Development of Methods for Leaching and Recovering Heavy Metal Ions from Fly Ash

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1.XRF analysis of fly ashes and leaching of metals from fly ashElemental compositions of fly ash were measured with a X-ray fluorescence spectrometer. The major elements in the fly ash were Ca > K, Na, Cl, Si, and the content of Zn was about 0.5 mol %. Cu and Pb were contained less than 0.05 mol %. Leaching behaviors of the hazardous heavy metals of Cu, Zn and Pb were investigated using aqueous solutions of HCl, HNO_3 and CH_3COOH as eluents in batch and percolation processes.In both processes, Zn was effectively extracted with every eluent used. While, Pb was well extracted with HCl (0.25 M and 0.5 M) and 0.25 M HNO_3 but slightly with 0.5 M HNO_3 and CH_3COOH. Cu was effectively extracted with HNO_3 and CH_3COOH rather than HCl.2.Recovery of metal ions using a water-soluble chelating polymer and a hollow fiberRecovering rate of metal ions (Cu(II) and La(III)) was measured in a circulating mode, where the aqueous solution of water-soluble chelating polymer (polyacrylic acid) flowed in the lumen side of the hollow fiber which was immersed in metal ion solution. Effects of flow rate of the polymer solution and stirring rate of metal ion solution on the recovery rate were examined, and the effective diffusion coefficients of Cu(II) and La(III) trough the membrane wall were determined to be 3.3×10^<-9> m^2/s and 2.8×10^<-9> m^2/s, respectively.3.Immobilization of metal ionsHydrogen phosphates (Na_2HPO_4, K_2HPO_4, MgHPO_4, CaHPO_4) could favorably remove Pb(II), Cd(II), Co(II) and Cu(II) from aqueous solutions. Calcium hydroxyapatite was shown to be useful to immobilize Ti(IV) and Zr(IV).