Method for recycling residual solutions comprising phosphorus and device for such a method

A process for purifying an aqueous residual solution comprising phosphorus molecules and undesirable volatilizable materials, comprising the following steps:

• (a) introducing into a gas-acid contactor (1) a feed stream F0 of a feed solution P0 which is aqueous and comprising phosphorus molecules preferably in the form of species such as orthophosphate at a mass concentration, xp0, of between 0 and 54% equivalent of P2O5 units,
• (b)introducing into the gas-acid contactor (1) a recirculation stream F2 of recirculated enriched phosphoric acid P2,
• (c) introducing into the gas-acid contactor (1) combustion gases G1,
• (d)contacting the feed stream F0 and the recirculation stream F2 and the combustion gases G1 to form in the gas-acid contactor, on the one hand,
• an enriched phosphoric acid solution P1 comprising a mass concentration, xp1, with a P2O5 content which is greater than xp0 (xp1>xp0) and, on the other hand,
• contacted combustion gases G3,
• (e) separating the contacted combustion gases G3 from the enriched phosphoric acid solution P1, and then
• evacuating the contacted combustion gases G3 from the gas-acid contactor (1), and
• removing the enriched phosphoric acid solution P1 from the gas-acid contactor (1),
• (f) forming from said enriched phosphoric acid solution P1, on the one hand,
• a recirculation stream F2 of recirculated enriched phosphoric acid P2 to introduce it into the gas-acid contactor (1) as defined in step (b) and, on the other hand,
• a spraying stream Fp of the enriched phosphoric acid solution P1 to introduce it into a combustion chamber (2),
• (a) spraying through a flame burning in the upper part of the combustion chamber (2) a mixing stream Fm of a mixing solution (Pm) comprising phosphorus at a mass concentration, xpm, and undesirable volatilizable materials, the mixing stream being formed by, on the one hand,
• the enriched phosphoric acid solution P1 and optionally, on the other hand,
• a residual steam Fr of an aqueous residual solution Pr comprising a mass concentration, xpr, of at least 1% P2O5,
• to:
• evaporate the water and thus concentrate the mixing solution Pm,
• optionally oxidize and in any case evaporate the undesirable volatilizable impurities,
• form combustion gases G1, and
• forming a combustion solution P3 having
• a mass concentration, xp3, of P2O5 which is higher than the concentration of the mixing solution Pm, and
• a content of volatilizable impurities which is lower than that of the mixing solution Pm,
• (g) separating the combustion solution P3 from the combustion gases G1 and
• recovering the combustion solution P3, and
• transferring the combustion gases G1 into the gas-acid contactor (1) as defined in step (c).