Ionic strength effect on heavy metal adsorption by soil

Copper adsorption in tropical oxisols

“…Choudhury and Khanif (2000) observed that Cu adsorption was not statistically different in three alluvial soils from Malaysia when concentrations varied from 200 to 500 µg g -1 of metal. At concentrations between 1 to 10 mg kg -1 , Cu had a high affinity for the adsorption surfaces and could be completely adsorbed (Petruzzelli et al,1985). Similar results were obtained by Jordão et al (2000), who demonstrated the occurrence of two phases in the adsorption curve.…”

“…With the increase in the metal concentration, more sites were filled and Cu retention became more difficult (Petruzzelli et al, 1985). At the lower concentrations of added Cu (up to 20 mg kg -1 ), all Cu was adsorbed by the three soils.…”

“…When applied to minerals, sediments and soils, it is used in the form: x/m= KbC/1 + KC, in which K = parameter related to the affinity of the adsorvent by the adsorvate b = maximum adsorption. Despite their limitations, the Freundlich and the Langmuir models have been used in various studies of Cu adsorption (Petruzzelli et al, 1985;Temminghoff et al, 1994;Yuan and Lavkulich, 1997;Jordão et al, 2000) and may be useful to predict the behavior of metals in the soil. The correlation coefficients obtained in these studies varied between 0.83 and 0.99, indicating that these models are well adjusted to diverse soil conditions and metal concentrations.…”

Cadmium accumulation in crops

“…Although Zn was not a strong competitor with Cd for binding sites in soils, increasing soil solution concentrations of Zn, H, or Ca increased Cd desorption and soil solution concentration of Cd (Christensen 1984b). Increases in ionic strength also increased the concentration of Cd in the soil solution (Petruzzelli et al 1985;Lorenz et al 1994). Garcia-Miragaya and Page (1976) suggested that the decrease in Cd sorption with increasing ionic strength of an electrolyte was due to: (i) competition of Cd 2+ with the electrolyte cations for available clay surface sites; (ii) decreased activity of the Cd 2+ in solution and; (iii) formation of uncharged ion pairs and/or uncharged and negatively charged complexes of Cd with the anions in the electrolyte.…”

Adsorption of Cd, Cu, Ni and Zn in tropical soils under competitive and non-competitive systems

“…The smaller steepness of the isotherms of these soils implies that most of the metals were adsorbed even at the smaller concentrations, decreasing as the metal concentration increased. For all soils, the amount of adsorbed Cd, Cu, Ni and Zn increased as the concentration of the metals increased, although the rate of the increase became smaller as lesser adsorption sites were available (Petruzzelli et al 1985;Ross 1994). Almost the whole amount of metals added were adsorbed in soils Oll, Ult2, Alf1 and Ox5, as can be seen by the steep isotherms of the group L1 (Figure 1).…”