Magnesium Recovery Process And Mechanism Using Ferronickel Slag As Resource

Ferronickel slag is the industrial waste produced in the process of ferronickel production.Generally,10-14 tons of ferronickel slag can be produced for one ton of ferronickel product.It has become the fourth largest metallurgical solid waste after iron slag,steel slag and red mud.Ferronickel slag usually contains valuable metal elements such as magnesium,nickel,iron and chromium.The content of magnesium oxide in ferronickel slag produced by electric furnace or rotary kiln is about 30%,which has high recovery value.This paper attempts to recover magnesium from ferronickel slag for the first time.Due to the advantages of wet recovery,such as good working conditions,easy to realize automation and comprehensive recovery,this paper uses this method to recover magnesium.The whole recovery process mainly includes ball milling,sulfuric acid leaching,vacuum filtration,cooling crystallization,washing and drying processes,and finally the relatively pure hydrated magnesium sulfate crystal is obtained.In this paper,the process of magnesium leaching by sulfuric acid is studied.Firstly,the feasibility of magnesium leaching by sulfuric acid is predicted by thermodynamic calculation.Under this premise,the influence of sulfuric acid concentration,leaching time,leaching temperature and stirring rate on the leaching rate was systematically studied by single factor leaching test,among which the influence of leaching temperature was more significant.In order to further improve the leaching rate of magnesium,nitric acid and hydrogen peroxide were selected as cosolvent,in which nitric acid had a significant effect on the leaching rate of magnesium.The results of orthogonal experiment of magnesium leaching showed that when the acid concentration was 15 mol/L,the leaching temperature was 180?,the leaching time was 120 min,the ratio of liquid to solid was 20:1,and 5% nitric acid was added as cosolvent,the leaching rate of magnesium reached 84.45%.The leaching kinetics shows that the leaching process of ferronickel slag belongs to the core shrinking model controlled by interface chemical reaction,which can be further confirmed by XRD and SEM analysis results.The activation energy?EA?is 12.72 kJ/mol.The best leaching solution was filtered to get magnesium sulfate solution for crystallization.The results of the orthogonal experiment of magnesium sulfate crystallization show that the crystallization rate of magnesium sulfate reaches 86.32%,when the initial crystallization temperature was 90?,the final crystallization temperature was 25?,the crystallization time was 10 hours,the stirring speed rate was 50 r/min and the seed coefficient was 0.5.However,there is still a small amount of sulfuric acid in the crystallization product.Because of its high boiling point,it is not easy to evaporate,which affects the purity of the crystallization product,so this paper uses ethanol cleaning.Under the condition of 3:1 liquid-solid ratio of ethanol washing solution and crystallization product,the sulfuric acid can be removed well by using the prefabricated slurry method,and the magnesium loss rate is only 3.18%.Under the best conditions of leaching,crystallization and proper washing,the crystal product was analyzed by XRD,and its phase was MgSO4·nH₂O?n=3,4,5? mixture,no other heterogeneous phase was found.Through ICP test,the content of MgSO₄ could reach 59.25%,if calculated according to 4.5 crystal water,the purity could reach 99.2%.