| Lead-acid batteries（LABs）are widely used in aerospace,communication,electricity and other fields because of its stable operating performance,low price and many other advantages,which have become the world’s most used secondary battery.It is reported that 87.6%of the world’s lead production is used in the preparation of LABs.However,due to the limited life of LABs（2～4 years）,the average annual amount of spent LABs remains high.In the context of excessive exploitation of lead resources and high demand for lead,it is of great significance to recycle lead from spent LABs with both resource and environmental attributes.However,as the mainstream process of spent LABs disposal,pyrosmelting has low lead yield,and produces a large number of lead-containing smelting slag,resulting in a large loss of lead resouces.Therefore,designing a new technology of efficient,stable and economical resource disposal of spent lead-acid battery smelting slag（lead smelting slag）is of great significance for the recovery of valuable metals.Aiming at the difficulties of recycling existing lead smelting slag,taking valuable metals in lead smelting slag as the research object,this paper revealed the spatial position relationship between main substances in lead smelting slag through various means,and the reasons for the low resource efficiency of valuable components were clarified.On this basis,a new recycling technology of comprehensive gradient enrichment of valuable metals was developed,which included phase transition regulation-acid leaching-p H regulation.Based on the causes of lead smelting slag,a pre-desulfurization and low-temperature melting system of lead paste for spent lead-acid battery（spent lead paste）based on highly efficient and recyclable sodium molybdate desulfurizer was constructed.Furthermore,a hydrogen peroxide（H2O2）production system was constructed with the preparation of tin self-doped lead-based organic framework（RPM）photocatalyst from spent lead paste desulfurization smelting precursor Pb O2.The main results are as follows:（1）In order to reveal the reasons for the low efficiency of wet leaching of valuable metals from lead smelting slag,three spatial position relationships of Fe2Si O4 and Pb S,which accounted for 40.3%of lead smelting slag,were clarified by various characterization methods,including wrapping,embedding,and loading.The encapsulated Pb S was the main reason of the low efficiency of wet leaching.It was found that under the conditions of mass ratio of Na OH/Pb smelting slag 10:1,mass ratio of water volume/Pb smelting slag 10:1,reaction temperature140℃and reaction time 4 h,the transformation of Fe2Si O4 to Fe O structure in Pb smelting slag could be achieved.This indicated that the binding relationship of Pb S in lead smelting slag changed from strong to weak,which demonstrated that the process of alkali treatment improved the spatial position relationship between main substances in lead smelting slag so that Pb S bound in Fe2Si O4 was exposed.The effect of alkaline treatment was evaluated in dilute acid leaching experiment（Optimal conditions:nitric acid=0.1 mol/L and reaction time 60 min）.In combination with p H regulation,98.9%of lead and 90.3%of iron in lead smelting slag were recovered in the form of Pb（OH）2/Fe（OH）3/Fe（OH）2 and Fe3O4/Fe O/Fe（OH）2,respectively.Experimental and theoretical cross-studies have clarified that Na OH induced the formation of a large number of hydroxyl Fe2Si O4（010）surface and near-surface Na+substitution（Metal-ONa formation）,modulated the local electronic structure and coordination environment of Fe2Si O4,promoted the phase conversion of Fe2Si O4 to Fe O and the unshackling of Pb S.（2）In order to avoid problems such as the generation of lead smelting slag in the subsequent smelting process due to incomplete desulphurization of waste lead paste and the high cost and environmental risks caused by the non-recycling of traditional desulphurization agent,a pre-desulfurization and low-temperature smelting system of spent lead paste based on highly efficient and recyclable sodium molybdate desulfurizer was developed for the first time..The feasibility and effectiveness of Na2Mo O4 desulfurizer for desulfurization of spent lead paste were analyzed.The effectiveness of desulfurizer regeneration/recovery and recycling was analyzed,and the purification method of mixed spent salt after multiple cycles was explored.The results showed that sodium molybdate could remove 99.13%sulfur from spent lead paste which entered into solution in the form of sulfate.The desulfurization products were purified and recrystallized by acid leaching and p H regulation.Lead dioxide（Pb O2）with 93.7%purity and lead molybdate（Pb Mo O4）with 98.4%purity were recovered and used as smelting precursor,respectively.Then with LABs shell and Na OH as carbon and sodium sources respectively,elemental lead preparation and sodium molybdate regeneration could be achieved only at 600℃（the traditional smelting temperature was 1200℃and the participation of reduced iron powder was needed）.Lead and desulfurizer solutions could be separately recovered from the smelting products through simple water washing,without the generation of waste water or smelting slag.The desulfurization efficiency of regenerated/residual Na2Mo O4was basically the same as that of commercial reagents,which confirmed the feasibility of its reuse.At 5℃,the purification of Na2Mo O4 waste salt solution could be achieved with only3.9%sulfur remained in the obtained Na2Mo O4 solution.Overall,the method obtained 95.3%lead recovery and achieved 99.83%Na2Mo O4 recycling rate,which greatly reduced the production cost of recycled lead enterprises and had good environmental benefits and application prospects（3）In order to promote the high value utilization of spent lead paste desulfurization smelting precursor Pb O2 in multiple ways,a tin（Sn）self-doped Pb-MOFs（RPM）photocatalyst was successfully synthesized by by redox coupled with low temperature solvothermal method,and the RPM photocatalytic system for the preperation of H2O2 was proposed.Compared with the pure Pb-MOFs（PPM）prepared by analytically pure Pb O2,the XRD peaks of the successfully synthesized series of RPM shifted and morphologies changed in different degrees.Among them,1.4RPM photocatalyst showed the best H2O2 production rate up to 2023.76μmol.g-1.h-1,which was 1.5 times that of 1PPM,and the photocatalytic material had good stability.TEM,DFT,XAFS and other characterization methods showed that Sn preferentially self-doped 7-coordination Pb sites of Pb-Mo Fs and entered Pb-Mo Fs lattice structure in the form of S-Pb-N chemical bond.The results of experiments and DFT calculation showed that the self-doping of Sn in Pb-MOFs could increase the adsorption capacity of O2,enhance the light absorption capacity,improve the separation efficiency of photogenerated e--h+and improve the internal electric field and other multiple effects.ESR and free radical capture experiments confirmed that the H2O2 production path with PPM photocatalysis included non-free radical path（92.01%）and free radical path（6.85%O2·-and 1.14%1O2）,while Sn self-doping greatly promoted the free radical path of RPM photocatalytic H2O2 production.The paths of O2·-and 1O2 were increased by 12.12%and 10.02%,respectively.To sum up,this study revealed the reasons why the existing lead smelting slag was generated and difficult to be recycled by wet technology,and developed a new process of combined efficient gradient recovery of valuable metal lead and iron,which included phase transition regulation of key substances,dilute acid leaching and p H regulation.A pre-desulfurization-low temperature smelting system of spent lead paste based on recyclable Na2Mo O4 desulfurizer was constructed.On this basis,a new way of high-value reuse of spent lead paste desulfurization smelting precursor Pb O2 was developed,which provided new strategy and theoretical basis for the comprehensive sustainable development,large consumption and high resource utilization of spent LABs. |
