Speciation and solubility of Cu, Ni and Pb in contaminated soils

Abstract

A long-term incubation experiment was established to assess the solid Ð solution equilibria of (Cu 2þ ), (Pb 2þ ) and (Ni 2þ ) in soil pore water. The experiment comprised 23 soils spiked with 135, 300 and 75 mg kg À1 of Cu, Pb and Ni, respectively, added as nitrate salts in solution. Samples of soil pore water were extracted several times during the incubation period of 818 days and concentrations of Cu, Pb, Ni, dissolved organic carbon and major cations and anions were measured. Similar measurements were carried out on a smaller selection of historically contaminated soils to extend the range of data and assess compatibility of the measurements with the incubated soils. The chemical speciation program 'WHAM VI' was used to speciate metal ions in solution. A pH-dependent Freundlich equation was used to describe free ion activities, p(M 2þ ), for Cu, Pb and Ni using total adsorbed metal, soil pH, soil organic carbon content and ionic strength as determining variables. For all three metals the greatest improvements in model fit were found when metal ions were assumed to be adsorbed exclusively on soil organic carbon rather than on the 'whole soil'. Further improvements in the description of p(Cu 2þ ) and p(Ni 2þ ) were found when the ionic strength of the soil pore water was included within the model formulation. Residual standard deviations (-log 10 (M 2þ ) units) for the best-fit models were 0.36, 0.53 and 0.29 for p(Cu 2þ ), p(Pb 2þ ) and p(Ni 2þ ), respectively. The effects of progressive fixation of Pb, Cu and Ni on model parameterization, during the course of the experiment, were found to be small. Independent datasets from both published and unpublished sources were used to compare experimental protocols and validate the model for the determination of (M 2þ ) in soil pore water.

Sources, lability and solubility of Pb in alluvial soils of the River Trent catchment, U.K.

“…NPOC concentrations also showed little variation with depth. There was not a significant correlation between Pb concentration in pore water and pH, although it was noted that Pb concentrations sharply decreased at soil pH>7 due to the greater Pb sorption with increasing pH (Tye et al, 2004). No correlation was found between Pb concentrations in pore solution and NPOC or any sorptives phases (LOI, FeO or clay).…”

“…Other studies have reported that decreased lability of Cd and Zn is associated with stronger adsorption, which is essentially pH-dependent (Tye et al, 2002;Young et al, 2007). Lead solubility in moderately contaminated soils is usually controlled by sorption and complexation processes rather than precipitation (McBride et al, 1997;Welp and Brümmer, 1999) is added to soils, the majority of the fixation occurs within ~300 days (Tye et al, 2004). Much of the Pb has probably been in contact with the soil for considerable periods (possibly 1000's of years) and has reached a pseudo-equilibrium with the soil properties before being eroded and re-deposited.…”

Lability, solubility and speciation of Cd, Pb and Zn in alluvial soils of the River Trent catchment UK

“…Input data to WHAM 7 40 included solution pH, temperature (277 K) and solution concentrations of Na, Mg, Al, K, Ca, Fe(III), Mn, Ni, Cu, Zn, Cd, Pb, Cl -, NO 3 -, SO 4 2-, CO 3 2-, F -and PO 4 3-. Colloidal fulvic acid was also included assuming that fulvic acid contains 50% nonpurgable organic carbon (NPOC) and only 65% was active, the 45 remainder being inert with respect to ion binding 46 …”

“…Input data to WHAM 7 40 included solution pH, temperature (277 K) and solution concentrations of Na, Mg, Al, K, Ca, Fe(III), Mn, Ni, Cu, Zn, Cd, Pb, Cl -, NO 3 -, SO 4 2-, CO 3 2-, F -and PO 4 3-. Colloidal fulvic acid was also included assuming that fulvic acid contains 50% nonpurgable organic carbon (NPOC) and only 65% was active, the 45 remainder being inert with respect to ion binding 46 . The possible existence of sub-micron FeOx and AlOx colloidal complexes was overcome by including the FeOx and AlOx precipitation option in WHAM 7 where the metals are allowed to precipitate out with a surface charge 47 .…”

Humic Ion-Binding Model VII: a revised parameterisation of cation-binding by humic substances

“…Examples include 71 the acidification of soils [7][8][9][10][11][12][13][14] and surface waters [15] , trace metal behaviour in soils [16][17][18][19][20][21][22] , surface 72 waters [23][24][25][26][27][28][29][30][31] and groundwaters [32] , lake sediment diagenesis [33,34] , rare earth geochemistry [35-73 37] , iron and manganese geochemistry [38][39][40][41] , radionclide geochemistry [42][43][44][45] , organic matter 74 solubility in soils [46,47] , catchment modelling [48,49] , interactions of metals with biota [50,51] , 75 ecotoxicology [52][53][54][55][56][57][58][59] and Critical Loads …”