Batteries Recycling

This line of research began in the 1990s. Since then, several projects have been carried out studying the recycling of common and alkaline batteries, nickel-cadmium batteries, nickel metal-hydride batteries, lithium-ion batteries and mixtures of batteries and batteries.

The following summary shows the thesis work of Profa. Dr. Denise Crocce Romano Espinosa.

RESUME

The recycling of electro-electronic products is one of the main current challenges, with emphasis on the recycling of batteries, that is, portable energy storage equipment. This is the objective of characterizing a sample of 200 kg of used batteries and batteries that were returned to a public collection point and studying the main parameters for a pyrometallurgical and hydrometallurgical route of tests of contained metals.

The characterization of the material was made by the segregation and classification of the batteries. Representative prints of 10 kg were produced with approximate compositions of the aggregate sample. These labels were ground in the hammer mill with 9mm grid. The ground material was subjected to tests for its chemical characterization, grain size and moisture content. The magnetic selection of the material milled in hammer mills does not show good results, because there was contamination of the magnetic fraction caused by the trapping of the particulate material. The material greater than 3,360 mm was ground in the knife mill to release particulate material that was trapped inside the carcasses during a mill in the hammer mill. The homogenized material was quartered and briquetted for reduction tests, which were carried out in an electric resistance oven with a stainless steel ruler inside. An inert gas injection system was attached to this rule. The exhaust gases pass through a condenser (cold finger) and a paper filter, followed by bubbling in deionized water.

The results of the reduction tests showed the evaporation of the Hg and Cd compounds below 800ºC, the evaporation of Zn at 900ºC and the pre-reduction of manganese oxides to MnO from 900ºC. The material reduced to 1100ºC was subjected to magnetic separation with recovery of at least 80% of the iron contained. In addition to the reduction tests, tests were carried out on a thermogravimetric scale. The analysis of the results of thermogravimetry showed that at 900ºC the reaction time is quite prolonged, and that most of the loss of mass occurs at this level of temperature. After reduction to 1100ºC, the reduced material was subjected to magnetic separation. The non-magnetic fraction was taken for hydrometallurgical tests, which consisted basically of leaching in a 2M sulfuric acid solution, precipitation with NaOH and precipitation with ammonium oxalate 70ºC.

The results showed that 88% of the reduced non-magnetic material is soluble in sulfuric acid, 6% is inert organic material (insoluble in HNO3: HCl) and 6% insoluble non-inert (soluble in HNO3: HCl). The non-inert insoluble fraction is composed of 30 to 40% copper. The precipitation tests of the soluble fraction showed that rare earth elements can be recovered in the pH range between 0.3 and 1.0. Iron and aluminum precipitate to pHs above 3.5. The addition of ammonium oxalate promotes the precipitation of manganese oxalate from a pH equal to 1.0.