Using chitosan as a selective depressant in the differential flotation of Cu–Pb sulfides

N-Alkylated Chitin Nanocrystals as a Collector in Malachite Flotation

The majority of reagents currently used in mineral flotation processes are fossil-based and potentially harmful to the environment. Therefore, it is necessary to find environmentally-friendly alternatives to reduce the impact of mineral processing activities. Chitin nanocrystals are a renewable resource that, due to the natural presence of amino groups on its surface, represents a promising collector for various minerals of economic relevance. This study examines the one-pot functionalization of chitin nanocrystals with aldehyde structures to obtain hydrophobized colloids suitable for mineral flotation. The chemical properties of these nano-colloids were investigated by nuclear magnetic resonance spectroscopy, their colloidal behavior and structure by electrophoretic light scattering and atomic force microscopy, and their wettability through water contact angle measurements. The functionalized N-alkylated chitin nanocrystals possessed a hydrophobic character, were able to dress mineral particles and featured a performance in the flotation of malachite similar to commercial collectors, which proves the high potential of chitin nanocrystals in this field of application.

Surface interaction between phyllosilicate particles and sustainable polymers in flotation and flocculation

Non-renewable chemical reagents are commonly used as dispersants or flocculants of phyllosilicate clay particles in several industrial fields such as water/wastewater treatment, food production, papermaking, and mineral processing. However, environmentally benign reagents are highly desired due to the non-biodegradability and negative impacts of synthetic reagents on aquatic life. In this work, the dispersion and flocculation behavior of sustainable polymers (anionic and cationic biopolymers) sourced from proteins and polysaccharides were studied in serpentine phyllosilicate suspensions using the following bench-scale tests: zeta potential, microflotation, settling and turbidity, and isotherm adsorption using total organic carbon. The anionic polysaccharide-based biopolymer pectin acted as a switchable biopolymer for serpentine. That is, it could switch from being an efficient flocculant at pH 7 to an effective dispersant at pH 10.

Biopolymers with different backbones have the potential to disperse the phyllosilicate particles in flotation or release the water trapped within tailing particles in flocculation and could decrease environmental problems of conventional reagents.

A Review of Recent Advances in Depression Techniques for Flotation Separation of Cu–Mo Sulfides in Porphyry Copper Deposits

Porphyry copper deposits (PCDs) are some of the most important sources of copper (Cu) and molybdenum (Mo). Typically, the separation and recovery of chalcopyrite (CuFeS2) and molybdenite (MoS2), the major Cu and Mo minerals, respectively, in PCDs are achieved by two-step flotation involving (1) bulk flotation to separate Cu–Mo concentrates and tailings (e.g., pyrite, silicate, and aluminosilicate minerals) and (2) Cu–Mo flotation to separate chalcopyrite and molybdenite. In Cu–Mo flotation, chalcopyrite is depressed using Cu depressants, such as NaHS, Na2S, Nokes reagent (P2S5 + NaOH), and NaCN, meaning that it is recovered as tailings, while molybdenite is floated and recovered as froth product. Although conventionally used depressants are effective in the separation of Cu and Mo, they have the potential to emit toxic and deadly gases such as H2S and HCN when operating conditions are not properly controlled. To address these problems caused by the use of conventional depressants, many studies aimed to develop alternative methods of depressing either chalcopyrite or molybdenite. In this review, recent advances in chalcopyrite and molybdenite depressions for Cu–Mo flotation separation are reviewed, including alternative organic and inorganic depressants for Cu or Mo, as well as oxidation-treatment technologies, such as ozone (O3), plasma, hydrogen peroxide (H2O2), and electrolysis, which create hydrophilic coatings on the mineral surface.

Investigation of the specularite/chlorite separation using chitosan as a novel depressant by direct flotation

Chlorite is one of the representative iron-bearing silicates gangue minerals existed in the specularite ores which the traditional depressants are incapable of action in specularite/chlorite separation flotation. An attempt was conducted for the separation of specularite/chlorite with chitosan as a novel depressant through microflotation tests, Zeta potential measurements, adsorption tests, FT-IR, and XPS analysis. The microflotation results show that chitosan selectively depresses chlorite while specularite still keeps in high floatability. Zeta potential measurements and adsorption tests indicate that chitosan mainly adsorbed on chlorite surface, hindering the subsequent adsorption of dodecan-1-amine and leading the hydrophobicity distinction. The FT-IR spectra of chlorite validate the adsorption of chitosan on chlorite. The results of XPS illustrate that electrons partially transferred from chitosan to the aluminum, iron, magnesium, silicon, and adjacent oxygen atoms of silicon atoms in chlorite during the adsorption process.

