Influence of calcium and ferric ions on the depression of chalcopyrite by CMC: Flotation performance and adsorption mechanism study
Introduction
Chalcopyrite (CuFeS2) is one of the most important copper-containing minerals in the nature, but it always encounters other easily floatable sulfide minerals in practical ore, such as pyrite, sphalerite, galena and molybdenite. To obtain high grade Cu concentrate before smelting, selective depressants are indispensable to reject these “impurities” in the flotation process. In practice, various inorganic depressants have been utilized routinely, whereas this flotation reagent scheme is exposing an increasing number of problems. One of the most urgent problems is that some reagents are extremely toxic and environmentally unacceptable, such as sodium cyanide and potassium dichromate. Another problem is that strong alkaline depressants, such as lime and sodium sulfide, have low efficiency and easily lead to the deterioration of the recovery of associated gold and silver. Taking these drawbacks into consideration, nontoxic and biodegradable natural organic depressants are receiving increasing attention in the field of mineral processing (Li et al., 2021).
Carboxymethyl cellulose (CMC) is a cheap natural organic polymer. It is originally studied as an effective silicate and carbonate depressant utilized in the suppression of talc, quartz, and calcite. It is also researched to separate chalcopyrite from molybdenite, galena and talc selectively (Fletcher et al., 2020, Kasomo et al., 2020, Liu et al., 2019, Wang et al., 2021d, Wang et al., 2018, Xuemin et al., 2020, Yuan et al., 2019b). In general, CMC physically adsorption on molybdenite and talc surface (Qian et al., 2017, Steenberg and Harris, 1984, Yuan et al., 2019a). The chemisorption of CMC on galena surface is pushed by the chelation between C-OH and –COOH groups of CMC molecule and Pb2+ on galena surface (Xuemin et al., 2020). Few research report that CMC depress chalcopyrite flotation, however, Qiu put forward that CMC depress chalcopyrite flotation at pH 4–6, and this effect gradually disappear under more alkaline or acid conditions (Qiu et al., 2018). Carboxyl group (–COOH) is the active group for CMC attachment on chalcopyrite surface. The reactive group for CMC adsorption on chalcopyrite surface is –COO-, however, it would protonate below pH 4 and result in less CMC adsorption due to the descend content of –COOH (Fullston et al., 1999, Wuestenberg, 2014). The positive charged Fe and Cu species are the CMC adsorption sites, while copper and iron mainly exist in the negatively changed forms on chalcopyrite surface at strong alkaline conditions, which lead to the descend of CMC adsorption (Jenkins and Ralston, 1998).
The above studies have excluded metal ions, while metal ions are widely distributed and inevitably present in the pulp, and their occurrence may impact the adsorption behavior of organic depressants significantly. On the one hand, the selectivity of organic polymers could be destroyed by the presence of metal ions. For example, pectin strongly depresses sphalerite and it has no depression effect on galena flotation; thus, it is successfully utilized to achieve Pb–Zn separation (Wang et al., 2021a). However, pectin molecule is induced adsorption on galena surface when Cu2+ is introduced to the flotation system; hence, the selective separation of galena is impossible (Wang et al., 2021c). Likewise, galena could be selectively depressed by dextrin in chalcopyrite flotation, but dextrin would be induced adhesion on chalcopyrite surface in the presence of Ca2+, therefore, chalcopyrite could not be selectively separated (Liu and Zhang, 2000). On the other hand, the depression effect of organic depressants could be enhanced by metal ions to varying degrees. For example, CMC’s efficiency is too low to depress talc flotation, but the introduction of Al3+ significantly facilitates CMC adsorption and strengthens its suppression of talc (Li et al., 2021). In addition, the depression effect of CMC on chlorite is affected by Cu2+ and Ca2+; Cu2+ could obviously enhance CMC adhesion on chlorite surface, while that of Ca2+ is less effectivity (Feng et al., 2013).
Overall, it is necessary to introduce metal ions into the flotation system when using organic polymers as depressant. In the flotation of sulfide ore, metal ions, such as Al3+, Ca2+, Mg2+, Pb2+, Zn2+, Cu2+ and Fe3+ (originated from crystal lattice, chemical reagents, or grinding medium) are the most typical ones in the pulp (Deng et al., 2017, Dong et al., 2021a, Wang and Peng, 2014, Zyga et al., 2021). Among these metal ions, Al3+ and Mg2+ are usually researched in the flotation of non-sulfide minerals, such as talc (Khraisheh et al., 2005, Li et al., 2021), fluorapatite (Eskanlou et al., 2022), smithsonite and dolomite (Araújo and Lima, 2017), thus, they are excluded in this study. In general, the contents of Fe-containing minerals (such as pyrite, pyrrhotite and hematite) and Ca-containing minerals (such as dolomite, gypsum and calcite) are much greater than that of chalcopyrite, galena and sphalerite. Hence, the contents of Fe3+ and Ca2+ in the pulp are much greater than that of Cu2+, Pb2+ and Zn2+. In this study, the depression effect of CMC on chalcopyrite flotation is investigated in the presence of Fe3+ and Ca2+, and the hydrophilic strengthen mechanism by Fe3+ is revealed through contact angle measurements, adsorption studies, TOF-SIMS, and XPS analysis.
Section snippets
Materials and reagents
Fig. 1 showed the XRD spectra of chalcopyrite sample, which was purchased from Jiangxi Province, China. No obvious impurities were observed in Fig. 1 and the purity of chalcopyrite was 94.34% according to chemical analysis results. A few chalcopyrite flakes were selected to detect contact angle. Other chalcopyrite sample was crushed by a laboratory jaw crusher in the first stage and a porcelain ball mill in the second stage to reduce the sample size. Then standard sieves were utilized to screen
Flotation results
Micro-flotation tests were carried out to investigate the influence of Fe3+/Ca2+ on CMC’s depression effect towards chalcopyrite flotation. Fig. 2 depicted the flotation behavior of chalcopyrite at different pH conditions. The pristine chalcopyrite showed good floatability and its recovery was maintained at around 80% within detected pH 4–12. It is obviously that chalcopyrite was hardly affected by CaCl2, and its recovery maintained around 80%. However, FeCl3 possessed a certain depression
Conclusions
CMC physically adsorbed on blank chalcopyrite surface, and strong electrostatic repulsion existed between CMC molecule and chalcopyrite surface over pH 6, which resulted in its insufficient depression effect towards chalcopyrite flotation. After the surface modification, CMC's depression effect on chalcopyrite was severely enhanced. The detailed mechanism was that the attachment of positively charged Fe species on chalcopyrite surface shifted upward its zeta potential and decreased the
CRediT authorship contribution statement
Changtao Wang: Investigation, Formal analysis, Writing – original draft. Runqing Liu: Writing – review & editing, Visualization, Supervision. Qilin Zhai: Investigation, Formal analysis, Methodology. Meirong Wu: Investigation, Resources. Nianwen Jing: Investigation, Methodology, Data curation. Feifei Xie: Project administration, Funding acquisition, Conceptualization, Methodology, Supervision. Wei Sun: Investigation, Software.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
The authors would like to thank the National Natural Science Foundation of China (No. 52174272), the Joint Funds of the National Natural Science Foundation of China (No. U1704252), the Fundamental Research Funds for the Central Universities of Central South University (No. 2021zzts0306, No. 2021zzts0896), and the Hunan Provincial Natural Science Foundation of China (No. 2020JJ5736) for supporting this study.
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