| High titanium-blast furnace slag（TBFS）is an industrial solid waste produced from smelting high titanium vanadium titanium magnetite by blast furnace.It has the regional particularity that only existing in Panxi area of China,and the characteristics of rich content of valuable components.The production of TBFS is large,generating about 3.6 million tons every year,and the historical accumulation amount has reached 70 million tons.A large number of TBFS is easily to lead to the pollution of surrounding water,soil and air atmosphere,and even lead to safety accidents such as landslide and debris flow.At present,there is not the most effective technology for the resource utilization of TBFS,and only one method that is"high temperature carbonization and low temperature chlorination"has been in pilot production,however,its development is limited because it produces large number of chlorinated tailings.Therefore,the development and utilization technology of TBFS has always been an important topic in the field of environment and resources at China and abroad.In many resource utilization processes,sulfuric acid process has a good development trend because it can extract a variety of valuable components from TBFS at the same time and the extraction rate is high.However,acid mist and gypsum colloid produced in the process are the main obstacles to its application.Based on the traditional sulfuric acid method,the innovation is made in this paper.Taking the water quenched-TBFS as the experimental raw material,aiming at the content of Ti,Mg and Al is high and easy to be extracted,establishing the process route that―activation by concentrated sulfuric acid roast,then extraction of Ti,Mg and Al by dilute sulfuric acid,and then prepare TiO2 by boiling hydrolysis,finally preparation of hydrotalcite by coprecipitation hydrothermal method.The mineral composition,chemical composition,element valence state,micro morphology and element distribution characteristics of TBFS were characterized by XRD,XRF,XPS and other analysis methods.The main chemical components of TBFS are CaO,SiO2,TiO2,Al2O3,MgO,and some SO3,Fe2O3.Among which Ti and Fe have two valence states.The main phases are perovskite and some amorphous phases,which have high chemical activity.The structure of TBFS is relatively stable,chemical reaction with oxygen occurs only when the temperature is above 800℃.The microscopic morphology of TBFS is irregular particles with dense surface,most of particle have smooth surface and a few have rough surface.The correlation between Mg and Al elements is good,there are more enrichment both in smooth particles and rough particles.While Ti element are mainly enriched in rough particles.Ti,Mg and Al are mainly in the form of residue state,so the occurrence state is relatively stable.The extraction of Ti,Al and Mg from TBFS by concentrated sulfuric acid roasting was studied.The optimum technological parameters were acid slag ratio:1.4,roasting temperature:130℃,roasting time:40 min.The extraction rate of Ti was 82.85%,and the extraction rate of Mg and Al was over 90%under the conditions.The main phases of the roasted slag are II-anhydrite,aluminum sulfate,titanium sulfate and magnesium sulfate.The micromorphology of roasted slag shows that the square sheet with side length is 24μm and the block with unspecific shape.After using deionized water to leach roasted slag,the viscosity of water-leached slurry is 3040 mpa.s,and the filtration rate is only 47%-65%when filtration time reaches 30 minutes.The main phase in water-leached residue is gypsum,and the micromorphology shows diamond plate structure with complete crystal shape and smooth surface.Due to the plate-like structure of gypsum particles in leached residue and the uneven distribution of particle size,the particles are easy to stack together horizontally,and there are few gaps between them.So it is easy to cause the formation of compact accumulation,thus affecting the filtration effect of water-leached slurry.The reaction rate of roasting process was controlled by the internal diffusion in the"shrinkage unreacted nucleus model",and the apparent activation energy was 19.05 kJ/mol.In order to improve the filterability of leached slurry,the roasted slag was leached by dilute sulfuric acid.The optimum technological parameters were sulfuric acid concentration:0.6mol/L,leaching temperature:60℃,leaching time:40 min.under this condition,the viscosity of acid-leached slurry was 15.32 mpa.s,and the complete liquid-solid separation could be achieved in 15 seconds.The main phase of acid-leached slag is II-anhydrite,the particle size of II-anhydrite is large and particle distribution is uniform,so it is not easy to form a compact accumulation.Besides,the micromorphology of the acid-leached slag is intersected many small sheets,this structures has many"gaps",which is conducive to the filtration of the liquid.In the process of leaching roasted slag with dilute sulfuric acid,the transformation process of phases is that the II-anhydrite in roased slag reacts with dissolved Al2（SO4）3 to form the unstable complex hydrate Al2（SO4）3·mCaSO4·nH2O,the hydrate immediately decomposed into Al2（SO4）3·（n-2m）H2O and gypsum,and then the H+in H2SO4is complexed to form H3O+by strip the H2O from the surface of gypsum,so making gypsum dehydration to formed II-anhydrite again.Titanium dioxide was prepared from acid-leached solution by boiling hydrolysis.The optimum technological parameters were pH value of the bottom solution:1.7,hydrolysis temperature:105℃,feeding rate:6.6 mL/min,aging time:25 min,and the second boiling time:60 min.Under this condition,the hydrolysis rate of Ti was 90.71%.The each particle size of hydrolysis product is relatively uniform,all of it are less than 5μm and good dispersibility.The main phase of the hydrolysate is uncrystallized metatitanic acid and some anatase titanium dioxide.When the pH value of the bottom solution is too high,it will promote the hydrolysis of the Fe component in the leached solution,so which is not conducive to obtain the metatitanic acid with high purity and whiteness.In addition,the increase of pH value of the bottom solution,feeding speed and aging time is beneficial to the increase size and dispersion of the metatitanic acid,while the increase of hydrolysis temperature is not conducive to the increase of them.The micromorphology of metatitanic acid shows that it is composed of regular globules with uniform size and irregular blocks with edges and corners.The calcined product of metatitanic acid is anatase titanium dioxide.The micromorphology shows that it is spherical particles with serious agglomeration and uniform size.The performance of titanium dioxide conforms to the standard of non-pigment grade titanium dioxide of China.The hydrolysis process of Ti is in accordance with the kinetic model of"nucleation process control".The number of nucleation is greatly affected by the pH value of bottom solution,and the apparent activation energy is 197.93 kJ/mol.The hydrotalcite was prepared from Mg,Al-riched solution by coprecipitation-hydrothermal method.The optimum technological parameters were hydrothermal temperature:150℃,hydrothermal time:14 h,and the molar ratio of Mg to Al ratio:2.5.Under this condition,the purity,crystallinity and crystal integrity of hydrotalcite were high.The increase of hydrothermal temperature in a certain range is beneficial to the improvement of the crystallinity and the crystal integrity of hydrotalcite,and the crystal of hydrotalcite tends to grow along the radial direction.In addition,the increase of hydrothermal time and the ratio of Mg to Al are also beneficial to the crystallization of hydrotalcite and the regularity of crystal structure,but when the ratio of Mg to Al is too high to easily generate the hydrated magnesium carbonate,which affects the integrity of crystal structure.The micromorphology of hydrotalcite obtained under the optimized synthesis conditions is an irregular sheet structure with the size of 0.52μm.The BET specific surface area is 105.35 m2/g,and the most of pore in hydrotalcite are mesoporous. |
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