Enhanced removal of Cu(II) and Ni(II) from saline solution by novel dual-primary-amine chelating resin based on anion-synergism.

A novel dual-primary-amine chelating resin (EDTB) was newly synthesized for the effective removal of Cu(II) and Ni(II) from saline solutions. NaNO3 as well as Ca(NO3)2, NaCl and CaCl2 unexpectedly promoted the adsorption of Cu(II) or Ni(II) by up to 63.42% or 133.49% in single heavy-metal species systems. Meanwhile, inorganic salts enhanced both Cu(II) and Ni(II) uptake capacities in binary heavy-metal species systems. Anions significantly increased the amount of adsorption sites by condensing the double electric layer. Interestingly, increasing Ni(NO3)2 concentrations elevated the adsorption capacity of EDTB for Cu(II) by 2.10-11.69% in aqueous media without salts while in the presence of salts, rising Ni(NO3)2 concentrations suppressed Cu(II)-adsorption by 2.42-7.68%. The marginal analysis of anion-synergism depending on salt concentrations quantitatively explained such opposite effects using a promotion index. Furthermore, the solid characterizations and a newly-proposed metastable-state model based on pre-loading experiments conformably indicated the reciprocal relationships between cations and anions involving site competition, displacement effect and anion enhancement. Because of such salt-enhanced removal performance and excellent regeneration efficiency higher than 99%, EDTB is potentially eligible for reusing heavy-metals from actual wastewaters especially containing high-concentration salts.