Synthesis of sulfomethylated depolymerized alkali lignin and its application in scheelite flotation

Zheng Q., Dong L., Shen P., Liu D.

Scheelite and cassiterite often coexist in skarn deposits, which are prone to excessive crushing during dissociation, and gravity separation faces a challenge. However, research on flotation separation is limited. This study aimed to investigate the selective depression behavior and depression mechanism of a combined depressant containing ferric chloride and citric acid on cassiterite to successfully achieve the flotation separation of scheelite and cassiterite. Experimental studies on single minerals and artificially mixed minerals indicated that the individual ferric chloride or citric acid exhibited weak depressive abilities and poor selectivity toward cassiterite. However, a combination of ferric chloride and citric acid in a mass ratio of 3:7 achieved better separation results. At a pH of 8, with a concentration of 1 × 10–3 mol/L mixed depressant, and a sodium oleate concentration of 5 × 10–5 mol/L, scheelite and cassiterite exhibited recovery of 73.35 % and 19.98 %, with grades of 61.76 % and 16.18 %, respectively. Fourier–transform infrared spectroscopy and X–ray photoelectron spectroscopy analyses revealed that the mixed depressant strongly chemically adsorbed on the cassiterite surface, forming FeOOH at ferric species sites. Contact angle measurements indicated a significant reduction in surface hydrophobicity of the cassiterite surface due to mixed depressant components. Atomic force microscopy imaging analysis elucidated the adsorption morphology of the mixed depressant depressive component FeOOH on the cassiterite surface in both 2D and 3D imaging, indicating abundant high–intensity reagent peak adsorption. Therefore, the mixed depressant enhanced the selectivity of the depressant, facilitating the effective separation of scheelite and cassiterite.

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.

Yang X., Geng F., Yang Z., Rezayan A., Xu C.C., Wu D., Zhang Y.

Yu A., Ding Z., Yuan J., Yu P., Chen L., Zhang Y., Wen S., Bai S.

Liu C., Xu L., Deng J., Han Z., Tian J., Xue K., Wang D.

The surface characteristics of fluorite and calcite exhibit a close analogy, posing a formidable challenge to flotation separation. Hence, the development of a highly efficient reagent for fluorite holds paramount significance and value in addressing the challenging separation of fluorite and calcium-bearing minerals. In this study, a novel collector, decyl-bishydroxamic acid (DCBHA), has been ingeniously designed and synthesized to effectively separate fluorite and calcite. Conducting micro-flotation experiments encompassing single minerals and artificially mixed minerals, we systematically investigate the flotation performance of DCBHA in fluorite flotation systems. It was observed that DCBHA exhibited commendable collective and selective ability compared to BHA and OHA, yielded a concentrate grade of up to 70.99% with a recovery of 76.24%. at optimal conditions. The zeta potential, AFM, FTIR and XPS examinations indicated the selective chemical adsorption of DCBHA on the metallic sites of the fluorite surface. The incorporation of a second hydroxamic acid group concurrently enhanced the collecting capacity and selectivity of the reagent. The mechanism of interaction between the novel collector DCBHA and mineral surfaces was investigated through Density Functional Theory (DFT), revealing that DCBHA exhibited a "bidentate" adsorption pattern upon losing a proton H, forming bonds with the mineral surface. Furthermore, the adsorption affinity of DCBHA to fluorite surpassed that to calcite, providing advantageous support for experimental findings.

Peng T., Tao L., Wang J., Dong L., Jia W., Wang F., Hu J., Gao Z.

Scheelite, a strategic calcium-bearing mineral, usually coexists with calcite. Froth flotation is the most commonly used method of separating scheelite from calcite, but it is difficult to selectively separate them because of their similar Ca active sites. Sodium silicate with a high dosage and low selectivity is usually used as calcite depressant, which leads to the loss of scheelite and formation of stable colloidal dispersions of fine particles in the tailings slurry, making tailings treatment difficult. Therefore, this work developed a novel depressant, hexamethylenediamine tetramethylene phosphonic acid (HDTMP or H6L), which is a hexabasic acid. The flotation results of single mineral and binary mixed minerals showed that HDTMP at a concentration of 2 × 10−5 mol/L could selectively depress calcite with 4 × 10−5 mol/L NaOL at pH 10.0. Adsorption capacity, Ca2+ concentrate, and contact angle measurements showed that HDTMP was adsorbed more on calcite. Zeta potential measurement and solution chemistry calculations indicated that HL5− anion was the main active species of HDTMP at pH 10.0. Density functional theory (DFT) calculations further revealed that HDTMP had stronger interaction with calcite through chemically bonding with Ca sites and hydrogen bonds (P-O⋯Hwater and P-O H⋯Ocalcite) formed by the phosphate groups in HDTMP and H/O atoms on calcite surfaces. Therefore, HDTMP presents substantial potential for practical applications as a novel calcite depressant in scheelite flotation.

