Accelerated screening of arsenic and selenium fractions and bioavailability in fly ash by microwave assistance

High-End Reclamation of Coal Fly Ash Focusing on Elemental Extraction and Synthesis of Porous Materials

“…Combinations of techniques can achieve a higher efficiency of elemental extraction than their individual applications. For example, acidic dissolution and ion exchange, microwave irradiation and acid dissolution, carbothermal reduction and magnetic separation, alkali and acid dissolution, , alkali fusion and acid dissolution, ,, and multistep sequential extraction have all been attempted. , Sequential extractions of Si and Al have been extensively studied, based on which mesoporous silica or alumina has been synthesized for wider use. , Such combinations and multistep strategies have been explored to improve extraction results, confirming that the combination of various extraction techniques can improve the extraction efficiency and selectivity.…”

“…Specifically, Cr, Mo, Cd, and W were highly enriched in the quartz–mullite mixture, while Mn, Co, Ni, Cu, Zn, and As were the amorphous components . He et al divided As and Se in CFA into five fractions: nonspecifically sorbed fraction, specifically sorbed fraction, amorphous Fe and Al oxide-bound fraction, crystallized hydrous Fe and Al oxide-bound fraction, and residual fraction; As and Se in CFA are mainly present in the first three fractions . A six-step sequential extraction made it possible to determine water-soluble, exchangeable, acid-soluble (bound to carbonate), reducible (bound to Fe/Mn), oxidizable (bound to organic matter), and residual fractions .…”

“…Acid dissolution is the most basic and commonly used technique to extract metal elements from CFA. In addition to acids (e.g., hydrochloric acid (HCl), nitric acid (HNO 3 )), some acidic salts (e.g., ammonium dihydrogen phosphate (NH 4 H 2 PO 4 ), ammonium oxalate ((NH 4 ) 2 C 2 O 4 ), ammonium bisulfate (NH 4 HSO 4 )) are used in elemental extraction. Innovatively, most metal elements can be extracted with a sufficient concentration of the correct acid, with Si remaining as a solid after other elements are dissolved in solution, thereby enabling separation and obtaining Si.…”

“…The leaching rate of different trace impurities in CFA decreases in the order B ≥ Mo ≥ Se > Li > Sr ≥ Cr ≥ As = Ba = Cd = V > Sn > Rb = Zn ≥ Cu = Ni = Pb > U > Co > Mn . Sequential extraction is widely used. , For instance, He et al conducted a five-step extraction to investigate the environmental mobility and distribution of As and Se from CFA, in which ammonia sulfate ((NH 4 ) 2 SO 4 ), NH 4 H 2 PO 4 , (NH 4 ) 2 C 2 O 4 , (NH 4 ) 2 C 2 O 4 + ascorbic acid (C 6 H 8 O 6 ), and hydrofluoric acid (HF) + HNO 3 + hydrogen peroxide (H 2 O 2 ) were used separately as extractants; they found that the majority of As and Se existed in the first three fractions, and recovery efficiencies of 80.4–121.4% and 81.8–116.8% were achieved for As and Se, respectively.…”