Investigação de interações de moléculas de água e íons em materiais lamelares contendo ferricianeto

Abstract

Ferricyanide, [Fe(CN)6] 3-, is considered as the most stable cyanometallic complex among iron cyanides, making it the predominant complex found in effluents from gold mining operations. Improper disposal of effluents by mining operations is the major contributor to the degradation or alteration of water quality. The toxicity of this complex is a major concern, since as exposure to sunlight causes it to undergo photodecomposition, releasing CN- , which extremely harmful to health. This fact highlights the need to withdraw ferricyanide from effluents. To explore the potencial of lamellar compounds, especially layered double hydroxides (LDH) and layered hydroxide salts (LHS), in capturing ferricyanide, ab initio calculations based on Density Functional Theory (DFT) with periodic boundary conditions and plane waves basis set were conducted. For all calculations, the GGA-PBE functional and Ultrasoft-Vanderbilt pseudopotencials were used. Analyses based on electronic structure, including band structure, project density of states (pDOS), charge density difference, and Bader charges were used to evaluate the electronic properties of the two materials. These analyses help predicting the possible interactions between lamella and complex, thereby indicating whether intercalation occurs. Phonon calculations were employed in order to thermodynamically analyze dehydration and ion exchange on the materials. Significant interactions between the complex and the lamella in both materials were observed, indicating that ferricyanide intercalation occurs in both LDH and LHS. In both materials, ferricyanide exhibited Lewis base behavior, while the hydroxyl species or groups of the lamellae acted as Lewis acid by receiving electron density from the complex. The combination of thermodynamic analysis and comparison of basal spacing with experimental results enabled us to define the most stable structures for hydrated HSL and HDL: Zn-[FeIII(CN)6].3H2O e Mg-Al-[FeIII(CN)6].7H2O, respectively. These material are stable at room temperature preserving its hydrated form. Furthermore, calculations evaluating the potential for ion exchange indicated that this process occurs spontaneously in both materials. This study suggests that removing ferricyanide ions using LDH or LHS from wastewater is feasible.