Performance of a modified alkaline lignin towards copper adsorption under different conditions

Polyethyleneimine and carbon disulfide were employed to modify alkaline lignin (AL) in order to introduce-NH,-NH₂ and-CSS-groups. Its adsorption performance towards Cu(II) was evaluated based on the residual concentration (C_r) against the discharge permissible concentration for Cu(II) (2.0 mg/L) established by the World Health Organization. The evaluation was operated under different conditions such as adjusting the solution pH, Cu(II) coexisting with K(I), Na(I), Ca(II) or Mg(II), changing the contact time (t) and initial concentration of Cu(II) (C₀), as well as regeneration. When t and C₀ equaled to 180 min and 50 mg/L, C_r was less than 2.0 mg/L at pH of 5.03 to 5.65. Under the situation of Cu (II) coexisting with 50 mg/L of K(I), Na(I), Ca(II) or Mg(II), C_r was as low as 1.96, 1.53, 1.97 or 1.55 mg/L (t = 180 min, C₀ = 50 mg/L), respectively. Even the modified AL was regenerated and reused four times, C_r was closed to 2 mg/L for each time (t = 180 min, C₀ = 51 mg/L). By comparing with other lignin-based materials according to the adsorption equilibrium time, the maximum adsorption capacity, and C_r, the modified AL exhibited higher application potential in copper-loaded water treatment.