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

Abstract

(superfície) a 1002-1334 mg kg -1 (subsolo). Foi observada forte dependência da adsorção de Cu em relação ao pH nas amostras do subsolo, com nítido aumento da retenção de Cu (20-90%) no intervalo de pH do solo entre 4,0-5,0. A adsorção de Cu foi alterada pelo aumento da I e indicou diferentes mecanismos (esferas interna e externa) de retenção do metal. A reação foi favorável e espontânea, conforme indicado pelos valores negativos da variação da energia livre (∆G) e pelo fator de separação KR < 1. A interface solo-solução e a adsorção de Cu foram termodinamicamente descritas por uma abordagem teórica. Effects of pH and ionic strength (I) on copper (Cu) adsorption and the driving force of the reaction in variable charge soils were evaluated from batch studies. Experimental results of Cu adsorption fitted Langmuir model. According to adsorption isotherms, Cu affinity (K L) was greater in the subsoil (0.061-0.468 L kg -1 ) than in the topsoil samples (0.169-0.359 L kg -1 -1 (subsoil). Strong dependence of Cu adsorption on the pH was observed in subsoil samples. Adsorption edges showed sharply increase of Cu adsorption (20-90%) in the 4.0-5.0 pH range. Copper adsorption changed with increase in I and indicated different metal retention mechanisms (outer- and inner-spheres). Adsorption reaction was favorable and spontaneous, as indicated by negative values of the free energy variation (∆G) and the separation factor KR < 1. Soil-solution interface and Cu adsorption were also thermodynamically described by a theoretical approach.