A study on the modification of rice husk by various carboxylic acids showed that tartaric acid modified rice husk (TARH) had the highest binding capacities for Cu and Pb. The carboxyl groups on the surface of the modified rice husk were primarily responsible for the sorption of metal ions. A series of batch experiments using TARH as the sorbent for the removal of Cu and Pb showed that the sorption process was pH dependent, rapid and exothermic. The sorption process conformed to the Langmuir isotherm with maximum sorption capacities of 29 and 108 mg/g at 27 +/- 2 degrees C for Cu and Pb, respectively. The uptake increased with agitation rate. Decrease in sorbent particle size led to an increase in the sorption of metal ions and this could be explained by an increase in surface area and hence binding sites. Metal uptake was reduced in the presence of competitive cations and chelators. The affinity of TARH for Pb is greater than Cu.

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Hydroxamic acids (N-hydroxy carboxylic amides) may be regarded as derivatives of both hydroxylamine and carboxylic acids. The general formula of hydroxamic acid is R-CO-NHOH. In recent years, hydroxamic acids derivatives have received a lot of attention due to their biological activity as growth factors, food additives, antibiotics, antifungal agents, cell division factor and metal chelators (1), enzyme inhibitors (2), matrix metalloproteinase (MMP) inhibitor (3-5) and tumor inhibitors (6). Their complexes with various metal ions have been used for analytical chemistry as reagents for gravimetric and spectrometric metal determination (7), as collector for rare earth mineral (8), and for metal ions extraction from aqueous media (9). Simple and polymeric hydroxamic acids have also been extensively investigated for several successful analytical separations of metal ions. Besides their ability to form complex with metal ions, long-chain hydroxamic acids, by modi-fication of the terminal OH group, are of considerable interest as efficient surfactants in the detergent industry (10).Hydroxamic acids, in general, have been synthesized by adopting Blatt's procedure (11). In this method, the reaction of an alkyl or aryl ester (RCOOEt) with hydroxylamine in the presence of alkali and the free acid is obtained by the addition of acid in the appropriate quantity in cold solution. However, this chemical method, which is in alkali system, could evoke decomposition or degradation of the desired products due to presence of double bond.An enzymatic route for the synthesis of hydroxamic acid, with the inherent advantages of selectivity, mild reaction conditions and enantioselection, is of considerable synthetic interest. The synthesis of alkanohyroxamic acids (N-acyl hydroxylamines) by Rhizomucor miehei lipase-catalyzed hydroxylaminolysis of fatty acids and soybean methyl ester was reported (12). Later, Candida parapsilopsis was also found to mediate 33 JOS