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Speciation of heavy metals in the surface waters of a former tin mining catchment

Posted on 19. March, 2012.

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This study was conducted to investigate the chemical speciation of dissolved and particulate elements (Pb, Zn, Cu, Cr, As and Sn) in mining wastewater.

Speciation patterns of dissolved elements were estimated by adsorptive stripping voltammeter while particulate elements were analysed using a newly developed sequential extraction leaching procedure. The procedure has been operationally defined among five host fractions, namely exchangeable, carbonate, reducible, organic bound and residual. A total of six elements (Pb, Zn, Cu, Cr, As and Sn) were analysed in 30 samples at 10 locations (P1–P10) representing three subsequent samples at the same location to obtain the average value from ex-tin mining catchment. The results showed that the heavy metal pollution in P4 and P8 was more severe than in other sampling sites, especially Sn and Pb pollution. In the water samples at P4 and P8, both the total contents and the most dangerous non-residual fractions of Sn and Pb were extremely high. More than 90% of the total concentrations of As and Cr existed in the residual fraction. Cu and Zn mainly (more than 60%) occurred in the residual fraction. However, Pb and Sn were predominantly present in the non-residual fractions of the surface water. For all the six dissolved elements, the less labile species formed the predominant fraction in their speciation patterns. We conclude that the speciation patterns of particulate elements show that most of the Pb, Zn, Cu, Cr, As and Sn were found in the reducible fraction whereas Pb and Sn were mainly associated with the organic fraction.

Water bodies are important in the ecological system. In recent years, due to rapid industrialization and excessive mining activities, these water bodies have been contaminated by different forms of heavy metals. These contaminations pose severe ecotoxicological threats to aquatic wildlife and humans. The biogeochemical behaviour, nutritional bioavailability and toxicity of metals are largely dependent on their chemical speciation. These areas have been extensively studied in recent years. The objective of this study is to investigate the speciation of heavy metals and arsenic by developing a suitable sequential extraction procedure followed by ICP-MS detection in the water bodies of the former tin mining catchment, Bestari Jaya Peninsular, Malaysia.

Conclusions
The newly developed sequential extraction leaching method for particulate phase of water has been successfully applied to the analysis of the metal distributions in the mining waste waters of former tin mining catchment Bestari Jaya, Peninsular, Malaysia. The results obtained provide the following information:
(1) As and Cr were found predominantly in the residual fraction in the studied region. The other elements were found in all of the fractions with different proportions. The significant proportion of the total concentration was also in the residual fraction. The dominant proportion was found in the non-residual fractions for Sn and Pb, the sum concentration of the non-residual fractions was significant.
(2)Overall, the planar distribution of metals indicated that P4 and P8 were more severely polluted than other sampling sites by heavy metals, especially by Sn and Pb. Interventions should be made to reduce anthropogenic discharges in this region

doi: 10.3184/095422912X13259575370081

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Keywords: particulate metals, dissolved metals, anodic stripping, sequential leaching, fractions

Muhammad Aqeel Ashraf(i), Mohd. Jamil Maah(i) and Ismail Yusoff(ii) and Mohamadreza Ghararibreza(ii)
(i)Department of Chemistry University of Malaya, Kuala Lumpur 50603, Malaysia.
(ii)Department of Geology, University of Malaya, Kuala Lumpur 50603, Malaysia.