Development of lead-acid battery paste hydrometallurgical recycling process
Name: DEISE MENEZES SANTOS
Type: PhD thesis
Publication date: 28/09/2022
Advisor:
Name |
Role |
|---|---|
| MARCOS BENEDITO JOSÉ GERALDO DE FREITAS | Advisor * |
Examining board:
| Name |
Role |
|---|---|
| CLEOCIR JOSÉ DALMASCHIO | Internal Examiner * |
| DENISE ROCCO DE SENA | External Examiner * |
| GILBERTO AUGUSTO DE OLIVEIRA BRITO | External Examiner * |
| JOSIMAR RIBEIRO | Internal Examiner * |
| MARCOS BENEDITO JOSÉ GERALDO DE FREITAS | Advisor * |
Summary: Over 9 million tonnes of lead, more than 80% of global lead consumption, goes into lead-acid batteries production yearly. In Brazil, the smelting industry recycles 98% of batteries. Despite the National Solid Waste Policy, economics is the primary motive for recycling batteries. Pyrometallurgy emits over 84600 tonnes of CO2 and up to 156 tonnes of toxic waste per year in Brazil. In developed countries, alternative processes to pyrometallurgy are exceeding academic research. Companies such as Aqua Metals and Engitec are known for their hydrometallurgical and electrolytic processes with less environmental impact but high energy consumption and hazardous reagents usage. This thesis describes a new hydrometallurgical recycling process development for lead-acid battery paste (PbSO4, PbO, PbO2, and Pb) using organic acids such as citric and acetic at a moderate temperature, aiming at the production scaling for a 1-ton capacity pilot plant in Governador Valadares-MG. Initially, the goal was to scale up the process patented by the University of Cambridge by calcining lead citrate from the reaction between the lead paste and aqueous solution of citric acid, sodium hydroxide, and hydrogen peroxide in a single step. However, after ten laboratory recycling tests, the product did not meet the parameters of purity, maximum characteristic dimension, free lead content, acid absorption, total lead content, and morphology. Then, leaching the paste with acetic acid reduced impurities content in the product from 12 to 0.01%. The influence of lead citrate calcination atmosphere revealed an impressive result, metallic lead as the main product within an oxygen gas atmosphere at 350°C. Lead factories donated ten lead pastes samples and five leady oxides for this research; therefore, nineteen lead pastes recycling tests were performed, which resulted in 2.5 kg of lead citrate (intermediate) and 1.45 kg of leady oxide (Pb/PbO, product). Techniques such as x-ray diffraction, thermogravimetric analysis, and scanning electronic microscopy allowed verifying lead citrate synthesis and its morphology repeatability. The recycled Pb/PbO meets the purity, acid absorption, free and total lead content criteria, but grinding must fit the maximum characteristic dimension. The recycled leady oxide morphology differs from the battery assembly industry; the product is mainly yellow lead oxide (β-PbO, orthorhombic) instead of red lead oxide (α-PbO, tetragonal). The developed process can reduce solid waste generation by 95% and provide high purity metallic lead to the market (a commodity), including the regular battery assembling industries.
