Study On Purification Process Of Aluminum Alloy Polishing Liquid

It has the advantages of strong applicability,low price and convenient operation to polish aluminum profile surface with diacid polishing solution.However,aluminum ions are continuously dissolved in the polishing solution during repeated use,which eventually leads to the failure of the polishing solution.Waste polishing fluids with high acidity and corrosiveness are expensive and difficult to treat.Therefore,the recovery and recycling of aluminum profile polishing fluid can not only save resources and costs,but also improve the environmental pollution problems in the industry,which has important practical significance.In this thesis,aluminum ions in diacid polishing solution were removed by fluoride precipitation method.In order to reduce the aluminum ion content in the polishing solution,the ammonium fluoride and the mixture of sodium hydroxide and potassium hydroxide were used as precipitants to convert the aluminum ions in the polishing solution to K₂NaAlF₆.The optimum technological conditions were as follows:molar ratio of fluoride ion to aluminum ion 5:1(n?F^-?:n(Al³⁺)=5:1);molar ratio of the mixture of sodium ion and potassium ion to aluminum ion 2:1(n?Na⁺+K⁺?:n(Al³⁺)=2:1),in which molar ratio of sodium ion to potassium ion is 1:2?n?Na⁺?:n?K⁺?=1:2?;reaction temperature 50?;reaction time 40 min,and static time 1 day.Under those conditions,the removal rate of aluminum ion is 95.43%,and the content of fluoride ion in polishing solution is 0.15%.It not only achieves better effect of removing aluminum,but also controls the content of fluoride ion in polishing solution in a lower range.The precipitation was analyzed by X-ray diffraction?XRD?.The results showed that the precipitation was Na₅AlF₁₄ and K₂NaAlF₆,respectively,when sodium hydroxide,the mixture of sodium hydroxide and potassium hydroxide were used as precipitator.The morphology of the precipitates was characterized by scanning electron microscopy?SEM?,and it was found that the morphology of Na₅AlF₁₄ and K₂NaAlF₆ were significantly different.Among them,K₂NaAlF₆ particle size is larger,which is conducive to solid-liquid separation of suspension.The composition of precipitate and the proportion of each element were determined by chemical method and X-ray energy spectrum?EDS?respectively.The results showed that the precipitation product was K₂NaAlF₆ and the impurity content was low,which was consistent with the XRD results.On the basis of laboratory scale-up experiments,pilot-scale experiments were carried out.The optimum technological conditions of pilot-scale experiments were as follows:molar ratio of fluoride ion to aluminum ion 5.5:1(n?F^-?:n(Al³⁺)=5.5:1);molar ratio of the mixture of sodium ion and potassium ion to aluminum ion 2:1(n?Na⁺+K⁺?:n(Al³⁺)=2:1),in which molar ratio of sodium ion to potassium ion is 1:2?n?Na⁺?:n?K⁺?=1:2?;reaction time40 min;stirring speed 50 r/min until the end of the reaction and static time 3 days.The removal rate of aluminum in the waste polishing liquid reached 94.8%,and the content of the fluoride ion in the waste polishing liquid was 0.14%,respectively.According to the cost estimation,it can be seen that the treatment of waste liquor by chemical precipitation method has low cost and good economic benefits.