This study has investigated the selective immobilization of antimony using the brucite (magnesium hydroxide)-rich precipitate (BP) collected from a hypochlorous storage tank in a nuclear power plant of South Korea. The energy dispersive X-ray and X-ray diffraction analyses revealed that the BP mainly consisted of magnesium (72.5%) and its dominant mineral phase was brucite (Mg(OH)2). Therefore, brandholzite (Mg[Sb(OH)6]2·6H2O) was newly formed through the surface-induced precipitation during the adsorption of antimony using the BP. The adsorbed amount of antimony increased with decreasing pH values because of the increased positive surface charge of the BP (pHpzc = 9.6). The maximum adsorption capacity (Qmax) of BP, calculated by Langmuir adsorption isotherm, was 11.02 mg/g. The presence of competitive anions did not significantly affect the adsorption of antimony toward the BP due to its high selectivity. These results suggest that the facile utilization of the BP as a low-cost adsorbent seems to be a practical option for the selective removal of antimony from wastewater.