High-Pressure Oxidative Leaching and Iodide Leaching Followed by Selective Precipitation for Recovery of Base and Precious Metals from Waste Printed Circuit Boards Ash

Abstract

: This paper deals with the recovery of gold from waste printed circuit boards (WPCBs) ash by high-pressure oxidative leaching (HPOL) pre-treatment and iodide leaching followed by reduction precipitation. Base metals present in WPCB ash were removed via HPOL using a diluted sulfuric acid solution at elevated temperatures. Effects of potassium iodide concentration, hydrogen peroxide concentration, sulfuric acid concentration, leaching temperature, and leaching time on gold extraction from pure gold chips with KI–H2O2–H2SO4 were investigated. The applicability of the optimized iodide leaching process for the extraction of gold from the leach residue obtained after HPOL were examined at different pulp densities ranging from 50 g/t to 200 g/t. Results show that the removal efficiency was 99% for Cu, 95.7% for Zn, 91% for Ni, 87.3% for Al, 82% for Co, and 70% for Fe under defined conditions. Under the optimal conditions, the percentage of gold extraction from the gold chips and the residue of WPCBs was 99% and 95%, respectively. About 99% of the gold was selectively precipitated from the pregnant leach solution by sequential precipitation with sodium hydroxide and L-ascorbic acid. Finally, more than 93% of gold recovery was achieved from WPCB ash by overall combined processes.

Systematic Assessment of Precious Metal Recovery to Improve Environmental and Resource Protection

“…In the I 2 –KI–H 2 O 2 system, I 2 reacts with potassium iodide (KI) to form I 3 – , which is a key species for Au leaching, and the [AuI 2 ] − and [AuI 4 ] − complexes formed by I 3 – and Au are stable throughout the pH range . In the KI–H 2 O 2 –H 2 SO 4 system, H 2 SO 4 provides H + to promote the oxidation of KI by H 2 O 2 , and the subsequent reaction is similar to the I 2 –KI–H 2 O 2 system . Both leaching Au systems are feasible, and the I 2 –KI–H 2 O 2 system has a faster Au dissolution rate than the KI–H 2 O 2 –H 2 SO 4 system. …”

Leaching Kinetics of Valuable Metals

“…The paper by Batnasan et al [6] deals with the recovery of gold from waste printed circuit boards (WPCBs) ash by high-pressure oxidative leaching (HPOL) pre-treatment and iodide leaching followed by reduction precipitation. Under the optimal conditions, the percentage of gold extraction from the gold chips and the residue of WPCBs was 99% and 95%, respectively.…”

Iodine‐Catalysed Dissolution of Elemental Gold in Ethanol

“…Main established Au recovery processes include environmentally challenging and toxic methods, such as cyanidation[ 4 , 6 , 16 , 17 , 18 , 19 ] (Figure 1 , a), and in less developed regions, even the amalgam process. [20] Other dissolution procedures,[ 4 , 5 , 6 , 16 , 17 , 18 , 19 ] including aqueous iodine‐iodide leaching[ 5 , 6 , 7 , 8 , 16 , 17 , 18 , 19 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 ] (Figure 1 , b), come with marked improvements in safety and environment issues. As previously reported, elemental halogens can oxidize Au 0 to Au I or Au III cations and stabilize the formed Au cations in the solution as Lewis bases.…”

“…[ 32 , 33 ] Nevertheless, in addition to the moderate toxicity and costly production, over stoichiometric amounts of iodine are usually needed to afford a quantitative dissolution of Au, hence making this procedure less sustainable and less financially feasible. [ 5 , 16 , 18 , 21 , 34 ] Even with the assist of more environmentally benign oxidants, especially aqueous H 2 O 2 ,[ 5 , 6 , 19 , 21 , 23 , 24 , 25 , 26 , 27 ] large amounts of iodine are consumed in the processes.…”