Effects of Anions on the Capacity and Affinity of Copper Adsorption in Two Variable Charge Soils

Abstract

Effects of nitrate ðNO À 3 Þ, chloride (Cl À ), sulfate ðSO 2À 4 Þ, and acetate (Ac À ) on Cu 2+ adsorption and affinity of the adsorbed Cu 2+ were evaluated in two Fe and Al enriched variable charge soils from Southern China. The maximum adsorption of Cu 2+ (M, a parameter from the Langmuir isotherm model) in the presence of different anions decreased in the order Cl À > Ac À > NO À 3 > SO 2À 4 for both soils. The clayey loamy soil (mixed siliceous thermic Typic Dystrochrept, TTD), developed on the Arenaceous rock, adsorbed less Cu 2+ than the clayey soil (kaolinitic thermic Plinthudults, KTP), derived from the Quaternary red earths, regardless of anion type present in the medium. The affinity of adsorbed Cu 2+ to both soils could be characterized by the Kd (distribution coefficient) values and successive extraction of the adsorbed Cu 2+ with 1-mol NH 4 Ac L À1 . The log 10 Kd value was smaller for the TTD soil than for the KTP soil and decreased in the order of Cl À > NO À 3 > SO 2À 4 > Ac À at low initial Cu 2+ concentrations ( £ 40 mg Cu 2+ L À1 ), whereas at 80 mg Cu 2+ L À1 , the log 10 Kd value was similar for NO À 3 , SO 2À 4 , and Ac À , but was slightly higher for Cl À . Complete extraction of Cu 2+ adsorbed in the presence of Ac À was achieved. Influence of NO À 3 and SO 2À 4 on the affinity of adsorbed Cu 2+ was similar, but the effects of Cl À depended on the initial Cu 2+ concentrations. The extracted percentage of the adsorbed Cu 2+ in the presence of NO À 3 or SO 2À 4 increased with increasing Cu 2+ adsorption saturation. The presence of Cl À , NO À 3 , or SO 2À 4 markedly decreased the equilibrium solution pH for both soils with increasing initial Cu 2+ concentrations, and the delta pH values at the highest Cu 2+ level were 0.5, 0.63, and 0.55 U for the TTD soil and 0.79, 0.84, and 0.93 U for the KTP soil, respectively for the three anions. The presence of Ac À had a minimal influence on the equilibrium solution pH because of the buffering nature of the NaAc/HAc medium which buffered the released protons. The effects of anions on Cu 2+ adsorption and affinity of the adsorbed Cu 2+ were dependent on anion types and were apparently related to the altered surface properties caused by anion adsorption and/or the formation of anion-Cu 2+ complexes.Abbreviations: AAS -atomic absorption spectrometry; Ac À -acetate; CEC -cation exchange capacity at pH 7.0; Cl À -chloride; Freundlich equation -q ¼ k F C n , where q is the amount of adsorbed Cu 2+ , k F is a constant related to total adsorption capacity of the soils.; Kd -distribution coefficient; KTP soil -a soil of kaolinitic thermic Plinthudults; Langmuir equation -q ¼ (k L MC)/(l+k L C), where q is the amount of adsorbed Cu 2+ , M is the maximum adsorption of Cu 2+ , and k L is a constant related to binding energy; NaAc/HAc medium -a buffering medium consisting of sodium acetate and acetic acid; NH 4 Acammonium acetate; NO À 3 -nitrate; rcf -rotational centrifugal force; SO 2À 4 -sulfate; TTD soil -a soil of mixed siliceous thermic typic Dystrochrept B...

Effects of inorganic electrolyte anions on enrichment of Cu(II) ions with aminated Fe3O4/graphene oxide: Cu(II) speciation prediction and surface charge measurement

“…The neutral CuSO 4 complex could be more easily adsorbed by the positively charged AMGO than the Cu 2+ , thereby resulting in the increase of Cu(II) removal. The effect of SO 4 2À on Cu(II) adsorption was also related to the change of zeta potential caused by anion adsorption (Yu et al, 2005). From the inset of Fig.…”

“…1a-c, the presence of Cl À , ClO 4 À , and NO 3 À slightly increased the Cu(II) adsorption at low pH, whereas no significant changes in Cu(II) adsorption to the AMGO composites were observed at high pH. It is well known that the copper speciation in equilibrium solution is influenced by accompanying anions (Yu et al, 2005). Distributions of Cu(II) in solution with addition of 10 mM NaCl, NaClO 4 , and NaNO 3 , as a function of solution pH were obtained by using the program Visual MINTEQ and the results are showed in Fig.…”

Trace elements in agroecosystems and impacts on the environment

“…h. Companion anions, especially Cl À , influence adsorption of the metals Cu, Pb, and Cd. This influence is related to the formation and stability of Cu-anion complexes [38].…”

Copper adsorption as a function of solution parameters of variable charge soils

“…The effect of organic anions on Cu adsorption performance in soils with variable charges is still little understood and, although it is very difficult to generalize about the influence of organic complexing on metal adsorption, it is known that the organic treatments widely influence Cu adsorption. 26 Increase in the pH generally decreases the quantity of Cu organically complexed in the soil solution, that means alterations for species with greater affinity for adsorption. 63 Rodda et al 20 presumed that Cu 2+ , Cu(OH) + and Cu 2 (OH) 2 2+ were the dominant species that compete for adsorption sites on the goethite surface.…”

“…17 Copper adsorption was studied in pure systems, such as Fe and Al (oxy)hydroxides (hematite and goethite) [18][19][20] and clay minerals (kaolinite, illite etc), [21][22][23] and in complex systems such as soil, under natural, agricultural or waste application conditions. 7,[24][25][26] Metal adsorption by soil (oxy) hydroxides has been identified as the main mechanism by which the metals are retained by the inorganic constituents of weathered soils. 12,19,27 Even so, sufficient data has not yet been gathered on Cu adsorption by soils with variable charges in the wet tropics that would ensure the implementation of consistent techniques for prevention/ remediation of soil contamination.…”