Formation constants for selected organo—metal (Al³⁺, Fe³⁺)—phosphate complexes

Abstract

. Can. J. Chem. 63, 3357 ( 1985). The possible formation of organo-metal-phosphate complexes (0-M-P) in aqueous solutions is examined by potentiometric titration analysis. The complex-forming solutions contain A?+-ions or Few-ions, organic acids (salicylic, phthalic, oxalic, and citric acids) and phosphate ions. The titrations are done within the precipitation-free pH-region from 2 to 4.5 (approximately) at 25°C under nitrogen at an ionic strength of 0.2 M KC1. ' The calibration of the electrode pair (glass-electrode, calomel-reference electrode) and the determination of the formation constants are facilitated by analyzing the pertinent curves with the ACBA-(Arena et 01.) and MINIQUAD-(Cans et 01.) computer programs. The results suggest (i) that 0-M-P complexes are readily formed, and that the power of selected organic acids to form ternary mixed-ligand complexes with A1"-ions and phosphate ions decreases in the order salycilate > citrate > oxalate > phthalate. Also, Fe"-ions are found to be more strongly bound by salicylate and phosphate ions than ~l'+-ions. The effect of 0-M-P formation on the chemical speciation of Al in buffered aqueous solutions containing mineral nutrients for the growth of biological organisms is demonstrated for a special case study. Dans une etude d'un cas spCcial, on a pu demontrer I'influence de la formation du complexe 0-M-P sur la speciation chimique de I'aluminium dans des solutions aqueuses tamponees contenant des sels mintraux facilitant la croissance d'organismes biologiques.[Traduit par le journal]

Does variscite control phosphate availability in acidic natural waters? An experimental study of variscite dissolution rates

“…Although these pH buffers may induce the formation of aqueous organo-aluminumphosphate species (e.g. Arp and Meyer, 1985), which have been suspected of affecting the dissolution rates of some minerals (e.g. Ganor et al, 2009), rates generated using these solutions are consistent with those obtained in buffer-free solutions (see below).…”

Phosphate Polymer Nanogel for Selective and Efficient Rare Earth Element Recovery

“…Trivalent cations had a more significant impact on REE sorption by the PPN, as the ligation constants for Fe and Al with phosphate are much higher than for common divalent ions. ,, The Fe 3+ did not show significant competition at 10–100-fold excess concentrations (Figure j,k). However, REE uptake was inhibited at 1000-fold excess (100 mg L –1 ) Fe 3+ concentration.…”

Cycling of As, P, Pb and Sb during weathering of mine tailings: implications for fluvial environments

“…For example, oxalic acid (a ubiquitous dicarboxylic acid) forms an uncharged ternary complex with Al 3+ and H 2 PO 4 À as [OxÀAlÀH 2 PO 4 ], which is stable at pH <4. Generally, Fe 3+ forms more stable complexes with phosphate and low MW organic ligands than does Al 3+ , due to differences in the electron orbital configuration and ionic radius (r Fe 3+ = 0.60 Å ; r Al 3+ = 0.53 Å ) (Arp and Meyer, 1985). Reactions and formation constants shown below for citrate complexes illustrate this difference in stability for Al and Fe:…”

“…6). We attribute this loss largely to the formation of mobile organoÀmetal (Al 3+ ,Fe 3+ )Àphosphate complexes (Arp and Meyer, 1985). For example, oxalic acid (a ubiquitous dicarboxylic acid) forms an uncharged ternary complex with Al 3+ and H 2 PO 4 À as [OxÀAlÀH 2 PO 4 ], which is stable at pH <4.…”