Hydrometallurgical processes for recovery of valuable and critical metals from spent car NiMH batteries optimized in a pilot plant scale

Abstract

With the increasing use of hybrid and electrical cars comes an increasing demand for rare earth elements (RREs) needed for the production of car batteries. Currently NiMH batteries contain approximately 3kg of REEs, 11kg of nickel and 1.5kg of cobalt. Leaching with HCl and solvent extraction using Cyanex 923 have been applied to recover metals from this waste. Process has been developed for NiMH car batteries, which can be dismantled manually or mechanically. Depending on the way of dismantling, three different materials can be obtained (cathode plates, anode plates or mixed material). Developed technologies have been designed to recover metals either from cathodic and anodic material or from mixed (cathodic and anodic) material. Hydrochloric acid (8M) is used as a leaching agent at a temperature of 30°C. The extraction system consists of the solvating extractant trialkylphosphine oxide mixture (Cyanex 923) and tributyl phosphate (TBP) diluted in kerosene. A pre-main extraction (8% Cyanex 923, 10% TBP, 82% kerosene) is used to remove Fe and Zn from cathode and mixed material leachates. Zn and Fe are extracted in four extraction stages followed by three scrubbing stages to remove co-extracted metal ions and four stripping stages to remove extracted Zn and Fe (99.9%). Aluminium and REEs are separated from Ni, K, and Mg in three main extraction stages (70% Cyanex 923, 10% TBP, 10% kerosene, 10% 1-Decanol). High purity Ni (>99.9%) in a raffinate is obtained after main extraction. Loaded organic phase is stripped with mixture of 0.9M NaNO3 and 0.1MHNO3 to remove co-extracted Co, Mn and Ni. Aluminium and REEs are recovered by stripping step using 1M HCl after previous scrubbing of organic phase with 1M NaNO3 to remove residual Co and Mn. To determine required parameters McCabe-Thiele diagrams were constructed. Obtained parameters were tested in a counter-current system using pilot plant scale mixer-settlers and all three processes were optimized.