Guan Z., Zhang Y., wen S., Wu Y., Li X., Li X.

In this study, the effect of a novel depressant system consisting of manganese chloride and sodium silicate (Mn-SS) on the selective flotation of scheelite from calcite was investigated. When the Mn-SS ratio and dosage were 1:3 and 100 mg/L, respectively, the scheelite recovery was 87.6% higher than that of calcite. The zeta potential and infrared spectroscopy (IR) measurements revealed that Mn-SS chemisorbed onto the calcite surface and inhibited the subsequent adsorption of sodium oleate collector. The X-ray photoelectron spectroscopy (XPS) analysis demonstrated that the chemisorption of Mn-SS altered the chemical state of Ca on the calcite surface. The contact angle test indicated that the hydrophobicity of the calcite surface was significantly reduced by Mn-SS treatment. The scanning electron microscopy (SEM) images confirmed that Mn-SS formed a precipitate layer on the calcite surface. The density functional theory (DFT) simulation corroborated that the Mn-SS system had a stronger affinity for the calcite surface than for the scheelite surface, which agreed well with the flotation performance.

ZHAO G., FENG B., ZHU D., QIU X., GAO Z., YAN H., LAI R., QIU T.

The effect of metal-inorganic complex depressant composed of aluminum sulfate and sodium silicate (AlSS) on the flotation separation of scheelite and calcite was studied. Zeta potential and adsorption measurements confirmed that the negatively charged colloidal particles composed of Al(OH)4− and SiOm(OH) n4−2m−n tended to be adsorbed on calcite surface, inhibiting the adsorption of sodium oleate (NaOL), while the adsorption of negatively charged colloidal particles on scheelite surface was relatively low, which resulted in the great adsorption capacity of NaOL on scheelite. The contact angle measurements showed that the hydrophobicity of scheelite was significantly better than that of calcite in the NaOL+AlSS solution. XPS measurement results indicated the adsorption of Al and Si on the calcite surface rather than on the scheelite surface. Compared to adding water glass (sodium silicate, SS) only, the depression effect on calcite was significantly enhanced by the combination of AlSS, while scheelite flotation was hardly affected. Scheelite concentrate with WO3 grade of 68.34% and WO3 recovery of 83.14% could be obtained from mixed scheelite and calcite ores by adding AlSS.

Weng G., Liu J., Carranza E.J., Zhai D., Wang J., Wang H., Zhang B., Zhang F., Wang Y., Jiang D., Sun B.

Scheelite, one kind of common REE-rich and U-bearing hydrothermal mineral, is extensively developed in various types of gold deposits, which can be used to record nature and timing of metallogenesis. The Zhaishang Carlin-like gold deposit in the Qinling Orogen is a giant Au deposit, hosting 127t of Au @ 2.67 g/t with economic concentrations of tungsten and antimony. The study reports two types of scheelite based on the characteristics of petrography and geochemistry. Sch A shows significant oscillatory zoning with dark gray cathodoluminescence (CL) response, whereas Sch B displays patchy textures with brighter CL response. Systematic LA-ICP-MS U–Pb dating of Sch A and Sch B yields ages of 227.1 ± 3.2 Ma and 226.2 ± 6.9 Ma, respectively. The new dates, constraining the Zhaishang Au–W mineralization to ~ 227Ma, coincide well with the western Qinling magmatism, metallogenic and tectonic events. There are significant variations in concentration, the Sch A has low REE content (mean = 41.3 ppm), negative Eu-anomaly with slightly positive Ce-anomaly, whereas Sch B, with small negative or positive Eu-anomaly, has higher REE content (mean = 247 ppm) and higher positive Ce-anomaly. The positive correlation of EuN and EuN* records oxidizing condition during the whole W mineralization event. Additionally, Sch B intergrown with selenides with an increase in the Ce-anomaly supports that the latter has higher oxygen fugacity environment. The Sr isotope signature for scheelite supports that ore-forming metals mostly inherited the host rock component, while the proportion of magma-derived Sr increased in the Sch B. Fluid–rock interactions co-precipitated Au and W caused by the release of Fe and Ca cations and the increase of pH. The study highlights that scheelite as a recorder can help in deciphering the nature and timing of metallogenesis of the studied Au–Sb–W deposit, and thus other similar Au–W deposits.

