sorption and desorption of lead in some calcareous soils of western azerbaijan province

abstract the availability of heavy metals in the soil is related to their partitioning between solution and solid phases and expressed by sorption isotherm. twenty surface soil samples (0-30 cm) belonging to five soil subgroups were taken from agricultural regions of western azerbaijan province. the sorption isotherms of pb were determined by equlibrating the soil with solutions containing 0, 100, 300, 500, 700, 900, 1100 and 1300 mg pb l-1 from pb-nitrate source in 0.01 m nano3 as background electrolyte. illite was the dominant clay mineral in typic calcixerepts (tc), typic haploxerepts (th) and typic endoaquepts (te) whereas in vertic calcixerepts (vc) and vertic endoaquepts (ve) the clay mineralogy was dominated by smectite. active and equivalent calcium carbonate and clay contents ranged from 4.3 to 7.8%, 6.2 to 16% and 31 to 45%, respectively. the linaer, langmuir and freundlich isotherm equations were fitted to the experimental data of pb sorption and desorption. both the freundlich (0.98< r2 <0.70) and linear (0.94< r2 <0.51) approaches described the pb sorption and desorption data well, and the lagmuir model (0.99< r2 <0.71) was well fitted to some of the soils, mostly, those soils with low cce content. a significant positive correlation was found between cce and the lagmuir adsorption maxima (b) (r = 0.84, p≤ 0.01) and also the freundlich constant a (r = 0.78, p≤ 0.001). the soil partition coefficient (ksd) showed a positive correlation (r = 0.55, p≤ 0.05) with acce. stepwise regression showed that 62% of variation in lead sorption was accounted for cce content. however, the relatively high ph (7.0 to 8.0) of the experimental soils and a presence of relatively high values of free and active carbonate in the soils along with the large sorption capacity of these soils suggest the possibility of solid phase precipitation as pbco3. a strong and irreversible binding of pb in the soils were recorded. results showed that the cce and clay contents were of more importance in controlling the sorption of pb in the studied soils.