RES³T - Rossendorf Expert System for Surface and Sorption Thermodynamics

Differences in the coordination chemistry of divalent metal ions affect their adsorption onto goethite (a-FeOOH) surfaces and their subsequent release by acidification, Fell addition, and picolinic acid addition. Equilibrium constants for adsorption onto FeOOH (goethite) decrease in the order: Cu^II > Pb^II > Ni^II = Co^II > Mn^II. Equilibrium constants for picolinic acid complexation follow the Irving-Williams series; complex formation with Pb^II and Mn^II is nearly negligible. Divalent metal ion release 24 h following acidification or picolinic acid addition is typically less than the amount predicted using an equilibrium speciation model, indicating adsorption/desorption hysteresis. Experiments performed under strict exclusion of O₂ reveal a slight increase in Co^II, Ni^II, and Cu^II adsorption upon the addition of 1000 pM Fe^II. Fe^II interferes with the ability of picolinic acid to cause divalent metal ion release.