Wei Z., Sun W., Han H., Gui X., Xing Y.

Scheelite has emerged as the primary source of global tungsten resources. The flotation separation of scheelite, which is hindered by its interface similarity with calcium-containing minerals, remains a worldwide challenge. Achieving precise regulation of interfacial physicochemical properties constitutes the scientific foundation for successful scheelite flotation. In this paper, the progress and prospects of scheelite flotation chemistry and its practice are summarized, encompassing various fields — such as crystal chemistry, solution chemistry, interface chemistry, and coordination chemistry — and providing guidance for the development of new scheelite flotation reagents and processes. The evolution of the scheelite flotation process has been predicated on the advancement of flotation reagents, which has resulted in the creation of the fatty acid flotation process, chelating collector flotation process, and metal–organic complex flotation process, all of which are integral to the three primary scheelite flotation processes. Moving forward, the development and implementation of highly selective complexes collector will be a crucial avenue to facilitate the environmentally-friendly and effective progression of the flotation process.

XiaomengYang, Zhang Z., Shao P., Rezayan A., Wu D., Charles Xu C., Wang J., Zhang Y.

Selective hydrogenolysis of 4-O-5 bond in lignin under relatively mild conditions is an important strategy for the production of valuable aromatic products, e.g. phenols, from renewable carbon resources. However, the easy saturation of benzene rings under reductive conditions over metal catalyst reduces the selectivity to aromatics. In this work, we investigated the effect of bromination of supported Ni nanoparticles on the phenol selectivity during the hydrogenolysis of diphenyl ether (DPE), a commonly used lignin model compound. Compared with the unmodified catalysts, Br-Ni/Al2O3 catalyst derived from Ni-Al layered double oxides exhibits enhanced phenol selectivity (37% vs. 15%) under similar DPE conversions (60%). Various characterizations including transmission electron microscopy (TEM), in-situ X-ray photoelectron spectroscopy (XPS), extended X-ray absorption fine structure (EXAFS), and CO-Fourier transform infrared spectroscopy (FTIR) indicate that Br preferentially located at the terrace site of Ni nanoparticles, deactivating the continuous Ni sites for benzene ring hydrogenation. In addition, the electron-withdrawing effect of Br creates positively charged Ni sites at the corners, facilitating the hydrogenolysis of C–O aryl ether bonds. During the hydrogenation of real lignin, the selective poisoning and electronic effects introduced by Br synergistically increased the yield of phenols from 12.20% on the initial Ni/Al2O3 to 30.47% over the Br-Ni/Al2O3 catalyst. This work provides an advanced strategy for the catalytic valorization of lignin by halogen modified metal-based catalysts.

Yang X., Cui Y., Qi Y., Fu L., Rezayan A., Xu C.C., Wang J., Sui D., Zhang Y.

The rapid development of consumer electronics, electric vehicles, and smart meters demands high-performance energy storage devices. By now, supercapacitors are expected to become one of the most promising energy devices for future energy technology. In this work, NiO nanoparticles supported on activated carbon nanofibers (NiO/ACNFs) have been synthesized by atomic layer deposition technique, which is directly used as self-supporting binder-free electrodes for supercapacitors. Scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman results show that NiO nanoparticles (3.1 nm) are uniformly coated on ACNFs. The NiO/ACNFs-600 electrodes demonstrate a specific capacitance of 870 F·g−1 (1 A·g−1) and good rate capability (remain 67% at 10 A·g−1). The asymmetric supercapacitor devices with NiO/ACNFs-600//ACNFs electrodes yield a fairly high energy density of 39.85 Wh·kg−1 at 2000 W·kg−1 and excellent capacitance retention of 87% after 10,000 cycles. The excellent electrochemical capacitance performance for NiO/ACNFs is attributed to the high conductivity and large specific surface area of ACNFs, high capacity, small size, and even dispersion of NiO as well as the synergistic effect between them. These results demonstrate that NiO/ACNFs can serve as excellent electrode materials for high-performance asymmetric supercapacitors.

