Wet separation between palladium(II) and molybdenum(IV) ions by using laser-induced particle formation: Enhancement of recovery efficiency of palladium by laser condition

• We performed wet separation of Pd and Mo by using laser-induced particle formation.
• We selectively reduced Pd ion by laser and successfully recovered as particles.
• Laser condition had an influence on recovery efficiency of Pd.
• Recovery efficiency and particle size of Pd increased in using pulsed laser.
• Laser contributes not only in reduction of Pd ions but also Pd particle growth.

Metal separation by using laser-induced particle formation was applied to the recovery of Pd from a mixed solution with Mo. In this separation, the Pd ions in the mixed solution containing 1 vol% ethanol were selectively reduced by irradiation of pulsed laser (10 Hz repetition rate) and high-repetition-pulse (HRP) laser (30 kHz repetition rate) with the wavelength of 355 nm while keeping irradiation power constant. The laser-induced reduction resulted in the generation of the Pd neutrals, which is followed by the aggregation of Pd neutrals in the absence of a stabilizing agent. The generated Pd particles were recovered and separated from the Mo ions by filtration. ICP-AES analysis of the filtrate elucidated that the Pd metals were successfully separated from Mo with a high recovery efficiency (84%). The recovery efficiency of Pd was different in the irradiation between the pulsed and HRP lasers; the efficiency obtained using the pulsed laser was 12% higher than that from the HRP laser. XRD analyses demonstrated that the Pd particles subjected to pulsed laser irradiation were 30 times larger than those subjected to the HRP laser. Based on TEM observations, the sizes of the Pd primary particles were approximately 200 nm (pulsed laser) and <10 nm (HRP laser). The formation of submicron Pd particles using the pulsed laser increased the recovery efficiency of Pd in this separation, because the Pd particles were recovered by a 0.2 μm pore size filter. The formation of different size Pd particles in the irradiation between the pulsed and HRP lasers clearly suggests that the pulsed laser irradiation contributes not only to the reduction of the Pd ion but also to the Pd particle growth in the laser-induced particle formation.

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