Study On In-situ Doped,Extraction Of Perovskite From Ti-bearing Blast Furnace Slag And Its Application

With the rapid development of the society,non-renewable mineral resources become significantly demanding witha large amount emmisions of metallurgical solid waste and toxic harmful gases.For example,the process of Panzhihua Iron and Steel with using local vanadium-titanium magnetite has generated a large amount of titanium-containing blast furnace slag?Ti-slag?,which is extremely difficult to be recycled compared to the ordinary blast furnace slag.Many efforts have been made,however it still be the case regarding exploring an economic and environmental friendly strategy to solve thorny problem.Based on the previous research on the direct extraction of perovskites from Ti-slag,in-situ doped and enriching perovskite from Ti-slag with two transition metal elements?Cu and Mn?and Na₂CO₃,respectively,were studied in this thesis.After the mineral phases reconstruction,not only the Mn or Cu dopped perovskite CaTiO₃ but also the silicates with completely being dissolved by hydrochloric acid can be obtained.Via a facile being leached and washed of the treated slag with hydrochloric acid solution and water,respectively,a low-cost,high-efficiency flue gas photo-assisted selective catalytic reduction de-NO_x?Photo-SCR?Photocatalysts has been prepared.The main results of this thesis are as follows:?1?Cu and Mn had been used to be the dopants as the in-situ resource endowment modification of Ti-slag with CuO and MnO₂.The effect of adding CuO and MnO₂ addition on the mineral phases of Ti-slag was studied,especially on the perovskite phase.The in-situ modification does not change the basic mineral phases of Ti-slag.The main mineral phases are still perovskite?CaTiO₃?and diopside in the modified slag.However,CuO aggregates in the slag and forms a new phase,while Mn is dispersed in the diopside and perovskite phases.?2?Na₂CO₃ was added to be treated with in-situ doped Ti-slag for mineral phase reconstruction.The effect of Na₂CO₃ on the enrichment of Ti in the perovskite mineral phase,the reconstruction of the silicate mineral phases and the statement of dopants in perovskite were investigated.The results showed that this process not only promoted the enrichment of Ti from the silicate mineral phase into the perovskite phase,but also changed the complex silicates into the silicates with completely being dissolved by hydrochloric acid.Furthermore,the percentage of Mn element in the perovskite can reach about 9%.?3?Direct extraction of different amounts of CuO and MnO₂ in-situ doped perovskite CaTiO₃ from reconstructed slag was performed by dilute hydrochloric acid solution.The sodium salt modified silicate phase?sodium aluminosilicate?can be completely dissolved by hydrochloric acid.The content of SiO₂ in the leached productis about 7%in CuO in-situ doped slag,and the content of CuO is not more than 1%.However,the content of SiO₂ is low?about 4%?in the leached product in MnO₂ in-situ doped slag,which the MnO content can reach the maximum of 21.24%.Mn is more easily doped into the perovskite phase than Cu.The suitable acid leaching conditions were as follows:leaching temperature 30°C,stirring time 1 h,hydrochloric acid concentration 8%,slag acid ratio 1 g:15 mL.?4?In order to explore the high value-added applications of Cu/Mn in-situ doped perovskite in the photocatalysis field prepared by our strategy,we studied the optoelectronic properties of the leached slag.The maximum of transient photocurrents of CuO and MnO₂ in-situ doped perovskite CaTiO₃ composites reached 130 nA and150 nA,respectively.And the photocurrent density was approximately 520 nA/cm²and 600 nA/cm² for the Cu-doped and Mn-doped ones,respectively.The photocatalytic degradation of methylene blue showed that the removal of methylene blue for MnO₂ in-situ doped CaTiO₃ composites was higher than CuO in-situ doped CaTiO₃ in 180 min.This was basically consistent with the transient photocurrent and UV-visible absorption spectra.?5?Compared to the low activity of degrading organic dyes with the leached slags,it exhibited superior performance while used in simulated exhaust gas photo-thermal coupled catalytic denitration.With the increasing of Mn content in CaTiO₃composites,the photocatalytic denitration performance has been significantly improved.The NO removal rate can reach to 93%at 300?when using the in-situ doped CaTiO₃ composites with adding 5%MnO₂.In summary,the results of this thesis has set up a method for the in-situ modification of Ti-slag.The Cu/Mn in-situ doped perovskite CaTiO₃ composites have been extracted via the mineral phase reconstruction and the chemical separation.Preliminary evaluation of its application in the field of environmental aspects regarding the degradation of organic dye and removal of NOx from flue gases via Photo-assisted SCR.The results can not only provide the theoretical basis for optimizing the in-situ resource endowments of Ti-slag,but also set up a new approach for the direct materialization of Ti-slag.Furthermore,it is of important reference value for the high value-added utilization of such solid wastes.