Physical-separation procedures for recovering metals from spent Ni–Cd batteries

Abstract

While their heyday as the leading rechargeable cell system is probably over, Ni–Cd batteries remain the main sink for cadmium production and, at the same time, the major source of cadmium contamination to the environment. Whatever happens in the (near) future, there is an evident need for an abatement in such an input. This study deals with the initial (physical) stage of an integrated process for recovering Cd, Ni and Co from spent Ni–Cd batteries, namely with the granulometric separation by wet sieving of shred-to-pieces, scrap cells. Regardless of the shredder's output, the results point to a major separation around 2.8 mm for an intense flow. Generally speaking, toxic metals (Cd, Co, Ni) concentrate in the infra fractions, whereas ferrous and organic scrap are retained above. Upper fractions still contain a fair share of non-ferrous metals though, so an additional process like leaching is required. Infra fractions can proceed directly to the recovery stages downstream. The amount of material in the finest fractions (under 0.355 mm) is inversely proportional to the mesh of the shredder's output, yet this parameter appears to have no influence on their granulometry.