Study On Influencing Factors Of Removing Nitrogen And Phosphorus From Simulated Electroplating Wastewater By Struvite Crystallization

The rise of electronic manufacturing industry has promoted the rapid development of electroplating industry,but also accompanied by a large amount of electroplating wastewater.The composition of electroplating wastewater is complex,including heavy metal ions such as copper,zinc,and nickel,organic compounds such as complex compounds,additives,and other organic substances,as well as fluoride,nitrogen,and phosphorus.Its concentration far exceeds the environmental tolerance.Therefore,the harmless treatment and recycling of electroplating wastewater have received widespread attention.In this paper,the research object is wastewater from electroplating pretreatment,electroplating,and post plating treatment with different components.The nitrogen and phosphorus in wastewater are recovered using struvite crystallization method,and the effects of heavy metal ions,complexes,and fluorine ions in electroplating wastewater on the nitrogen and phosphorus during the struvite crystallization process are investigated.In addition,the effects of three crystal seeds（raw materials and ball milling treatment）on nitrogen and phosphorus during the crystallization process of struvite were also investigated.Combined with SEM,XRD,FTIR,and XPS tests,the properties of struvite crystal products were analyzed and compared with pure struvite crystal seeds.Research has shown that at a pH of 9,struvite crystallization can achieve the best nitrogen and phosphorus removal efficiency.When heavy metal ions are present in the solution,the pH value for obtaining the optimal nitrogen and phosphorus removal rate is also 9.At this pH value,with the rise in the concentration of heavy metals,the removal rate of PO₄^3--P increases,while the removal rate of NH₄⁺-N decreases.Because heavy metal ions can combine with PO₄^3-,they can also be formed on the surface of struvite through surface enrichment and precipitation of metallic amorphous phases,greatly changing the structure of struvite,thereby reducing the purity of struvite crystals.When there are fluorine ions in the solution,the main effect of fluorine ions on struvite is to compete PO₄^3-with Mg²⁺,which decreases the nitrogen and phosphorus removal rate in the solution.However,low concentration of fluorine ions(0-40 mg·L^-1)has no significant impact on the crystal shape of struvite.When fluorine ions coexist with metal ions,fluorine ions can affect the reaction process,resulting in different forms of metal containing phases in struvite deposits.When there is a complex in the solution,the removal rate of PO₄^3--P in the solution decreases with the increase of the density of the complex.The complex can chelate with magnesium ions to inhibit the crystallization of struvite.In addition,the complex can prolong the induction time and reduce the growth rate of struvite crystals,thereby reducing the removal rate of PO₄^3--P.The presence of a complex in the solution can affect the morphology and size of struvite,and the complex can interact with the crystal surface,causing the complex to adsorb on the crystal surface.Adding crystal seeds to the solution,using raw materials such as red mud,attapulgite,and brick powder as crystal seeds,the order of influence on the removal rates of PO₄^3--P and NH₄⁺-N by struvite crystallization is as follows:attapulgite>red mud>brick powder.The experiment determined that the optimal dosage is 0.2 g·（250 m L）^-1.The effect of ball milling materials such as red mud,attapulgite,and brick powder as crystal seeds on the removal rates of PO₄^3--P and NH₄⁺-N by struvite crystallization method is ranked as follows:attapulgite>brick powder>red mud.Ball milled attapulgite was selected as the best seed crystal,and the optimal dosage was 1.0 g·（250 m L）^-1.