Experimental thermodynamic and kinetic studies on extraction and recycling of lead from spent lead-acid battery paste
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School of Chemical Engineering |
Doctoral thesis (article-based)
| Defence date: 2019-05-28
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Authors
Li, Yun
Date
2019
Major/Subject
Mcode
Degree programme
Language
en
Pages
57 + app. 68
Series
Aalto University publication series DOCTORAL DISSERTATIONS, 95/2019
Abstract
Lead recycling from complex secondary materials has gained increasing interest in recent years. Around 80-85% of the total secondary lead is recycled from lead paste. Due to the high toxicity of lead and increasingly stringent environmental regulations, cleaner and efficient processing of such materials and development of industrial processes are urgently required. In the present work, an innovative and clean lead-acid battery paste recycling technique is proposed. Iron-containing waste materials are utilized as sulfur-fixing agents to capture sulfur as FeS, instead of generating excessive amount of SO2. Na2CO3 or Na2CO3-Na2SO4 salt mixture is added to the smelting system to promote the reactions and improve valuable metals' recovery and sulfur-fixation efficiency.Thermodynamic calculations and experimental determination of the reaction mechanisms in the PbSO4-Fe2O3-C, PbSO4-Na2CO3-C, and PbSO4-Fe2O3-Na2CO3-C systems are carried out to build the fundamental knowledge. Thermogravimetric analysis and quenching method coupled with a direct spectroscopic analysis of the phase and chemical compositions of the resulting phases, i.e. XRD and SEM-EDS, are employed to investigate the phase transformation mechanism. The results indicate that without Na2CO3 addition, lead in lead paste is shown to be extracted mainly through the sequence of PbSO4→PbS→PbO→Pb. Sulfur in PbSO4 is thus first transferred to PbS and finally fixed as FeS. In the presence of Na2CO3, at low temperatures and in weakly reductive atmospheres, lead is extracted mainly through the sequence of PbSO4→PbO→Pb. Na2CO3 helps to transform SO3 from PbSO4 to Na2SO4. At high temperatures and strong reducing atmospheres, PbSO4→PbS dominates the reactions, and lead and sulfur are conserved as PbS. Lead can not be effectively extracted from PbS without a sulfur-fixing agent. When Fe2O3 is presented, lead in PbS will further be extracted through the sequence of PbS→PbO→Pb. Finally, sulfur is fixed as FeS, NaFeS2 and Na2S. A series of bench-scale experiments are conducted to detect the influence mechanisms of smelting conditions on lead extraction and sulfur fixation efficiency. The optimum smelting parameters obtained are integrated to an industrial pilot campaign. Under the optimum conditions, three smelting products, crude lead, ferrous matte, and slag, are formed. 91%-96% lead in the initial raw materials is found to be enriched in crude lead bullion. 97%-99% sulfur is fixed in the sulfide matte and slag. Purity of the crude lead reaches 96%-98%. Lead concentrations in the matte and slag are below 2.4%-4.1% and 0.5-1.2%, respectively, without subsequent matte and slag cleaning. The addition of sodium salts, e.g. Na2CO3 and a Na2CO3-Na2SO4 mixture, is seen to promote the reductive sulfur-fixing reactions and improve extraction and sulfur-fixation efficiency.Description
This doctoral thesis work was conducted under a double-degree project between Central South University (CSU, School of Met-allurgy and Environment) and Aalto University (Aalto, School of Chemical Engineering). The research presented in the thesis was carried out in both universities, Metallurgy (MTG) research group in Aalto and School of Metallurgy and Environment in CSU.
Supervising professor
Yang, Shenghai, Prof., Central South University, P.R. China; Jokilaakso, Ari, Prof., Aalto University, Department of Chemical and Metallurgical Engineering, FinlandThesis advisor
Chen, Yongming, Prof., Central South University, P.R. ChinaTaskinen, Pekka, Prof. Emeritus, Aalto University, Finland
Keywords
lead-acid battery paste, lead recycling, SO2-free sulfur-fixing smelting, waste co-treatment and recycling, lead-iron containing wastes, phase diagram
Other note
Parts
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[Publication 1]: Yun Li, Shenghai Yang, Pekka Taskinen, Jing He, Fangwen Liao, Rongbo Zhu, Yongming Chen, Chaobo Tang, Yuejun Wang, Ari Jokilaakso. Novel recycling process for lead-acid battery paste without SO2 generation - Reaction mechanism and industrial pilot campaign. Journal of Cleaner Production, 2019, volume 217, pp. 162-171.
Full text in Acris/Aaltodoc: http://urn.fi/URN:NBN:fi:aalto-201902252077DOI: 10.1016/j.jclepro.2019.01.197 View at publisher
- [Publication 2]: Yun Li, Shenghai Yang, Pekka Taskinen, Jing He, Yongming Chen, Chaobo Tang, Yuejun Wang, Ari Jokilaakso. Spent lead-acid battery recycling via reductive sulfur-fixing smelting and its reaction mechanism in the PbSO4-Fe3O4-Na2CO3-C system. Accepted.
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[Publication 3]: Yun Li, Shenghai Yang, Wenrong Lin, Pekka Taskinen, Jing He, Yuejun Wang, Junjie Shi, Yongming Chen, Chaobo Tang, Ari Jokilaakso. Cleaner Extraction of Lead from Complex Lead-Containing Wastes byReductive Sulfur-Fixing Smelting with Low SO2 Emission. MDPI. Minerals, 2019, volume 9, Issue 2, 119.
DOI: 10.3390/min9020119 View at publisher
- [Publication 4]: Yun Li, Shenghai Yang, Pekka Taskinen, Jing He, Chaobo Tang, Yongming Chen, Yuejun Wang, Ari Jokilaakso. Cleaner recycling of spent lead-acid battery paste and harmless treatment of pyrite cinder via reductive sulfur-fixing method for valuable metals recovery. Submitted to Resources, Conservation and Recycling in 2019.