Selective Flotation of Pyrite from Galena Using Chitosan with Different Molecular Weights

Pyrite is a major gangue mineral associated with galena and other valuable minerals, and it is necessary to selectively remove pyrite to upgrade the lead concentrate by froth flotation. In this study, the flotation experiments of a single mineral and mixed minerals were performed using chitosan with different molecular weights (MW = 2−3, 3−6, 10 and 100 kDa) as a depressant, ethyl xanthate as a collector, and terpineol as a frother, in a bid to testify the separation of pyrite from galena. Flotation results showed that the selective flotation of pyrite from galena can be achieved under the preferred reagent scheme, i.e., 400 g/t chitosan (10 kDa), 1600 g/t ethyl xanthate, and 100 g/t terpineol, while chitosan with other molecular weights cannot. Furthermore, the results of the zeta potential and contact angle measurements revealed that chitosan (10 kDa) has a strong adsorption on galena yet a very weak adsorption on pyrite at the dosage of 400 g/t. This study showed that chitosan (10 kDa) has great potential in the industrial flotation separation of pyrite from lead concentrates.

An Alternative Depressant of Chalcopyrite in Cu–Mo Differential Flotation and Its Interaction Mechanism

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 (Mw) of CMC. The low DS and high Mw 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 Fe3+ on the chalcopyrite surface and the carboxyl groups in the CMC molecular structure.

Effect of H2O2 on the Separation of Mo-Bi-Containing Ore by Flotation

Hydrogen peroxide (H2O2) is a strong oxidizer that causes non-selective oxidation of sulfide minerals, and its influence on bismuth sulfide ores is not well-documented. In this study, H2O2 was proposed as an alternative bismuthinite depressant, and its effect on a Mo-Bi-containing ore was intensively investigated by batch flotation tests. Results showed that the addition of H2O2 significantly destabilized the froth phase, thus decreasing the solids and water recovery. The recovery of bismuth in molybdenum concentrate was dramatically decreased to 4.64% by H2O2 compared with that in the absence of H2O2 (i.e., 50.14%). The modified first-order kinetic model demonstrated that the flotation rate of molybdenite slightly declined after H2O2 addition, whereas that of bismuthinite was drastically reduced from 0.30 min−1 to 0.08 min−1 under the same condition. Simulation revealed that H2O2 affected the floatability of both molybdenite and bismuthinite but resulted in more detrimental effect to bismuthinite. Hence, H2O2 has the potential to act as an effective depressant in bismuth sulfide ore flotation.

Flotation Behavior of Complex Sulfide Ores in the Presence of Biodegradable Polymeric Depressants

In this study, chitosan polymer was tested as a potential selective green depressant of pyrite in the bulk flotation of galena (PbS) and chalcopyrite (CuFeS2) from sphalerite (ZnS) and pyrite (FeS2) using sodium isopropyl xanthate as a collector and 4-methyl-2-pentanol (MIBC) as a frother. Flotation tests were carried out in a D12-Denver flotation laboratory cell in the presence and absence of chitosan and/or sodium cyanide depressant which is commercially used as pyrite depressant in sulfide mineral flotation process. Flotation recoveries and concentrate grades (assay) were studied as a function of polymer concentration and flotation time. It was found that at 50 g/ton, chitosan depressed 5.6% more pyrite as compared to conventional depressant NaCN at its optimum dosage. Furthermore, the measured assay values of pyrite in concentrates dropped by ~1.2% when NaCN depressant was replaced with chitosan polymer. Zeta potential measurements of galena, chalcopyrite, sphalerite, and pyrite suspensions before and after chitosan’s addition revealed that the polymer has preferential adsorption on pyrite minerals as compared to other sulfide minerals specially galena. Results obtained from this work show that chitosan polymer has a promising future as a biodegradable alternative to sodium cyanide for the purpose of depressing pyrite in sulfide minerals flotation.

Carboxymethylcellulose adsorption on molybdenite: the effect of electrolyte composition on adsorption, bubble-surface collisions, and flotation

The adsorption of carboxymethylcellulose polymers on molybdenite was studied using spectroscopic ellipsometry and atomic force microscopy imaging with two polymers of differing degrees of carboxyl group substitution and at three different electrolyte conditions: 1 × 10(-2) M KCl, 2.76 × 10(-2) M KCl, and simulated flotation process water of multicomponent electrolyte content, with an ionic strength close to 2.76 × 10(-2) M. A higher degree of carboxyl substitution in the adsorbing polymer resulted in adsorbed layers that were thinner and with more patchy coverage; increasing the ionic strength of the electrolyte resulted in increased polymer layer thickness and coverage. The use of simulated process water resulted in the largest layer thickness and coverage for both polymers. The effect of the adsorbed polymer layer on bubble-particle attachment was studied with single bubble-surface collision experiments recorded with high-speed video capture and image processing and also with single mineral molybdenite flotation tests. The carboxymethylcellulose polymer with a lower degree of substitution resulted in almost complete prevention of wetting film rupture at the molybdenite surface under all electrolyte conditions. The polymer with a higher degree of substitution prevented rupture only when adsorbed from simulated process water. Molecular kinetic theory was used to quantify the effect of the polymer on the dewetting dynamics for collisions that resulted in wetting film rupture. Flotation experiments confirmed that adsorbed polymer layer properties, through their effect on the dynamics of bubble-particle attachment, are critical to predicting the effectiveness of polymers used to prevent mineral recovery in flotation.