Treatment Of Rinse Wastewater From Electroless Nickel Plating Process By Reduced Iron Powder

Nickel plating is a very important surface modification treatment technology,which rank only second to zinc plating in electroplating industry,widely used in many fields.A large number of nickel-containing wastewater is produced by nickel plating process.However,nickel is internationally recognized as a king of carcinogen.So,the nickel-containing wastewater must be treated before discharged.In November 30,2012,the Guangdong Province has issued a document wich require electroplating industry perform the nickel emission standards for less than 0.1 mg/L in the Pearl River Delta region since December 31,2012.However,in the specific implementation process,it may be due to the current process is difficult to steadily achieve the emission standards of 0.1 mg/L or the cost is too high,Guangdong Province had to suspend the above emission standards.Electroplating wastewater discharge standards（DB 44/1597-2015）of the local standards in Guangdong Province is issued which require existing electroplating industry perform the nickel emission standards for only less than 0.5 mg/L.Therefore,treatment of wastewater from electroless nickel plating process that is simple,high efficiency,low processing cost and easy recovery of nickel resources is an important and urgent research direction.Different treatment methods were used to treat three kinds of electroless nickel plating wastewater with different concentrations.The rinse wasterwater containing a low total nickel content of 7.2 mg/L from electroless nickel plating was treated by reduced iron powder 30 min when the initial pH value was 9 and the reduced iron powder addition was 1.5 g/L at room temperature（20 ℃）,the concentration of total residual nickel in effluent was stably under 0.1 mg/L.The rinse wasterwater containing total nickel content of 21.8 mg/L from electroless nickel plating was treated by reduced iron powder 150 min when the initial pH value was 6.1 and the reduced iron powder addition was 4 g/L at temperature of 50 ℃,the concentration of total residual nickel in effluent was 0.12 mg/L.But when the reaction temperature was raised to 60 ℃,the concentration of total residual nickel in effluent was 0.09 mg/L under 0.1 mg/L.When the rinse wasterwater containing total nickel content of 45.6 mg/L from electroless nickel plating was treated by reduced iron powder,the concentration of total residual nickel in effluent can not be under 0.1 mg/L.But when the initial pH value was 5.8 and the reduced iron powder addition was 10 g/L at temperature of 50 ℃,the rinse wasterwater was treated by reduced iron powder and after 120 min the concentration of total residual nickel in effluent was 0.37 mg/L.And then treated by Fenton advanced oxidation process,when the initial pH value of 4,dosage of H₂O₂ and FeSO₄·7H₂O were 1.7 m L / L and 3.1 g / L,the reaction after 90 min of water to be adjusted with pH of 7 8,the concentration of total residual nickel in effluent can be reduced to 0.06 mg/L.And the COD of the rinse wasterwater can be reduced to 63.7 mg/L.And then the effluent of Fenton advanced oxidation process was treated by BAF with 4h,the COD of the rinse wasterwater can be reduced to 45.7 mg/L that is under the emission standards of 50 mg/L.The reaction mechanism of treatment of rinse water from electroless nickel plating process by reduced zero-valent iron powder is analysed simply.The mechanisms of the treatment are mainly redox reactions and coagulating sedimentation.