Immobilization of citric acid and magnetite on sawdust for competitive adsorption and extraction of metal ions from environmental waters

A promising new biosorbent with potential applications in both environmental monitoring and treatment is citric acid-coated magnetic sawdust. In this work, this product was prepared and compared with citric acid-coated magnetite in terms of surface characteristics, adsorption and suitability for magnetic solid phase extraction (MSPE) of Cu(II), Co(II) and Zn(II) in water. Five adsorbents were prepared: magnetite (Mag), citric acid-coated magnetite (cit-Mag), olive wood sawdust (OW), magnetic olive wood sawdust (MOW) and citric acid-coated magnetic olive wood sawdust (cit-MOW). The adsorption by cit-MOW (L-2 shape) was fast, physi-sorption, endothermic, spontaneous and favored. Cit-MOW had adsorption capacities (at pH5.6) of: 21.0, 14.4, 17.6 mg g−1 for Cu(II), Co(II), Zn(II), respectively; while cit-Mag had adsorption capacities (at pH5.6) of: 5.0, 1.6, 4.4 mg g−1 for Cu(II), Co(II), Zn(II), respectively. Competitive adsorption studies showed that Zn and Co were significantly affected by the presence of Cu. A precise, accurate MSPE procedure was optimized using cit-MOW (at pH5.6) for extraction of metals in unspiked and spiked tap, well and rain water samples prior to their determination by atomic absorption spectrometer.