Fig 1. Peclet and Reynolds numbers.

Peclet and Reynolds numbers for a spherical particle suspended in different salt solutions as a function of particle diameter. The graph shows pairs of curves of Peclet and Reynolds numbers for three different salt solutions typically used for extraction of plastics: NaCl, ZnCl₂, and NaI. Curves were calculated using the following parameters (for details on how these parameters were obtained, see Section A in S1 Appendix): T = 25°C, ρ_NaCl = 1.2 g/cm³, ${\rho }_{{\text{ZnCl}}_2}=1.6\text{g}/{\text{cm}}^3$, ρ_NaI = 1.8 g/cm³, η_NaCl = 1.76 mPa s, ${\eta }_{{\text{ZnCl}}_2}=1.96\text{mPa}\text{s}$, η_NaI = 2.32 mPa s. For the density of the plastic particle we assumed ρ = 1.05 g/cm³ (polystyrene). Shaded ranges show validity of Stokes’ law for the ZnCl₂ solution.