| 摘要 |
PURPOSE:In adding an acid to waste liquor containing EDTA to adjust the waste liquor to a specific pH and to crystallize EDTA as a free acid, to advantageously recover EDTA from the waste liquor, by partially feeding the waste liquor from the bottom of a crystallizing tank to fluidize seed crystal of the free acid. CONSTITUTION:An acid is added to waste liquor containing ethylenediaminetetraacetic acid(EDTA), the waste liquor is adjusted to <=3pH and EDTA as a valuable substance is crystallized and collected from the waste liquor such as waste liquor of chemical plating, etc. as a free acid(H4Y). In the operation, the waste liquor adjusted to <=3pH is partially fed from a bottom 9 of a crystallizing tank 2 charged with seed crystal 3 of H4Y, the seed crystal 3 is fluidized by an upward cocounter flow, simultaneously the waste liquor sent from a bottom 1 to carry out crystallization and the seed crystal 3 of H4Y having desired, grown particle diameters is taken out from a bottom 10. By this method, since the particle diameters of H4Y crystal can be continuously and efficiently enlarged and EDTA can be recovered as approximately spherical high-purity crystal, the following washing and dehydrating processes can be made efficient and simplified and improvement in recovery ratio can be contrived.
|
