Ionic Strength Effects Upon Sorption of Inorganic Contaminants by An Aluminum Mining by-Product.

A better understanding of factors influencing the behavior of solutes at the soil:solution interface is important in assessing the availability/mobility of cations and anions in the soil. This study evaluated the effect of solution ionic strength (IS) upon the adsorption of Zn, Cu, Cd, Pb, As, and P on an aluminum mining by-product aimed to be used as a soil amendment. The choice of IS to be used (47 and 470 mmol L^-1) was made based on initial measurements of the original electrolytic conductivity of supernatant suspensions of the by-product. After that, we measured adsorption (pH 5.5) by reacting the adsorbent with Zn, Cu, Cd, Pb, As, and P solutions (0.67 mmol_c L^-1 initial concentration; adsorbent:solution ratio 1:100). Subsequent cation and anion desorption was evaluated by adding electrolyte solutions – 30 mL of 15 and 150 mmol L^-1 Ca(NO₃)₂ and 45 and 450 mmol L^-1 NaCl – to the remaining adsorption residue. Changing solution ionic strength interfered in Zn, Cd, Cu, and As adsorption, while no effect was observed for Pb and P. The percent adsorption increased similarly in both ionic strengths: Cd <Zn <Cu = As <Pb = P. Based on K_d values, the sequence of solute affinities for the adsorbent was as follows: Cd = Zn = Cu = As <Pb <P for I=47 mmol L^-1; Cd = Zn = Cu = As <P <Pb for I=470 mmol L^-1. Increasing ionic strength decreased the desorbed amounts of Cd, Zn, Cu, and As. Changing IS did not interfere in the amount effectively adsorbed and in the percentage of effectively adsorbed Zn, Cd, Pb, As, and P. Among the elements, Cd followed by Zn are noteworthy for having adsorbed the least and desorbed the most with a greater risk of environmental contamination. Sponsored by CNPq, CAPES and FAPEMIG.