New method for recovery of nickel and cadmium from the ”black mass” of spent Ni-Cd batteries by solvent extraction

The paper presents experiments with solid–liquid-liquid extraction of heavy metals from the "black mass" (BM) of waste batteries related to the recycling of nickel and cadmium, as well as cobalt (for several samples) from spent Ni-Cd batteries. The extraction and separation of Ni(II) and Cd(II) from the solid BM with Deep Eutectic Solvents (DESs) and other extractants dissolved in toluene or naphtha (kerosene) have been investigated in detail. It has been shown that the extraction efficiency of DESs, contrary to ionic liquids (ILs), is at the level of 30 wt% Ni(II) and 100 wt% Cd(II) from the BM, without the primary process of leaching with sulphuric acid. Solvent extraction has been proposed with two DESs (choline chloride + lactic acid and choline chloride + malonic acid), with ionic liquids (ILs): trihexyltetradecylphosphonium chloride [P6,6,6,14][Cl] (Cyphos IL 101) and trihexyltetradecylphosphonium thiocyanate [P6,6,6,14][SCN], and with organophosphorous-based acids (OPBAs) such as bis(2,4,4-trimethylpentyl) phosphinic acid (Cyanex 272) and di-(2-ethylhexyl) phosphoric acid (D2EHPA). Process factors such as extracting solvents and additives, solvent concentration, holding time, pH and liquid/solid, as well as organic/aqueous (O:A) ratios were studied. For all the systems, the extraction efficiency (E) and the distribution ratio (D) were specified. The metal content in the solid BM was analyzed by the SEM/EDS method and with the use of the UltraWAVE digestion system combined with an atomic absorption spectrometer (FAAS and FAES techniques). An inductively coupled plasma optical emission spectrometer (ICP-OES) was used to determine the concentration of metal ions in aqueous solutions and stripped organic solutions.