Water-soluble radiostrontium (Sr-90) was efficiently removed as a carbonate form through microalgal photosynthetic process. The immobilization of soluble Sr-90 radionuclide and production of highly-precipitable radio-strontianite ((SrCO3)-Sr-90) biomineral are achieved by using Chlorella vulgaris, and the biologically induced mineralization drastically decreased the Sr-90 radioactivity in water to make the highest Sr-90 removal ever reported. The high-resolution microscopy revealed that the short-term removal of soluble Sr-90 by C. vulgaris was attributable to the rapid and selective carbonation of Sr-90 together with the consumption of dissolved CO2 during photosynthesis. A small amount of carbonate in water could act as Sr2+ sinks through the particular ability of the microalga to make the carbonate mineral of Sr stabilized firmly at the surface site. (C) 2014 Elsevier Ltd. All rights reserved.