Copper desorption in a soil with variable charge

Abstract

Adsorption processes of heavy metals in soils have been more extensively studied than desorption, in spite of this latter process being related to nutrient bioavailability in the soil solution. Copper desorption from surface (0-0.2 m) and subsurface (1.0 -1.2 m) samples of an Anionic Acrudox was studied at two pH values (4.5 and 7.5). Soil samples were incubated with Cu rates varying from 0 to 400 mg kg Complete soil adsorption of added Cu was observed at pH 7.5 in all incubation periods, indicating that a 24h-shaking period was enough to reach equilibrium and maximum adsorption. Copper adsorption varied with the incubation period and was much lower at pH 4.5 than at pH 7.5, after the 24 hour-incubation period. After 4 and 12 weeks, Cu adsorption values were higher and similar for all soil samples, irrespective of pH or depth of sampling. The effect of the incubation period on soil Cu adsorption surpassed the pH effect for all Cu rates. The hysteresis was expressive, suggesting that Cu enhances high-energy bonds with the soil colloids. Calcium chloride was not efficient in promoting native soil Cu desorption in the studied concentrations. . No pH mais elevado (7,5), em todos os períodos de incubação, as amostras adsorveram praticamente todo o cobre adicionado, indicando que o tempo de 24 h de agitação para se atingir o equilíbrio foi suficiente para atingir a adsorção máxima. A adsorção de Cu variou com o tempo de incubação do elemento com o solo. No pH mais baixo (4,5), a adsorção foi bem menor após 24 h de incubação. Após 4 e 12 semanas, as adsorções foram elevadas e semelhantes para todas as amostras, independentemente da profundidade e do pH. Para todas as doses estudadas, o efeito do tempo de incubação na adsorção de cobre pelo solo sobrepujou o efeito do pH. O fenômeno de histerese foi expressivo, sugerindo que o Cu forma ligações de alta energia com os colóides do solo. O cloreto de cálcio não foi eficiente para dessorver cobre nativo do solo.

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

“…Surface functional groups of Fe, Al and Mn oxides are very selective for Cu adsorption, making highly stable inner-sphere complexes. 17,18,60,61 …”

“…12 Organic complexes are particularly important in Cu retention by the soil under a wide variety of conditions, [13][14][15][16] that influence the adsorption 7 and desorption of the metal. 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.…”

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

“…The interaction between ionic species in solution and the variety of soil components increase the complexity of this mechanism (Casagrande et al, 2004). In addition, these ionic species compete for the adsorption sites on the soil colloidal surfaces.…”

Efeito da natureza do eletrólito e da força iônica na energia livre da reação de adsorção de níquel em solos

“…Na amostra coletada em superfície, a carga foi negativa devido ao efeito da MO (Quadro 1 (Uren, 1992;Alleoni & Camargo, 1995 bibliográficas relacionadas a solos altamente intemperizados (Alleoni & Camargo, 1994;Casagrande et al, 2002Casagrande et al, , 2004. Para as amostras subsuperficiais do LVwf, os valores de PESN foram mais elevados em razão, provavelmente, da pequena participação da MO e do predomínio de componentes com carga variável, como minerais oxídicos e caulinita (Naidu et al, 1994), cujos valores de PESN são mais elevados (em torno de 8,0 e 4,7, respectivamente), o que contribui para aumentar o PESN do solo (Miranda-Trevino & Coles, 2003).…”