Removal of free and complexed heavy-metal ions by sorbents produced from fly (Musca domestica) larva shells

Fly larva shells (FLS) are formed as a side product in the biological treatment of organic wastes, and chitin and chitosan produced from the FLS have been used as sorbents for heavy-metal ions. Sorbents are characterised by FT-IR measurements and pH-potentiometric titration and by determination of their surface area, and the content of main elements (C, N, P, S) and ashes. Free metal ions are sorbed best (up to 0.5–0.8 mmol g−1) onto chitin and chitosan. The sorption ability for free metal ions of chitin decreases in the order Fe(III)>Cu(II) (Pb(II)>Zn(II). >Ni(II)>Mn(II) and that of chitosan decreases in the order Cu(II)>Mn(II)>Ni(II)>Zn(II)>Pb(II)>Fe(III). The complexed metal ions are sorbed by the FLS up to 0.2–0.4 mmol g−1. The sorption ability for metal ions and ligands depends on pH, concentration of complexed metal ions and the ligand species in the solution. Glycine has the retarding effect on the sorption of Ni(II) and Cu(II) ions, and EDTA enhances the Cu(II) ion sorption. Ni(II) and glycine sorption obeyed the Langmuir isotherm. The observed sorption data show the promising potentialities of the FLS for the heavy-metal removal from the solutions, containing strong complexing agents. Mechanisms for the removal of free and complexed metal ions by chitin, chitosan and the FLS have been discussed.