Fundamentals For Deep Reduction Of Jinchuan Nickel Flash Slag On Efficient Recovery Of Valuable Metals

Deep reduction-magnetic separation is put forward to treat the nickel flash smelting furnace slag of JinChuan,aiming to recover the iron,nickel,copper and cobalt metal.Using the deep reduction technology,the iron in the flash furnace slag is reduced to metal iron,and some nickel,copper and cobalt in the form of molten matte are reduced to metal.The valuable metals are recovered by grinding and magnetic separation of the deep reduction materials.The fundamental research provides a theoretical basis for the recovery of valuable metals in nickel flash smelting slag and has a guiding significance for the comprehensive utilization of flash slag to develop circular economy and environmental protection.Chemical composition,mineral composition and crystalline size of the slag and reduction were analyzed by optical microscope,x-ray diffraction,scanning electron microscopy and spectrum analysis.The result shows that the main chemical elements of flash furnace slag are iron,silicon and oxygen,contains a small amount of magnesium,calcium,sulfur,copper,nickel and cobalt.The main mineral composition is fayalite,contains a small amount of magnesium silicate and iron sulfide,nickel,copper and cobalt are distributed unevenly in the fayalite matrix in the form of matte.The thermodynamic calculation and simulation of the deep reduction process were carried out.The calculation shows that in the standard state,between the temperature of 1473K and 1623K,the C and CO can reduce iron complex compounds such as FeO·SiO2and 2FeO·SiO2,and can not reduce the non-ferrous oxides such as CaO,MgO,SiO2 and some kinds of sulfides in the matte.By using the HSC chemistry software to simulate the composition of the deep reduction equilibrium phase,it can be concluded that 2FeO·SiO2 is finally reduced to Fe and SiO2.The Ni,Cu and Co in the matte are partially reduced to metal elements.Adding CaO has an effect on the reduction of Ni,Cu and Co.The dynamics research of depth reduction shows the isothermal reduction process can be divided into three stages which are named the initial stage,middle stage and final stage.Dynamic mechanism function and restriction are different in three stages.The most probable mechanism function is chemical reaction model for the initial stage,and the 3-d diffusion(z-l-t)spread model for the middle stage,and the randomized nucleation and subsequent growth of avrami-erofeev Equation is a restrictive link in final stage of reducing.The XRD map analysis of the reduction process shows that the iron in olivine and magnesite is directly reduced to metal iron.The study of the formation and growth mechanism of metallic iron particles shows that temperature and time of the reduction has a significant effect on the average particle size of the metal particles.The dynamic model of the metal-particle growth can be used to describe the growth of metal iron particles.Research on the XRD,EDS and the surface scanning images of reduction product shows that nickel,copper and cobalt in the form of matte in the slag exists mainly in iron metal particles in the form of alloy or elemental after the deep reduction.Adding CaO impacts on the existential state and distribution of nickel and cobalt.The results show that the reducing temperature,reducing time,carbon coefficient and adding CaO have an important influence on the metallized ratio and particle size of metallic iron.The experiments show that the optimal conditions were reduction temperature of 1573 K,reduction time of 60 min,carbon coefficient of 2.0 and CaO dosage of 15%.Under the condition,the metallization rate of iron was 99.22%in the reduction product.The suitable technological conditions for the separation of reduction products are:the grinding fineness is 82.00 percentage of-0.045mm,two stage magnetic separation is used,the magnetic field strength is 800Oe and 600Oe,the concentrate with iron grade of 77.91%and iron recovery of 92.79%was obtained.In this paper,the research achievements deepens the understanding of the depth of slag reduction process,enriches the theory of depth reduction system of nickel flash furnace.Not only provides theoretical support for breaking down the key technical difficulties of the depth of nickel flash furnace slag but also a good reference to the efficient utilization of other smelting slags.