| 摘要 |
EDTA and its complexes, esp. the Ca complex, is removed from waste water by oxidn. of the EDTA with persulphate (S2O8--) at acid pH. Pref. acidification is with an acid, esp. HCl, to pH about 1. Oxidn. is at not below 60 deg.C., pref. using solid Na2S2O8, with at least 2 mols. of Na2S2O8 w.r.t. 1 mol. of EDTA. After acidification, pref. to pH 1, pptd. EDTA and complexes are sepd., followed in a 2nd stage by oxidn. of the EDTA with persulphate. USE/ADVANTAGE - Examples of waste waters contg. EDTA are those from water treatment, e.g. by reverse osmosis, and from prodn. of photochemicals. The process is simple, very efficient, and cheap. The residual content is less than 10 mg EDTA; (in the H4Y form). In an example, waste water from a reverse osmosis plant which had been flushed periodically with a soln. of an EDTA salt (Na2H2Y.2H2O), contg. complexes of EDTA with metal ions, mostly Ca, was brought to pH 1 with HCl. 80% of the EDTA pptd. and was filtered off. The filtrate contg. 20% of the EDTA, as complexes with metal ions, was treated cold with at least 2 mols. of solid Na2S2O8 w.r.t. 1 mol. of EDTA, and stirred for 90 mins., when the temp. rose to 80 deg.C.. The treated waste water contained less than 10 mg/l of EDTA (as H4Y). Residual Na2S2O8 was not harmful, but oxidised residual organic matter in the water.
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