Gold Recovery from E-Waste by Porous Porphyrin–Phenazine Network Polymers

Abstract

Gold recovery from electronic waste could prevent excessive mining with toxic extractants and provide a sustainable path for recycling precious metals. Unfortunately, no viable recycling is practiced, except burning electronic circuit boards in underdeveloped countries, mainly because of the lack of chemical scavengers as adsorbents. Here, we report the synthesis of a family of porphyrin− phenazine-based polymers and their gold-capturing properties as well as application in gold recovery from actual e-waste. The polymers show high selectivity toward gold as well as other precious metals. The Au(III) adsorption isotherms were well-fitted to the Langmuir adsorption model and proportionality between porosity and uptake capacity was observed. Solution pH values and illumination conditions were shown to have influences on the performance of the adsorbents with the highest capacity of 1.354 g/g obtained in acidic pH and under continuous UV irradiation. Such a remarkable capacity of 7 times the theoretical estimate was achieved through photochemical adsorption−reduction mechanism supported by the observed suppressing effect of oxidant on gold-capturing ability. The adsorbents are robust and recyclable, a significant advantage over other emerging materials.

A Facile Approach to Sulfur‐Rich Covalent Organic Frameworks for Selective Recovery of Trace Gold

“…The selective adsorption capacity of SCOFs toward Au (III) ions in the presence of other metal ions in aqueous solution was evaluated. Fe 3+ , Cu 2+ , Ni 2+ , Mg 2+ , and Zn 2+ were chosen as the interference ions, as they are not only the most common coexisting elements with Au (III) ions in electronic wastewater, [ 6 ] but also can interfere with the adsorption of Au (III) ions. As shown in Figure 4C, SCOFs can effectively adsorb Au (III) ions in the presence of other interfering and competing ions.…”

“…Apparently, the scrapped electric and electronic devices are the main solid secondary sources for gold recovery, due to their relatively high content of gold (over 200 g ton -1 ). [5,6] To extract gold from electronic scraps, hydrometallurgy is primarily utilized to convert solid gold from the electronic waste into soluble Au (III) ions in acidic leachates, which are then subjected to the treatment of extraction and purification. [5,7] In addition, the secondary liquid sources of gold can be found in the spent process solutions produced in semiconductor industry and pregnant leach solutions, which are aqueous solutions containing a plenty of gold ions, mainly Au (III).…”

Pollutant removal with organic macrocycle-based covalent organic polymers and frameworks

“…These same hydroxyl groups can also be easily modified or further functionalized. 16,17 Porphyrins are 10 Copyright 2020 American Chemical Society. ll composed of four modified pyrrole subunits interconnected at their a-carbon atoms via methine bridges.…”

Alkyl‐Linked Porphyrin Porous Polymers for Gas Capture and Precious Metal Adsorption

“…Porous polymers, in general, are also emerging as selective adsorbents for metals from wastewater. [ 22–25 ] Precious metals such as gold, platinum, palladium, and silver are promising target metals for recovery because of their high values and widespread use in chemical industries. [ 26,27 ] These metals can be recovered from electronic waste (e‐waste), which is called urban mining.…”