NaBH₄ regeneration from NaBO₂ by high-energy ball milling and its plausible mechanism

In this paper, we developed an easy and simple method (high-energy ball milling) for recycling NaBO₂ (the hydrolysis byproduct) back to NaBH₄ by a reaction with MgH₂. To optimize the yield of NaBH₄, we investigated the effect of four parameters, e.g. the ball milling time, the molar ratio of MgH₂/NaBO₂, H₂ pressure and addition of methanol, on the NaBH₄ regeneration. Accordingly, the maximum yield of NaBH₄ (89 wt. %) was achieved. The mechanism of NaBH₄ regeneration has been discussed. It is indicated that the NaBH₄ formation involves a two-step substitution in which NaBOH₂ is an intermediate confirmed by solid-state nuclear magnetic resonance (NMR).