Most of soils of Iran are calcareous in nature.High pH and carbonate levels are common characteristics of these soils.In these conditions the heavy metals tend to occur in insoluble forms,mainly precipitates as carbonates or oxides.The heavy metal Pb contaminates soils,plants,water,the atmosphere,animals and humans,especially in areas of heavy traffic.This experiment was conducted to find the relationship between the Pb adsorption and selected properties of calcareous soils. Twenty surface (0-20 cm) soil samples with pH ranging from 7.6 to 8.2 and calcium carbonate equivalent (CCE) ranging from 27 to 64% were used in the Pb adsorption study. Two-gram subsamples of each soil were equilibrated with 50 mL of 0.01 M KNO3 solution initially containing 30,000 to 300,000 mg Pb L. The Pb that disappeared from solution (after 2 h shaking at 25c) was considered as adsorbed Pb. The adsorption data showed a highly significant fit to Freundlich and Langmuir adsorption isotherm. The coeficients of both isotherms showed significant positive correlations with CCE, OM and clay, except for A Freundlich and OM for which the correlation is negative. Distribution coefficient (also called maximum buffering capacity) calculated as the product of Langmuir K and b, was also found to be significantly related to CCE and OM.
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