Computational study on interaction of heterocyclic, triazine and thionocarbamate collectors with pentlandite (Fe,Ni)9S8 mineral surfaces

Abstract

Due to the demands of nickel, substantial effort has been put into the recovery of pentlandite. Enhancing the separation of pentlandite minerals from the gangue in the extracted ores remains a problem. Pentlandite is the major source of nickel as well as a major carrier of platinum group elements (PGEs). Nickel is utilised in a wide range of industrial applications such as stainless steel, coinage, and rechargeable batteries. There is a need for selective collectors that can supplement the available xanthates, dithiophosphate and dithiocarbamate collectors for recovery of pentlandite and nickel ores. This study adopted density functional theory (DFT) with dispersion correction by Grimme to investigate the interaction with selective thiol collectors: S-allyl-N-diethyl-dithiocarbamate (ADEDTC), O-isopropyl-N-diethyl-thionocarbamate (IPDETC), Sodium mercaptobenzothiazole (MBT) and Sodium-2,6-Dithio-4-Butylamino-1,3,5-Triazine (SDTBAT) collectors. The bulk Fe5Ni4S8 pentlandite was previously determined as the most stable compound from cluster expansion which was tetragonal with space group of P42/nmc. The optimised structure had lattice dimensions of a = b = 7.020 Å and c = 9.930 Å. The XRD was used to predict the most dominant surface which were found as (111), (211), (224), and (311) surface, with the (311) surface displaying the highest intensity. These were cleaved from the relaxed bulk structure and their surface energies were computed as 1.622 J/m2 (111 surface) 1.843 J/m2 (211 surface) 1.844 J/m2 (224 surface) and 1.484 J/m2 (311 surface). The most stable surface was found to be the (311) surface which was in agreement with the experimental X-ray diffraction pattern. The adsorptions were performed on Ni and Fe atoms of Fe5Ni4S8 (311) surface as preferred adsorptions sites. It was found that ADEDTC gave the most exothermic adsorption energy of –460.581 kJ/mol compared to MBTNa (–249.59 kJ/mol), IPDETC (–161.012 kJ/mol) and SDTBAT (–352.481 kJ/mol). Most significantly these collectors preferred to bind on Ni atoms than Fe atoms, which indicated their selectivity towards the pentlandite mineral. These suggested that ADEDTC was the best co-collector compared to IPDETC, SDTBAT and MBTNa collectors for utilisation in the flotation of pentlandite mineral. The adsorption strength decreasing in order: ADEDTC > MBTNa > SDTBAT > IPDETC. This suggests that the ADEDTC collector has the potential to replace and/or be a co-collector with the widely used collectors in the recovery of pentlandite minerals.