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Sodium sulfide has been widely used as a bismuth depressant in the flotation separation of molybdenum–bismuth sulfide ores. However, the selective depression mechanism of sodium sulfide on bismuthinite remained unclear. In this study, the effect of sodium sulfide on the flotation performance of molybdenite and bismuthinite was systemically investigated through micro-flotation tests, bench-scale flotation tests, Fourier transform infrared (FTIR) measurements, adsorption experiments, and X-ray photoelectron spectroscopy (XPS) analyses. Micro-flotation tests indicated that sodium sulfide had excellent depressing effect on the bismuthinite in alkaline condition. The recovery of bismuthinite dramatically decreased from 86.7% to 16.5% with the concentration of sodium sulfide increased to 1 × 10−3 mol/L. By contrast, the depressing effect of sodium sulfide on the flotation of molybdenite was weak. The flotation recovery of molybdenite remained above 60% in the whole pH range tested. Surface analysis using FTIR and XPS analysis revealed that the surface of bismuthinite was covered by hydrophilic sulfide ions after treatment with sodium sulfide, which not only decreased its surface hydrophobicity but also prevented the subsequent adsorption of collector xanthate. While the surface of molybdenite was slightly affected and remained hydrophobic as indicated by high flotation recoveries. Bench-scale flotation tests confirmed that sodium sulfide could be used as an efficient depressant for flotation separation of molybdenite from bismuthinite. The work presented here not only provides a new perspective on the inhibition mechanism of sodium sulfide but also gives a theoretical support for the industrial application of sodium sulfide. [ABSTRACT FROM AUTHOR]

In this paper, the effect mechanism of calcium hypochlorite on the adsorption of the collector DDTC on the surface of molybdenite and bismuthinite was explored. The single mineral flotation test showed that calcium hypochlorite had significant inhibition on the flotation behavior of bismuthinite, but had no similar effect on that of molybdenite. The results of FT-IR spectra and contact angle measurement indicated that the collector DDTC was not able to adhere to the bismuthinite surface treated with calcium hypochlorite, but could adhere to the molybdenite surface treated with the same way. Synthesizing the results of electrochemical test, thermodynamic analysis, Raman spectra, and Time of Flight Secondary Ion Mass Spectrometry (TOF-SIMS) test, it could be confirmed that calcium hypochlorite could react on the surface of bismuthinite and molybdenite, and the reaction on the bismuthinite surface first produced Bi3+ and Cl-, which continued to react in solution and finally formed BiOCl precipitation, while the reaction on the molybdenite surface formed soluble components, which dissolved into the solution. Therefore, the hydrophilic BiOCl precipitation covered the bismuthinite surface, hindering the adsorption of DDTC, while the soluble components produced on the molybdenite surface entered the solution without affecting its surface wettability and collector adsorption, which maybe was the root cause of the selective depression of calcium hypochlorite. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Ca(ClO) 2 exhibited a stronger depressing power to bismuthinite than molybdenite. • Bismuthinite surface became rough and hydrophilic due to the deposition of BiOCl. • The presence of BiOCl impeded the adsorption of kerosene onto bismuthinite surface. • Molybdenite surface was not affected by Ca(ClO) 2 and remained affinity to kerosene. • Ca(ClO) 2 showed superior separation performance than conventional depressant Na 2 S. Molybdenite and bismuthinite are valuable components arising from Mo–Bi sulfide ore, and their recoveries are considerably limited by separation efficiency. Herein, calcium hypochlorite (Ca(ClO) 2) was first introduced as bismuth depressant for efficient separation of molybdenite and bismuthinite, and its depression mechanisms were investigated through a series of analytical techniques supplemented with solution chemistry and thermodynamic calculations. Flotation results showed that Ca(ClO) 2 had a stronger depressing ability than conventional depressant sodium sulfide and exhibited superior selectivity for bismuthinite against molybdenite. At pH around 8.0, the high-selective separation of Mo–Bi bulk concentrate was realized, where more than 96% of molybdenite was recovered and over 98% of bismuthinite was depressed. Solution chemistry and thermodynamic analysis indicated that the bismuthinite surface was preferentially oxidized by Ca(ClO) 2 to SO2- 4 and Bi3+. The former dissolved into solution and existed as stable ions, whereas the Bi3+ further interacted with Cl− and was hydrolyzed as BiOCl precipitates. Surface analysis demonstrated that the deposition of BiOCl on the bismuthinite surface not only made its surface rougher but also enhanced its surface hydrophilicity. In comparison, the surface of molybdenite was slightly oxidized and it remained hydrophobic as confirmed from scanning electron microscopy with energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and contact angle results. The difference in surface characteristics resulted in the selective adsorption of collector on the surface of molybdenite rather than that of bismuthinite, thus improving the floatability of molybdenite and drastically deteriorating the floatability of bismuthinite. This work suggests that Ca(ClO) 2 could be a promising depressant for bismuthinite in the flotation separation of Mo–Bi sulfide ore. [ABSTRACT FROM AUTHOR]

