Study On Treatment Of Electroplating Wastewater By Reduction And Fractional Precipitation

Electroplating industry has an important position in the manufacturing industry,involving dozens of industries,such as aerospace,machinery manufacturing,integrated circuits,electronic components.But there is a large amount of waste water in this industry,of which did not meet the national emission standards.Due to improper treatment of electroplating waste liquid,a great deal of metal resources are lost every year.In order to protect environment,prevent pollution and save resources,it is very important to study the technology of electroplating wastewater treatment and metal recovery in wastewater.In this paper the containing chromium electroplating wastewater and comprehensive electroplating wastewater from an electroplating factory in Xianyang City is studied.The content of metal ion in waste water is measured.The optimum conditions,pH=3.0,for reducing of Chromium(?)in wastewater have been found by using oxalic acid as a reducing agent of Chromium(?)through theoretical and experimental study,while the addition of oxalate is 1.4 times greater than the theoretical value.More than 30 minutes of reaction time is needed.The sodium hydroxide and sodium hydroxide sodium sulfide were used as precipitant respectively to study the fractional precipitation of metal ions in wastewater.Single factor experiments were conducted to investigate the effects of three factors,such as pH,precipitant,and amount of precipitant,on the precipitation of metal ions in wastewater and the recovery of metals.The results show that the precipitation of chromium,nickel and copper can be achieved by controlling the pH of water sample with sodium hydroxide as precipitant.That is,the chromium ion,copper ion and nickel ion in the wastewaters can be precipitated completely,when pH is 6,8 and 10 respectively.The precipitation of chromium,nickel and copper can be achieved by controlling the pH of water sample and sodium sulfide addition with sodium hydroxide as precipitant.That is,the chromium ion in the wastewaters can be precipitated completely,when pH is 6;the copper ion in the wastewaters can be precipitated completely,when pH is 4 and the sodium sulfide addition is 1.2 times of the theoretical value of copper;the nickel ion in the wastewaters can be precipitated completely,when pH is 7 and the sodium sulfide addition is 1.2 times of the theoretical value of nickel.According to the experimental results of wastewater treatment,the automatic wastewater treatment process was designed,and the technological process and design parameters were described.