Research Of Preparation Of Zero-valent Iron Nanoparticles Using Oolitic Hematite

In this paper,the physicochemical properties and technological mineralogical characteristics of oolitic hematite in Guizhou are studied.Using oolitic hematite and pulverized coal as raw materials,Zero-valent iron nanoparticles?nZVI?is prepared by direct reduction-leaching-reduction in liquid phase process.The factors affecting preparation of nZVI with oolitic hematite are investigated by single factor test and orthogonal test.The concrete conclusions are as follows.The sample ore is typical of high phosphorus,high alumina and low sulfur oolitic hematite,and the grade of iron is 40.45%,the grade of phosphorus is 0.45%,the content of Al₂O₃ is 11.16%,the grade of sulfur is 0.057%;iron minerals are more complex,mainly contain hematite,limonite and siderite;secondly hematite,limonite,siderite and gangue mineral compose oolite,and the oolitic nuclei are mostly composed of dolomitic carbonate minerals and quartz sand.The ore is used for the processing of metallurgical iron concentrate,technology of separation and purification are limited.When sulfuric acid concentration is 20%,the ratio of liquid and solid is 10:1,leaching time is 30 min,leaching temperature is 25?,iron leaching rate of oolitic hematite is 5.34%;iron leaching rate of ore concentrate by magnetic roasting is 8.35%under the same leaching conditions;iron leaching rate of ore concentrate by direct reduction is 8.35%under the same leaching conditions,obviously the direct reduction process of the samples is more favorable.The condition tests of direct reduction show:The calcination temperature is between1000?and 1100?,the calcination time is between 60 min and 150 min,the ratio of carbon and oxygen is between 0.7-1.6,they are independent of each other that three kinds of factors affect iron recovery rate of direct reduction,and there are no obvious interaction,and descending order is calcination temperature,calcination time,the ratio of carbon and oxygen.The optimum conditions are as follows:the ratio of carbon and oxygen is 1.3,the calcination temperature is 1100?,and the calcination time is 120min.The recovery rate of magnetic concentrate is 75.22%.The XRD diffraction pattern shows that iron element which are not reduced mainly exists in hercynite and?FeO?₂SiO₂.The condition tests of leaching process show:During the leaching process of direct reduction magnetite concentrate,the concentration of sulfuric acid,the ratio of liquid and solid,the time of leaching are the main factors that affect the rate of iron leaching.Stirring speed,concentrate fineness and leaching temperature are secondary factors affecting iron leaching rate.When the leaching time is between 10min and 40min,the concentration of sulfuric acid is between 8%and 20%,and the ratio of liquid and solid is between 6:1 and15:1,descending order three factors affect the leaching rate is the concentration of sulfuric acid,the ratio of liquid and solid,the time of leaching.The optimum conditions are as follows:sulfuric acid concentration is 20%,leaching time is 30min,ratio of liquid and solid is 12:1 ml/g,stirring speed is 200r/min and leaching temperature is 20?,and the corresponding iron leaching rate is 81.83%.During leaching,hercynite is not leached causes the rate of iron leaching.The preparation experimental of nZVI by reduction in liquid phase show:the removal rate of Al and Si in leaching solution is 95.67%and 93.24%after adjusting pH of leaching solution to 5 with NaOH and filtering.After removing impurities,the filtrate is diluted to 0.02 mol/L Fe²⁺,and polyvinyl pyrrolidone?PVP?powder is added to make10mg/ml PVP.0.02 mol/L KBH₄ adds PVP solid and make it's concentration to 10 mg/ml.And KBH₄ as reducing agent is poured into the Fe²⁺solution to prepare nZVI.Under this condition,the impurity content of nZVI prepared is less.The morphology and particle size of nZVI are observed by SEM.It was found that nZVI is spherical,and the particle size is more uniform,about 114-220 nm,and the average particle size is about 154 nm.After EDS analysis,it is concluded that nZVI is a kind of nuclear-shell structure,the shell is iron oxide and the nucleus is iron.