Mineralogical Characteristics Of Guizhou Zhenning Devonian Barite And Its Solid Phase Reaction Behavior In The Carbothermal Reduction Process

Barite is the main raw material for barium salt production.Guizhou Province is the most important barium salt production base in the world for its rich barite resources and known as"the world barium salt in China,China barium salt in Guizhou".Barite carbothermal reduction is the main method of barium salt production,but there are some problems in this process,such as low conversion of BaSO₄,large slag and high energy consumption.Improving the conversion of BaSO₄ in barite carbothermal reduction process has always been a hot topic in this field.With the transformation and upgrading of China's industry,the demand for intensive use of resources and environmental protection,it is more urgent to solve the major common key technical problems in this field.However,the current research is mainly based on the chemical reaction principle of the carbothermal reduction process,focusing on the macro-properties of the process and optimization of process parameters,while little attention is paid to the mineralogical characteristics of barite and the complex solid-state reaction behavior of the carbothermal reduction process,which may be one of the main reasons for the unsatisfactory research results of barium salt production technology by carbothermal reduction of barite at present.The process of barite carbothermal reduction is essentially a phase transformation process from BaSO₄ to BaS.Barite,however,is a non-metallic mineral mixture mainly composed of barium sulfate?BaSO₄?,which is often associated with gangue minerals such as quartz,clay,sericite and limonite.In the actual reaction process,these mineral components will participate in complex solid-state reactions that including solid-solid reaction,gas-solid reaction,carbon-gasification reaction,heat transfer,mass transfer and material diffusion during the high temperature carbothermal reduction process.Mutual restriction or mutual promotion of various reactions in the system may affect the solid-state reaction of BaSO₄ phase to BaS phase,resulting in a low BaS conversion in barite carbothermal reduction process.This paper takes Zhenning barite deposit,a typical large sedimentary barite deposit in China,as the research object.Based on the systematic study of mineral characteristics,the phase transformation behavior and reaction mechanism of barite carbothermal reduction were systematically studied by means of thermodynamics,dynamics,molecular simulation and experimental mineralogy methods.According to the phase transformation law based on the study,the corresponding control measures are put forward to optimize the experimental results.The development of the paper can provide basic data,theoretical guidance and technical support for the improvement of the actual barite carbon thermal reduction process.The main findings are as follows:?1?The Zhenning barite deposit in Guizhou Province is horizontally stable and is vertically divided into three sedimentary deposits separated by thin siliceous rocks and siliceous dolomite.The ore types are mainly massive,banded and laminated.The content of Sr,Cu,Zn,Cl,Ni,Nb and other trace elements in the ore is relatively high,Sr element is enriched,MgO is depleted,and it has obvious sedimentary rock characteristics.?2?The main phase of barite is BaSO₄ with orthorhombic system,and the main gangue minerals are mainly quartz,sericite and limonite.Among them,the content of SiO₂ with hexagonal system is the highest.?3?The thermodynamic analysis and calculation by the atomic matrix method showed that 10independent reactions exist in the carbothermal reduction process of barite.It mainly includes the reduction of BaSO₄,the gasification of C and the formation of acid-soluble barium salts during the carbothermal reduction process of barite.?4?Through the combination of thermodynamic calculation and experimental mineralogical experiment,it is found that the generation of acid-soluble barium is mainly contributed by SiO₂side reactions.Reducing impurity content and increasing reaction temperature are beneficial to the improvement of barite conversion.?5?The kinetic analysis shows that the carbothermal reduction process of barite was mainly controlled by a gas–solid topochemical reaction,and the kinetic equation can be expressed by Erofeev equation,as following:ln[-ln?1-x?]=nlnt+lnk.At the same time,the process is also affected by heat and mass transfer.?6?During the barite reduction process,SiO₂ has undergoing crystal transition from quartz phase to tridymite phase and cristobalite phase.At this time,SiO₂ can easily react with barium salt to form BaSiO₃ and Ba₂SiO₄,which results in the decrease of conversion to BaS.Fe₂O₃ is easily reduced to Fe₃O₄ and Fe by carbon in the system,and then reacts with barium salts to produce acid-soluble barium.Al₂O₃ mainly forms Al₂O₃-SiO₂ solid solution with silica,and then reacts with barium salts in the system to form barium aluminosilicate.?7?Molecular simulations show that O atom has the strongest reactivity in BaSO₄cell.In the carbothermal reduction process of BaSO₄,CO molecule can form dominant oxygen adsorption on the surface of BaSO₄,which leads to the weakening and breaking of Ba-O bond in BaSO₄;C atom can enter into BaSO₄ supercell and interact with O atom,and the C-O distance is close to the bond length of free CO,which indicates that it has formed the trend of deoxidization reaction.Under the same simulated conditions,more CO molecules were added and distributed uniformly on the surface of BaSO₄ compared with C,indicating that the interaction force between CO and BaSO₄was stronger than that between C and BaSO₄.?8?The reaction surface method was used to optimize the carbothermal reduction process of barite,which showed that the calcining temperature had the greatest influence on the conversion of BaS,and the size of grain was second.And the optimized process parameters are:calcination temperature 950?,calcining time 30min,raw material ratio 3:1,raw material size 200Mesh,and under this condition,the conversion rate of barium sulfide is 90.2%.?9?The barite sample in Zhenning,Guizhou,was treated by chemical flotation,and the barite samples with different impurity content were obtained.The effect of impurity content on the carbon thermal reduction conversion rate of barite was investigated.It is found that,as the main impurity in Zhenning barite ore in Guizhou Province,SiO₂ is concomitant with BaSO₄ mainly in the form of independent mineral quartz,and about 1.5%of SiO₂ exists in the form of BaSO₄inclusion;flotation technology can realize separation of BaSO₄ and SiO₂ very well,but it's difficult to separate SiO₂ existing in the form of inclusion.The effect of SiO₂ on barite carbothermal reduction reaction is mainly due to the influence of SiO₂ existing in the form of independent minerals.With the increase of SiO₂ content,the conversion rate of water soluble barium decreased and barium acid transformation rate increased.?10?By comparing the anaerobic reduction of barite to the aerobic reduction system,it is found that the anaerobic reduction system can reduce the carbon thermal reduction temperature of barite about 100?,but at the same time it promotes the formation of barium silicate under anaerobic conditions,which makes the water-soluble conversion rate of barite is not significantly higher than that of aerobic system.?11?The carbon thermo reduction reaction of barite is regulated by adding carbonate mineralizer.It is found that CaCO₃,Na₂CO₃and K₂CO₃can promote the carbon gasification reaction in barite and reduce the carbon thermo reaction temperature.When adding CaCO₃,the conversion of BaS is the most promising at 850?,and it also has the function of sulfur removal and desilication,and makes clinker loose compared with that non-mineralizer.