Paula C. Oliveira

Separation of Cadmium, Cobalt, and Nickel by Solvent Extraction using the Nickel Salts of the Extractants

A new solvent‐extraction process for the separation of cadmium, cobalt, and nickel in sulphate solutions coming from the hydrometallurgical processing of spent Ni‐Cd batteries is proposed. The main innovation is to use nickel salts of the extractants, thus avoiding external pH control in the extraction operation. The extractants are first loaded with nickel in conditioning steps, using a neutralizer for pH control, and afterwards contacted with the aqueous processing solutions for extraction of interested metals with no further need of neutralization. This process is an alternative to the usual approach, which uses the sodium or ammonium salts of the extractants, avoiding introducing these cations in the process stream. Using this approach, the extraction of cadmium with nickel salt of 1 M DEHPA was performed at resulting pH values of 3.8–4.3 producing an organic phase loaded with 35 g/L Cd. Cobalt extraction with the nickel salt of Cyanex 272 was further achieved at resulting pH of 5.1–5.7 obtaining a organic loaded with 6.5 g/L Co.

Scrubbing of Cadmium and Nickel from Cyanex 272 Loaded with Cobalt

Abstract A process for the scrubbing of cadmium and nickel from Cyanex 272 loaded with cobalt was studied and is presented in this paper, as a part of a global solvent extraction process proposed for the recycling of spent Ni‐Cd batteries. After cadmium recovery in a first extraction circuit, the resulting solution containing about 80 g/L Ni, 1 g/L Co, and a residual Cd concentration of 0.10 g/L is processed in the second circuit where cobalt is extracted by 0.5 M Cyanex 272. The resulting organic phase containing about 7 g/L Co is contaminated with about 2 g/L Ni and 0.5 g/L Cd. The removal of nickel was successfully attained by scrubbing with cobalt sulphate solutions containing more than 8.7 g/L Co, at organic/aqueous (O/A) = 4 (95–98% efficiency in a single stage), while cadmium removal by this process was inefficient. The scrubbing of cadmium was achieved with high efficiency using aqueous complexing agents, namely 1 M sodium thiosulphate or 3 M ammonium chloride (scrubbing efficiencies of 97% and 80%, respectively, in a single stage at O/A = 4). The selectivity Cd/Co observed when using these two inorganic ligands was very promising since only about 0.01% or 0.14% of cobalt was scrubbed. An overall countercurrent multistage system was proposed consisting on two scrubbing operations: (1) scrubbing with a cobalt sulphate solution (8.7 g/L Co) for Ni removal and (2) scrubbing with 1 M sodium thiosulphate or 3 M ammonium chloride for Cd removal. The overall scrubbing efficiencies were respectively, 98.6% for Ni and 99.1% or 97.9% for Cd. The final organic phase contained 9.1 g/L Co, 0.03 g/L Ni and 0.005 or 0.012 g/L Cd, anticipating the recovery of a cobalt product with good purity.

Printed Circuit Boards Recycling: Characterization of Granulometric Fractions from Shredding Process

In electronic appliances, printed circuit boards (PCB) represent an important component, containing high grade of valuable metals, besides organic resins and some ceramic materials. Copper is the major metal in PBC’s composition (normally higher than 20% w/w) but many other secondary and minor metal elements, including precious metals, are found in PCB’s. Recycling of PCB´s involves firstly the shredding operation, which is crucial in order to liberate particles from different materials, allowing its further processing by other mechanical, physical and chemical technologies. An efficient shredding operation is difficult to achieve due to the high heterogeneity of these wastes involving materials with different mechanical properties and complex assemblies. This paper presents results from laboratorial studies of shredding of PCB’s and the evaluation of size reduction efficiency as well as the chemical characterization of the obtained shredded fractions. Results showed that an efficient size reduction (characteristic average diameter d50=1.0mm) is obtained using two shredding stages of PCB’s, the first one with a grab shredder and the second one with a cutting mill. Chemical analysis of shredded PCB’s indicated that copper is the principal metal present (28%) followed by Sn, Zn, Pb and Al (3-5%) and many other minor elements. The fine fractions were rich in plastic materials while the metals were essentially present in the intermediate fractions (0.3-1.5 mm). These results can lead to guidelines regarding further design of the physical separation steps in the recycling processes.

Acid Leaching of Leather Tanning Sludges: Metals Behaviour

Sludges generated in leather tanning processing are very complex wastes with potential deleterious effect on the environment and its management constitutes a high cost for the companies. In this work, sludges from a Portuguese tanning company were characterized and leached with acid solutions in order to evaluate the metals removal yields. The sludges contain, as main metals, 15% Ca, 5% Fe and 2.2 % Cr, in a dry basis. Other minor elements namely Al, Ti, Zn, Pb and Cu were also detected. The leaching experiments were carried out with two types of acids – hydrochloric and sulfuric – and the effects of the reaction time, temperature and leachant concentration were evaluated. The reaction conditions strongly affected the chromium leaching yields, being temperature and acid concentration highly significant (confidence level above 99.9%). About 90% of Cr was leached using the higher levels of the factors (4h, 80°C and 2M H+, with both acids). Concerning the other major metals, iron leaching was very efficient (yields usually above 90%) whatever the conditions tested while calcium behaviour was quite different, depending on the type of acid used for the same H+ concentration: H2SO4 leaching efficiency was generally lower than HCl, probably due to the formation of less soluble calcium sulfate. The maximum calcium removal achieved was near 75%. The leaching process developed can be useful not only as a decontamination step of the tanning sludges, but also as a process for metals recovery to be potentially applied in an integrated recycling system, where several metal wastes from different sources could be processed.