Environmentally Benign, Rapid, and Selective Extraction of Gold from Ores and Waste Electronic Materials

Abstract

The extraction of gold from ores and electronic waste is an important topic worldwide, as this precious metal has immense value in a variety of fields. However, serious environmental pollution and high energy consumption due to the use of toxic oxidation reagents and harsh reaction conditions is a well-known problem in the gold industry. Herein, we report a new chemical method based on the combined use of N-bromosuccinimide (NBS) and pyridine (Py), which has a greatly decreased environmental impact and reagent cost, as well as mild reaction requirements. This method can directly leach Au from gold ore and electronic waste to form Au in water. The process is achieved in a yield of approximately 90 % at room temperature and a nearly neutral pH. The minimum dose of NBS/Py is as low as 10 mm, which exhibits low toxicity towards mammalian cells and animals as well as aquatic creatures. The high leaching selectivity of Au over other metals during gold leaching is demonstrated, showing that this method has great potential for practical industrial application towards the sustainable refining of gold from ores and electronic waste.

Unexpectedly High Salt Accumulation inside Carbon Nanotubes Soaked in Dilute Salt Solutions

“…These findings will be beneficial for the development of novel ideas related to CNT-based desalination and purification, such as applying an electric field to push the cations away from the inlets of the CNTs as proposed for the thin CNTs in our previous theoretical study [8]. The high salt accumulation could also be used for the collection/extraction of noble metals by using CNTs in solutions containing trace amounts of noble metal salts for the production/recycling of noble metals [34], environmental conservation [71], and directional transport in biological systems [72]. It should be noted that conventionally, noble metal accumulations [33,73,74] in CNTs have only been observed in high-concentration solutions, and a cation-anion pair have been reported within nanotubes [75].…”

“…This discovery helps explain the recent findings of negligible water flow and ion permeation across wider CNTs in salt solution and opens new avenues for the development of novel ideas related to CNT-based desalination. It also provides a new strategy for the collection of noble metal salts in solutions containing traces of noble metal salts, which has great economic value [34] and significance for environmental conservation. Our theoretical studies reveal that this high salt accumulation of CNTs can be mainly attributed to the strong hydrated cation-π interactions between hydrated cations and π electrons in the aromatic rings of CNTs.…”

New Insights into the Recovery of Strategic and Critical Metals by Solvent Extraction

“…Very recently, a new, low-toxicity method for the leaching of gold from WPCBs using a synergistic mixture of N-bromosuccinamide (NBS) as an oxidant and pyridine (py) as a ligand has been described ( Figure 23) [97] Experimental variation of the reagents and conditions showed that gold dissolution was maximised (90%) using 10 mM NBS, 100 mM py, at pH 8.2 and 25 o C, and contrasts to only 77% gold dissolution using KI/I2; the cost of these latter reagents is 20x greater.…”

Pyridinethiol‐Assisted Dissolution of Elemental Gold in Organic Solutions

“…They are, therefore, precious and their demand is continuously growing. The possibility to recycle the elements from multi‐metal materials such as printed circuit boards (PCBs) is crucial when sustainability and the circular economy are considered . In general, recovery of Au in the mining industry is mostly based on the hydrometallurgical cyanidation process, which relies on the use of stoichiometric amounts of cyanide salts and produces large amounts of hazardous waste .…”