Leaching foams to extract metals from electronic wastes – FOAMEX

The recovery of metals from WEEE, Waste from Electrical and Electronic Equipment, is becoming a major challenge to preserve natural metal resources while treating a large amount of waste. Available recycling processes present several drawbacks : pyrometallurgy, based on a smelting process, is highly energy consuming, generates large amounts of off-gases and there are only a few installations in EU requiring non ecological transportation of wastes. Hydrometallurgy, which consists in leaching the metal wastes to extract metal ions in solution, is more suitable for small and local installations, but it generates very large volumes of effluents which need to be treated. The goal of this project is to use foams as a leaching medium to extract and concentrate metal ions from shredded PCBs (Printed circuit boards), the most valuable WEEE. Foams contain 90% of air and 10% of liquids, therefore this idea would help decreasing the amount of effluents. Moreover we expect to improve the efficiency of standard leaching methods due to a better dispersion of waste particle in the foam channels. The first task of the project will consist in shredding PCBs into particles of controlled granulometry and characterize their metal composition as a function of shredding technique (Task 1.1 performed at BRGM, Bureau des recherches géologiques et minières, experts in waste management). We will then leach these particles in leaching solutions chosen to be selective to groups of metals. We will characterize the release of the ions using standard chemical analysis (Task 1.2. performed at ICSM, experts in metal extraction and speciation). This task will include the development of a sampling and characterization method of the particles, which is crucial to evaluate to efficiency of the proposed leaching process. In Task 2 we will then screen foaming agents (surfactants and polymers) which can produce stable foams and interact with the metal ions to concentrate them at the bubbles surface. We will use test homemade stimuli responsive polymers, which should complex the ions more efficiently than surfactants and increase foam stability. Their thermo and pH responsivity will enable us to break the foams and dissociate the metal/polymer complexes on demand and hence to recycle the polymers. We will characterize the bulk and interfacial complexations of the metal ions and foaming agents. This Task will be performed at SIMM and ICSM, which combine complementar expertise in surfactants and polymers synthesis, interfacial dynamics, and foams. In Task 3, we will introduce model monometal particles (3.1) in the foam formulations and will study the extraction kinetics as a function of time, foam structure and formulation. We will study the case of mixtures of different monometal particles to evaluate the selectivity of the process (Task 3.3). In Task 3.3. We will then study the leaching of PCB shredded particles produced in Task 1. Task 4 will involve a start up company, Extracthive, which focuses on waste management. Extrachive will perform a technico-economical study to evaluate the feasibility of the process, considering several process geometries and formulations. They will then build a pilot unit, in collaboration with other partners, and will operate this pilot unit. We expect that our project, by reducing the amount of effluents generated during leaching, will contribute to solving some of the issues of current hydrometallurgy methods and which prevent their industrial development at very large scale. This project will be an opportunity for the start up Extracthive to develop an expertise on foam processes for recycling metals from WEEE, which then may be applied to other types of waste such as batteries and therefore to reach new clients.