Sequential separation of Cu(Ⅱ)/Ni(Ⅱ)/Fe(Ⅱ) from strong-acidic pickling wastewater with a two-stage process based on a bi-pyridine chelating resin

A self-synthesized bi-pyridine chelating resin (PAPY) could separate Cu(Ⅱ)/Ni(Ⅱ)/Fe(Ⅱ) sequentially from strong-acidic pickling wastewater by a two-stage pH-adjusted process,in which Cu(Ⅱ),Ni(Ⅱ),and Fe(Ⅱ)were successively preferred by PAPY.In the first stage (pH 1.0),the separation factor of Cu(Ⅱ) over Ni(Ⅱ)reached 61.43 in Cu(Ⅱ)-Ni(Ⅱ)-Fe(Ⅱ) systems.In the second stage (pH 2.0),the separation factor of Ni(Ⅱ)over Fe(Ⅱ) reached 92.82 in Ni(Ⅱ)-Fe(Ⅱ) systems.Emphasis was placed on the selective separation of Cu(Ⅱ) and Ni(Ⅱ) in the first-stage.The adsorption amounts of Cu(Ⅱ) onto PAPY were 1.2 mmol/g in the first stage,while those of Ni(Ⅱ) and Fe(Ⅱ) were lower than 0.3 mmol/g.Cu(Ⅱ) adsorption was hardly affected by Ni(Ⅱ) with the presence of dense Fe(Ⅱ),but Cu(Ⅱ) inhibited Ni(Ⅱ) adsorption strongly.Part of preloaded Ni(Ⅱ) could be replaced by Cu(Ⅱ) based on the replacement effect.Compared with the absence of Fe(Ⅱ),dense Fe(Ⅱ) could obviously enhance the separation of Cu(Ⅱ)-Ni(Ⅱ).More than 95.0％ of Cu(Ⅱ) could be removed in the former 240 BV (BV for bed volume of the adsorbent) in the fixed-bed adsorption column process with the flow rate of 2.5 BV/h.As proved by X-ray photoelectron spectrometry (XPS) and density functional theory (DFT) analyses,Cu(Ⅱ) exerted a much stronger deprotonation and chelation ability toward PAPY than Ni(Ⅱ) and Fe(Ⅱ).Thus,the work shows a great potential in the separation and purification of heavy metal resources from strong-acidic pickling wastewaters.