Using Cyanex 923 for selective extraction in a high concentration chloride medium on nickel metal hydride battery waste: Part II: mixer–settler experiments

Nickel metal hydride batteries are extensively used throughout society and represent a large and complex metallic mixture requiring recycling. This paper deals with the recovery and separation of metals from nickel metal hydride battery waste dissolved in 8 M hydrochloric acid. Three processes based on leachates from individual electrode materials and a mixed material have been evaluated using mixer–settlers. The solvating extractant used is the trialkylphosphine oxide mixture Cyanex 923. The batteries used in this study contained thirteen metals and the processes separate them in up to four fractions. The main fraction in each process successfully creates a high-concentration nickel stream with low levels of potassium and magnesium (if present in the feed) by extracting the other metals. The purity of the nickel stream after the main process step (4–5 stages) is > 99.9%, excluding magnesium and potassium. The extracted metals are separated using a nitrate strip, which allows the rare earth metals and aluminium to be separated from cobalt and manganese.

► We show the feasibility of three cases of NiMH recycling in mixer-settlers.
► The solvating extractants in Cyanex 923 separates the 13 metals into 4 groups.
► The initial step separates and purifies nickel from the other high value metals.
► Selective stripping of the loaded organic phase using nitrates is possible.
► High concentration leach liquors, approximately 4 M metal and 8 M chloride.