Qian H., Bao J., Shen C., Wu D., Wang J., Hao H., Zhang Y.

Low-grade and high-reserve scheelite, which is associated with calcite, has similar surface properties that cause difficulty in separation. In this study, sulfomethylated kraft lignin (SMKL) was used as a novel eco-friendly inhibitor for the flotation separation of scheelite and calcite. The flotation test results showed that 60 mg/L SMKL had a significant influence on depressing calcite flotation, while it had a slight effect on scheelite flotation. Furthermore, it enhanced the WO3 grade of the concentrate in the artificial mixed ore to 62.02% with a recovery rate of 80.37%. The contact angle and zeta potential showed that SMKL could effectively decrease the surface floatability of calcite and caused the negative shift of minerals’ surface potential. XPS and DFT calculations revealed that the sulfonic acid group of SMKL had an electron-donating ability and was easily adsorbed on the positively charged surface of calcite, which hindered the adsorption of sodium oleate on calcite. SMKL could separate calcium-bearing minerals with a high efficiency and selectivity, providing a new method for industrial production.

Zhang Y., Yang X., Bao J., Qian H., Sui D., Wang J., Xu C.C., Huang Y.

Phenolic resins were employed to prepare electrospun porous carbon nanofibers with a high specific surface area as free-standing electrodes for high-performance supercapacitors. However, the sustainable development of conventional phenolic resin has been challenged by petroleum-based phenol and formaldehyde. Lignin with abundant phenolic hydroxyl groups is the main non-petroleum resource that can provide renewable aromatic compounds. Hence, lignin, phenol, and furfural were used to synthesize bio-based phenolic resins, and the activated carbon nanofibers were obtained by electrospinning and one-step carbonization activation. Fourier transform infrared and differential scanning calorimetry were used to characterize the structural and thermal properties. The results reveal that the apparent activation energy of the curing reaction is 89.21 kJ·mol−1 and the reaction order is 0.78. The activated carbon nanofibers show a uniform diameter, specific surface area up to 1100 m2·g−1, and total pore volume of 0.62 cm3·g−1. The electrode demonstrates a specific capacitance of 238 F·g−1 (0.1 A·g−1) and good rate capability. The symmetric supercapacitor yields a high energy density of 26.39 W·h·kg−1 at 100 W·kg−1 and an excellent capacitance retention of 98% after 10000 cycles. These results confirm that the activated carbon nanofiber from bio-based phenolic resins can be applied as electrode material for high-performance supercapacitors.

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

Separation of scheelite from calcite by froth flotation using a new amidoxime surfactant - 3-dodecylamine propyl amidoxime (DPA). • A new amidoxime surfactant DPA was used to flotation separate scheelite and calcite. • Scheelite and calcite recovery were 92% and 4.5% respectively. • DPA exhibited preferable selectivity than NaOL in the absence of depressant. • The interaction of DPA surfactant on scheelite surface is electrostatic adsorption. With its high electrical conductivity, thermal creep resistance and compression modulus, tungsten take an irreplaceable position in modern industry, defense, and high technology. Scheelite, as the main raw material of tungsten resources, usually adopts Petrov’ process: steam heating 80 °C-90 °C, stirring in a tank containing 2%-4% sodium silicate solution for more than half an hour to make sodium oleate desorbed on the calcite surface, and repeated cleaning. Herein, a new amidoxime surfactant 3-dodecylamine propyl amidoxime (DPA), had been synthesized and used as a collector for the first time in the flotation separation of scheelite and calcite at room temperature without any sodium silicate, and compared with the traditional collector sodium oleate (NaOL). The flotation behavior of DPA was studied by micro-flotation and mixed binary mineral flotation tests, which showed that DPA has good collection ability and excellent selectivity for scheelite. Meanwhile, the interaction mechanism of DPA on the mineral surface was discussed by FTIR analysis, zeta potential test, contact angle measurement and density functional theory (DFT). FTIR analysis and zeta potential test confirmed that DPA collector had adsorption on scheelite surface but had little effect on calcite. DFT calculation further confirmed that the positively charged –C(NOH)N + H 3 group in DPA had electrostatic adsorption on the negatively charged scheelite surface. The contact angle measurement results revealed that DPA can enhance the surface hydrophobicity of the scheelite particles. Therefore, this highly selective DPA surfactant can achieve effective separation of scheelite and calcite, contributing to environmental protection and sustainable green development of resources.