Theoretical And Technological Study On Ammonia Leaching Of High-phosphorus And Low-grade Rhodochrosite Ore

Manganese ore is an important raw material for smelting ferromanganese alloy.With the increase of steel production in China,the demand for manganese ore is increasing gradually.However,93.6%of manganese ore resources in China are low-grade manganese ore.Relying on the output of local manganese ore cannot meet the needs of the development of China's iron and steel industry.The gap between the supply and demand of manganese ore is more than 10 million tons all the year round,so the utilization technology of low-grade manganese ore development is imperative.More than 49.6%of manganese ore in our country is high phosphorus and low-grade rhodochrosite,this kind of manganese ore of low grade of manganese(Mn<20%),high phosphorus manganese ratio(P/Mn>0.01),phosphate rock distributed embedded throughout manganese ore stone,separation is difficult,how to effectively reduce the phosphorus content of high phosphorus low-grade rhodochrosite and improve its grade of manganese is an important topic of the manganese industry researchers concern at home and abroad.Ammonia leaching has the advantages of good selectivity,less waste liquid and high purity of product in the beneficiation of many high-phosphorus and low-grade rhodopsinite ores,which shows a good prospect.But current deal about ammonia leaching manganese research focused on the manganese steel slag,high-iron manganese ore and low grade pyrolusite,for ammonia leaching of high phosphorus low-grade rhodochrosite processing research is still lack,especially lack research of high phosphorus low-grade rhodochrosite roasting process of phase transition and the behavior of impurities,ammonia leaching process of the dissolution behavior of manganese and manganese phosphate separation characteristics problems in ammonia leaching process.Based on problems exist in ammonia leaching method treatment of high phosphorus low-grade rhodochrosite,for the roasting—ammonia-ammonium carbonate leaching—evaporation process,roasting phase transformation rule and microstructure characteristics,behavior and control of the impurity in the roasting process,manganese and phosphorus dissolution behavior of the ammonia-ammonium carbonate solution and evaporation process.The results show that the ammonia-leaching process can realize the efficient extraction of manganese and the effective separation of phosphorus from the high-phosphorus and low-grade siderite,which lays a foundation for the theory and practical application of the ammonia-leaching technology for the treatment of high-phosphorus and low-grade siderite,and is conducive to promoting the resource utilization of high-phosphorus and low-grade siderite in China.The specific research results of this paper are as follows:? By means of ICP-OES,XRD and SEM,the properties of the high-phosphorus low-grade rhodamine were characterized,and the chemical composition,mineral composition and distribution characteristics of main elements of the high-phosphorus low-grade rhodamine were found out,which provided basic data for the experiments of roasting,ammonia leaching and evaporation.The Mn content of high-phosphorus and low-grade rhodochromine is 18.62%,P content is 0.42%,P/Mn=0.022,and the main phases are MnCO3,CaMg(CO3)2,Ca(Fe,Mg)(CO3)2 and SiO2.In manganese ore,P is dispersed in all regions of manganese ore.Si and Mn have obvious distribution boundaries.Mn and Si in manganese ore belong to different mineral phases.The Ca and Mg have a very similar distribution pattern.The Ca and Mg in manganese ore exist in the form of CaMg(CO3)2.? The phase transformation and microstructure changes of the main components of high phosphorus and low grade rhodochrosite under different roasting atmosphere were investigated.The influence of roasting factors on manganese leaching rate was analyzed.High phosphorus and low grade rhodochrosite is roasted in different atmospheres(nitrogen atmosphere,air atmosphere and carbon dioxide atmosphere)to produce different products.MnO is produced when High phosphorus and low grade rhodochrosite is roasted in nitrogen atmosphere and carbon dioxide atmosphere,while Mn2O3 is produced when roasted in air atmosphere.The temperature required for MnO roasting under nitrogen atmosphere is 700?,which is lower than about 100? under carbon dioxide atmosphere.From the perspective of obtaining the MnO required in the subsequent ammonia leaching process and energy saving,this paper chooses to prepare MnO by roasting high phosphorus and low grade rhodochrosite in nitrogen atmosphere.The effect of roasting temperature and roasting time on manganese leaching rate under nitrogen atmosphere was investigated.When the roasting temperature was less than 500?,the structure of MnCO3 was not damaged and the manganese leaching rate was low.When the roasting temperature was 600??700?,MnCO3 was gradually decomposed into MnO,and the leaching rate of manganese gradually increased.When the roasting temperature exceeds 700?,the particle size of roasted sand increases obviously,the specific surface area decreases sharply,the pore volume and pore size of roasted sand particles decrease significantly,and manganese leaching decreases significantly.The suitable conditions for the preparation of MnO were established:the leaching rate of manganese reached 83.3%after roasting at 700? for 60min in the atmosphere of nitrogen.?Behavior and control of main impurity SiO2 and CaMg(CO3)2 in roasting high