Amidoxime collectors: Lead-free flotation performance and adsorption mechanism in the separation of wolframite, quartz and calcite

Dai L., Liu J., Li D., Hao J., Gao H.

The hydroxamic acid reagents are extremely pervasive in the collector of scheelite flotation. The high flotation cost is caused by its large dosage and high price. A novel auxiliary collector 4-methodybenzoicacid (4-MBA) was used in combination with benzohydroxamic acid (BHA) to optimize the flotation reagents system for scheelite in the study. A single 4-MBA has weak collection capacity for scheelite. Nevertheless, the combination of 4-MBA and BHA optimized the flotation system of scheelite by ensuring its recovery and reducing the reagent consumption. The results of solution surface tension and contact angle measurements showed that the surface tension of the mixed reagent solution is a relatively lower and the hydrophobicity of the scheelite surface is a relatively higher in the BHA and 4-MBA mixed reagent system. Additionally, a synergistic effect between BHA and 4-MBA on Pb2+ activated scheelite is revealed by the Zeta potential measurements, infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The addition of 4-MBA promoted the physical and chemical adsorption of BHA. The results of molecular dynamics simulation (MDS) further explained that the collector adsorption layer of the surface of scheelite (1 1 2) is more compact under BHA and 4-MBA mixed reagent system, which prevents the vertical entry of water phase and improves the hydrophobicity of scheelite. Finally, the bench-scale flotation experiment verified that the addition of 4-MBA enhanced scheelite flotation with BHA, and decrease the flotation cost of scheelite.

Sun W., Han H., Ni Y.

Cheng C., Wu J., Huang Z.

In this study, a novel collector, N1,N10-dihydroxydecanediamide (DHH) was synthesized in our lab and introduced in flotation of malachite ore. The separation performance and action mechanism of DHH were explored and compared with octyl hydroxamic acid (OHA). The results of single mineral flotation tests indicated that DHH exhibited a stronger collecting ability to malachite and better selectivity against quartz and calcite than OHA, and floated out 94 % malachite, 8.5 % quartz and 17 % calcite at pH = 10 with a collector concentration of 60 mg/L. The FTIR spectra, zeta-potential tests and XPS tests proved that DHH could absorb onto malachite surface though a chemical mode. DFT calculation results showed that DHH anion owned a stronger affinity to malachite than DHH molecular and OHA anion/molecular, and its bis-minerophilic groups could form C(=O)NHO-Cu bond with surface Cu atom. It exhibited that DHH was an excellent candidate and capable for high efficiency flotation of malachite ore.

Che Y., Chen W., Liu S., Zeng G., Liu G.

Talc has long been a problematic gangue mineral in sulfide ore flotation due to its natural hydrophobicity. The as-investigated anionic depressants which reacted with the Mg sites on the edge plane of talc always exhibited limited effects because the negatively charged talc particle at pH > 5.0 showed electrostatic resistance for the anion adsorption. Thus, an electrically neutral reagent, fenugreek gum, was introduced as a highly efficient talc depressant in comparison with the sodium carboxymethylcellulose and sodium alginate, coupled with the surface detections on the selective depressant mechanism between chalcopyrite and talc. The micro-flotation results showed that fenugreek gum could selectively depress the talc flotation at lower dosage and wider pH range than sodium carboxymethylcellulose and sodium alginate, suggesting a more efficient depressant role. Surface detection implied that fenugreek gum selectively interacted with the basal plane of the talc surface and remarkably decreased its hydrophobicity mainly through physical adsorption originated from the hydrogen-bonding between the OH group and the [SiO4] tetrahedron. Fenugreek gum adsorbed onto talc with much larger capacity than on chalcopyrite, and had little influence on the adsorption density of collector adsorption on chalcopyrite, indicating the highly efficient selectivity of fenugreek gum toward talc depression.

Liu M., Cheng C., Qiu Z., Yang L., Liu S., Liu G.

The reduction of lime usage in flotation separation of lead–zinc sulfide ores has an interesting topic for protecting environment and recovering valuable metal minerals. In this study, BN (6-butylamino-1,3,5-triazine-2(1H)-thione-4-thiol sodium) was introduced for the first time as a selective collector for galena flotation. The results of UV spectra, adsorption capacity, zeta potential and in-situ AFM manifested that BN exhibited the selective affinity towards Pb2+ over Zn2+ ions, and preferred to adsorb on galena surface, not on sphalerite. The FTIR and XPS further uncovered that BN assembled on galena via bonding its sulfur atoms with lead ions of galena to form the surface BN-Pb complexes. The micro-flotation findings revealed that BN returned the stronger collecting power and higher selectivity than isobutyl xanthate during flotation separation of galena from sphalerite, and achieved their effective separation at low alkaline conditions (pH ∼ 8.0). This study also offers an enlightenment for the design of chelating collectors suitable for use under weak alkaline conditions.

