Abstract
Spodumene, a lithium aluminum inosilicate, is recovered by froth flotation using surfactants, so-called collectors. Therefore, the behavior and properties of the water-mineral interface in saline solutions are central. Here, molecular dynamics simulations are used to study the adsorption of alkali and alkaline-earth metal cations from concentrated solutions on the weakest (110) surface plane of negatively-charged spodumene. Results include the envelope density function of inner-sphere complexes for each cation and the density of complexes according to their adsorption contacts. Visualization of complexes for each cation is also included. Once the structure of the cation layers adsorbed on the surface of spodumene is defined, its role as a catalyst or barrier for adsorption of the spodumene collector in flotation is evaluated. The collector studied is the typical sodium oleate. The results show that oleate adsorption is poor and that the few adsorption contacts are mainly via cation bridges. The findings here indicate that molecular simulation can facilitate the search for effective collectors for environmentally sustainable spodumene flotation processes in saltwater.
Highlights
Spodumene (LiAlSi2O6) is a pyroxene mineral found in lithium-rich pegmatite rocks
The zdensity function of spodumene and the RDF of alkali and alkaline-earth cations are used to identify cations that are adsorbed without the intermediation of water giving rise to inner-sphere complexes with a number of irreversible adsorption contacts with the spodumene surface
When the cation-spodumene distance falls in the range of distances covered by the first cation adsorption peak in the RDF (Figure 2), the cation forms an inner sphere complex with the spodumene
Summary
Spodumene (LiAlSi2O6) is a pyroxene mineral found in lithium-rich pegmatite rocks. The stoichiometric chemical composition of spodumene is 8.0% Li2O, 27.4% Al2O3, and 64.6% SiO2. We found through DFT that the arrangement of surface groups for the energetically most favorable termination of neutral (110) surfaces of spodumene includes one AlOH2+1/2, one AlOH−1/2 and one AlOSi+1/2 moieties per unit cell and that the addition of OH- (pH > pH of zero charge of spodumene) generates a new AlOH−1/2 surface moiety per unit cell, in addition to existing AlOH−1/2 and AlOSi+1/2 moieties per unit cell [5] In principle, these new groups on the surface of the spodumene anticipate that anionic collector adsorption may not be as ideal as it was once raised, which would explain the low recoveries of spodumene in flotation processes. Cations that are adsorbed without the intermediation of water give rise to inner-sphere complexes [6] with a number of irreversible adsorption contacts with the spodumene surface
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