Preparation of metaettringite from ettringite and its performance for boron removal from boric acid solution

Metaettringite was prepared by heat treatment of ettringite, and its boron removal performance from solutions at low concentrations (25 mg/L boron (mg-B/L)) was investigated. With a calcination temperature of > 65°C, amorphous metaettringite formed, and this showed better boron removal performance than ettringite. The dominant mechanism for boron removal by metaettringite was incorporation of B(OH)₄ - in the ettringite structure during its regeneration from metaettringite by hydration. The highest uptake was 15.1 mg of boron per gram of metaettringite. Boron in solution could be effectively removed by metaettringite over a wide initial pH range of 5.22 to 11. Residual boron concentrations were lower than those specified by the Japanese effluent standard (10 mg-B/L) even when using metaettringite with a large particle size. Boron removal was strongly suppressed by high temperatures, but a residual boron concentration lower than 10 mg-B/L was obtained when the mass concentration of adsorbent in the boron solution was increased.