Dysprosium adsorption on expanded vermiculite: Kinetics, selectivity and desorption

Dysprosium obtainment from secondary sources is a current theme in the scientific scenario due to the high demand and environmental issues related to primary production. Hydrometallurgy applied to urban mines can be a potential alternative to separate and recover critical metals as dysprosium. Thus, the present work evaluates the dysprosium adsorption, a secondary separation process in the hydrometallurgical routes, onto expanded vermiculite through kinetic, selectivity, and desorption aspects. The adsorption process had a kinetic governed by the external mass transfer model, in which the primary mechanism of adsorption is the ion exchange. The adsorption efficiency of vermiculite towards dysprosium from a multicomponent solution indicated that the vermiculite adsorbed preferably Dy (97.6%) followed by Pb (80.1%) > Ni (70.1%) > Cd (52.0%) > Cu (51.7%). A desorption efficiency of 89% was reached using magnesium nitrate hexahydrate as eluent (0.2 mol/L), contact time (3 h), and solid/liquid ratio (14 g/L) determined by surface response methodology from a rotational central composite design of experiments. The characterization of the loaded adsorbent indicated that vermiculite, after the adsorption of dysprosium, lost expansion, enlarged the interlayer space due to the exchange of magnesium, and maintained its alumino-phyllosilicate characteristic composition. Therefore, the adsorption of dysprosium is efficient, fast, selective, and did not promote relevant structural changes in the adsorbent structure. Moreover, the very successful dysprosium desorption favors expanding vermiculite as adsorbent in further applications.

Automated summary

The study shows that expanded vermiculite has high adsorption efficiency, selectivity, and desorption efficiency towards dysprosium. This makes expanded vermiculite a promising adsorbent for further applications in the separation and recovery of critical metals.