Jo K., Je J., Lee D., Cho H., Kim K., You K.

Despite the long history of flotation in the mineral processing industry, its prediction and understanding remains a great challenge owing to its many variables acting in a complex manner. In this study, we introduced machine learning (ML) models to predict the grade and yield of a multi-stage flotation process of a complex lead–zinc sulfide ore. Over 100 batch flotation tests were conducted in a stepwise manner to characterize different rougher-cleaner-scavenger configurations. Performing a pre-flotation of talc prior to sulfide flotation remarkably improved the grade of lead concentrate. The experimental data were divided into four subsets for the ML models: rougher without pre-flotation, rougher with pre-flotation, cleaner, and cleaner-scavenger datasets. Different ML models were evaluated to determine whether they could predict the lead grade, zinc grade, and yield related to key flotation parameters, including particle size, reagent dosage, and pulp pH. The integrated ensemble neural network and random forest model yielded the best prediction results with R2 values of 0.924, 0.902, 0.973, and 0.894 for the rougher without pre-flotation, rougher with pre-flotation, cleaner, and cleaner-scavenger subsets, respectively. The developed ML model, with the connection of subset models, effectively predicted the flotation outcome of the rougher-cleaner-scavenger circuit, demonstrating a better prediction performance than previous methods. This indicates that the developed ML model can potentially predict flotation process performance and evaluate the efficiency of newly designed multi-stage froth flotation processes.

Fizer M., Fizer O., Hryhorka H., Slivka M., Šoral M., Dujnič V., Kopáčová M., Pantyo V., Mariychuk R.

New 5-alkyl-1,2,4-triazole-3-thiones containing structural fragments of anionic surfactants have been synthesized and examined as stabilizers in the wet chemistry synthesis of silver nanoparticles (AgNPs). The synthesis of the new 1,2,4-triazole-3-thiones was done via the cyclization reaction of 4-acyl-thiosemicarbazides in basic conditions. The structure of the new surfactant was analyzed by spectroscopic (infrared and nuclear magnetic resonance) and theoretical DFT methods. The surface activity characteristic, such as critical micelle concentration, was estimated using the conductivity method and the 1H NMR technique. The structural peculiarities of the new compounds testify to their surfactant properties, which is why they were explored as stabilizers in the chemical synthesis of silver nanoparticles from silver nitrate in an aqueous solution. The UV–VIS spectroscopy technique confirmed the formation of AgNPs in aqueous solutions of 5-alkyl-1,2,4-triazole-3-thiones. The stable AgNPs were obtained only using 1,2,4-triazole-3-thiones with longer alkyl chains (pentadecyl and heptadecyl), whereas the 5-pentyl-1,2,4-triazole-3-thione and the 5-heptyl-1,2,4-triazole-3-thione have not shown considerable stabilization activity. To better understand the interaction of the 1,2,4-triazole-3-thiones with AgNPs, Raman spectra analysis, quantum chemical modeling, and force field molecular dynamics were performed. The new triazoles were studied for their antifungal activity by the determination of minimal inhibition concentrations and docking studies.

Wang Y., Shen Y., Yang G., Ding F., Hong J., Yin M., Pan N.

Wastewater with contaminants such as heavy ions, organic dyes, and bacteria is extremely damaging to the environment and human life. In this study, N-halamine modified poly(amidoxime) nanofibrous membranes (PAO-Cl) were prepared using amidoxime-modified polyacrylonitrile (PAN), followed by chlorination. The amidoxime conditions of PAN were investigated, and the micromorphologies of each sample were examined. The durability, water release properties, antibacterial activities, and adsorption properties of the Cu2+ ions and methyl orange(MO) were investigated. The results demonstrated that PAO and PAO-Cl exhibited an adsorption capacity toward Cu2+ ions and MO, respectively. Chlorination of PAO resulted in the loss of Cu2+ ion adsorption properties of PAO-Cl. Nevertheless, PAO-Cl presented a higher MO adsorption capacity than poly(amidoxime) nanofibrous membranes (PAO). When the pH value less than 4, the adsorption properties of PAO-Cl was significantly enhanced, and the adsorption process was optimal, as described by the pseudo-second-order kinetic and Langmuir models. For PAO-Cl, the chemical structure changes and adsorption mechanism toward MO were thoroughly studied. After 5 min of contact time, the chlorinated sample displayed excellent antimicrobial capacities against 100 % of S. aureus (6.2 log) and E. coli O157:H7 (6.0 log), making it a promising candidate for use in water disinfection fields.

