Zinc and Chromium elimination from complex aqueous matrices using a unique aminopropyl-modified MCM-41 sorbent: Temperature, kinetics and selectivity studies

Abstract

An aminopropyl-modified MCM-41 sorbent obtained by grafting amino groups on the surface of a previously synthesized MCM-41, was used for the removal of Cr(VI) and Zn(II) from different aqueous matrices: solutions of Zn(II) and Cr(VI) in distilled water, in distilled water with high-salt content, and in a natural river water sample. The sorbent particles are spherical with a mean diameter of ≈500nm, surface area >600m2g−1 and uniform aminopropyl function distribution. Single component adsorption batch experiments, fitted with the Langmuir model, show that MCM-41-NH2 has high removal capacity for Cr(VI) and for Zn(II), 87.5 and 58.9mgg−1, respectively. Binary component adsorption experiments show that the selectivity toward chromium oxyanions or zinc cations could be adjusted by changing the pH of the solution to be treated. When pH was fixed at acidic conditions chromium was preferentially removed, while the MCM-41-NH2 sorbent retained selectively zinc species when pH was increased up to 7. The presence of salts, either added (i.e. KCl) or natural as those present in river water, resulted in an improvement in the selectivity for both metals removal reaching values of up to 97%. The obtained results indicate that MCM-41-NH2 is an efficient and selective sorbent capable of removing Cr(VI) oxyanions and/or Zn(II) cations from complex polluted water matrices.