Method of recycling hydrochloric and hydrofluoric acid effluent

A process for producing boron trifluoride hydrates, comprising:

• (i) at least one step during which at least one boron compound chosen from boric acid (H3BO3), metaboric acid (HBO2) and boric anhydride (B2O3) is placed in contact with an aqueous solution of hydrochlorofluoric acid at atmospheric pressure to give a mixture of fluoroboron compounds and of hydrochloric acid;
• (ii) a distillation step performed at atmospheric pressure to yield a first fraction comprising hydrochloric acid and a second fraction comprising water, residual hydrochloric acid, and a mixture of fluoroboron compounds;
• and
• (iii) a step of vacuum distillation of the second fraction obtained in step (ii) to remove the residual hydrochloric acid and the water, wherein the temperature of the second fraction is increased during the vacuum distillation step so as to give a concentrated aqueous solution of boron trifluoride hydrates, and wherein the absolute pressure of the vacuum distillation step is between 10 and 100 mbar, and the concentrated aqueous solution of boron trifluoride hydrates obtained after step (iii) contains less than 100 mg of chloride per kg of boron trifluoride hydrates.