Subcritical water extraction of indium from indium tin oxide scrap using organic acid solutions

Abstract

Environmental contextIndium is a metal increasingly used in high-technology industries, creating a demand for efficient recycling technology. We investigated extraction of indium from waste using a subcritical water extraction with organic acids. Compared with conventional methods employing concentrated mineral acids, the new method is less corrosive, more efficient and required shorter extraction times. AbstractSubcritical water extraction (SWE) was applied to extract indium (In) from indium tin oxide (ITO) scrap. Four organic acids, acetic acid, gluconic acid, citric acid (CA) and etidronic acid (EA), were used at a solid-to-liquid ratio (S/L) of 10gL−1. Neither acetic acid nor gluconic acid yielded significant extraction of indium. A total of 70.71% and 96.93% of indium was extracted using 1M of CA and EA respectively at 150°C and a final pressure of 18–19 bar within 30min. The extraction efficiency of In was shown to increase with the increase in acid concentration and in temperature. Compared with conventional extraction methods, SWE was more effective using less concentrated acids and required a shorter reaction time.

Process intensification for valuable metals leaching from spent NiMH batteries

“…The dissociation constant (pK a ) value of HCl, H 2 SO 4 and HNO 3 is -7.0, -3.0 and -1.3, respectively, which implies that the strength of the acids is in the order of HCl > H 2 SO 4 > HNO 3 . Similar results were found when three mineral acids were applied for the extraction of In from indium tin oxide (ITO) scraps [31]. Therefore, HCl was used for further experiments.…”

“…When utilizing SWE, the extraction efficiency of Y and Eu from waste CRT phosphor increased significantly as temperature increased from 100 to 125 • C using 0.75 M of H 2 SO 4 [16]. The extraction efficiency of indium (In) from waste ITO by SWE increased with increasing temperature as well [31].…”

“…The application of SWE for the extraction of valuable metals from electronic waste (e-waste) is still limited. It has been examined on leaching of yttrium (Y) and europium (Eu) from waste cathode-ray tube (CRT) phosphor [16], leaching of lithium (Li), cobalt (Co) and manganese (Mn) from spent Li-ion batteries [15] and the extraction of indium (In) from indium tin oxide (ITO) scraps [31].…”