Abstract: Pure boric acid is obtained by a high-yield method with a non-pollutant effluent discharge, comprising the following stages carried out in succession:a) dissolving impure boric acid in an aqueous vehicle to form an aqueous solution of impure boric acid;b) separating pure crystalline boric acid from the aqueous solution of stage a) by crystallization;c) treating the discharge liquor from the crystallization of stage b) firstly through a strong cation exchange resin and then through a weak anion exchange resin;d) recycling the discharge liquor treated in stage c) for use as the aqueous vehicle for dissolving the impure boric acid in stage a).

Abstract: High-purity boric oxide which does not adhere to the reactor walls is obtained by:(a) gradually heat in boric acid, with the absence or substantial absence of fusion phenomena, at increasing temperature to a value not exceeding about 150.degree. C.; operating at below atmospheric pressure, to eliminate water until the boric acid has been completely or substantially completely converted into metaboric acid;(b) gradually heating the metaboric acid obtained in stage (a), with the absence or substantial absence of fusion phenomena, at increasing temperature to a value not exceeding about 400.degree. C., operating at below atmospheric pressure, to eliminate water until the metaboric acid has been completely or substantially completely converted into boric oxide.

Abstract: High-purity sodium tetraborate pentahydrate (Na.sub.2 B.sub.4 O.sub.7.5H.sub.2 O) is produced by:(a) reacting the mineral colemanite (2CaO.3B.sub.2 O.sub.3.5H.sub.2 O) with sodium carbonate (Na.sub.2 CO.sub.3) in an aqueous environment to produce an aqueous solution of sodium tetraborate and sodium hydroxide, with precipitation of solid calcium carbonate;(b) treating the aqueous solution obtained in stage (a), after separating the precipitated calcium carbonate, with boric acid (H.sub.3 BO.sub.3) to neutralize the sodium hydroxide and form a further quantity of sodium tetraborate;(c) separating sodium tetraborate pentahydrate by crystallization from the aqueous solution obtained in stage b.