Synthesis and characterization of hydroxamic acid N,3-dihydroxy-2-naphthamide and its copper (II) complex per keto/enol forms and rare earth flotation

Abstract

Flotation is the most common beneficiation process used for separating minerals, but for rare earth minerals (REMs), performance can suffer due to the dilute nature of the rare earth elements. Furthermore, the REMs tend to possess smaller grain sizes, making the use of traditional flotation cells difficult if total liberation is needed. Consequently, improved efficiencies are needed for extracting REMs from various sources. For these systems, hydroxamic acids are commonly used as flotation collectors. Two such hydroxamic collectors were studied in this work: salicylhydroxamic acid (SHA) and N,3-dihydroxy-2-naphthamide (H2O5). Because there is no documented synthesis route for H2O5, several synthesis approaches were examined. Furthermore, because there is no information on H2O5, important structural and characteristic data was gathered regarding its (1) preferred structural isomer as a Cu2+ complex and (2) electrostatic potential values of the possible dentate groups in different tautomeric forms, thereby allowing H2O5 to be compared to SHA, particularly regarding flotation behavior. Hydrogen nuclear magnetic resonance (H-NMR), Laser Raman Spectroscopy (LRS), and predominantly Fourier-Transform Infrared (FT-IR) spectroscopy showed that both SHA and H2O5 preferred to be keto tautomers when uncomplexed; however, once chelated to Cu2+ ions, the collectors adopted enol forms. Molecular modeling using Spartan software showed an increase in the electrostatic potential of the possible dentate groups in both molecules for the enol form. H2O5 also resulted in an increased recovery by flotation of REMs of about 23% compared to SHA at similar reagent dosages.

Introduction to the highlights of articles in Volume 3, Issue 1

“…The first article, titled "A Review of Mechanical Properties and Carbonation Behavior Evolution of Lime Mortar for Architectural Heritage Restoration", delves into crucial aspects of preserving architectural heritage [1] . The second, "35 Years of Lessons Learned Designing, Building, and Monitoring Passive Treatment Systems for Mining Influenced Water (Part 1)", offers insightful reflections drawn from extensive experience [2] . Lastly, "Synthesis and Characterization of Hydroxamic Acid N,3-Dihydroxy-2-Naphthamide and Its Copper (II) Complex Per Keto/Enol Forms and Rare Earth Flotation", presents innovative research on chemical synthesis and its applications [3] .…”