Polyethyleneimine functionalized mesoporous diatomite particles for selective copper recovery from aqueous media

To date, the quest for cost-effective methods for removal of dissolved metals from aqueous solutions remains a daunting challenge for many industries. This paper reports on the development of an effective, hybrid adsorbent for selective copper recovery from aqueous solutions under industrially relevant conditions. The work involved (i) purification and functionalization of diatomaceous earth (DE) particles with glutaraldehyde(GA)-crosslinked polyethyleneimine(PEI), (ii) physicochemical characterization of the product and (iii) metal adsorption from solutions containing Cu(II)/Ni(II)/Fe(II)/Ca(II)/Mg(II)/Mn(II)/Al(III)/Na ions and their subsequent elution behaviour. Acid leaching of the pristine DE led to a significant reduction in its metal oxide (e.g., Al₂O₃, Fe₂O₃) constituents and a concomitant increase in both SiO₂ content and specific surface area. Upon functionalization with GA-crosslinked PEI, the DE particles' interfacial chemistry was completely altered to that of the polymer with no change in specific surface area. Isothermal batch adsorption from saline (15 g/dm³ NaCl) and non-saline solutions containing 500 and 1000 mg/dm³ of Cu at ~ pH 4 revealed > 97% Cu(II) removal by functionalized DE within 3 min in both cases. Subsequent water elution tests at pH 1 showed complete release of the adsorbed Cu confirming pH-dependent interaction between dissolved Cu and GA-crosslinked PEI. The preliminary batch adsorption/elution tests involving 1000 mg/dm³ solutions of Ni, Ca, Mg, Mn, Fe, Na and Al showed little or negligible affinity of the functionalized DE towards these elements, suggesting good selectivity for Cu. Furthermore, it is shown that the functionalized particles are chemically stable at H₂SO₄ concentrations up to 2 M and may be recycled > 10 times without loss in their Cu adsorption/desorption performance.