-Heavy metal pollution is a major problem in the environment. The impact of toxic metal ions can be minimized by different technologies, viz., chemical precipitation, membrane filtration, oxidation, reverse osmosis, flotation and adsorption. But among them, adsorption was found to be very efficient and common due to the low concentration of metal uptake and economically feasible properties. Agro waste materials are of low cost and widely used, and very promising for the future. These are available in abundant quantity, are cheap and have low or little economic value. Different forms of agro waste materials are used as adsorbents such as fibers, leaves, roots, shells, barks, husks, stems and seed as well as other parts also. Natural and modified types of cellulosic materials are used in different metal detoxifications in water and wastewater. In this review paper, the most common and recent materials are reviewed as the efficiency of Pb(II), Hg(II) & Cr(VI) removal from aqueous solution.Keywords: Pb(II), Hg(II) & Cr(VI), agricultural wastes adsorbents, adsorption 1 .INTRODUCTION Environmental pollution due to heavy metals like lead, mercury, cadmium, chromium etc. is of serious concern throughout the world. Due to anthropogenic activities, the concentrations of heavy metals have increased in the environment. Though many methods are available for mercury removal, adsorption is considered as simple, economical and versatile method. Heavy metals are abundant in our drinking water, air and soil because they are present in every area of modern consumerism like construction materials, cosmetics, medicines, processed foods and personal care products (Abia et al., 2003). In small quantities, certain heavy metals are nutritionally essentially for a healthy life, but in large amounts they may cause acute or chronic toxicity (poisoning). The absorption of this hazardous substance into the bloodstream, distribution to the entire tissues and bioaccumulation in the receptive sites leads to adverse effects, such as potent neurotoxicity, blood vessel congestion and kidney damages (Kidd et al., 2012) In the present work, we have reviewed the recent articles on the lead (II), mercury(II)and Cr(VI) removal from aqueous solution by considering the effect of various parameters such as pH, temperature, metal ion concentration, contact time, and adsorbent dosage on mercury uptake. These factors are of the utmost significance, as any change in these parameters may considerably change the heavy metals removal efficiency of an adsorbent. In this paper the efficiency of Pb(II), Hg(II) and Cr(VI) removal from aqueous solution using agricultural waste material were reviewed.2. GENERAL OBSERVATIONS Most of the studies have been performed in batch mode operation. Synthetic stock solutions were prepared by dissolving lead/mercury compounds (mercury nitrate, mercury chloride etc) and dichromates of chromium for adsorption studies. Effect of pHAdsorption of Pb(II), Hg(II) and Cr(VI) are very sensitive to the pH. The adsorption capaciti...

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The potential of ethylenediamine modified date plam trunk (MDPT) for the adsorption of Hg(II) from aqueous solutions. Factors influencing mercury(II) adsorption onto MDPT such as initial Hg(II) concentration (12.5-100 mg/L), pH (1-6), contact time (5-120 min), and adsorbent dosage (2.0-20.0 g/L) were investigated. The adsorption equilibrium was established within 120 min. Maximum adsorption of Hg(II) occurred at pH~5. Before and after adsorption, MDPT was characterized by Fourier transform infrared spectroscopy (FTIR) and in order to prove its Hg(II) adsorption capacity. The results show that the adsorption rate could be well fitted by pseudo-second-order rate model, and the adsorption isotherm data obeyed Langmuir model. The adsorption capacity for Hg(II) was found to be 29.25 mg/g. Evidently, the high efficiency and fast removal of mercury using MDPT suggest the synthesis of modified adsorbents with similar physical and chemical properties of MDPT as a valuable and promising wastewater treatment.

Ethylenediamine modified date palm trunk an attractive approach for improvement of lead (II) uptake from aqueous solutions. Factors influencing Pb(II) adsorption onto MDPT such as initial Pb (II) concentration, pH, contact time, and adsorbent dosage were investigated. The adsorption equilibrium was established within 120 min. Before and after adsorption, MDPT was characterized by Fourier transform infrared spectroscopy (FTIR). The results showed that the pseudo-second order model fits the experimental data very well. The equilibrium data have been analysed using Langmuir and Freundlich isotherm models. The recovery of Pb(II) adsorbed on MDPT was found 98.5% using 0.2 M HCl. Desorption experiments showed the feasibility of the regeneration of MDPT.