Optimization Routes for the Bioleaching of MSWI Fly and Bottom Ashes Using Microorganisms Collected from a Natural System

This paper presents a route for the treatment of MSWI fly (FA) and bottom ashes (BA) usingmicroorganisms to critically assess whether bioleaching is within reach of effective industrial application.The leaching of metals from BA and FA was investigated in a controlled laboratory environment using aculture isolated from a natural system where the dominant strains are acidophilic bacteria, mainlyAcidothiobacillus thiooxidans and Acidothiobacillus ferrooxidans. The community of microorganisms(mostly acidophilic, S- and Fe-oxidizing bacteria) was collected directly from overflows and ponds at thesediment-water interface of a natural system near a post-mining site. Pre-cultivation was done in 250 mLflasks followed by the adaptation to the different substrates (both FA and BA). The effect of differentmaterial pre-treatment and elemental sulphur concentrations were evaluated for both BA and FA, at astarting pH of 4. The bioleaching of BA and FA substrates experienced good yields of metal extraction withan optimum duration of two weeks. The results showed that more than 90% Zn, Cu, and 10% Pb areremoved from FA; while 100% Cu, 80% Zn and 20% Pb are removed from BA samples. Batch experimentswith regenerating ion-exchange resins did not perform well for metal recovery, but could serve as a valuabledecontamination step. The techniques used here with FA and BA can be used for urban mining purposes(e.g. ashes and other meal-rich anthropogenic wastes), but also low-grade ores in the mining industry,contributing to resource recovery or decontamination agendas