Sorption of Zn(II) and Cu(II) by four Argentinean soils as affected by pH, oxides, organic matter and clay content

Abstract

Increasing heavy metal applications to agricultural soils in the form of phosphatic fertilizers and/or atmospheric deposition have led to extensive research on the chemistry of Zn and Cu in soils. Cu(II) and Zn(II) sorption onto different soil fractions of three Mollisols and one Entisol from the southwest of Buenos Aires Province, Argentina, was studied. Different variables affecting the sorption capacity such as pH, cation exchange capacity, specific surface area (SSA), type and amount of clay minerals present, content of Fe-, Al-, and Mn-oxides and oxohydroxides, organic matter and electric charge parameters were investigated. To assess the monometal sorption, batch equilibrium experiments were performed using Cu(II) and Zn(II) metal solutions over a pH range from 4.0 to 7.0. The increase in metal sorption with increasing pH for both metal cations was attributed to an increase in the negative surface charges. At pH 5.0, Cu(II) showed more affinity than Zn(II) for reactive surface soil sites. Removal of organic matter via H 2 O 2 treatment (\2-mm OMR fraction) dramatically decreased the sorption of both cations; however, Cu(II) was sorbed more than Zn(II). The variation in SSA (obtained by water vapor adsorption) in \2-lm (clay fraction) and \2-mm (whole soil fraction) after Zn(II)/Cu(II) sorption at pH 4 and 6 reflected a different interaction between both cations and binding surface sites. Sorption isotherms correlated better with Langmuir than Freundlich equations. Sorption capacities (q max ) in \2-lm fraction, ranged from 166 to 111 mmol kg -1 for Cu(II), and from 62 to 31 mmol kg -1 for Zn(II). This study extends the understanding of the sorption mechanisms of Cu(II) and Zn(II) to agricultural soils from the semi-arid Pampean region of Argentina. An understanding of the local soil environment is important in order to reduce or prevent contamination of this valuable resource, especially from fertilizers and other such anthropogenic additions to the soil.

Isomorphic Substitutions in Clay Materials and Adsorption of Metal Ions onto External Surfaces: A DFT Investigation

“…In all cases, crystallographically distinct T sites exert a minor influence, which is quite different from the scenario in zeolites. − Quantity of negative charges is the foremost factor that differentiates the adsorption performances for different clay materials. In addition, for clay materials with variable charges, the adsorption of metal ions will be significantly altered by external conditions such pH, as supported by experimental observations that the enhanced adsorption of metal ions on clay materials at higher pH values is attributed to the increase of negative charges. , …”

“…In addition, for clay materials with variable charges, the adsorption of metal ions will be significantly altered by external conditions such pH, as supported by experimental observations that the enhanced adsorption of metal ions on clay materials at higher pH values is attributed to the increase of negative charges. 55,56 Adsorption can be also affected by the other factors but to a less extent. For different clay particles with close charge quantities, the adsorption performances of metal ions will not differ substantially, and structural alterations may be the primary factor (Figure 10).…”

Sorption and Desorption of Copper and Cadmium in a Contaminated Soil Affected by Soil Amendments

“…Harter stated that SOM is an important factor in affecting sorption of heavy metal ions by soil. Removal of organic matter in soil dramatically decreased the sorption of heavy metal ions . Yu reported that the contribution of organic matter to the total negative surface charges of the paddy soils (derived from red soils) was 5–42% with an average of 21%.…”

DTPA‐extractable zinc threshold for wheat grain yield response to zinc fertilization in Mollisols

“…In that sense, sorption on the surface of CaCO 3 , coprecipitation with carbonates, and formation of calcium zincate all reduce the amount of soil Zn extracted by DTPA in calcareous soils (Baruah, 2018). High carbonate content also increases soil pH, which is a driving factor of Zn availability, because the solubility of Zn minerals and the Zn desorption from clays and oxides decreases with increasing soil alkalinity (Catlett et al, 2002;Fernández et al, 2015).…”