Introduction |
Mobilisation of heavy metals in the environment due to industrial activities is of serious concern as these metals are toxic to all forms of life including humans. Chemical oxidation-reduction, precipitation, adsorption, solidification, electrolytic recovery and ion exchange are some of the commonly adopted physico-chemical wastewater treatment processes for heavy metal removal. However, technical or economical constraints restrict wide application of such processes. In this regard, biosorption or biological metal removal has distinct advantages over conventional methods. These techniques are non-polluting, highly selective, more efficient, easy to operate and hence cost-effective for treatment of large quantities of wastewater containing low concentration of heavy metals. Low cost adsorbents like seaweeds, molds, yeast, bacteria, crabshells, agricultural products such as wool, rice, straw, coconut husks, peat moss, exhausted coffee (Macchi et al., 1986; Baran et al., 2005; Akinala and Ekiyoyo, 2006), waste tea leaves (Tee and Khan, 1988), walnut skin, coconut fibre (Espinola et al., 1999), polymerized corn cob (Odozi et al., 1985), melon seed husk (Okieimen and Onyenkpa, 1989), defatted rice bran, rice hulls, soybean hulls and cotton seed hulls (Marshall and Champagne, 1995; Marshall et al., 1993) wheat bran, hardwood (Dalbergia sissoo) sawdust, pea pod, cotton and mustard seed cakes, petiolar felt sheath of palm (Iqbal and Saeed, 2002; Iqbal et al., 2002; Saeed et al., 2002) have been attempted in recent years for heavy metal removal. In the present study, tur dal husk (TDH) (Cajanus cajan), which is a low cost, milling agrowaste available in plenty in a tropical country like India, is used for the removal of Cr (VI) and Fe (III) ions from synthetic solutions.