A Computational and Experimental Study on the Binding of Dithio Ligands to Sperrylite, Pentlandite, and Platinum

Abstract

This benchmark study documents a combined computational and experimental investigation into the binding of three commercial dithio collector ligands used in industrial froth flotation processes to separate high value minerals from lower value material. First principles condensed matter simulations showed that ethyl xanthate, N,N-diethyl dithiocarbamate and diisobutyl dithiophospinate anions all bind least strongly to the [100] Miller index plane of the platinum-containing mineral sperrylite, followed by the [111] MI surface of the mixed nickel/iron sulphide mineral pentlandite, while all ligands showed strongest binding affinity to the [111] MI surface model of pure platinum. Calculations also support experimental observations that neutral ethyl xanthogen disulphide formed on oxidation of ethyl xanthate binds much more weakly than the monomer. A monolayer of water molecules would easily be displaced from all surfaces by any of the collector ligands. The hydroxide anion was found to have binding energies of comparable magnitude to the collector ligands on all surfaces. Cyclic voltammetry measurements performed on working electrodes constructed from sperrylite, pentlandite and platinum permitted measurement of the mixed oxidation potential associated with the surface dimerization reaction for all three collector ligands, although the data obtained for diisobutyl dithiophospinate was less clear cut than for the other ligands. Comparison of the relative ordering of the mixed potentials for the three ligands gave a favourable match with the predicted outcome of binding energy strengths obtained from the modelling study. This study demonstrates that first principles simulations can be used to predict the binding energies of collector ligands to mineral and metallic surfaces.

A Molecular-Scale Approach to Rare-Earth Beneficiation: Thinking Small to Avoid Large Losses

“…Studies have begun to extend a molecular-level approach beyond the hydroxamic acid moiety, toward a comprehensive understanding of adsorption in terms of specific structural interactions among functional groups in the collector, water molecules, and atoms in the mineral surface. This detail-oriented perspective, which has been employed for other metal- and mineral-ligand systems ( Frey et al., 2000 ; Rio-Echevarria et al, 2008 ; Waterson et al., 2016 ), can lead to the rational design of future collector ligands.…”

Revelation of the Nature of the Ligand–PbS Bond and Its Implication on Chemical Functionalization of PbS

“…The valence electrons were presented in planewaves with a kinetic energy cutoff of 450 eV. The exchange and correlation interactions were described by the Perdew–Burke–Ernzerhof-generalized gradient approximation functional which has been widely used in the flotation systems. ,, The electronic occupancies were determined by the Gaussian smearing method at a smearing width of 0.05 eV, and the total energy extrapolated to zero broadening was used. The k -point mesh of 7 × 7 × 7, as sampled by the Monkhorst–Pack scheme, was set for the PbS unit cell.…”

“…In parallel with the rapidly developing experimental approaches, the past several decades have witnessed radical advancement of the accuracy of theoretical description of surface chemical reactions. , The first-principles study, particularly the density functional theory (DFT) calculation, is increasingly becoming an indispensable tool to provide atomistic insights into the adsorption mechanism as well as the identification of key descriptors linking the intrinsic attribute of the material with the activity of interest. − For instance, the remarkable d-band model has been successfully applied as the computational guideline for the design of transition-metal-based catalysts for a number of catalytic reactions. , Regarding the chemical functionalization of metal sulfides, the computed binding energy is generally used to assess the relative ligand functionality. − However, this descriptor fails to match with the recognized experimental metrics in certain cases, especially when evaluating the hydrophobization of lead sulfide in the context of froth flotation . To date, this issue still represents a major challenge, leaving the fundamental understanding of ligand–metal sulfide binding ambiguous and the predictive descriptors for the rational design of ligand lacking.…”

Reconstruction of Cooperite (PtS) Surfaces: A DFT-D+U Study

“…Another study investigated the stability of cooperite and its mixture with Pd atoms, where the Pt 37.5 Pd 12.5 S 50 mixture system was the most stable . Computational methods have been widely used to investigate a wide range of minerals, including pyrite; , chalcopyrite; , pentlandite; − sperrylite, pentlandite, and platinum; and sperrylite and platarsite . These also include the reconstruction of different surfaces, , oxidation mechanism, − and separation of minerals. , Nevertheless, there is no computational study that investigated the cooperite surfaces.…”