Applied circular economy, FHNW School of Life Sciences

In biohydrometallurgy, microorganisms are used to form acids, bases and complexing agents for the aqueous extraction of metals from solids. Furthermore, microorganisms can be used to remove metals from the liquid phase by precipitation reactions. We use these natural processes for the leaching of raw materials from waste, the treatment of metal-containing wastewater and the biological remediation of contaminated sites. The goal here is always to close material cycles as resource-efficiently as possible.

The basis for all processes is the understanding of so-called "metal speciation". Metal speciation refers to the specific form in which a chemical element exists. The chemical properties (e.g. solubility) as well as the biological effect (e.g. toxicity) of different metal species can be very different. Microbes naturally change the speciation, a fact that we exploit in our processes. Direct measurements by mass spectrometry (e.g. LC-MSn; GC-MS, LC-ICP-MS) and spectroscopy (e.g. XAFS) as well as thermodynamic modelling form the basis for understanding speciation.

Microorganisms actively change the surrounding medium by forming acids and complexing agents. We use this circumstance to recover so-called critical raw materials from industrial residues (e.g. gallium from red mud from aluminium production) by means of "bioleaching". By the same means, metals can also be washed out of contaminated sites and subsequently recovered. We also use microbes to remove elements from wastewater by precipitation and return them to the cycle. The formation of insoluble metal species due to microbial metabolism is called "biological precipitation".

Critical raw materials are elements that are of great economic importance, but whose supply is not guaranteed. Industrial waste often contains such valuable elements. The elements in question may even be more concentrated in wastes than in the ores from which they were originally extracted.

We use hydrometallurgical methods to dissolve these elements from the waste and then recover them. We are developing new hydrometallurgical processes for metal recovery based on advanced filtration processes. For example, we use nanofiltration to retain charged ions and to concentrate and separate them from impurities. Metal speciation again serves as the basis for understanding the processes. For nanofiltration, we use both commercially available membranes and our own membranes. These are produced layer-by-layer by us. With the help of nanofiltration, we have already recovered critical raw materials from various industrial wastes, such as waste from TiO2 production and waste from photovoltaics.