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Abstract:The adsorption of cysteine on the pyrite (1 0 0) surface was evaluated by using first-principles-based density functional theory (DFT) and X-ray photoelectron spectroscopy (XPS) measurements. The frontier orbitals analyses indicate that the interaction of cysteine and pyrite mainly occurs between HOMO of cysteine and LUMO of pyrite. The adsorption energy calculation shows that the configuration of the -OH of -COOH adsorbed on the Fe site is the thermodynamically preferred adsorption configuration, and it is the strongest ionic bond according to the Mulliken bond populations. As for Fe site mode, the electrons are found transferred from cysteine to Fe of pyrite (1 0 0) surface, while there is little or no electron transfer for S site mode. Projected density of states (PDOS) is analyzed further in order to clarify the interaction mechanism between cysteine and the pyrite (1 0 0) surface. After that, the presence of cysteine adsorption on the pyrite (1 0 0) surface is indicated by the qualitative results of the XPS spectra. This study provides an alternative way to enhance the knowledge of microbe-mineral interactions and find a route to improve the rate of bioleaching.

Carboxymethylcellulose (CMC) is a nontoxic and biodegradable polysaccharide, which can potentially replace the frequently used hazardous depressants in Cu-Mo separation. However, a lack of understanding of the interaction mechanism between the CMC and the minerals has hindered its application. In the present study, it is found that 50 mg·L −1 CMC can inhibit chalcopyrite entirely in the pH range 4-6, while having little effect on molybdenite. The results also showed that the inhibition effect of the depressant for chalcopyrite enhanced with the increase of the degree of substitution (DS) and molecular weight (M w ) of CMC. The low DS and high M w of CMC were detrimental to the Cu-Mo separation flotation. Furthermore, CMC adsorption was found to be favored by a positive zeta potential but hindered by the protonation of the carboxyl groups. An electrochemical study showed that CMC inhibited 92.9% of the electrochemical reaction sites of chalcopyrite and greatly reduced the production of hydrophobic substances. The XPS and FTIR measurements displayed that the chemisorption was mainly caused by Fe 3+ on the chalcopyrite surface and the carboxyl groups in the CMC molecular structure. Minerals 2019, 9, 1 2 of 11 polysaccharides as a chalcopyrite depressant in Cu-Mo separation flotation, including ATDT [23], DMTC [24], tannin [25], chitosan [26], and so on. Carboxymethylcellulose (CMC), a natural polysaccharide which is widely used as a talc depressant and food additive [27][28][29], might be suitable for this purpose. CMC is known to inhibit chalcopyrite under certain conditions [30,31]. However, the interaction mechanism between CMC and the chalcopyrite surface has rarely been investigated. The general interaction between polysaccharides and sulfide ores is highly controversial and needs resolving in many further studies. The present study assessed the efficiency of CMC as a depressant of chalcopyrite in Cu-Mo differential flotation and elucidated the underlying interaction mechanism.

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