Enhanced geopolymeric co-disposal efficiency of heavy metals from MSWI fly ash and electrolytic manganese residue using complex alkaline and calcining pre-treatment

Abstract

The predominant heavy metals in MSWI fly ash and electrolytic manganese residue (EMR) were determined to be Zn, Pb, Cd, and Mn, with lesser amounts of Cu and Cr. The curing efficiency of heavy metals in MSWI fly ash and EMR was improved using complex alkaline activators (NaOH and KOH), base addition (calcium hydroxide and complex Portland cement), and EMR calcining (at 800 °C for 3 h) based on a geopolymeric system. The best formulation of the geopolymeric system was composed of 75 wt% MSWI fly ash and 25 wt% EMR with a KOH/NaOH (1:1) complex solution (7.5 M OH^-)/solid of 0.5. Calcium ions were dissolved aluminosilicate under the strongly basic conditions to form complex products (ternesite) which further improved the strength. The primary curing mechanism of heavy metals (Pb, Zn, Cd, Mn, Cr, and Cu) mainly was primarily influenced by the acid-base buffering capacity of geopolymers, followed by the physical encapsulation of geopolymeric gels.

Keywords: Curing efficiency; Curing mechanism; Electrolytic manganese residue; Geopolymeric; MSWI fly ash.