Papers by Keyword: Physical Processing

Abstract: Laboratorial studies were carried out to characterise the influence of different cutting systems (grab shredder and cutting mill) on the physical processing efficiency of spent Zn-MnO2 batteries. The grab shredder operate based on an indented cutting rotor which applies shear and abrasion stresses with a moderate rotation speed, while the cutting mill operation is based on shear and impact stresses at higher rotation speed. After shredding with the grab shredder, two fractions of material were obtained (above and below the 6 mm discharge grid), which allows a previous separation of the scrap. With the cutting mill, all the grinded material passed the bottom grid (with the same 6mm opening). Results obtained showed that alkaline batteries were more efficiently shredded than saline batteries, mainly with the grab shredder. Average diameters (d50) for saline and alkaline batteries fragmented with the grab shredder were 2.29 and 1.47 mm respectively, while with the cutting mill were 3.09 and 1.54 mm respectively. Chemical analyses were carried out for different size fractions allowing identifying metals distribution through size categories. In general chemical composition was not substantially different using both shredding systems. Zinc distribution was almost constant with the grain size while manganese distribution decreased with particle size. More than 94% of the iron scrap from the battery cases presents a particle size higher than 1.4 mm using both cutting systems. Due to this result, it is possible to separate the scrap retained in the coarse fraction by sieving with the identified mesh. Maximum selectivity points, corresponding to the maximum separation of zinc plus manganese from iron, were also determined. Higher zinc and manganese recoveries were obtained with the grab shredder, despite iron contamination (20-25%) can be considered significant.

Abstract: Domestic-type batteries sample was tested aiming at its characterization and the evaluation of the feasibility of physical separation of its main components. The sample was essentially constituted by saline and alkaline types (Zn-MnO2 based systems, >90% w/w) and cylindrical shape (> 90% w/w). The mass balance of alkaline battery samples indicated as main battery components the steel case materials (25 %), the electrodes (71%) and the connector and separator/insulating materials (4 %), while the corresponding values to the saline type are 16%, 72% and 12% respectively. Despite electrochemical principles are similar, internal constitution of saline and alkaline batteries is different. Differences in electrolytes are also relevant (KOH in alkaline type and chloride salts in saline type) affecting therefore the mass balances in the chemical treatment. Fragmentation of batteries was done aiming at to evaluate the efficiency of the liberation of different components, namely scrap and electrodes. Results obtained are very promising considering the good efficiency reached on the physical separation treatment and consequently the chemical step will be necessarily improved.