Effects of inorganic electrolyte anions on enrichment of Cu(II) ions with aminated Fe3O4/graphene oxide: Cu(II) speciation prediction and surface charge measurement

• Divalent anions had bigger effects on Cu(II) adsorption than monovalent anions.
• Both monovalent and divalent anions could alter the zeta potential of AMGO.
• Divalent inorganic electrolyte anions could significantly affect Cu(II) species.
• HPO42− had the biggest effect on Cu(II) removal in the multi-ion system.
• Interactions of Cl− × SO42− and Cl− × SO42− had big effects on Cu(II) removal.

The present work evaluated the effects of six inorganic electrolyte anions on Cu(II) removal using aminated Fe3O4/graphene oxide (AMGO) in single- and multi-ion systems. A 26−2 fractional factorial design (FFD) was employed for assessing the effects of multiple anions on the adsorption process. The results indicated that the Cu(II) adsorption was strongly dependent on pH and could be significantly affected by inorganic electrolyte anions due to the changes in Cu(II) speciation and surface charge of AMGO. In the single-ion systems, the presence of monovalent anions (Cl−, ClO4−, and NO3−) slightly increased the Cu(II) adsorption onto AMGO at low pH, while the Cu(II) adsorption was largely enhanced by the presence of SO42−, CO32−, and HPO42−. Based on the estimates of major effects and interactions from FFD, the factorial effects of the six selected species on Cu(II) adsorption in multi-ion system were in the following sequence: HPO42− > CO32− > Cl− > SO42− > NO3− = ClO4−, and the combined factors of AD (Cl− × SO42−) and EF (Cl− × SO42−) had significant effects on Cu(II) removal.