺ and Cu²⁺ increased it. The XPS results indicated that O(1s), Si(2p), and Al(2p) bind energy increased due to Cr³⁺ and Cu²⁺ addition, but it did not change significantly due to Pb²⁺ addition. The microstructure of calcium silicate hydrate (C-S-H) gel and sodium silicoaluminate hydrate (N-A-S-H) gel changed in different degree according to the ESEM results. The immobilization of Cr³⁺, Cu²⁺, and Pb²⁺ using fly ash based geopolymer is attributed not only to the physical encapsulation, but also to the chemical bonding interaction.

Keywords

geopolymer / heavy metal / chemical bonding interaction / physical encapsulation