A stepwise separation process for selective recovery of gallium from hydrochloric acid leach liquor of coal fly ash

The interest in gallium (Ga) recovery from coal fly ash has been driven by its rapidly growing demand for manufacturing and its extraction can facilitate the effective use of coal fly ash, which is conducive to reducing the soil degradation and environment danger. In this study, polyurethane foam (PUF) as an adsorbent for Ga(III) recovery was found to exhibit a good structural stability and a high selectivity in a strongly acidic solution. Adsorption measurements show that PUF has a good adsorption ability and its maximum adsorption capacity is 62.53 mg/g. Furthermore, its adsorption behavior can be described well by the pseudo-second-order model. The concentrations of Cl(I) played the key role in the adsorption. Meanwhile, the co-existed Fe(III) in the coal fly ash hydrochloric acid leach liquor (CFAHL) exhibits significant interference to the selective adsorption of Ga(III). Therefore, a stepwise process involving Fe(III) removal and Ga(III) adsorption is proposed for the recovery Ga from CFAHL. At an equilibrium pH of 0, the Fe(III) in the CFAHL can be removed by 1 mol/L P507. Then, the Ga (III) can be quantitatively adsorbed from the CFAHL using PUF with limited co-adsorption of Al(III), Mg(II), and Ca(II). The adsorption capacity of Ga(III) remains steady after PUF is used for more than 10 cycles. Based on the results of IR, XPS and DFT, it is speculated that the Ga(III) is probably coordinated in the form of GaCl3 with the donor O atoms of the urethane group (?NHCOO?) on the PUF surface. The overall results demonstrate the potential use of PUF for Ga recovery from acidic solutions.

Automated summary

This study demonstrates the potential use of PUF as an adsorbent for Ga(III) recovery in strongly acidic solutions, showing stable adsorption performance and high selectivity. A stepwise process involving Fe(III) removal and Ga(III) adsorption successfully recovered Ga from coal fly ash, with PUF maintaining its adsorption capacity after multiple cycles of use.