Study On Iron Removal Agent Of Zinc Liquid And Its Mechanism

Impurity iron is very difficult to be removed by the ordinary zinc liquid purification process,which is extremely harmful to the hot-dip galvanizing bath and coatings.At present,iron removal of hot dip galvanizing zinc liquid is a very urgent problem.The development of a high-efficiency iron removal agent is of great significance for improving the quality of hot dip galvanizing baths and coatingsIn this paper,based on chloride salt mixture and aluminum powder,the formula of zinc liquid iron remover was optimized by orthogonal test,the content of iron in zinc liquid was determined by spectrophotometry.The microstructure and phase composition of zinc slag were studied by scanning electron microscope and X-ray diffraction.The thermal stability of iron remover was tested by differential thermal analysis.The effect of iron removing process on the fluidity of zinc liquid and the quality of coating was studied by measuring the fluidity of zinc liquid.The effects of iron in liquid zinc,the content of iron removal agent,and the temperature and time of iron removing progress on the average iron removal rate were analyzed.The optimized components of the iron-removing agent are chloride salt（NaCl+ZnCl₂）25wt.%,Al powder 12wt.%,bentonite 24wt.%,NaF 8wt.%,NH₄Cl 16wt.%and NaNO₃15wt.%.The optimized parameters of iron removal process:the amount of iron removal agent is 3wt.‰,the tempreture of liquid zinc is 450℃and the time of iron removing is 60minutes.Under the optimum process conditions,the average iron removal rate of the zinc liquid is 42.53%.The fluidity of zinc liquid was improved by adding iron removing agent.The zinc liquid with iron content of 0.035%is added with the iron-removing agent,and the fluidity of it is increased by 9.1%.The thickness of the coating becomes thinner.Theδphase layer in coating becomes more uniform and the thickness of theζphase layer becomes thinner.Al in iron removal agent reacted with iron in the zinc liquid to form Fe₄Al₁₃ with lower density,which can be separated easily from zinc liquid.The melting point of the Al-NaCl-ZnCl₂ iron removing agent is about 349.9℃.The melting point of the Al-NaCl-ZnCl₂-NaF iron removing agent is reduced to 321.6℃.The melting point of Al-NaCl-ZnCl₂-NaF-NaNO₃ iron removing agent decreases to 294.4℃,which improves the fluidity and dispersibility of it.