phosphorus and low grade rhodochrosite were studied.SiO2 reacts with MnO produced by decomposition of MnCO3 during roasting to produce insoluble MnSiO3,which is an important reason for low manganese leaching rate in ammonia leaching process.To solve the problem of low manganese leaching rate in ammonia leaching,this paper proposed a method that can effectively improve manganese leaching rate in ammonia leaching,namely using NaOH solution for desi pretreatment.Without de-Si pretreatment,the leaching rate manganese was 82.4%.High phosphorus and low grade manganese ore was added to NaOH solution with a concentration of 25%at a temperature of 85? and a liquid-solid ratio of 5:1,and de-Si pretreatment was carried out for 60min.The Si removal rate in high phosphorus manganese ore was greater than 95%,and the manganese leaching rate could be increased to 91.2%.? The dissolution behavior of MnO in ammonia-ammonium carbonate solution in high phosphorus and low grade rhodochrosite roasted sand was studied theoretically,and the influence of pH value,total ammonia concentration and total carbon concentration on the concentration of manganese ions in the solution was revealed,which provided a theoretical basis for the development of ammonia leaching experiment.When MnO was dissolved in ammonia-ammonium carbonate solution,a variety of manganese-based ions would be generated,including manganese ions,manganese ammonia complex ions and manganese hydroxyl complex ions,which would convert to each other with the change of pH of the solution.The change trend of manganese-based ions in ammonia-ammonium carbonate solution with the increase of pH is free manganese ions and MnHCO3+?manganese ammonia complex ions?manganese hydroxyl complex ions.The pH of ammonia-ammonium carbonate solution was 10?11,which was suitable for MnO dissolution.Increasing the total ammonia concentration or total carbon concentration of ammonia-ammonium carbonate solution can increase the concentration of manganese ammonia complex ions.The experimental results of MnO dissolution properties show that the total manganese-based ions concentration in ammonia-ammonium carbonate solution increases with the increase of total ammonia concentration and total carbon concentration,but the higher ammonia concentration and carbon concentration has no obvious effect on the increase of total manganese-based ions concentration.In ammonia-ammonium carbonate solution with total ammonia concentration of 12?16mol/L,carbon concentration of 2?3mol/L and pH of 9.8?10.4,the total manganese concentration is high(more than 70g/L),and the results of MnO dissolution characteristics test are consistent with theoretic calculated results.? The leaching rule of phosphorus and manganese as well as the separation characteristics of phosphorus and manganese were studied in the process of ammonia-ammonium carbonate leaching.The effect of leaching temperature,particle size and liquid-solid ratio of ammonia and ammonium carbonate on leaching rate of phosphorus and manganese were researched.The optimum conditions for ammonia leaching were as follows:ammonia concentration was 14mol/L,ammonium carbonate concentration was 2mol/L,leaching temperature was 25?,stirring speed was 200r/min,particle size was-200 mesh,liquid-solid ratio was 5:1,leaching time was 120min,the leaching rate of manganese was 91.2%,99.08%of phosphorus entered the leaching residue,effectively realized the separation of phosphorus and manganese.Kinetic analysis showed that the reaction of calcined sand in ammonia-ammonium carbonate solution was controlled by internal diffusion,and the reaction activation energy was 30.8kJ/mol.The kinetic equation of leaching could be expressed as follows:1-2/3?-(1-?)2/3=0.001C(NH3·H2O)5.5251C((NH4)2CO3)1.1648·(dp)-0.7702exp(-3704T)·t? The effects of temperature and time of ammonia distillation on pH value and manganese precipitation rate were investigated.The ammonia molecules in the ammonia leaching solution,which are ammonium ions,NH4+and free ammonia converted into gas phase,escape from the solution by evaporotion.The reduction of the stability of the manganese ammonia complex and leads to the decomposition of the manganese ammonia complex into MnCO3 precipitation.Under the condition of evaporation temperature of 85? and evaporation time of 30min,the pH value of the solution decreased to 9.1,and the Mn precipitation rate reached 95%.The main component of evaporated product is MnCO3,the content of Mn is 44.12%,the content of P is 0.02%,and the content of Ca and Mg are 1.37%and 1.85%respectively.? When the ammonia leaching method was used to treat high phosphorus and low grade rhodochromine,the leaching rate of manganese reached 91.2%,and 99.08%of phosphorus entered the leaching residue.Manganese carbonate powder with high content of manganese and low content of impurity was obtained by calcination,ammonia-ammonium carbonate leaching and evaporation.The content of manganese and phosphorus in high-phosphorus and low-grade rhodochrosite is 18.62%and 0.42%,respectively.The content of manganese and phosphorus in the manganese carbonate powder obtained by roasting-ammonia-ammonium carbonate leaching-evaporation process is 44.12%and 0.02%,respectively,P/Mn=0.00045.The content of impurities is low,which meets the standard of industrial manganese carbonate grade one product.The ammonia leaching method has the advantages of good phosphorus and manganese separation and high purity of manganese carbonate,which is worth further popularizing.