Leaching Foams for Copper and Silver Dissolution: A Proof of Concept of a More Environmentally Friendly Process for the Recovery of Critical Metals

Abstract

The recovery of metals from WEEE, Waste from Electrical and Electronic Equipment, is a major challenge to preserve natural resources. Hydrometallurgy, which consists in leaching metals is a promising method but generates large amounts of polluting effluents. In this study we design aqueous leaching foams, composed of 90% v/v of gas and 10% v/v of HCl solution to oxidize and dissolve copper. We take advantage of the oxidizing power of the dioxygen (O2) present in the air bubbles whose fast transfer through the foams enables an efficient oxidation of copper. We then extend the concept of leaching foams to another gas, ozone, to oxidize silver (Ag). We finally show that using an anionic surfactant to complex cupric ions helps improving the dissolution of the metal. These promising results open new recycling routes for metals contained in WEEE, with a lower environmental footprint.

Copper leaching with aqueous foams for the processing of electronic waste

“…The use of O 2 as an oxidant suffers from slow gas-liquid transfer, so that the use of a hydrochloric acid solution stirred under air is not sufficient for copper leaching. Acceleration of gas-liquid transfer when employing a foam proved to be sufficient to observe significant leaching of copper in the above mentioned study [13], which lets suggest that further process development is possible using air as oxidant. It is thus the purpose of this article to report our progress on the leaching of copper from e-waste with hydrochloric acidbased foams.…”

“…Leaching of ores using foams was proposed in the 70's [12], however with scarce applications so far to our knowledge. Recently, the possibility to use foam based on diluted aqueous hydrochloric or sulfuric acid solutions for the leaching of metallic copper or silver has been demonstrated [13]. The perspectives opened by these model studies drove our attention to the application of foams for the leaching of copper from electronic waste (e-waste).…”

Probing foams from the nanometer to the millimeter scale by coupling small-angle neutron scattering, imaging, and electrical conductivity measurements

“…See DOI: 10.1039/cXsm00000x/ for industrial processes such as froth or foam flotation applied for materials or waste recycling, oil recovery from the ground, firefighting, mitigation of blast waves from explosions with very active research in each of these fields nowadays [20][21][22][23][24][25] . Depending on the application, the desired foam properties might vary considerably.…”

“…19 Foams are not limited to beverages, and can be found in many other applications: detergency, food, cosmetics, and also for industrial processes such as froth or foam flotation applied for materials or waste recycling, oil recovery from the ground, firefighting, mitigation of blast waves from explosions with very active research in each of these fields nowadays. [20][21][22][23][24][25] Depending on the application, the desired foam properties might vary considerably. Sometimes, an expanded and stable foam is required, for example in firefighting applications, to create a dense blanket acting as an insulating barrier between the fuel and the air and preventing the development of combustion.…”

Foam aging under free drainage analysed using associated operando techniques

“…To further develop on the example of beverages, superamphiphobic surface coatings are used to prevent the formation of unwanted foam during the filling of bottles 19 . Obviously, foams are not limited to beverages, and can be found in many other applications: detergency, food, cosmetic and also for industrial processes such as froth or foam flotation applied for materials or waste recycling, oil recovery from ground, firefighting, mitigation of blast waves from explosions with a very active research in each of these fields nowadays [20][21][22][23][24][25] . Depending on the application, the desired foam properties might vary con-However, the importance of each of the parameters listed above and more especially their coupled influences on the structural evolution of foams remain difficult to quantify because foams are multi-scale structures.…”