Physicochemical vs Electrochemical Technologies for Metal Recovery – Main Insights, Comparison, Complementarity and Challenges

Abstract

The quest toward the development of new, more eco-friendly removal/recycling/recovery methods for a range of valuable elements is intense nowadays. In this Review we present and discuss in a critical way the best available physicochemical processes versus modern electrochemical approaches for metal recovery of elements which form part of spent catalysts or other sources such as wastewater, mining waste and spent batteries. These techniques include coagulation/flocculation, precipitation, electrocoagulation/electroflotation, membrane electrolysis, electrodeposition/electrowinning and gas-diffusion electrocrystallization (GDEx). Several key performance indicators (KPIs) are utilized to facilitate the critical analysis of the different recovery methods. Such indicators have to do, for example, with the efficiency, the cost, the complexity, and the environmental friendliness of the methods used. In some cases, the recovered metals can be further used for specific applications, including the fabrication of electrocatalysts for reactions of interest. When possible, the more novel electrified technologies are benchmarked versus the state-of-the art approaches. This manuscript helps to summarize all types of approaches in a comparative manner. When the targeted metal cannot be recovered by any of the technologies explored, its removal can also be considered as satisfactory in some extent, especially if the element under discussion poses a risk of toxicity for the environment or for human health. Recovery technologies are sometimes combined for an optimum effect, exploiting the advantages of each approach and mitigating their drawbacks. Our review provides also some examples for ‘removal-only’ possibilities of the studied methods, though its primary focus is the metal recovery aiming for metal reuse in the best possible scenarios.