Study Of Treatment Of Nickel And Boron In Electroplating Nickel-Removing Wastewater

It can be seen from the electroplating nickel process that the discharge of nickel-containing wastewater is accompanied by the discharge of organic matter and inorganic matter.Many studies only consider the environmental hazard of heavy metal nickel and organic matter emissions,but the combination of heavy metal nickel and inorganic substances are more harmful to the environment,so it is also important to reduce the concentration of inorganic emissions while treating nickel.This experimental study takes the electroplating nickel-removing wastewater from an electroplating enterprise in Zhenjiang as the research object.After analyzing the nickel-removing wastewater,it contains high concentration of heavy metal nickel and inorganic boron.This paper focuses on the methods used to make the concentration of heavy metal nickel emitted to meet the emission limit of 0.5 mg/L and the concentration of boron to meet the emission limit of 5.0mg/L.The specific research conclusions are as follows:?1?Pretreatment with sodium hydroxide precipitation method reduces the concentration of nickel and boron in the electroplating nickel-removing wastewater.Through experimental research,at the optimum pH value of 9.5,the concentration of nickel and boron in wastewater decreased from 2735 mg/L and 248.73 mg/L to 12.78 mg/L and86.05 mg/L,respectively,and the corresponding removal rates were 99.53%and 65.40%.The precipitate reached the optimal reduction at a temperature of 100?.At this time,the reduction rate and the volume reduction rate were 97.85%and 98.33%,respectively.The precipitate after the reduction was calcined at different temperatures for calcination.The product was characterized by XRD,FESEM and TEM.It was confirmed that the calcined product at 750?and 900?was a mixture of NiO and Ni₃?BO₃?₂.The chemical reaction is combined to infer that a mixture of Ni?OH?₂ and NiBO₂?OH?was mainly formed during the wastewater treatment,and was in an amorphous state.?2?The nickel and boron wastewater after the pretreatment is further treated by iron microelectrolysis.Under the current conditions of the laboratory,the optimum conditions were 40 g iron,initial pH 2.0,and rotational speed 9 r/min.After 6 hours of reaction,the nickel concentration in wastewater decreased from 12.78 mg/L to 0.25 mg/L and the removal rate was 98.04%.The concentration of boron was reduced from 86.05 mg/L to85.98 mg/L,and the removal rate was 0.08%.At the same time,the pH of the wastewater changed from 2.0 to 7.12.After treatment,the concentration of nickel and boron was compared with the corresponding emission standard.The nickel could reach the standard but the boron could not.and the concentration of boron before and after treatment was almost unchanged.FESEM,XRD analysis and dissolution test analysis of the iron and precipitates after the reaction,91.74%of the nickel in the wastewater is on the surface of the iron,4.23%of the nickel is in the sediment,and the iron micro-electrolysis method has almost no removal effect on boron.?3?The nickel and boron wastewater after the pretreatment is further treated by electrocoagulation.Under the current conditions of the laboratory,the best conditions were obtained by multi-electrode aluminum plate and plate spacing of 0.5 cm.After 3 hours of reaction,the boron concentration of wastewater decreased from 86.05 mg/L to 24.49 mg/L and the removal rate was 71.17%.The nickel concentration was reduced from 12.78 mg/L to 0.25 mg/L,and the removal rate was 98.04%.After treatment,the concentration of nickel and boron is compared with the corresponding emission standard.The nickel up to standard but the boron cannot meet the standard.In order to further reduce the concentration of boron,the wastewater was subjected to MgO adsorption treatment on the basis of electrocoagulation.After 24 hours of reaction,the residual boron concentration in the wastewater was reduced to 4.92 mg/L,which reached the discharge standard.