Selective sorption of strontium using two different types of nanostructured manganese oxides

The aim of this study was to investigate the sorption properties of two different types of nanostructured manganese oxide materials for radioactive species such as strontium and cesium. Two different nanostructured manganese oxides were prepared using either hydrothermal and reduction methods. Manganese oxide nanowires were synthesized by the hydrothermal method followed by heat treatment. Nanostructured microspheres of manganese oxide were synthesized by reduction of MnO4 − with hydrochloric acid. Both the synthetic manganese oxides were characterized by powder X-ray diffraction, scanning electron microscopy, and Brunauer–Emmett–Teller specific surface area measurements. In order to examine the sorption characteristics of both the nanostructured manganese oxides, batch isotherm tests were carried out. The results showed that manganese oxide nanowires exhibited high affinity for strontium. The sorption capacity of manganese oxide nanowires for strontium was 124.0 mg/g (ca. 2.83 meq/g). The kinetics of strontium sorption by the two nanostructured manganese oxides were found to match well with pseudo-second-order rate model. Rapid removal of strontium by both the nanostructured manganese oxides occurred at initial stage of the sorption process. This result implies that the sorption mechanism of strontium is likely due to ion exchange and/or chemisorption. Based on these results, the manganese oxide nanowires could be an excellent sorbent or ion exchanger for the removal of radioactive strontium from nuclear waste water, surface water and groundwater.