Determination and assessment of potential mobility of heavy metals in solid samples by Sequential Extraction Procedures (SEP) / Keivan Nemati

• Main Author: Nemati, Keivan
• Format: Thesis
• Published: 2011
• Subjects: QD Chemistry
• Online Access: http://studentsrepo.um.edu.my/3739/1/Content.pdf; http://studentsrepo.um.edu.my/3739/2/Final_Tesis.pdf; http://pendeta.um.edu.my/client/default/search/results?qu=Determination+and+assessment+of+potential+mobility+of+heavy+metals&te=; http://studentsrepo.um.edu.my/3739/

The use of sequential extraction schemes for fractionation of metals in different substrates has grown exponentially over the past two decades. Despite the popularity of these schemes, they have been criticized for metal redistribution and the reagents used. The work presented in this dissertation is aimed at addressing these problems by, (i) a Tessier sequential extraction (ii) a BCR sequential extraction schemes and modified BCR method, (iii) a comparison between Tessier and BCR method for shrimp aquaculture sludge. From the sequential extraction, Cd, Mn and Pb were mostly found in exchangeable/carbonate form, showed its susceptibility to be leached easily. Also Cu and Zn were extracted predominantly in oxidizable form. All metal concentrations (except Cd, Zn and Cu) were extracted to be higher in residual fraction in this method. By comparing the percentage of recovery, the BCR method was better than Tessier method. Nevertheless, for both methods the percent of their recoveries were acceptable. (iv) a comparative study on open system digestion and microwave assisted digestion methods for metal determination in shrimp sludge composts was done. The compost made from shrimp aquaculture sludge co-composted with organic materials (peat, crushed bark and manure) was used as an organic growing medium for crop. Open system digestion and microwave assisted digestion procedures were employed in sample preparation. Various combinations and volumes of hydrofluoric, nitric and hydrochloric acids were evaluated for the efficiency of both methods. The best recoveries were found in the range between 95% and 99% for microwave assisted digestion with a mixture of 2 ml of HF, 6 ml of HNO3 and 2 ml of HCl. The concentration of heavy metals in different stations and different depths obtained for Sungai Buloh and the straits of Melaka sediments in Selangor, Malaysia by modified BCR method. The results of these samples showed high contamination in stations 1, 2 and 3. Also the concentration of heavy metals has been decreased from top to lower layers. Variation trends of concentration for each element in the seven sample cores were approximately similar. We can see a normal decreasing from top to down. Modified sequential extraction method (MSE) is broadly accepted and applied to elemental fractionation in different environmental samples. The main limitations of sequential extraction procedures are that, they are extremely time-consuming, and are less used for routine analysis. This problem has also been noted and is replacing the conventional procedure by other alternatives, such as microwave (MW) heating and ultrasonic (US) shaking. The results of ultrasound digestion showed in fraction 1, Cu, Pb and Zn showed highest recoveries in 40 min, while, for Cd , Cr and Ni it was obtained in 50, 50 and 30 min respectively. Fraction 2 showed highest recoveries for Cd, Cr, Pb and Zn in 50 min but Cu was found in 40 min and Ni in 30 min. In fraction 3, the highest recoveries have been found for Cu, Pb and Zn in 50 min while, for Cd and Cr found in 40 min and Ni in 30 min. The results of microwave assisted digestion method for CRM BCR 701 showed all recoveries have been obtained more than 98% except Zn that is about 96 %. In fraction 2, the highest recovery has been found for all metals more than 95 % except Pb about 94 %. In this case highest recoveries have been obtained for modified BCR more than 97 %. In fraction 3 lowest recoveries have been obtained for Pb and Zn same as Fraction 2.