Polyamine flocculation applied to household batteries recycling

Processing of spent household batteries to recover manganese and zinc involves grinding of the inner part of battery cells so as to obtain a black powder (BP) with average particle size of less than 2 mm. This is followed by washing the BP with plain water to eliminate soluble chemicals. A subsequent step consists in separating the BP from the aqueous suspension. This operation has proven to be a difficult one. This research showed that adding epichlorohydrin–dimethylamine (EPI–DMA) enhanced greatly the separation process while not inducing unwanted alterations in the chemical composition of the BP. Flocculation efficiency was determined by measuring the solution turbidity. Combining different analytical techniques [X-ray diffraction analysis, scanning electron microscopy, backscattered electrons and zeta potential measurements (Zetasizer Nano)], the research also assessed the effect of EPI–DMA on the solutes, defined the resulting chemical composition of BP and offered an insight into the flocculation mechanism. Central composite design was used to optimize the values of most important operating variables, i.e., EPI–DMA dosage and agitation time of the suspension at different BP/washing water ratios. Analysis of variance was used to study interactions among the process variables and define the conditions of highest separation efficiency.