Abstract
ABSTRACT Intrinsic equilibrium constants for 22 representative Brazilian Oxisols were estimated from a cadmium adsorption experiment. Equilibrium constants were fitted to two surface complexation models: diffuse layer and constant capacitance. Intrinsic equilibrium constants were optimized by FITEQL and by hand calculation using Visual MINTEQ in sweep mode, and Excel spreadsheets. Data from both models were incorporated into Visual MINTEQ. Constants estimated by FITEQL and incorporated in Visual MINTEQ software failed to predict observed data accurately. However, FITEQL raw output data rendered good results when predicted values were directly compared with observed values, instead of incorporating the estimated constants into Visual MINTEQ. Intrinsic equilibrium constants optimized by hand calculation and incorporated in Visual MINTEQ reliably predicted Cd adsorption reactions on soil surfaces under changing environmental conditions.
Highlights
Anthropogenic activities, such as mining or industrial activities, agricultural chemical applications - mainly phosphate and zinc micronutrients (Guilherme et al, 2014), and organic and inorganic residue application to soils may cause cadmium (Cd) concentration to build up over time
The values are close to the theoretical values for the clay minerals, and to reported values
capacitance model (CCM), respectively, than those calculated by hand (Table 4)
Summary
Anthropogenic activities, such as mining or industrial activities, agricultural chemical applications - mainly phosphate and zinc micronutrients (Guilherme et al, 2014), and organic and inorganic residue application to soils may cause cadmium (Cd) concentration to build up over time. Cadmium is bound to the solid phase of soils as a result of surface precipitation and adsorption processes. Its mobility and destination in the soil environment are directly related to processes that are highly pH dependent (Lee et al, 1996). Environmental and human health risk assessment of metals depends to a great extent on modeling the destination and mobility of metals based on soil-liquid partitioning coefficients (Sauvé et al., 2000) that can be estimated locally
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