Novel 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 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 in mineral processing.

Structures of Pb-BHA Complexes Adsorbed on Scheelite Surface

“…Some researchers confirmed that the Pb-BHA complexes existed mainly in the form of Pb-(BHA) n = 1, 2 in solution (Han et al, 2017b; Yue et al, 2017; He et al, 2018a), in order to compare the species between Pb-BHA complexes and Pb-BHA complexes adsorbed on mineral surface, the XPS measurements were conducted. Table 1 shows the electron binding energy of the different elements of BHA and Pb-BHA complexes.…”

“…In particular, solution-chemistry-based studies of the respective components of Pb-BHA complexes in cassiterite flotation (Tian et al, 2017, 2018a,b; Cao et al, 2019) showed that lead ions and their hydroxide ions form Pb(H 2 O) and Pb(OH)(H 2 O) with water and then react with the BHA anion to produce HO-Pb-BHA complexes. He et al (2018a,b) characterized the structure of Pb-BHA complexes in aqueous solutions through theoretical calculations and quantum chemical simulations; the results showed that the Pb-BHA complexes existed mainly in the form of Pb-(BHA) n = 1, 2 at various solution pH values, and first-principles calculations indicated that Pb(BHA) + is the most stable structure. Both studies concluded that the Pb-BHA complexes in the flotation did not consist of a single structure and proposed that Pb-BHA complexes with multiple structures acted simultaneously on the mineral surface.…”