Pretreatment Of Secondary Aluminum Ash And Preparation Of Aluminum-magnesium Spinel Refractory Materials

Secondary aluminum ash（SAD）is a solid waste in aluminum production enterprises,there is a certain leaching toxicity,reactivity,but because it contains a large number of metal aluminum and alumina,it has a high recycling value.Through composition analysis and XRD phase detection,secondary aluminum ash contains 13.98%metallic aluminum and 36.86%Al₂O₃is a useful component required for aluminum magnesium spinel raw materials,but due to the containing NaCl,KCl and K₂Na Al F₆,these substances will adversely affect the performance of refractory materials,and need to be recovered and removed before being used as a refractory raw material for the preparation of aluminum magnesium spinel.In the secondary aluminum ash wash recovery chloride and fluoride,the optimal condition for chloride and fluoride removal is the solid-to-liquid ratio of 1:4,the water immersion temperature is 65℃,and the stirring time is 30 min.After washing,the contents of Na,K,F,Cl and N were 1.46%,1.10%,2.70%,1.20%and 6.91%,respectively,and the removal rates of each element were 86.81%,72.00%,45.08%,87.68%and 47.91%.The main phases of washed aluminum slag are Al2O3,Al（OH）₃,Mg₂AlO₄and a small amount of fluoride and aluminum nitride;After the filtrate evaporates and crystallizes,the phases are NaCl,KCl and NaF.The best conditions for the removal of impurities obtained by high-temperature roasting of secondary aluminum ash obtained after water washing are roasting temperature of 900℃and heat preservation time of 1 h.Under these conditions,aluminum nitride can be completely converted into alumina,and the exfoliation rates of Na,K,F,Cl and N elements are 16.43%,37.18%,98.74%,97.42%and 98.58%,respectively.The content of secondary aluminum ash impurity elements Na,K,F,Cl and N decreased to 1.22%,0.69%,0.03%,0.03%,0.10%.Calcined pretreated secondary aluminium ash can be used for subsequent production of aluminum-magnesium spinel materials.After the treatment of aluminum ash with 10%MgO,1650℃sintering for 1 h can form a higher content of aluminum-rich magnesium aluminum spinel;with 20%MgO,at1550℃can form a higher content of magnesium aluminum spinel phase,the impurity phase content is the least,the impurity phase is composed of sodium feldspar and nepheline,Na,K and other elements are also present in these two heterogeneous phases;when adding 30%MgO,magnesium olivine（Mg₂SiO₄）phase will appear,of which1650℃will change the liquid phase,deteriorating the refractory performance.Among the three factors of magnesium mass fraction,sintering temperature and holding time,the magnesium mass fraction has the greatest impact on the performance of aluminum magnesium spinel refractory,followed by sintering temperature and holding time,and the best process conditions for the preparation of aluminum magnesium spinel refractory materials are 20%magnesium mass fraction,sintering temperature 1550℃,and heat preservation time 5 h.At this time,the average flexural strength of the spinel material is 76.53 MPa,the bulk density is 3.05 g/cm³,and the apparent porosity is 14.35%,which is in line with the national standard GB/T2275-2017,and can be used as a spinel refractory material.The optimal conditions for the secondary optimization of the aluminum-magnesium spinel process are 24%of the magnesium mass fraction,sintering temperature of 1625℃,and the holding time of 6 h,at this time,the average flexural strength of the aluminum-magnesium spinel material is 106.72 MPa,the bulk density reaches the maximum value of3.42 g/cm3,and the porosity reaches the minimum value of 8.83%,which can be used as a high-quality refractory material.