Highlights • Pyrogallic acid exhibit selective depression effect on bismuthinite flotation. • Pyrogallic acid expanded the difference in flotation rate of both minerals. • Pyrogallic acid has a destabilizing effect on the froth phase. Abstract Molybdenum ore flotation techniques are constantly challenged by the emergence of complex sulfide minerals, such as bismuthinite, in the mineral processing industry. Conventional flotation depressants, such as sodium sulfide, used in Mo–Bi-containing ore flotation require high dosages, which leads to high cost and low selectivity. Therefore, in this study, pyrogallic acid (PA), a widely distributed organic source, is tested as an alternative depressant to selectively depress bismuthinite in Mo–Bi sulfide ores from Shizhuyuan. Results show that PA has a minimal effect on molybdenite recovery; by contrast, PA has a high depressing effect on bismuthinite amelioration. At 500 g/t PA, molybdenum recovery slightly decreases by 2 percentage points, and bismuth content in molybdenum concentrate sharply declines by 34 percentage points, with respect to samples floated without PA. Batch flotation tests demonstrate that PA addition affects froth stability, as indicated by the variations of solid and water recoveries. The superior selectivity of molybdenite over bismuthinite is promoted by increasing the PA dosage. On the basis of these findings, PA is a feasible option and thus can be used as a depressant for bismuthinite in the flotation of sulfide minerals. [ABSTRACT FROM AUTHOR]

[Display omitted] • Molybdenite and bismuthinite exhibit excellent hydrophobicity in the acidic pH range. • Pyrite exhibit excellent hydrophobicity only under extremely acid conditions. • The higher the alkalinity of flotation, the lower the hydrophobicity of minerals. • The order of susceptibility to pH: pyrite > bismuthinite > molybdenite. Researchers in most of the published works paid a great attention in the effects of pH on the flotation behavior of minerals, where most of which ignored the influences of pH on the surface properties. Herein, the detailed surface analyses of several typical sulfide minerals, namely, molybdenite, bismuthinite, and pyrite, were conducted to identify the effect of pH on the mineral surface property. As observed, all these minerals exhibited excellent hydrophobicity under highly acid conditions. The surface chemical composition of molybdenite and bismuthinite remained relatively steady as pH increased, but the decrease in surface hydrophobicity of bismuthinite was more serious than that of molybdenite under the alkaline conditions. Pyrite was more affected by the pH value. At pH below 4.0, FeS 2 was the dominate species at pyrite surface. With the increase in alkalinity, the pyrite was gradually oxidized and the surface became hydrophilic. As the pH further increased to12.0, the hydrophobicity of pyrite almost vanished due to the deposition of hydrophilic oxidation products (e.g., Fe 2 (SO 4) 3 , Fe(OH) 3 , and FeOOH) on its surface. The differences in the surface characteristics of molybdenite, bismuthinite, and pyrite at different pH values can be used to design the flotation process for separation of these sulfide minerals. [ABSTRACT FROM AUTHOR]

An economical and environmentally friendly beneficiation process is of great practical significance for the mining industry to achieve green and sustainable development. This study aims to optimize the traditional flotation process of Mo–Bi sulfide ore by using the difference in natural floatability of minerals for cleaner production. Single-mineral flotation tests demonstrate that the natural floatability of the sulfide minerals investigated decreased in the following order: molybdenite > bismuthinite > pyrite. Molybdenite displayed the best natural floatability in a wide pH range, and pyrite exhibited the least naturally floatable under alkaline conditions. The moderately natural floatability of bismuthinite was observed at the pH below 6, but decreased with the shift of pH to the alkaline region. Batch flotation tests indicate that the collectorless flotation of Mo–Bi sulfide ore resulted in lower flotation kinetics but higher selectivity than those of the collector flotation process. Industrial-scale tests illustrate that introducing collectorless flotation into the sequential flotation in industrial production was a feasible and reliable method of simultaneously increasing economic benefits and improving product quality. The grades of the Mo and Bi concentrates generated from the modified flotation process were 2.78% and 2.81% higher than those produced by the traditional flotation process. The daily consumption of chemical reagents in the modified flotation process decreased by more than 10%, reducing the annual cost of flotation reagent by approximately USD 60407.0. Given the characteristics of low reagents dosage, slightly environmental pollution, and high economic benefits, the modified flotation flowsheet is a promising separation process that can be extensively employed for mineral sources with similar mineralogical properties. Image 1 • Natural floatability order, molybdenite > bismuthinite > pyrite. • Collectorless flotation resulted in lower flotation kinetic but higher selectivity. • Industrial application of collectorless flotation improve quality of final products. • Industrial application of collectorless flotation decreases environmental pollution. [ABSTRACT FROM AUTHOR]