Application Of High-level Complex Ni Removal From Electroplating Wastewater By The Na₂S-DDTC

Electroplating industry is one of global three large contaminated industry, the wastewater possess galactic virulence and harmfulness. On the wholly electroplating vocation, the process load of plating Ni was in the second place, Ni electroplating rinse wastewater contains a large number of free and complex forms Ni resources. In order to guarantee the property of the plating liquid, plating process will be adding complexing agent, such as EDTA, citric acid, NH3 etc, electroplating rinse wastewater maintain substantive Ni resource which of free form and complexation shape, because of complex’ impact, the conventional chemical process already insatiability meet the rigidly requirements of electroplating wastewater discharge. In recent years,chelate precipitation method ameliorate the shortage of traditional technical,restricting the key in application of this method lies in the reagent cost, that is to say:it be difficult to reach "electroplating effluent standard of pollutions (GB21900-2008) " second trial to Ni pollutant inter-alia emission limits require (<0.1mg/L) when adopting conventional method process.There is a higher medicament cost while adopting chelate precipitation method, By optimizing the ratio of reagents for coprecipitation technique in the treatment of electroplating heavy metal waste water with low cost, good effect and a series of advantage.In this study, the organic mercapto polymer chelating agent (DDTC), Na2S and NaOH were selected as the capturing agent and used to remove complex Ni deeply from the electroplating plant wastewater. It paid the key focus on the study of reaction pH, pharmaceutical dosage, reaction time and other factors that could influence the removal of Ni. Besides, the mechanisms of Ni2+removing by Na2S-DDTC was also discussed. The results showed that Na2S-DDTC had a high efficiency under the following conditions:p(Ni)=300mg/L of initial nickel concentration, pH 9.0, Na2S and DDTC dosing ratio was p(Na2S)/ρ(DDTC)=10, where ρ(Na2S)=600mg/L,ρ(DDTC)=60mg/L, the reaction time t=6.0min, the dosage of PAM was 1.0mg/L, leading to 0.064mg/L of residual Ni2+concentration, which meeting the nickel special emission limit of the emission standard of pollutants for electroplating (<0.1mg/L). Furthermore, precipitation dissolution test about Na2S-DDTC mixed with Ni showed that, the hybrid sediment had a high sability under the state of nature, and did not cause secondary pollution. Through the simulation experiment, it could provide theoretical support for process design to deal with the actual electroplating wastewater containing high complex Ni concentration using Na2S-DDTC.In order to further study the distribution of medicament treatment effect, the actual electroplating heavy metal wastewater treatment process conditions by Na2S-DDTC are optimized, toke the high-level complex Ni containing electroplating rinse wastewater from an electroplating factory as treatment object. The influence of reaction pH,dosage of Na2S-DDTC as well as initial Ni concentration on the Ni2+removal were studied. The experimental results show that:①Raction pH has a great influence on removal of Ni, the best influence for Na2S-DDTC is that when the pH is 9.0;②Na2S-DDTC can capture Ni ion efficiently, it is better than that of Na2S, DDTC used alone. The residual Ni concentrations is 0.062mg/L when at pH=9.0; nNa2s/nNi=1-5 mol; ρ(DDTC)=200mg/L,meeting the Ni special emission limit of the emission standard of pollutants for electroplating(GB21900-2008)(<0.1mg/L);③Na2S-DDTC has a wide concentration range for different initial concentrations of Ni containing wastewater, reagent dosage of Na2S has a relation of nNa2s/nNi=1-5 mol and DDTC has the different optimum dosage.Additionally, the article also explored the mechanism of removing Ni by Na2S-DDTC. The complexation competition mechanism and complexation coordination bonding process was analyzed, through the medium of size distribution statistical analysis and sem surface morphology observe analyzed, it be recognized that Na2S-DDTC had a certain flocculation-coprecipitation’synergy.Na2S-DDTC coprecipitation treating process act as a sort of new chemical treatment means on electroplating effluent,with low administration cost, fast response time, good sedimentation effect, residue stability higher a series of merits, in actual electroplating wastewater treatment application has a very high economic, environmental and social benefits, the application prospect is completely amplitude.