The mechanism was discussed for the removal of boron by the hydroxyapatite (HAp) formation reaction using Ca(OH)(2) and (NH4)(2)HPO4 in room temperature. Time required to remove boron was 20 min by adding Ca(OH)(2) and (NH4)(2)HPO4 for the remaining boron to below 1 mg/L The removal rate of boron was controlled by the HAp precipitate formation and the presence of ammonia. From the XRD patterns and SEM images, HAp could be confirmed in the precipitate product. The reaction between borate ions and calcium hydroxide was accelerated by dehydration with ammonia; the borate-calcium hydroxide compound coprecipitated with resulting HAp. Although the removal of boron decreased in the presence of sulfate, phosphate, and aluminum, these effects could be prevented by adding excess Ca(OH)(2). Interference of fluoride ions was eliminated by adding Al3+. Sodium alpha-olefin sulfonate was the most effective coagulant for HAp precipitation. The proposed boron removal method has several advantages about treating time and ability of boron removal. The method was successfully applied to the real hot spring wastewater. (C) 2012 Elsevier B.V. All rights reserved.