Iron Humate as a Low-Cost Sorbent for Metal Ions

Iron humate produced as a waste by-product during an industrial manufacture of humic substances from low-rank brown coals was tested as a sorbent for the removal of metal cations – Cd (II), Cu (II), Co (II), Ni (II), Zn (II), Tl (I), Eu (III), Cr (III) - as well as hexavalent chromium from waters. The Langmuir-type isotherms were used to describe the metal sorption; the respective equations may be derived and interpreted on the basis of a concept of surface–complexation reactions. Parameters of the sorption isotherms were estimated from experimental dependencies measured in a batch arrangement. The sorption capacities ranged from 0.024 mmol g−1 for Co (II) to 0.324 mmol g−1 for Tl (I). The metal uptake was affected by the presence of complexing agents (EDTA, salicylate, citrate), but this effect depends strongly on pH and the kind of complexing agent. The sorption of Cu (II) ions was suppressed in the presence of EDTA in an almost whole examined pH range (ca. 1 – 6.5) and in the presence of citrate at hig...