Study On Mechanism And Kinetics Of Nitric Acid Leaching Limonitic Laterite Ore

Limonitic laterite ore is an important resource rich in nickel,cobalt,and iron with significant comprehensive utilization value.Nitric acid pressure leaching of limonitic laterite ore not only achieves efficient leaching of associated components such as nickel,cobalt,aluminum,and scandium,as well as low-cost regeneration and recycling of nitric acid,but also achieves the enrichment of iron in leaching residue,which provides a good foundation for the reduction of"residue-free smelting".However,current research on nitric acid pressure leaching of limonitic laterite ore is mostly limited to process optimization and parameter studies,with little emphasis on the key leaching mechanisms and corresponding kinetics.Therefore,based on the nitric acid leaching of limonitic laterite ore,this study conducted fundamental research using a combination of macroscopic experiments and microscopic simulations around the leaching mechanism and kinetics of limonitic laterite ore,and obtained a series of research results.Taking the main phases of limonitic laterite ore(goethite and serpentine)as the research object,first-principles calculation was introduced to clarify the locations of nickel and cobalt in goethite and serpentine and the influence of nickel and cobalt on crystal structure.The substitution energy and formation energy showed that nickel tended to be stored in the octahedral tunnels of goethite,followed by the substitution of iron.Cobalt tended to be stored in the form of replacing iron,followed by storing in the octahedral tunnels of goethite.Nickel in serpentine tended to be stored in the interlayer of Si-O tetrahedron and Mg-O octahedron,followed by substitution of magnesium.When nickel and cobalt are stored in goethite and serpentine,the octahedral double chains of goethite and the layered stacking cells of serpentine are preferentially rotated.Therefore,the storage of nickel and cobalt has little effect on the bond length of goethite and serpentine but has a great effect on the bond angle.Under the atmospheric leaching system,the leaching of Ni can be described by the cylindrical particle-grain model.During the initial stage of leaching,the leaching is controlled by a chemical reaction with activation energy of 88.4 kJ/mol.In the late stage of leaching,the reaction is controlled by pore diffusion,with a diffusion coefficient of 1.37×10-11 m2/min at 90℃.Under the pressure leaching system,the leaching of Ni can be described by the grain model-pore diffusion-cylindrical particle,with a diffusion coefficient of 4.59×10-10 m2/min at 210℃.It is found that pressure leaching mainly accelerates the chemical reaction process in the pre-reaction stage and also increases the diffusion coefficient by an order of magnitude.The E-pH of the Mg-Si-Fe-H2O system shows that silicic acid is generated during the atmospheric leaching of limonitic laterite ores,and silicic acid affects the filtration performance of the pulp while adsorbing valuable metals.In contrast,under pressurized leaching conditions,Si and Mg formed silicate phases,and the filtration performance of the pulp was improved.Inspired by the porous kinetics study,two schemes for intensifying the limonitic laterite ore leaching were proposed,namely,bleeding air treatment and the addition of surfactants.Intensification experiments showed that both the bleeding air treatment and the addition of surfactants could effectively enhance the leaching of limonitic laterite ore.Among them,the intensification effect of DTAB was the best,and under the optimal process condition,the nickel extraction was increased by 5.7%under atmospheric pressure leaching(98℃,3.5 h,4.7 mL/g,487 g/L)and by 5.22%under pressure leaching(194 ℃,75 min,3.4 mL/g,178 g/L).In addition,it was found that DTAB could not only enhance the leaching of laterite ore but also improve the filtration performance of the atmospheric leaching slurry.When DTAB exists,its filtration rate is more than three times that without surfactants.The mechanism analysis of intensification indicated that the intensification effect of bleeding air was mainly to eliminate the obstruction of gas in the pores to the leaching reaction,thus accelerating the leaching reaction,and the intensification effect of surfactants was mainly based on the improvement of diffusion efficiency,the reduction of adsorption and the increase in permeability.The dissolution of goethite is an outward-moving disintegration process.Based on first principles calculations,H+ attacks the bridging O first,destroying the crystal structure of goethite,while NO3-attacks the surface Fe,accelerating the dissolve out of Fe from the crystal.Both H+and NO3-adsorption on goethite is chemical adsorption.The phase analysis of the leaching residue at different leaching stages shows that the pattern of hydrochloric acid and sulfuric acid leaching of limonitic laterite ore is consistent with that of nitric acid.The H+ plays a critical role in the disruption of goethite’s structure.By the calculation and fitting of Eyring equation,the lowest energy path for the removal of structural oxygen atoms and hydroxyls was found,and the process of water molecule removal was identified as the controlling step in the dissolution of goethite.In the atmospheric leaching systems,Cl-has a promoting effect on the extraction of valuable metals,while SO42-and NO3-have little effect.In the pressure leaching system,under the same leaching conditions,nitric acid pressure leaching of limonitic laterite is more complete than sulfuric acid pressure leaching,which is manifested as higher nickel extraction and more thorough iron hydrolysis.The difference in goethite dissolution is mainly due to two aspects:First,SO42has the highest adsorption energy,followed by Cl-and NO3-with the lowest adsorption energy.In addition,the size of the acid anion itself and the inhibition of water molecule removal also cause the difference in leaching goethite.