Dynamics and thermodynamics of toxic metals adsorption onto soil-extracted humic acid.Humic acids, HA represent a large portion of natural organic matter in soils, sediments and waters.  The thermodynamics and kinetics of the adsorption of Cd(II) and Cr(VI) onto solid soil-derived HA have been investigated at optimum conditions of pH (5.5±0.1), metal concentration (10-100mmolL(-1)) and different temperatures (293-323K).  The adsorption was well described by Langmuir isotherm model in multi-detectable steps.  The thermodynamic parameters of adsorption systems are correlated for each adsorption step.  The adsorption is endothermic, spontaneous and favorable. 
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