DETERMINING LEAD ACTIVITY IN AN EGYPTIAN ALLUVIAL SOIL USING COMPETITIVE CHELATION METHOD | ||||
| Zagazig Journal of Agricultural Research | ||||
| Article 10, Volume 44, Issue 4, July 2017, Page 1315-1323 PDF (312.98 K) | ||||
| Document Type: Original Article | ||||
| DOI: 10.21608/zjar.2017.52931 | ||||
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| Authors | ||||
Samer A. El-Gendi  1; M. A. Hassan1; E. A. El-Naka2
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| 1Soils Water and Environ. Res. Inst., Egypt | ||||
| 2Soil Sci. Dept., Fac. Agric., Zagzig Univ., Egypt | ||||
| Abstract | ||||
| Lead has been emitted into atmosphere since the birth of metallurgy in ancient times and with increasing intensity since the establishment of medieval and modern industries. In the present study lead activity was measured in six alluvial soil samples which were collected from 6 successive layers (15-cm thick, each) from surface soil to 90 cm depth to identify the various Pb minerals which might control Pb activities in that soils (using constructed lead stability mineral diagrams). The Pb content decreased with increasing soil depth, ranging from 20.50 µgg-1 in the surface layer to 11.03 µgg-1 in the deepest soil sample, which mostly reflect the impact of anthropogenic influences on lead–contamination in soil. The values of log Pb2+ activities varied from -4.9498 to -7.1098 and were inversely correlated with pH. The predicted relationship equation could be: Log (Pb2+) = 9.619-2.111 (pH), indicating that lead solubility in soil decreased about 100 folds for each pH unit increase. Plotting Pb activities on the constructed stability diagram of various Pb minerals indicated the solubility of PbO being too soluble to persist under normal conditions .Pb2SiO4 and PbSiO3 minerals in equilibrium with SiO2 (soil) or SiO2 (quartz) were too soluble to regulate Pb2+ activities. Pb5(PO4)3Cl was the most insoluble of lead phosphate minerals and controls lead solubility throughout pH range of most soils. Values of Pb2+ were lower than those maintaining by Pb5 (PO4)3.OH mineral. Pb- mixed carbonate and hydroxide minerals indicating that PbCO3.PbO , was too soluble to persist. Values of Pb+2 were super saturated with respect of Pb(OH)2, PbCO3 and Pb3(CO3)2(OH)2 at 0.0003 atm.CO2. In presence of 10-3 M SO4, PbSO4 mineral limits Pb at 10-4.79 M and its solubility changes one log unit per each log unit change in SO4-2. In the high-lead surface soil sample Pb+2 activity values were maintained by PbSO4.PbO and PbSO4 (log SO4 at -2), confirming the importance of studying environmental chemistry of the heavy metals. | ||||
| Keywords | ||||
| Lead; activity; Chelation; stability diagram; Pb-minerals | ||||
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