Potential use of native fungal strains for assisted uranium retention Anna Grandin a,⇑ , Anna Ogar b , Viktor Sjöberg a , Bert Allard a , Stefan Karlsson a a Man-Technology-Environment Research Centre, Örebro University, SE-70182 Örebro, Sweden b Institute of Environmental Science of the Jagiellonian University, Gronostajowa 7, 30-387 Krakow, Poland article info Article history: Received 2 October 2014 Revised 31 March 2015 Accepted 3 April 2015 Available online xxxx Keywords: Biotechnology Environmental Pollution Wasteprocessing abstract Uranium-stabilizing ligands can be useful complexing agents for uranium in aqueous solution. The dis- covery of novel ligand candidates for selective uranium capture in artificial and natural waters could pro- vide scope for their use in water remediation and metal recovery from low- and high grade ores. In this study we used seven fungal strains, isolated from shale waste, to monitor the uranium retention capacity from an aqueous solution. After four weeks of incubation, suspensions containing the fungal strains were filtered, and up to 100% of the total uranium inventory was removed from a 10 mg L À1 solution. Approximately 70% of the total uranium removal is attributed to complexation and/or adsorption by par- ticles in the malt extract and some 10% is adsorbed by the fungal biomass. The additional 20% uranium removed could be related to the excretion of fungal metabolites. From 58% to 90% of the uranium is removed within ten minutes. The formation of colloidal/particulate uranium is proposed to be controlled by organic ligands in the culture medium and organic ligands excreted by the fungi where phosphorus moieties seem to be important. Membrane fouling by the hydrocarbons is also suggested to contribute to a loss of uranium from the aqueous phase. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction 1.1. Site description and environmental aspects Black shale was mined in Kvarntorp, Sweden, some 200 km WSW of Stockholm, between 1942 and 1966 for oil production by pyrolysis. This shale contains 15–18% kerogen and 6–9% sulphur and is rich in vanadium, molybdenum, uranium (up to 0.030%) and rare earth metals (Andersson et al., 1985; Swanson, 1960). Besides the petroleum production, a small amount of uranium was also extracted. After mine closure most of the open pits were water filled. In the area there is a single waste pile containing some 40 million m 3 as a mix of processed and unprocessed shale with unknown proportions. Weathering of the pyrite rich waste has greatly affected surface and groundwater nearby with elevated concentrations of both major and trace elements (Allard et al., 2014). Many efforts are made regarding remediation of heavily contaminated sites but low- or moderately contaminated mine tailings and waters are often neglected since they often do not pos- sess an immediate health danger, even though a long term expo- sure of low levels of toxic metals might be just as severe. 1.2. Microorganisms in the biosphere Microorganisms play an important role in the biosphere regard- ing metal mobilization as well as immobilization (Gadd, 2007) and have been extensively studied in order to find alternatives to tech- nical/chemical processes. Many fungal species are able to tolerate high levels of toxic metals, and microorganisms such as bacteria, fungi and algae are being used in large scale removal of metals from industrial and domestic effluents (Zapotoczny et al., 2007). Microbial processes encompass both solubilization as well as immobilization of metals (Gadd, 2000), involving fungal biosorp- tion, bioaccumulation and precipitation (Fomina et al., 2007). Since free UO 2 2+ is bioavailable it may be accumulated by fungi, both intra- and extracellularly, through fixation by phosphate- and/or carboxylate ligands (Kelly et al., 2002) but can also be com- plexed by amino ligands present in chitin or chitosan (Guibal et al., 1995). Uranyl complexation with phosphate-, carboxylate- and amino ligands is highly dependent on solution pH (Kelly et al., 2002; Guibal et al., 1995), competing ligands in solution as well as surface bound ligands. With increasing pH, hydroxyl-, carboxyl- and amino groups (e.g. mannans, chitin/chitosan, beta-glucans and amino acids) become deprotonated thus increasing cell wall charge (Naeem et al., 2006). As shown by Kelly et al. (2002) this is impor- tant in the estimation of the number of uranyl ions bound to phos- phoryl and carboxyl ligands. The metal binding capacity of http://dx.doi.org/10.1016/j.mineng.2015.04.003 0892-6875/Ó 2015 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: anna.grandin@oru.se (A. Grandin). Minerals Engineering xxx (2015) xxx–xxx Contents lists available at ScienceDirect Minerals Engineering journal homepage: www.elsevier.com/locate/mineng Please cite this article in press as: Grandin, A., et al. Potential use of native fungal strains for assisted uranium retention. Miner. Eng. (2015), http:// dx.doi.org/10.1016/j.mineng.2015.04.003