| 摘要 |
PURPOSE:To treat liquid waste of high COD into a low-COD state, by adding the specified amount of a calcium compound to a washing solution containing citric acid, further adjusting a pH to a specified range, lowering the pH of a separated supernatant liquid below a specified value, and then adding a cupric compound. CONSTITUTION:The liquid waste of a chemical washing solution in which a corrosion inhibitor, a rust preventive agent, mainly ferric ion, etc. in addition to the mixture of citric acid and an ammonium salt are coexistent is introduced into a treating tank, wherein a calcium compound such as calcium hydroxide is added in a manner such that the concentration of calcium ion is 1 equivalent or more based on a citric acid part in the treating tank. Thereafter, a pH is adjusted to 11.5-13 using alkali such as caustic soda, to precipitate the citric acid part as calcium citrate. Cupric sulfate or the like is further added in a manner such that the concentration of cupric ion is 1 equivalent or more based on the calcium citrate part in a separated supernatant liquid, to form insoluble cupric sulfate. Then, the pH is readjusted to 5.8-8.6, and solid-liquid separation is performed.
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