ISSN:
1432-0495
Keywords:
Adsorption
;
Distribution coefficients
;
Lead
;
Zinc
;
Copper
;
Goethite
Source:
Springer Online Journal Archives 1860-2000
Topics:
Geosciences
Notes:
Abstract The adsorption of lead(II) and zinc(II) onto goethite was studied as a function of pH, total dissolved metal concentration, surface area of goethite, and ionic strength. The results for zinc and lead were compared with those for copper reported earlier. The adsorption edge of lead ranges from pH 4 to 7, similar to that of copper, but the adsorption edge of zinc is displaced by 1.5 pH units toward higher pH. A fourfold increase in goethite surface area had a significant effect on the adsorption edge of lead, but a tenfold increase in the ionic strength of the medium did not affect the adsorption edge of lead and zinc. At neutral pH, 50 percent of the zinc was still available for transport and reactions in aqueous solution, whereas almost 100 percent of the lead and copper were bound to the goethite surface. The distribution coefficients increase sharply with the increase in pH and ranged from 60 to 30,000 ml/g in 2.5 pH units for lead and from 60 to 3000 ml/g in 1.5 pH units for zinc, depending on the goethite surface area and metal concentration. Distribution coefficients were used to calculate the number of protons released per mole of metal adsorbed during the adsorption process, with the average number of protons released per mole of lead and zinc adsorbed estimated to be 0.97±0.07 and 1.32±0.06, respectively. Proton coefficients of copper, lead, and zinc were correlated to their ionic radii and apparent equilibrium binding constant. Although the adsorption behavior of copper and lead were similar and both have the same charge, the drop in pH per mole of metal adsorbed is more in copper than in lead.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00775914
Permalink
