Recovery and Isolation Strategies of Platinum, Palladium, and Rhodium from Spent Automotive Catalyst Leachate Using a Polyethylene-Imine-Grafted Cellulose Nanofibril Aerogel

A polyethylenimine-modified cellulose nanofibril (PEI-CNF) aerogel is investigated for the recovery and isolation of Pt-group metals (PGMs) from automobile catalyst leachate. The PEI-CNF exhibits excellent Pt, Pd, and Rh adsorption capacities. In particular, the PEI-CNF shows promising Rh uptake of 1.43 mmol/g (∼147 mg/g), whereas anion-exchange resins barely adsorb Rh. The adsorption of PGMs onto the PEI-CNF is attributed to ion exchange and coordination bond formation by amine (−NH2) and carboxylic acid (−COOH). In the simulated automobile catalyst leachate, PGMs are successfully recovered by the PEI-CNF, and only Zn is coadsorbed as an impurity. The isolation of Pt, Pd, and Rh by selective adsorption onto and desorption from PEI-CNF is also investigated. When the acidity of the leachate is modified, Rh can be isolated from a Pt/Pd/Rh mixture. The Pt is selectively desorbed from a Pt/Pd-adsorbed PEI-CNF aerogel using 0.5 M NaClO4 as an eluent. The isolation strategy of Pt, Pd, and Rh by the PEI-CNF aerogel was suggested for practical application.