Research On Aluminum And Iron Oxide Recovery From Coal Gangue Through Acid Leaching

Coal gangue is the largest amount of industrial solid waste in China and a large number of coal gangue had caused serious damage to the ecological environment.Therefore,it is of great significance to realize the resource utilization of coal gangue,protecting the environment and realizing the sustainable development of society.The samples selected in this paper was from Yangquhe coal mine,Hebei Fengfeng and Sanjiaohe coal mine in Huozhou.By analyzing the properties,composition of coal gangue mineral petrology,chemical composition,the basic properties of coal gangue foundation was analysis.The extraction of aluminum and iron from the coal gangue was using acid leaching method（hydrochloric acid and sulfuric acid）,and the kinetic of the acid leaching reaction process was calculated.The following conclusions are obtained.（1）The XRD analysis of Sanjiaohe coal gangue and Yangquhe coal gangue showed that the two main substance were the quartz and kaolinite.The ash composition analysis shows that SiO₂,Al₂O₃,Fe₂O₃ had a higher content,of which Sanjiaohe coal gangue,the aluminum content is higher.It also shows that the clay mineral content of Sanjiaohe was 51.2%,which belongs to the class of clay minerals in coal gangue.The content of inertinite in the organic matter is higher and the vitrinite content is lower.（2）Experiment on washability of the coal gangue was done by using heavy liquid of 1.8kg/m³,2.0kg/m³,2.5kg/m³ and 2.9kg/m³,the result showed that with the increased of heavy liquid density,floating mass increase,the calorific value of the floating matter reduced,in which,as the heavy liquid density was 1.8kg/m³,the maximum value reached 17233.6J/g.The coal gangue TG/DTG analysis shown that with the increased of the floating liquid density,the weightlessness of the samples decreased,which suggesting that the combustible of the coal gangue gradually reduced,while the DTG curve shifts to higher temperature with the proportion of liquid density increases,which indicated that the ignition temperature increased.（3）Reasearch on extraction of aluminum on Yangquhe coal gangue by hydrochloric acid were done,the factors of hydrochloric acid concentration,leaching time,solvent and sample ratio（NaF/samples）and leaching temperature on aluminum leaching rate coal gangue were investigated.4 factors and 4 levels orthogonal test was set,and the experiment found that when the ratio of solvent and sample was 0.05,the concentration of hydrochloric acid was 4mol/L,leaching time was 150min and leaching temperature was 100°C,the leaching rate of Al₂O₃ was 64.43%.The optimization of orthogonal test shown that when the solvent/sample ratio was 0.05,the concentration of hydrochloric acid was 5mol/L,leaching time was 120min and leaching temperature was 110℃,the leaching rate of Al₂O₃ reached 70.38%.（4）The extraction of Sanjiaohe coal gangue by sulfuric acid found that when the leaching time were 30,60,90,120,150 and 180 min,the leaching rates were 5.6,10.7,15.1,20.9,21.1 and 21.3%respectively.when the leaching reaction temperature is 40to 80°C,the leaching rate increased with the increase of temperature.When the reaction temperature was 80 to 120°C,the leaching rate increased significantly with the increasing of the temperature,and when the reaction temperature was 120 to 140°C,the leaching rate was almost the same.When the solid-liquid ratio were 1,5,10,15and 20ml/1g,the leaching rate increased gradually.When the solid-liquid ratio was1:1¹0:1,the leaching rate increased from 0.4 to 10.3.When leaching test was performed 10,30,60 and 90min of different boiling time,it was found that with the increasing of the boiling time,leaching rates increased first and decreased,the biggest leaching rate was reached at 30min,which was 11.1%.The leaching rate of orthogonal test design temperature,leaching time,liquid,and the test results shown that the influence sequence on leaching rate of aluminum was temperature,solid-liquid ratio,extraction time.When the reaction temperature was 90°C,solid-liquid ratio was 10:1,the leaching time was 120min,the leaching rate was 36.2%.The optimization experiments shown that when the liquid-solid ratio was 10:1,extraction temperature was 120°C,acid leaching time was 120min,solvent amount was 0.05%,the leaching rate is 98.78%.