Effect of B2O3 on the removal of phosphate ions from an aqueous solution in borosilicate glasses.

Recently, it was found by the authors of this study that glasses of a special composition have an ability to remove some hazardous ions from waste solutions. In the present study, a SiO(2)-B(2)O(3)-CaO-Na(2)O glass system has been chosen to remove phosphate ions from an aqueous solution. Several glasses with different amounts of B(2)O(3) in the SiO(2)-B(2)O(3)-CaO-Na(2)O glass system have been prepared, and these glasses have been reacted with a solution containing 155 ppm of phosphate ions. A silica-rich layer is first formed on the glass surface by leaching Na(+) and Ca(2+) ions from the glass, and then the Ca(2+) and PO(4)(3-) ions in the solution have been uptaken on the silica-rich layer to precipitate hydroxyapatite crystals. In this manner, the phosphate ions could be removed from the solution. The efficiency of removing the phosphate ions was found to depend strongly on the B(2)O(3) contents. With increase of B(2)O(3) contents in the glass, more Ca(2+) ions can be leach out of the glass, promotes the precipitation of hydroxyapatite. Therefore, the removal efficiency increases with increased B(2)O(3) content. The phosphate ion removal efficiency was also sharply enhanced by increasing the surface area of the glasses and decreasing the pH of the solution.