Recycling process of sodium metaborate to sodium borohydride

Sodium borohydride (NaBH4) was synthesized by reacting sodium metaborate (NaBO2) with magnesium hydride (MgH2) or magnesium silicide (Mg2Si) by annealing (350–750°C) under high H2 pressure (0.1–7 MPa) for 2–4 h. As the temperature and the pressure increased, the yield increased to have a maximum value (97–98%) at 550°C under 7 MPa, but the value was independent of time. A concept for converting NaBO2 back to NaBH4 using coke or methane is described.