Factors Affecting the Removal of Selected Heavy Metals using a Polymer Immobilised Sphagnum Moss as a Biosorbent

Abstract

A hydrophilic polyurethane foam was used to immobilise dried sphagnum moss as a polymer/biomass matrix. This was then tested for its ability to remove Cu(II), Zn(II) and Pb(II) from aqueous solution. Further selected experiments using copper looked at factors which it was thought might affect the performance of the biosorbent. The optimum pH for Cu(II) and Zn(II) sorption was found to be in the range 6 - 7, whilst Pb(II) showed a more uniform sorption profile over the pH range 3 – 8. At pH values above 8 there was significant leaching of organic components from the immobilisation matrix. The immobilised biomass maintained around 90% of its sorption capacity over 10 repetitive cycles of sorption/desorption using HCl as a desorbent with typically > 95% metal ion recovery from each cycle. There were no marked differences in the maximum sorption capacities for Cu(II) using different biomass particle sizes in the immobilisation matrix, but the affinity of the immobilised biomass for Cu(II) decreased with increasing particle size. Alkali and alkaline-earth metal ions did not affect the heavy metal biosorption, but aluminium ion had a significant influence and itself could be adsorbed to a large extent. Acetic acid, urea, and carrageenan did not affect the maximum biosorption capacity of Cu(II), but carrageenan significantly reduced the affinity of biomass to metal ions probably as a result of its own biosorptive properties.