Impact of leaching procedure on heavy metals removal from coal fly ash

Abstract

In this work, removal of heavy metals (Cr, Mn, Co, Ni, Cu, Zn, As, Cd, and Pb) from fly ash has been studied using acid leaching and wet oxidation methods. In parallel, microwave-assisted acid digestion was applied for determination of pseudo-total concentrations of heavy metals to estimate the leaching efficiency. Multivariate statistics (Pearson correlation, principal component analysis, and hierarchical cluster analysis) have shown two dominant groups of elements, depending on their characteristics and affinity towards the ash solid phase. Thus, Cr, Zn, Mn, Co, and Ni belong to the group I, while Pb, As, Cd, and Cu belong to the group II. It was demonstrated that the wet oxidation method was more suitable than acid leaching since the reduction in metal concentration was 30 to 75 % compared to 12 to 25 % obtained by acid digestion. The influence of fly ash treatment on the residue characteristics was investigated by X-ray diffractometry and scanning electron microscopy. The analyses revealed surface and structure changes of fly ash after the wet oxidation treatment. Overall, wet oxidation could be an appropriate treatment for heavy metal removal from fly ash, providing a material that could be further used, thus reducing the risk of pollution caused by the disposal of coal combustion fly ash. © 2024, Association of the Chemical Engineers of Serbia.

Uklanjanje teških metala (Cr, Mn, Co, Ni, Cu, Zn, As, Cd i Pb) iz elektrofilterskog pepela proučavano je korišćenjem metoda kiselog luženja i vlažne oksidacije. Paralelno je primenjena i kisela digestija uz pomoć mikrotalasne pećnice za određivanje pseudoukupnih koncentracija teških metala u cilju procene efikasnosti luženja. Multivarijantna statistika (Pearsonova korelacija, analiza glavnih komponenti i hijerarhijska klaster analiza) pokazala je dve dominantne grupe elemenata u zavisnosti od njihovih karakteristika i afiniteta prema čvrstoj fazi pepela. Grupe I (Cr, Zn, Mn, Co i Ni) i II (Pb, As, Cd i Cu) su međusobno diskriminisane. Pokazalo se da je metoda vlažne oksidacije prikladnija od kiselog luženja jer je smanjenje koncentracija metala bilo 30-75 % u poređenju sa 12-25 % dobijenih kiselom digestijom. Takođe je ispitan uticaj tretmana letećeg pepela na karakteristike čvrstog ostatka metodama rendgenske difrakcije i skenirajuće elektronske mikroskopije. Ovim metodama su otkrivene promene na površini i u strukturi letećeg pepela nakon tretmana vlažnom oksidacijom. Vlažna oksidacija se može smatrati kao moguća metoda za tretman u cilju uklanjanje teških metala iz letećeg pepela, obezbeđujući materijal koji bi se mogao dalje koristiti i smanjujući rizik od zagađenja izazvanog odlaganjem letećeg pepela.