Xie R., Zhao Z., Wang X., Song Q., Tong X., Xie X.

Cai J., Li S., Deng J., Wu B., Xu H., Yang L., Wu M., Qiu H., Chen N., Hu M.

In this paper, the effect of Tannic acid (TA), a green, biodegradable plant polyphenol, as a talc depressant on the separation behavior of talc and chalcopyrite was investigated. The results of micro-flotation studies revealed that at a TA dosage of 20 mg/L at pH 7, talc recovery was barely 10 % whereas chalcopyrite recovery remained above 90 %, indicating that TA can selectively depress talc flotation. The results of the artificial mixed minerals test further confirmed the depressive effect of TA. The adsorption results showed that the adsorption density of TA on talc was greater than that on chalcopyrite surface. Similar conclusions were observed in zeta potential tests. It is noteworthy that the zeta potential of the chalcopyrite treated with TA and butyl xanthate sodium continued to shift negatively in comparison to the zeta potential of chalcopyrite treated with TA alone, suggesting that butyl xanthate sodium can continue to adsorb on the surface of chalcopyrite following TA treatment. Besides, X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy tests concluded that TA adsorbs on talc surface by physical (hydrophobic) interaction. Differences in the crystal structures of chalcopyrite and talc, as well as the large number of phenolic hydroxyl structures contained in TA, are the main driving forces for the selective adsorption of TA on the talc surface. This work provides an insight to the selection of inhibitors for the separation of chalcopyrite and talc, particularly from the perspective of the hydrophobic effect of the talc layered structure.

Ouyang L., Huang Z., Wang H., He G., Yu X., Burov V.E., Poilov V.Z., Li F., Liu R., Li W., Shuai S., Zhang S., Cheng C., Fu W.

Rhodochrosite and calcite have similar physicochemical characteristics and floatability, making it difficult for conventional flotation collectors to effectively separate the two minerals. In this paper, a novel 3-tetradecylamine propyl amidoxime (TPA) collector with selective and excellent collection capability for rhodochrosite has been investigated. The micro-flotation experiments showed that the flotation performance of TPA is superior to that of the commonly used sodium oleate (NaOL) collector, and the separation of rhodochrosite and calcite can be achieved under neutral conditions. At a slurry pH of 7 and a dosage of 2.0 × 10−4 mol/L, TPA provided a recovery of 88.5% for rhodochrosite and only 15.0% for calcite. The mechanism of interaction between TPA and minerals was examined by contact angle, Zeta potential tests and Fourier transform infrared (FTIR) analysis, which indicated that TPA selectively adsorbed on the surface of rhodochrosite rather than calcite. Finally, the adsorption behavior of TPA molecules on the surface of rhodochrosite was confirmed by Density functional theory (DFT) calculation to be through electrostatic interaction. This paper provides a novel collector for the flotation separation of rhodochrosite from calcite with excellent collecting ability and selectivity, which is significant for the efficient utilization of manganese ore resources.

Zhao G., Liu S., Qi J., Yang L., Liu G.

To improve the flotation recovery of tungsten minerals, 4-alkoxy benzohydroxamic acids containing C3 alkyl (C3OBs), namely 4-propoxy benzohydroxamic acid (POB), 4-iso-propoxy benzohydroxamic acid (IPOB) and 4-allyloxy hydroxamic acid (AOB), were designed as scheelite and wolframite collectors. The micro-flotation results uncovered that C3OBs exhibited stronger collecting ability towards Pb(Ⅱ)-activated scheelite and wolframite than benzohydroxamic acid (BHA) and the collecting ability of C3OBs was in sequence of POB > IPOB > AOB. The density functional theory (DFT) calculation indicated that the alkoxy oxygen atom of C3OBs contributed to their highest occupied molecular orbital (HOMO), and the HOMO energy followed the order as IPOB > POB > AOB > BHA. The higher HOMO energy, the stronger electron-donating activity. Nevertheless, IPOB didn’t return the highest flotation recovery of tungsten minerals. On the other hand, the hydrophobicity of these four hydroxamate collectors was in sequence of POB > IPOB > AOB > BHA, corresponding to the results of contact angle, micro-flotation and adsorption capacity. Therefore, the hydrophobization of the four hydroxamate collectors played a key role in their flotation performance to the Pb(II)-activated scheelite and wolframite. Moreover, this work offered a new approach for developing superior collectors.

