Reuse iron and lead from waste lead-acid batteries

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A recent article published in the journal Resources, conservation and recycling proposed a novel mechanism to recover iron and lead from lead-acid battery disposal residues (DR-LAB).

Study: Efficient recovery of lead and iron from waste lead-acid battery disposal residues. Image Credit: tong patong/Shutterstock.com

Background

Lead is a strategically important and versatile non-ferrous metal resource for the global economy, as it is intrinsically associated with energy storage for renewable energy and automotive and backup power systems.

The increased demand for lead from different industrial and energy storage applications has led to a significant increase in the production of primary lead resources, such as cerussite and galena (PbS), worldwide.

The increase in the production of primary lead resources has led to a rapid depletion of their reserves, which has shifted the focus to the recovery of lead from lead waste, such as lead-acid batteries (LAB) put discarded and used.

LABs are widely used due to their high operational safety and low manufacturing cost. A substantial part of the lead produced in the world is used in LABs. Every year, millions of tons of LAB are discarded around the world, which can be used to recover lead.

Recovering lead from scrap and spent LABs is relatively easier and less energy dependent compared to primary production of lead from ores. Currently, lead recovery plants mainly rely on pyrometallurgical methods for the lead recovery process.

100.0 to 350.0 kg of DR-LAB containing 1.2 to 22.0% lead are generated for each ton of metallic lead produced in the secondary lead recovery process. Thus, a significant amount of lead can be produced annually from the DR-LABs, which required the identification of an efficient process to recover the lead from the DR-LABs and render the disposal residues harmless.

DR-LABs are mainly composed of lead-rich phases such as lead, lead oxide (PbO), PbS and iron-rich compounds, such as ferrous oxide (FeO), iron oxide (II, III) (Fe3O4), iron sulfide (FeS) and fayalite (Fe2SiO4). Among them, the Fe2SiO4 and PbS are the main iron- and lead-rich phases, respectively.

During the process of lead recovery from LABs, the stable and abundant Fe2SiO4 produced by high-temperature smelting possesses complex bonding effects or spatial positional relationships with lead compounds, potentially resulting in low leaching efficiency.

Although the iron concentration in DR-LABs ranges from 20.1% to 55.7%, only lead is extracted during the metal extraction process, resulting in the waste of a significant amount of iron resources. iron. Thus, a mechanism should be developed for the efficient recovery of iron and lead from DR-LABs based on the identification of spatial positional relationships between lead and Fe compounds.2SiO4.

The study

In this study, researchers proposed a mechanism for the efficient recovery of iron and lead from DR-LABs based on the identification of the spatial positional relationship between Fe2SiO4 and PbS.

Specifically, the researchers obtained the spatial position relationships between Fe2SiO4 and PbS from DR-LAB, assessed the feasibility of using sodium hydroxide (NaOH) to release Fe2SiO4-bound to PbS, identified Fe mechanism and pathway2SiO4 destruction, and evaluated the recovery of iron and lead by acid leaching, followed by pH adjustment using an alkaline waste solution.

Initially, DR-LABs were dried for 12 h at 100 ohC, crushed by jaw crusher, and sieved to control crushed particle size from 0.08mm to 0.16mm sequentially. Subsequently, the influence of different NaOH concentrations and liquid-solid (L/S) ratio on the processing of DR-LABs was investigated.

Experiments were conducted using NaOH/DR-LAB with a mass ratio of 10:1, 9:1 and 8:1 (S/S) under L/S mass ratio conditions of 15:1 and mechanical agitations of 300 rpm for six hours at 140℃ and using deionized water/DR-LAB with L/S mass ratio of 15:1, 12.5:1 and 10:1 in the conditions of 10:1 S/S mass ratio and 300 r/min mechanical agitations for six hours at 140 ℃.

Moreover, the influence of five, four and three hours of reaction time and temperature gradients of 140, 120 and 100℃ on the reaction were also evaluated. Finally, the residue obtained after the reaction was collected, cleaned and dried under vacuum for further testing.

HNO3 acid leaching tests of the treated DR-LABs were performed to recover iron and lead from the tailings, and the optimum conditions for nitric leaching were determined. The residue obtained after HNO3 the leach was dried under vacuum. The researchers then analyzed the magnetic separation, the abundance of iron and the phase of the residue.

Researchers also determined the iron and nitrate content, calculated the recovery efficiency of total lead, and studied the decomposition mechanism and pathway of Fe2SiO4 by NaOH using density functional theory (DFT) calculation.

X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and A digital dual-beam ultraviolet-visible (UV–vis) spectroscopy system was performed for the characterization of DR-LABs.

Comments

Three positional relationships, including loading, embedding, and packing, have been identified between Fe2SiO4 and PbS in the DR-LABs. Among them, packing was the strongest positional relationship between Fe2SiO4 and PbS in the DR-LABs.

PbS was effectively exposed on the DR-LAB surface after Fe2SiO4 destruction when the NaOH/DR-LABs S/S mass ratio, the deionized water/DR-LABs volume L/S mass ratio, the reaction time and the temperature were 10:1, 10:1, 4 h and 140 ohC, respectively.

Fe2SiO4 phase transformation, pH adjustment and acid leaching occurred at relatively low temperature with efficient recovery of iron and lead. 98.9% by weight of lead was recovered from DR-LABs as lead(II) hydroxide/iron(III) hydroxide/iron(II) hydroxide Pb(OH)2 /Fe(OH)3/Fe(OH)2 by acid leaching, followed by pH adjustment.

The relative abundance of FeO and Fe3O4 in the acid leach residue that can be magnetically recovered as feedstock was 66.1%, while the relative abundance of Fe(OH)2 recovered at 9.5 pH was 57.3%. Overall, 90.3% iron was obtained from the recovery process as raw material.

Both theoretical and experimental studies have confirmed that NaOH induces hydroxy Fe2SiO4 (010) surface formation and near-surface Na+ substitution, which modulated the coordination environments and local electronic structures of Fe2SiO4 and facilitated the Fe2SiO4 to the FeO phase transformation.

Conclusion

In summary, the results of this study demonstrated the feasibility of using the proposed strategy to achieve efficient recovery of iron and lead from DR-LABs. The proposed mechanism for the recovery of lead and iron from DR-LABs enabled full utilization of DR-LABs and reduced the need to extract primary iron and lead ore. The low carbon dioxide emission and energy consumption are the other major advantages of the method.

However, some of the iron was leached out during the HNO3 leaching process and precipitate with lead ions due to non-selectivity and high acidity of HNO3. Previous studies have shown that adding hydrogen peroxide can effectively prevent iron leaching. Thus, further research is needed to focus on selective iron leaching and lead to improved magnetic iron recovery efficiency and lead abundance.

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Source

Zhu, N., Li, F., Wu, P. et al. Efficient recovery of lead and iron from waste lead-acid battery disposal residues. Resources, conservation and recycling 2022. https://doi.org/10.1016/j.resconrec.2022.106614

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