3.2 Bonding Fractions of Heavy Metals Contained in Sludgs
The bonding fractions of various metals contained in the sludge are shown in Figure 2. For Cu, the
majority (74 %) exists in the sludge in organic bond fraction, about 73 % of Cr exists as residual fraction. Cd
about 60 % and 34 %, respectively exist in Fe-Mn oxide and carbonate fraction. About 77 % of Pb as residual
fraction, 40 % of the Ni distributes in the organic bonding fraction, followed by Fe-Mn oxide bonding (28%)
and residual fractions (22%). Most Zn exists in Fe-Mn oxide bonding (43 %) followed by organic bonding
form (29 %) and residual fraction (16 %). Among the five bonding fractions, the exchangeable and the
carbonate bonding fractions are the most easily absorbed by plants, followed by Fe-Mn oxides and organic
bonding fractions; the residual fraction is the least absorbable [9]. The results also indicate that heavy metals
contained in the sludge are low percent in exchangeable and carbonate bonding fractions thus alleviating the