He J., Liu R., Wu Y., Zhang Y., Sun W., Li G., Cao Y., Gao Z.

Zirconium and hafnium are critical metals mainly extracted from the zircon mineral. However, due to the unclear surface properties of zircon, most designed flotation collectors (Surfactants to selectively enhance the hydrophobicity of targeted materials) cannot recover zircon effectively. Herein, zircon surface hydration microstructures and their effects on the adsorption of typical flotation collectors (i.e., phosphates, hydroxamic acids, carboxylic acids) have been revealed by systematic first-principles calculations. The speciation diagram and the surface hydration microstructures of zircon have shown that surface Zr sites with small coordination numbers have stronger water affinity. Water molecules have affected the final stable adsorption configurations of the collector. The further obtained adsorption energy of collectors shows that water molecules have weakened the activity of zircon surfaces and reduced the interaction intensity between collectors and surfaces. These results indicate that collectors with stronger negative charges and a lower highest occupied molecular orbital(HOMO) energy can tightly bind with the zircon surface. The electron localization function, density of states, and crystal orbital overlap population have consistently shown that collectors have formed ionic bonds with surface Zr sites. These conclusions should be meaningful for further design of flotation collectors to realize selective zircon flotation.

Zhang W., Chen J., Xu S., Jin X., Sun W., Gao Z.

Molybdenite is the main source of molybdenum which is widely used in industry. Due to its excellent natural floatability, it is urgent to develop selective depressants, which is the key to achieve the flotation separation of molybdenite from other sulfide minerals such as chalcopyrite, galena and pyrite. In this work, a thiazole depressant 2,4-thiazolidinedione (CSD7) is developed based on the selective chelation of heteroatoms to Cu2+, Pb2+ and Fe2+. The flotation tests of single and mixed minerals confirm that CSD7 can achieve an efficient separation of molybdenite from chalcopyrite, galena and pyrite in a collector-free flotation system. Under the concentration of CSD7 with 5 × 10−4 mol/L and pulp pH of 7, the grades of molybdenite concentrate are higher than 50%, and the corresponding recoveries are higher than 80%. The Fourier Transform Infrared Spectroscopy (FT-IR) and electrochemical tests indicate that CSD7 can adsorb onto the surfaces of chalcopyrite, galena and pyrite, but can hardly adsorb onto the surface of molybdenite. CSD7 chelates with Cu2+, Pb2+ and Fe2+ on the surfaces of chalcopyrite, galena and pyrite through the four-membered ring formed by the bonds of −S−M2+ and =O−M2+. Moreover, the contact angle measurements also manifest that CSD7 selectively strengthen the hydrophilicity of the surfaces of chalcopyrite, galena and pyrite rather than molybdenite. The simply synthesized, low-cost and green CSD7 has a great potential in the separation of molybdenum from other sulfide minerals in flotation plant.

Qi J., Yang J., Liu G.

The combination of lead nitrate and benzohydroxamic acid (BHA) has succeeded in the commercial flotation of wolframite for years, regardless of the detrimental effects of Pb2+ on environment. In this work, a clean flotation technology was developed to remove the use of lead nitrate. The oxidation flotation with sodium hypochlorite (NaClO) and N-[(3-hydroxyamino)-propoxy]-N-hexyl dithiocarbamate (HAHD) achieved an effective separation and enrichment of wolframite from calcite, while NaClO and BHA combination delivered an inefficient floatation recovery of wolframite. The flotation mechanism in the HAHD-NaClO-wolframite system was further explored by in situ AFM, FTIR, UV and XPS. The findings deduced that NaClO treatment increased the proportion of Fe(III) and Mn(IV) species in wolframite interface, which benefited the chelation of HAHD’s hydroxamic group with Fe(III) and the oxidation of HAHD’s dithiocarbamate group by Mn(IV). Thus, with the help of NaClO, HAHD was changed into (HAHD)2 thiuram disulfide which anchored on wolframite surface through its double hydroxamate groups, leaving the two hexyl groups and the thiuram structure outward for attaching air bubbles. As a result, the hydrophobicity and floatability of wolframite significantly strengthened.

Zhong S., Xu T., Chi X., Tan W., Weng W., Tang D.