Red mud is a by-product of alumina production containing lanthanides. Growth of green microalgae on red mud and the intracellular accumulation of lanthanides was tested. The best growing species was Desmodesmus quadricauda (2.71 cell number doublings/day), which accumulated lanthanides to the highest level (27.3 mg/kg/day), if compared with Chlamydomonas reinhardtii and Parachlorellakessleri (2.50, 2.37 cell number doublings and 24.5, 12.5 mg/kg per day, respectively). With increasing concentrations of red mud, the growth rate decreased (2.71, 2.62, 2.43 cell number doublings/day) due to increased shadowing of cells by undissolved red mud particles. The accumulated lanthanide content, however, increased in the most efficient alga Desmodesmus quadricauda within 2 days from zero in red-mud free culture to 12.4, 39.0, 54.5 mg/kg of dry mass at red mud concentrations of 0.03, 0.05 and 0.1%, respectively. Red mud alleviated the metal starvation caused by cultivation in incomplete nutrient medium without added microelements. Moreover, the proportion of lanthanides in algae grown in red mud were about 250, 138, 117% higher than in culture grown in complete nutrient medium at red mud concentrations of 0.03, 0.05, 0.1%. Thus, green algae are prospective vehicles for bio-mining or bio-leaching of lanthanides from red mud.

Department of Mineralogy Geochemistry and Petrology University of Szeged Egyetem u 2 H 6722 Szeged Hungary

Institute of Medical and Pharmaceutical Biotechnology IMC FH Krems Piaristengasse 1 A 3500 Krems Austria

Laboratory of Cell Cycle of Algae Centre Algatech Institute of Microbiology Czech Academy of Sciences Novohradská 237 379 81 Třeboň Czech Republic

Laboratory of Cell Cycle of Algae Centre Algatech Institute of Microbiology Czech Academy of Sciences Novohradská 237 379 81 Třeboň Czech Republic Department of Functional Ecology Institute of Botany Czech Academy of Sciences Dukelská 135 379 81 Třeboň Czech Republic

Laboratory of Cell Cycle of Algae Centre Algatech Institute of Microbiology Czech Academy of Sciences Novohradská 237 379 81 Třeboň Czech Republic Faculty of Science University of South Bohemia Branišovská 1760 370 05 České Budějovice Czech Republic

Laboratory of Predictive Toxicology National Institute of Public Health Šrobárová 48 100 42 Prague Czech Republic

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