The Process And Mechanism Of Removal Of Zn²⁺ And Ni²⁺ From Wastewater By Sinusoidal Alternating Current Electrocoagulation With Double Iron Electrodes

Nowadays,with increasing of heavy metal pollution and water consumption,the shortage of freshwater resources is one of the greatest challenges human facing.The arbitrary discharge of industrial wastewater will seriously damage the ecological environment,so it should be treated thoroughly before discharge.The electroflocculation method has great advantages in the sustainability and low-cost treatment due to it is simple operation,high efficiency and no secondary pollution in industrial polluted wastewater treatment.In this paper,Zn²⁺and Ni²⁺in wastewater were treated respectively by sinusoidal alternating current flocculation with double-iron electrode,and the removal efficiency of heavy metal ions was studied by optimizing the electrocoagulation parameters.Under the optimal parameters,the possible mechanism of sinusoidal AC flocculation removing heavy metal wastewater was explored.The specific research contents are summarized as follows:?1?Process parameters had a great influence on electroflocculation performance.Under the optimal process parameters,the initial pH of 7,the current density was 5mA?cm^-2 and the NaCl concentration was 100 mg?dm^-3,the double-iron electrode sinusoidal AC flocculation?SAC-EC?could effectively remove containing Zn²⁺wastewater which the initial concentration was 100 mg?dm^-3.Under the circumstances of operating parameters,which electrolysis time was 25 min,the number of reactors was 5,current density was 7 mA?cm^-2 and initial pH of 7,100 mg?dm^-3 synthetic wastewater containing Ni²⁺could be effectively treated.The zinc content was 0.215mg?dm^-3 and the nickel content was 0.440 mg?dm^-3,The corresponding removal rates were 99.79%and 99.56%respectively,which both meet the GB21900-2008 emission standards(total zinc content<2 mg?dm^-3,total nickel content<1 mg?dm^-3).?2?The comprehensive kinetic equation and isotherm adsorption model analysis showed that sinusoidal alternating current flocculation removing wastewater Zn²⁺was complex electrochemical process,including precipitation,coprecipitation,adsorption and cathodic reduction.Thermodynamic fitting showed that the process of floc adsorption of Zn²⁺was endothermic and spontaneous.?3?The composition and morphology of the electrocoagulation produced by the three methods were analyzed by SEM and EDS.The floc produced by sinusoidal alternating current flocculation exhibited fine nanospheres with larger specific surface area,and the content of zinc atoms in the wastewater adsorbed by flocs was the most.?4?The products of sinusoidal AC flocculation were analyzed by FTIR and XRD.It was found that the process of iron hydroxide floc adsorbing zinc and nickel forms many complex hydrates,which had the characteristics of poor amorphous crystallinity.?5?The sinusoidal AC flocculation method was used to treat real industrial wastewater(Cr⁶⁺,Cu²⁺,Zn²⁺,Ni²⁺)which initial concentration were below 100mg?dm^-3.The concentrations of Cr⁶⁺,Cu²⁺,Zn²⁺,and Ni²⁺after treatment were 0.119,0.220,0.270,and 0.107 mg?dm^-3 respectively.The treated industrial wastewater also exceeds the national discharge standard for electroplating wastewater,which proved that this method is feasible in the treatment of industrial wastewater in practice.