PRODUCTION OF NANO-LEAD(II)OXIDE FROM WASTE AUTOMOBILE LEAD-ACID BATTERY PASTE

Abstract

Recycling of Waste Lead-Acid Batteries (WLABs) by smelting produces high leaded materials which are harmful to the health of the populace. Hydrometallurgical process offers a better alternative of converting these materials to nanoparticle. Production of nano-lead(II)oxide (nano-PbO) from WLABs has been reported by few studies. However, in these studies the nano-PbO produced contains undesirable impurities such as sulphur, carbon, iron and this necessitates the need for impurity-free nano-PbO. The aim of this study therefore, was to produce and characterise high purity nano-PbO from waste automobile LABs. Fifty (50) waste automobile LABs samples were collected, manually dismantled and the pastes were isolated, washed with distilled water and oven dried. A composite of the dried powdery material was made and analysed for chemical phases using X-ray diffraction (XRD). The morphological properties and elemental mapping were determined with Scanning Electron Microscope/Energy Dispersive X-ray (SEM/EDX). Samples were analysed for elemental composition by inductively coupled plasma optical emission spectroscopy. Concurrent leaching was optimised using citric, ethanoic, methanoic acids, sodium salt of citric acid, sodium salt of ethanoic acid and sodium salt of methanoic acid with hydrogen peroxide using a standard method. Leaching parameters (concentration of leachants, paste/leachant ratio, temperature, stirring rate and reaction time) were also optimised by standard method. The lead citrate precipitated from citric acid, sodium citrate, and hydrogen peroxide was characterised with XRD and SEM/EDX. Thermal decomposition/calcination temperature of the precipitate was identified by thermogravimetry-differential thermal analysis. The calcination product was characterised thereafter using the same methods. Data were analysed using descriptive statistics. The major phases identified in the powdery material were lead sulphate (PbSO4), lead(IV)oxide (PbO2), lead(II)oxide (PbO) and lead oxide sulphate (Pb3O2SO4) indicating high lead components/phases. The morphological and elemental composition/mapping of the powdery material revealed irregular bulk crystals consisting of 63.5% lead, 11.2% sulphur, 18.1% oxygen, 2.2% carbon and 5.0% iron. Concentration of lead in the fifty powdery samples ranged from 350,000 to 960,000 mg/kg. The optimum condition for leaching and precipitating lead citrate was 1 M citric acid, 2 M sodium citrate and 2 M hydrogen peroxide (2:1:2, v/v). Leaching parameters of 100 g/L, 30 oC, 500 rpm for 3 hours showed the highest lead recovery of 98.8%. The resulting sheet-shaped lead citrate precipitate contained 81.5% lead, 1.7% sulphur, 7.0% oxygen and 9.8% carbon. Calcinating the precipitate at 400 oC resulted into production of impurity-free spherical shaped nano-PbO of 85.2% lead and 14.8% oxygen. The calcination products were Massicot (α-PbO) and Litharge (β-PbO) with particle sizes ranging from 19 to 100 nm. Highly purified nano-lead(II)oxide was produced from waste lead-acid battery paste. This could be an alternative material for the production of new lead-acid battery.