Sorption and desorption of cadmium from some New Zealand soils: effect of pH and contact time

Abstract

The effects of soil pH on the desorption of native soil cadmium (Cd), and on the sorption and desorption of added Cd at low concentrations, have been examined for 6 New Zealand soils ranging from pH 4·9 to 6·2. The effect of contact time with added Cd on subsequent desorption from soil has also been studied. Cadmium desorption was determined by repeated equilibrations in 0·01 М Ca(NO3)2 solution. Cadmium sorption ranged between 38% and 96% from an initial addition of 2 µg Cd/g soil. The effect of increasing soil pH was to increase substantially the amount of Cd sorbed. Sorption isotherms were all linear, with a negative intercept on the y-axis. Sorption data also fitted a linearised Freundlich sorption equation. Cadmium desorption was also very sensitive to pH, with a dramatic reduction in the amount of native Cd desorbed from the soil as pH increased, as was observed for samples where Cd was added. The cumulative amounts of native Cd desorbed represented only a relatively small proportion (0–22%) of total soil Cd concentrations. Added Cd desorption ranged between 22% and 99% of the Cd initially sorbed on the soil at varying pH. Organic matter appeared to be the most important soil component controlling both sorption and desorption in the soils studied. In the contact period experiment, the proportion of Cd desorbed was decreased by increasing initial contact time to 70 days before desorption for all 4 soils studied. Contact time had the greatest effect on Cd desorption in soils with the highest amounts of soil oxide components. Implications of the study are that, for the soils studied, soil pH, Cd contact time, and soil organic matter content are controlling factors on Cd desorption into soil solution, and are therefore likely to play an important role in Cd phytoavailability.

Effect of organic acids on adsorption and desorption of rare earth elements

“…For Heilongjiang, Zhejiang and Guangdong soils, in the presence of citric, malic and tartaric acids, desorption of REEs decreased with increasing pH values, so it did for Jiangxi soil in the presence of NO À 3 , acetic acid and tartaric acid. A similar phenomenon was also reported for other metal ions such as Cu 2þ (Padmanabham, 1983), Cd 2þ (Gray et al, 1998) and Zn 2þ (Pardo and Guadalix, 1996). It is generally recognized that pH can affect desorption of heavy metal from two aspects.…”

Effect of soil pH on cadmium phytoavailability in some New Zealand soils

“…As soil pH increases, sorption of Cd onto soil components, i.e., clay, organic matter and soil oxides also increases. There is also an accompanying decrease in desorption of Cd from these components into soil solution with increasing soil pH as previously demonstrated (Gray et al 1998). Therefore, increasing soil pH leads to a reduction of Cd in soil solution, the Cd pool in soils most readily available for plant uptake.…”

“…The results of several previous studies have also identified soil pH as an important soil property controlling sorption/desorption and solubility of native and added soil Cd (Salam & Helmke 1998;Gray et al 1998Gray et al , 1999, and therefore likely to play an important role influencing Cd phytoavailability. As a soil property that is relatively easy to manipulate, soil pH may be important in the management and control of plant Cd concentrations.…”

Efeito do pH na adsorção e dessorção de cádmio em Latossolos brasileiros

“…A Cd %ads foi, em média, de 27, 35 e 55 %, para pH 4,5; 5,5; e 6,5, respectivamente. A importância do pH como fatorchave em controlar a adsorção de Cd tem sido demonstrada em vários trabalhos (Naidu et al, 1994;Gray et al, 1998Gray et al, , 1999Krishnamurti & Naidu, 2003). Os dados obtidos neste trabalho estão de acordo com relatos prévios da literatura, segundo os quais o aumento do pH do solo resulta em um aumento da capacidade adsortiva dos mesmos (Alloway, 1990;Kabata-Pendias & Pendias, 2001;Dias et al, 2001).…”

“…É amplamente relatado na literatura que os processos de adsorção de elementos-traço não são completamente reversíveis. Explicações para esse fato incluem: difusão dos elementos para o interior das partículas ou microporos dos óxidos (Backes et al, 1995;Gray et al, 1998); precipitação (Farrah & Pickering, 1978); incorporação na estrutura cristalina dos óxidos (Ainsworth et al, 1994) e readsorção ao adsorvente (Davis & Upadhyaya, 1996).…”