Physicochemical changes of lead(II) contaminated sand–clay mixture

Abstract

In this study, the influence of lead nitrate as a hazardous environmental pollutant was studied through experimental tests to assess its physicochemical effects in soils. Artificially contaminated soil specimens were prepared using sand and two kinds of clays. Direct shear, consolidation, electrical resistivity and unconfined compression tests were conducted. In addition, the influence of lead cation on atterberg limits, pH and particle size distribution of soils was evaluated. Overall, the presence of lead ion in mixtures including bentonite increased the shear strength due to a flocculated structure and replacement of sodium cations by hydrogen ions which is along with the reduction of double-layer thickness. However, due to the broken bonds and rearranging of kaolinite particles to a weaker form, the strength of sand–kaolinite mixtures decreased with the increase of lead concentration. Based on the obtained results, with the addition of lead concentration, the compression index and electrical resistivity of all specimens decreased. Due to the acidic nature of positively charged lead cations, pH of the specimens directly affected and tended to a more acidic range. These findings indicate that the presence of lead ion improves the strength of some kinds of soils including bentonite and decreases the strength parameters of soils with kaolinite.