| 摘要 |
Boric acid is made by treating an aqueous solution of an alkali metal borate with a cationexchange resin containing COOH groups. A Na borate, e.g. tetra borate decahydrate (borax), tetrahydrate (kermite), pentahydrate, or a polyborate may be treated at below 100 DEG C., e.g. 80 DEG C., with a cross-linked methacrylic acid resin, e.g. by passage through beads of resin in a column, and the boric acid may be crystallized from the solution by cooling. Further borate may be added to the mother liquor which may then be treated with resin. The resin may be regenerated by treatment with an aqueous solution, e.g. 20% of a strong acid, e.g. H2SO4, HCl or HNO3, in not greater than the theoretical amount for conversion to the H+ form. The acid solution may contain the alkali metal-acid salt in such amount that the solution is not saturated at the resin treatment temperature, e.g. 70 - 90 DEG C., but is saturated at a lower temperature, e.g. 20 DEG C., and treatment of the resin with the acid solution is preceded by treatment with a neutral solution of the alkali metal salt, e.g. Na2SO4, which is crystallized by cooling (which may be preceded by evaporation) the effluent from the above acid solution. Further acid may be added to a portion of the mother liquor which is then used to regenerate the resin. The boric acid production and resin regeneration steps may be cyclic and the resin may be washed with water before each step. |
