Study On The Reaction And Regulatory Mechanism Of Nickel Sulfide Concentrate During Sulfation Roasting Process

Nickel,one of the most important strategic non-ferrous metals in China,plays a supportive and leading role in the development of the high-tech national defense industry and new energy field.And the consumption of nickel is increasing year by year in China.The reserves of nickel ore resources in China are relatively abundant.Jinchuan sulfide nickel ore accounts for more than 70%of the country's nickel resources,of which low grade nickel sulfide ore accounts for more than 65%.Synchronous separation and extraction of valuable metals from low-grade nickel sulfide ores is an important breakthrough in nickel metallurgy,and it is of great strategic importance to promote the development of nickel industry in China.With the difficulty of flotation of low-grade nickel sulphide ore,the grade of concentrates decreases year by year.It has been difficult to achieve high-efficiency simultaneous extraction and separation of nickel,cobalt and copper by the traditional pyrometallurgical smelting process.The sulfation roasting-water leaching process combines the advantages of pyro-and hydrometallurgy.This process is theoretically feasible to handle complex low-grade polymetallic sulfide ore,and is expected to achieve the synchronous separation and extraction of valuable metals environmentally friendly and efficiently.Therefore,how to optimize the roasting process to increase the extraction rate of valuable metals,horten and simplify the process,which is a technical bottleneck problem of the sulfation roasting of nickel sulfide ore and needs to be solved urgently.In this dissertation,Jinchuan Sulfide Nickel Ore is selected as the research object,and a fixed bed sulfation roasting process is used to realize the high-efficiency extraction of nickel,cobalt and copper simultaneously from polymetallic sulfide ore.extract.The pathways and mechanisms for the selective sulfation roasting with the addition of Na2SO4,(NH4)2SO4,and NH4Cl,have been explored.Different roasting routes were selected for different additives.The phase reconstruction mechanism and its regulation mechanism during the roasting procee were further explored.Firstly,the oxidation mechanism of nickel sulfide concentrate during continuous temperature roasting pocess under static air atmosphere was studied.The possible phases formed during the oxidation roasting process were accurately predicted by phase diagram calculations.The in-situ high-temperature XRPD was used to characterize the phase transformation of nickel sulfide concentrates during the oxidized roasting process.Combined with EDS mapping analysis,the internal migration of pentlandite and chalcopyrite particles in the oxidation process was characterized in detail.The results show that under the static air atmosphere,the surface Fe of pentlandite and chalcopyrite particles preferentially oxidizes during the continuous temperature-rising oxidation process of Jinchuan sulfide sulfide concentrate,and the mineral particles form an outer layer of Fe-rich coating as the reaction progresses.Subsequently,Fe,Cu,and Ni were successively sulfated to produce Fe2(SO4)3,CuSO4 and NiSO4,respectively.In the roasting process,chalcopyrite or iron-deficient chalcopyrite can directly sulfate;While pentlandite is first decomposed into monometallic sulfides,and then gradually oxidized to NiSO4 and NiO,thus the degree of sulfation is lower than chalcopyrite.When the temperature is higher than 700oC,the nickel sulfide ore can easily generate a large number of high-temperature stable phases-spinel-type ferrite(NiFe2O4 and CuFe2O4).If appropriate regulation measures can be taken to increase the degree of sulfation of Ni,it is entirely possible to achieve efficient sulfation of the valuable metals(Ni,Co,and Cu)in the nickel sulphide concentrates through the continuously heated sulfation roasting process.Based on the study of the sulfation of valuable metals during the continuous temperature-rising roasting process of nickel sulfide ore,Na2SO4 was selected as an additive,and a heating-holiding two-stage roasting process was designed.After optimization of the process parameters,the water leaching extraction rates of Co,Ni,and Cu in the calcine were all higher than 90%,while the leaching rates of Fe were lower than 1%.During the roasting process,Na2SO4 reacted with the metal sulfate to form a large amount of liquid phase of eutectic compound sulfate(Na2SO4-M*SO4),which was wrapped on the surface of the solid mineral particles.The sulfate liquid medium can dissolve the buffered SO2,and provide the gas-liquid-solid three-phase reaction interface for the sulfation reaction.In addition,the liquid-phase coating also has a large heat capacity and can improve the interface heat transfer in strong exothermic sulfation reactions.Therefore,the Na2SO4 additive perfectly achieves the coupling of the thermodynamic and kinetic factors of the sulfation roasting of valuable metals during the two-stage roasting process,which improves the utilization of excess sulfur in the mineral and greatly promotes the sulfation of the valuable metals.This process breaks the technical bottleneck of the Ni leaching rate below 80%in the conventional sulfation roasting process of nickel sulfide ore,and is expected to develop into a green and highly efficient metallurgical new process for low-grade nickel sulfide minerals.Considering that Na2SO4 additive would bring Na~+impurities into the leachate,(NH4)2SO4 was selected as an additive,and a three-stage roasting process was proposed.After optimizing the roasting process parameters,the leaching rates of the valuable metals Co,Ni,and Cu in the calcined sand can reach 90%,80%,and 98%,respectively,while the leaching rate of Fe is less than 1%.The results show that(NH4)2SO4 can react directly with Fe-bearing sulfide in the low temperature stage to produce relatively stable intermediate phases of NH4Fe(SO4)2 and Fe2(SO4)3.As the roasting temperature increases,NH4Fe(SO4)2 and Fe2(SO4)3 gradually decompose to release SO3 gas,increase the SO2/SO3 partial pressure at the reaction interface,and thus promote the sulfation of Ni-containing sulfides.Taking the large amount of(NH4)2SO4 additive into account,NH4Cl is selected as an additive and a three-stage roasting process is proposed.After optimizing the process parameters,the water extraction rates of Ni,Co,and Cu can reach 97%,95%,and99%,respectively,while the leaching rate of Fe can be controlled at about 1%.During the holding process at 250 ~oC,NH4Cl chlorinated directly with polymetallic sulphides to form a variety of monometallic sulphides and chlorides.Then the metal chloride salt acts as a strengthening agent for sulfation and reacts with unreacted sulfides to generate a large amount of metal sulfates and release Cl2 during the heating stage,which finally realizes the efficient sulfation of valuable metals.Compared with Na2SO4,NH4Cl not only does not bring in impurity elements,but also can be recycled.Compared with(NH4)2SO4,the effect of NH4Cl for strengthening sulfation is more significant and the dosage is lower.Therefore,based on the characteristics of China's nickel sulfide resources,combined with the advantages of pyro-and hydro-metallurgy,the sulfation roasting-water leaching process has theoretical and practical feasibility to handle the low-grade nickel sulfide ores.In this dissertation,Three roasting routes with different additives(Na2SO4,(NH4)2SO4 and NH4Cl,respectively)were designed to achieve high-efficiency simultaneous extraction of Ni,Co,and Cu,which is expected to become a new technology route for handling low-grade complex polymetallic sulfide mineral resources.