Experimental Study On The Treatment Of Ammonia Nitrogen Wastewater In Metallurgical Industry By Precipitation Method

Magnesium ammonium phosphate precipitation method is widely used in the treatment of high-concentration ammonia-nitrogen wastewater due to its fast reaction speed and high removal rate,but there are few reports on its application in the treatment of low-concentration ammonia-nitrogen wastewater.In order to explore the effect of precipitation method on low-concentration ammonia-nitrogen wastewater,the most critical factor pH and the molar ratio of precipitant input(magnesium-nitrogen ratio,phosphorus-nitrogen ratio)were selected among the various influencing factors of the precipitation method.Carry out a large number of single factor experiments and orthogonal experiments.Considering that if the low-concentration ammonia wastewater is directly precipitated,it may be difficult to analyze the experimental data due to the insignificant effect.Therefore,this topic first uses the two precipitants of Na₂HPO₄,MgCl₂,NaH₂PO₄,and MgSO₄ to treat high-concentration ammonia wastewater,And then apply to the treatment of low-concentration ammonia nitrogen wastewater after obtaining the best process conditions.The main research contents and conclusions are as follows:(1)Na₂HPO₄,MgCl₂ and NaH₂PO₄,MgSO₄ are used as precipitating agents to treat high-concentration ammonia nitrogen wastewater,the best precipitation conditions are:pH=9.5,n(Mg):n(P):n(N)=1.2:1.2:1.(2)From the overall ammonia removal situation,although the ammonia removal effect of NaH₂PO₄ and MgSO₄ is slightly better than that of Na₂HPO₄ and MgCl₂,from the perspective of the final results,Na₂HPO₄ and MgCl₂ precipitation agents can remove 600 mg/L of ammonia.The ammonia nitrogen was reduced to about 13 mg/L,while NaH₂PO₄ and MgSO₄ reduced the ammonia nitrogen of 600 mg/L to about 15mg/L,and there was no significant difference.However,the alkali consumption of the latter group of precipitating agents is significantly higher than that of the former group.From the perspective of saving reagent usage,the precipitating agents should be Na₂HPO₄ and MgCl₂.(3)Under the process conditions that the precipitation agent is Na₂HPO₄,MgCl₂,pH=9.5,n(Mg):n(P):n(N)=1.2:1.2:1,the precipitation method is suitable for 30 mg/L?200 mg/L The final treatment effect of low-concentration simulated ammonia-nitrogen wastewater is about 15 mg/L,and the final treatment effect of 55 mg/L actual low-concentration ammonia-nitrogen wastewater is about 20 mg/L,which meets the secondary discharge standard.Concentrated ammonia nitrogen wastewater also has a certain ammonia nitrogen removal effect.(4)The XRD analysis and SEM analysis results of the precipitated product show that the precipitated product generated at pH=9.5 is basically magnesium ammonium phosphate crystals,but at pH=11,although the precipitated product is mainly magnesium ammonium phosphate,there are others.Substances such as Mg(OH)₂,Mg₃(PO₄)₂.