Research On The Treatment Of HEDP Copper-electroplating Wastewater

HEDP copper-electroplating is a new type of non-cyanide copper plating process which is more promising alternative to cyanide copper plating. While, for a variety of reasons such as the stability constants of HEDP-Cu is high (lgK=12.48), and the nature of HEDP is stable which is not easy to degrade, temperature and pH resistant, acid and alkali resistant, oxidation and chloridization resistant, under the natural conditions of shine and heat, the wastewater of this process is hard to be treated. The effective treatment of this wastewater is not reported so far.The research is about the treatment of HEDP copper-electroplating wastewater generated in the manufacturing line of CNGC JIANGNAN MACHINERY (GROUP) CO.LTD in Hunan Province. The treatment efficiency and main factors of iron chips micro-electrolysis treatment, CaCl₂ chelate precipitation-Fenton/NaClO oxidation process were investigated in treating HEDP copper-electroplating wastewater, and its reaction mechanism is discussed. The main conclusions are as follows:(1) HEDP copper-electroplating wastewater can be treated efficiently by iron chips micro-electrolysis process. The optimum conditions were as follows: initial pH value 2.0, iron filings dosage 10 g/L, react time 90 min, pH value of coagulation 11.0. Under the optimal conditions, the removal rate of COD, total phosphorous and copper reached 97.10%, 99.89% and 99.87% respectively. COD, total phosphorus and copper concentration in effluent is 29 mg/L, 0.58 mg/L and 0.17 mg/L. Total iron concentration was below 0.5 mg/L. The treated water meet the emission standard of pollutants for electroplating.(2) Though the treated water meet the emission standard of pollutants for electroplating in 20 batches intermit running in batch reactor system of iron chips micro-electrolysis, when run continuously, a great number of problems have arisen such as the surface passivation of iron chips, lumps of iron chips, channel flow and so on,and which led to a decline of the treatment efficiency.(3) Add CaCl₂ into HEDP copper-electroplating wastewater, at the initial pH value, CaCl₂ dosage 3.4 g/L, react time 20 min, the removal rate of COD, total phosphorous and copper reached 92.6%, 86.9% and 90.8% respectively. COD, total phosphorus and copper concentration in effluent is 74 mg/L, 70.5 mg/L and 11.6 mg/L. The treated water can't meet the emission standard of pollutants for electroplating with the single CaCl₂ chelate precipitation.(4) The HEDP in the treated water survived the chelating of CaCl₂ was further decomposed by Fenton reagent or NaClO.The optimum conditions of Fenton oxidation were as follows: initial pH value 3.0, [Fe²⁺]/[H₂O₂] for 1.2:1, H₂O₂ dosage 2 mL/L, react time 10 min. The optimum conditions of NaClO oxidation were as follows: pH value 4.5, NaClO dosage 3.5 mL/L, react time 10 min. Under the optimal conditions of these two oxidation process, the removal rate of COD, total phosphorous and copper reached 95.8%, 99.8%, 99.87% and 94.7%, 99.1%, 99.8% respectively. The treated water basically meet the emission standard of pollutants for electroplating.(5) A better efficiency in the treatment of HEDP copper-electroplating wastewater was achieved by Fenton reagent comprised of H₂O₂ and iron powder or iron fillings which was a substitution for FeSO₄·7H₂O. But a long-term operation should be avoided as bulks would be formed at the bottom of the reactor due to the electric reaction of Fe powder, which could be resolved by replacing iron powder with iron fillings.(6) The extent of oxidation and decomposition of HEDP using NaClO was enhanced in the presence of Mg²⁺ and Br-. Concentration of TP was decreased to 0.7⁰.8 mg/L with 0.3g/L Mg²⁺ or 0.1g/L Br-, meeting the emission standard of pollutants for electroplating.(7) Through comparing and analyzing, it was concluded that CaCl₂ chelate precipitation-Fenton oxidation process is of better economic feasibility.