New Insights into the Configurations of Lead(II)-Benzohydroxamic Acid Coordination Compounds in Aqueous Solution: A Combined Experimental and Computational Study

Abstract

Novel collector lead(II)-benzohydroxamic acid (Pb(II)–BHA) complexes in aqueous solution were characterized by using experimental approaches, including Ultraviolet-visible (UV-Vis) spectroscopy and electrospray ionization-mass spectrometry (ESI-MS), as well as first-principle density functional theory (DFT) calculations with consideration for solvation effects. The Job plot delineated that a single coordinated Pb(BHA)+ should be formed first, and that the higher coordination number complexes can be formed subsequently. Moreover, the Pb(II)–BHA species can aggregate with each other to form complicated structures, such as Pb(BHA)2 or highly complicated complexes. ESI-MS results validated the existence of Pb-(BHA)n=1,2 under different solution pH values. Further, the first-principles calculations suggested that Pb(BHA)+ should be the most stable structure, and the Pb atom in Pb(BHA)+ will act as an active site to attack nucleophiles. These findings are meaningful to further illustrate the adsorption mechanism of Pb(II)–BHA complexes, and are helpful for developing new reagents in mineral processing.

Interface Interaction of Benzohydroxamic Acid with Lead Ions on Oxide Mineral Surfaces: A Coordination Mechanism Study

“…Flotation is one of the most efficient methods to purify useful minerals from the complex raw ores based on the distinct surface hydrophobicity of minerals. − In the flotation system, metal ions are conventionally pre-added as activators to alter the surface, which means that metal ions are pre-adsorbed on the surface and restricted on the surface. Flotation reagents are subsequently added to alter the surface hydrophobicity.…”

“…Flotation reagents are subsequently added to alter the surface hydrophobicity. Collectors such as hydroxamic acids (HAs) bearing reagents can interact with metal ions such as Cu 2+ , Cd 2+ , Co 2+ , Ni 2+ , Pb 2+ , Zn 2+ , and Fe 3+ , thus taking on abundant chelate structures at the mineral surface via surface coordination. ,− It has been reported that the lead ion (Pb 2+ ) with benzohydroxamic acid (BHA), salicylhydroxamic acid (SHA), and cupferron can enhance the selectivity of flotation performance of the metal oxide minerals. − However, the understanding of their surface coordination structure and mechanism is still lacking …”

“…Previous studies have shown that the hemi-directed species of the Pb–BHA complex may dominate the aqueous solution. , The chelation of BHA with Pb 2+ is more thermodynamically favorable than that of BHA with the ubiquitous water species (H 2 O, OH – ). , Unfortunately, the surface coordination mechanism between the lead ion and BHA is not well-understood. Lead can retain a non-centrosymmetric coordination structure in many lead complexes due to the lone pair effect, such as the litharge structure (e.g., PbO), and the organic metal complex (e.g., picolinate chelating complexes, lead–glutathione complexes), where the coordinated anions are found in the half side of Pb .…”

Editorial for Special Issue “Modeling, Design and Optimization of Multiphase Systems in Minerals Processing”

“…Published articles can be analyzed following the same scale logic. Molecular modeling has allowed for an improved understanding of the mechanisms of interaction between minerals, the aqueous medium, and flotation reagents [13][14][15]. For example, studies on the behavior and molecular mechanism of adsorption of the collector sodium oleate were carried out by density functional theory and experimental techniques [13].…”

“…Density functional theory is one of the most used methods in quantum calculations of the electronic structure of matter. Usually, functional density theory is combined with experimental studies; for example, molecular modeling helps identify the most stable structure of ionic species and identify active sites, while experimental techniques such as electrospray ionization-mass spectrometry and ultraviolet-visible spectroscopy allow the existence of molecules or complexes to be validated qualitatively and quantitatively [15]. These three manuscripts are good examples of the useful tool that molecular modeling can be for understanding the performance and development of new reagents.…”