（5）Air atmosphere has a preferable activation effect because carbon combustion in the coal gangue promoted the transformation of kaolinite and to metakaolin.The effect of hydrogen atmospheres was mainly in the high temperature.Carbon preferentially reacted with CO₂,but not with aluminum under the CO₂ atmosphere.When coal gangue was calcinated at 650°C under air,air–hydrogen,carbon dioxide,hydrogen,or nitrogen atmospheres,the decomposition rates of kaolinite were 52.44%,50.90%,47.04%,45.36%,and 43.42%,respectively.The acid leaching rate of coal gangue calcinated under different atmospheres were 93.66%under the air atmosphere,90.90%under the air–hydrogen mixed atmosphere,84.06%under the carbon dioxide atmosphere,81.91%under the hydrogen atmosphere,and 77.54%under the nitrogen atmosphere.Under the conditions of reaction temperatures 40,60 and 80℃the sulfuric acid leaching of coal gangue conformed to unreacted shrinking core model.The reaction kinetics equation of the process was 1-（1-x）2/3=kt.And under the conditions of reaction temperatures 100,110 and 120℃the sulfuric acid leaching of coal gangue reaction kinetics equation of the process was 1-（1-x）1/3=kt.（6）Considering the high content of Fe₂O₃ in Sanjiaohe coal gangue,the extraction of Fe from coal gangue take Sanjiaohe as the research object.Effects of leaching temperature,time,solid-liquid ratio,boiling time and boiling extraction effect of Fe₂O₃on the amount of coal gangue in single factor and orthogonal test,and the experimental factors were optimized,the experiment found.1g coal gangue and 15m L sulfuric acid,boiling time was 30min,boiling water was 50mL,acid leaching time was 60min,and when the extraction temperature is 40¹00°C,the leaching rate of Fe₂O₃ increased from 1.5%to 42.3%,and when the temperature is less than 80°C,the leaching rate increases slowly,when the extraction temperature is 60°C the leaching time was30¹80min,with the increased of acid leaching time,the leaching rate gradually increased.when the acid leaching time increased to 120min,the leaching rate increased with reaction time slowly.when the solid-liquid ratio was 1g/1m L¹g/20m L,with the increase of solid-liquid ratio,the effective reaction area increases,and the leaching rate increased.The acid leaching temperature,acid leaching time and liquid solid ratio of Sanjiaohe were three factors in the orthogonal test,weight from large to small impact was temperature,liquid solid ratio,acid leaching time.The optimal conditions and the experiment was that when the reaction temperature was 90°C,the liquid-solid ratio was 10:1,the leaching time was 120min,and the leaching rate reached 31.2%;When the ratio of liquid to solid was 10:1,acid leaching temperature was 120°C,acid leaching time was 150min,the leaching rate reached 90.1%.Under the temperature of40,60,80 and 90°C the dissolution rate of Fe₂O₃ was in accordance with the film diffusion control of particle size reduction kinetics equation shrinkage core model.The reaction kinetics equation of the process was 1-（1-x）2/3=kt.And 1-（1-x）2/3 has a large linear relationship with the reaction time t curve.（7）The removal of impurities of silicon-aluminum iron hydroxide separation purification and ultrafine alumina preparation to achieve acid leaching purification and preparation,and product characterization.First of all through the formation and occurrence process of silicon impurity analysis of extraction of coal gangue acid,put forward using microporous membrane physical crude desilication and depth of lime water chemical desilication two step desilication method,realize the preparation of pure sodium aluminate solution;secondly,based on the different chemical properties of each element,by adjusting the solution pH（10）to achieve the separation of the target product of alumina and other impurities from coal gangue by acid leaching filtrate;pH difference extraction properties of the iron oxide by-product from coarse slag precipitation method,investigated the effect of pH variation on iron hydroxide precipitation,determination of iron increase and the best p H value of 3,extraction the rate of iron oxide reaches 99.87%;the sodium aluminate solution carbon fractionation process of aluminum,aluminum hydroxide precipitation to determine the optimum pH=6.42,optimum calcination temperature of 900°C,through the selection of experiment condition Choose the best dosage of polyethylene glycol（PEG）-butanol composite dispersant were 2%and 1%,under the condition of obtaining ultrafine alumina particle size in the range of 40-60nm,the higher dispersion of coal gangue by acid method;extraction ultrafine nano alumina product was up to 98.56%,in line with the national standards of the two product purity of iron oxide;80.2%,which belongs to the category of high quality iron concentrate.After the whole preparation process,0.220g Al₂O₃ and 0.035gFe₂O₃ products can be obtained by treating 1g coal gangue raw materials.The yield of Al₂O₃ and Fe₂O₃ is 81.87%and 82.55%respectively.The process has higher extraction rate and yield of valuable metals.（8）A preliminary analysis of coal gangue extraction process shows that in each processing 1g coal gangue material,can make 0.220g Al₂O₃ and 0.035g Fe₂O₃products,the corresponding Al₂O₃ and Fe₂O₃ yield were 81.87%and 82.55%,the process has a higher yield of extraction of valuable metals.