ferrihydrite and phthalic-acid

This work studied the structural effects of hematite (α-Fe

Topics: Ferric Compounds; Hydrogen Peroxide; Iron Compounds; Kinetics; Minerals; Models, Chemical; Phthalic Acids; Ultraviolet Rays

Understanding the chemical interactions that occur in complex natural systems is fundamental to their management In this work the distribution of cadmium in the presence of phthalic acid (H2Lp), ferrihydrite, and bacteria cells (Comamonas spp., heat killed) was measured and modeled for systems with incrementally increasing complexity. In binary systems, cadmium adsorption onto bacteria or ferrihydrite was accurately predicted using the nonelectrostatic four site model (NFSM) and the diffuse layer model (DLM), respectively. Phthalic acid (0.6 mM) enhanced Cd2+ adsorption onto ferrihydrite (due to surface ternary complex formation) butinhibited Cd2 adsorption onto bacteria to the same extent as predicted by Cd-phthalate solution complex formation constants, implying no significant surface ternary interaction occurred in this system. In Cd-ferrihydrite-bacteria systems, Cd2+ adsorption was up to 10% lower than that predicted by additive adsorption onto the pure phases which suggests that an interaction between ferrihydrite and the bacteria is occupying or masking adsorption sites. By adding a generic reaction to the model for the interaction between ferrihydrite and the bacteria, the adsorption of Cd2+ onto Comamonas spp.-ferrihydrite was accurately predicted and Cd2+ distribution and speciation in systems containing ferrihydrite, Comamonas spp., and H2Lp could be predicted.

Topics: Adsorption; Cadmium; Comamonas; Ecosystem; Ferric Compounds; Phthalic Acids

Copper, cadmium, and phthalic acid (H2Lp) adsorption by ferrihydrite was examined for binary and ternary systems. In binary systems adsorption was well reproduced using the diffuse layer model (DLM), and H2Lp adsorption was analogous to that of inorganic diprotic acids in terms of the relationship between the adsorption constants and acidity constants. In ternary systems H2Lp caused both the enhancement (due to ternary complexformation) and inhibition (due to solution complex formation) of Cu2+ and Cd2+ sorption depending on the conditions. The DLM could only describe the effect of H2Lp on metal ion sorption by including ternary complexes of the form [triple bond]FeOHMLp (0), where [triple bond]FeOH is a surface site and M is Cu or Cd. The relationship between binary metal adsorption constants and the ternary complex adsorption constants from this and previous studies suggest several properties of ternary complexes. First, ternary complex structures on both ferrihydrite and goethite are either the same or similar. Second, those cations having large adsorption constants also have large equilibrium constants for ternary complex formation. Third, ligands forming stronger solution complexes with cations will also form stronger surface ternary complexes though, because of the strong solution complex, they will not necessarily enhance cation adsorption.

Topics: Adsorption; Cadmium; Copper; Ferric Compounds; Models, Chemical; Phthalic Acids

Cadmium sorption by ferrihydrite in the presence of phthalic acid was examined over a range of pH (4.0 approximately 8.5) conditions and sorbate/sorbent ratios. The presence of phthalic acid enhanced Cd(2+) sorption by forming ternary complexes on ferrihydrite surface, especially at low pH, but for high pH and high total organic ligand/Fe(mmol/mol) ratios, it decreased Cd(2+) sorption onto ferrihydrite by forming soluble complexes with the phthalate in solution. In binary systems, Cd(2+) and phthalic acid sorption by ferrihydrite was well reproduced using the diffuse layer model with sorption constants derived from the experimental data. Prediction using the optimised binary sorption constants for Cd(2+) sorption onto ferrihydrite in the presence of phthalic was poor and achieving a good fit required the inclusion of two additional ternary complexes.

Topics: Adsorption; Cadmium; Ferric Compounds; Models, Chemical; Phthalic Acids