A Pitfall in Heavy Metal Separation with Amino‐modified Silica Adsorbents from Aqueous Solution: The Occurring pH Shift. Issue 5 (10th March 2022)

• Record Type: Journal Article
• Authors: Kriese, Friederike; Lassen, Stephan; Horn, Helena
• Is Part Of: ChemistryOpen. Volume 11:Issue 5(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-03-10
• Subjects: adsorption -- amino-functionalization -- heavy metal -- nickel -- cobalt; Chemistry -- Periodicals; 540; 540.5
• DOI: 10.1002/open.202200034
• Languages: English
• ISSNs: 2191-1363

Abstract

Abstract: Selective separation of heavy metal ions from acidic aqueous solutions is of strong interest for certain industrial processes, such as electroplating, as well as environmental protection, for example battery recycling. Amino‐functionalized adsorbents are often discussed as suitable material for this purpose. Herein, two silica‐based adsorbents functionalized with 3‐aminopropyl‐ and 3‐[2‐[2‐aminoethylamino]‐ethylamino]‐propyl‐ligands resulting in adsorbents MonoA and TriA, respectively, were investigated regarding their separation behavior with focus on nickel(II) and cobalt(II) in batch as well as continuous flow experiments in acidic aqueous solutions. For both adsorbents, pH shifts into the alkaline range were observed in the process solutions, causing precipitation of metal hydroxides mainly in the particle pores in case of adsorbent MonoA and a combination of precipitation and adsorption regarding adsorbent TriA. Contrary to prior studies, our findings evidence that amino‐functionalized adsorbents are not applicable for nickel(II) and cobalt(II) in selective adsorption processes and additionally demonstrate that, besides batch investigations, continuous flow experiments are essential for well‐founded adsorbent selections in process development. Abstract : Unspecific separation of heavy metal ions such as cobalt(II) and nickel(II) on amino‐functionalized adsorbents has been found due to severe pH shifts into the basic milieu caused by metal hydroxide precipitation instead of specific metal complexing. These findings contradict reports on such adsorptive processes in literature and prove that continuous flow examinations are necessary for a sufficient adsorbent selection.