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Solvent extraction is the most important method for rare earth extraction and separation. Currently, di(2-ethylhexyl) phosphoric acid (HDEHP) and 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (HEH/EHP) are widely used in industrial production, but there are still obvious deficiencies that require further research to resolve. In this paper, the unsaponification extraction of light rare earth ions in a hydrochloric acid medium by di(2-ethylhexyl) phosphoric acid-di(1-methyl-heptyl) methyl phosphonate (HDEHP-P350) system was studied. The results show that the addition of P350 reduces the extraction capacity of HDEHP, and also greatly reduces the concentration of acidity required for the back-extraction. It still has a good separation factor for light rare earths without saponification, and the extractant is not easy to emulsify. With an aqueous phase of pH = 2.85, and HDEHP mole fraction XHDEHP = 0.9 (compared with O/A = 2), the separation effect of light rare earth is the best, resulting in the separation coefficient βCe/La = 3.39, βPr/Ce = 1.67 and βNd/Pr = 1.45, respectively. The loaded light rare earth ions extracted by HDEHP-P350 can be easily stripped when 2 mol/L HCl is used as the stripping agent. Finally, the extraction mechanism is discussed using a slope method, and the final structure of the extracted complex is determined to be RECl[(DEHP)2]2P350(o), based on a combination of infrared spectra and 1H NMR and 31P NMR analyses.

The ferrite process can not only purify wastewater containing heavy metal ions but also recycle valuable metals from wastewater. Therefore, it is considered a promising technology to treat chromium-containing wastewater. However, the process has not been extensively applied in industry due to its high synthesis temperature. In this paper, the feasibility of chromite synthesis at room temperature was comprehensively studied. The effects of critical factors on the effluent quality and the crystallization behavior and stability of the synthetic products were investigated. Results showed that the removal ratio of chromium from wastewater was over 99.0%, and the chromium concentration in the supernatant reached the sewage discharge standard after undergoing the ferrite process at room temperature. Increases in the aeration rate, stirring rate, and reaction time were favorable for the formation of stable chromite. The particles obtained by the ferrite process at room temperature were characterized by a compact structure, and the maximum size of the particles reached 52 μm. Chromium gradually entered the spinel crystal structure during the synthesis process, and the molecular formula of the synthetic chromite might be Fe3-xCrxO4, in which x was approximately 0.30. The path of the microscopic reaction was proposed to illuminate the synthesis mechanism of chromite under room temperature conditions. The present study has laid the foundation for the industrial application of the ferrite process in the purification and utilization of chromium-containing wastewater.

Centrifugal high gradient magnetic separation (CHGMS) operates through a rotating matrix in a magnetic field, so that its separation performance is closely related to the coupling of magnetic field and rotating magnetic wires of the matrix. In this work, the capture characteristics of magnetic wires rotating at two different patterns, i.e., revolving around the center of separating cylinder and spinning around the axis of wire in a given uniform magnetic field, were comparatively described; and using a capture set-up, they were experimentally verified by their actual magnetic capture to ilmenite particles from a primary ilmenite concentrate assaying 13.04% TiO2. It was found that the centrifugal force and hydrodynamic drag acting onto the particles of the spinning wire, as well as the required magnetic force to the particles for effective magnetic capture, is much smaller than that of the revolving wire. According to the COMSOL Multiphysics simulation, there is a large velocity gradient between the slurry around the rotating wire and the separating cylinder, producing a fluid shearing stress to particles in the slurry and thus improving the loose state of the slurry around the wire; in addition, the effect of wire spinning on the motion trajectories of particles is much weaker than that of the revolving one. The capture experiments indicated that the rotating pattern of wire has a significant effect on the capture characteristics; specifically, the spinning wire obtained a much higher mass weight for ilmenite particles but a similar capture selectivity, in comparison with the revolving wire. For instance, when the rotation of 6 mm diameter wire was transformed from revolution to spinning at the same rotation speed of 120 r/min, the mass weight of ilmenite particles captured onto the wire was significantly increased from 1.1 g/cm to 2.0 g/cm, while their TiO2 grades reached 27.12% and 26.25%, respectively. It was concluded that the high capture selectivity of the rotating wire to ilmenite particles is primarily attributed to the effect of loosing particles in the fluid, as it facilitates the release of non-magnetic particles from the magnetic deposits captured on the wire surface. This investigation provides a valuable reference for the determination of matrix rotation pattern in the development of CHGMS technology.

Magnetic element is the basic component of matrix in high gradient magnetic separation (HGMS), and its configurative parameters such as size have marked effects on the capture efficiency of the matrix. Therefore, the geometric design of the element should be matched with the properties of the material to be separated, to optimize the HGMS performance. In this work, the capture of independent magnetic particles on a cylindrical element in pulsating HGMS process was theoretically described, and their size matching ratios (magnetic element to particle) under the maximum capture probability and critical capture conditions were specifically discussed. These theoretically calculated size ratios were much larger than that (2.69) in the literatures available, but generally consistent with those obtained from pulsating HGMS applications. The theoretical analysis were basically validated by the actual capture of ilmenite and hematite particles on cylindrical elements, using an experimental magnetic capture method. According to the new theoretical model, the size matching ratio is not fixed at the value of 2.69. It depends on the properties of the material to be separated such as volume magnetic susceptibility and the operating parameters of a HGMS process such as magnetic induction and flow velocity through the magnetic element. This theoretical description provides a new fundamental understanding in the size matching between magnetic element and particle, and would contribute to the solution of size matching issue in the real capture situation considering the interactions between magnetic particles, and therefore to the optimal design and operations of matrix in HGMS applications.

The sulfidization mechanism of S2 on the massicot surface was simulated by density function theory (DFT) calculation to illustrate the microscopic reaction mechanism during the surface sulfidization process of lead oxide minerals at high temperature. The calculated results showed that the massicot (1 0 0) surface was the most stable cleavage surface and the main active sites were the O atoms of the surface. The S atoms more easily absorbed on the O atoms of massicot surface in contrast with Pb atoms, leading to the formation of sulfur dioxide in the following reactions. The density of state (DOS) results revealed that O 2p orbital at surface layers of the massicot and S 3p orbital of S2 overlapped ranging from −0.7 to 0.7 eV, implying that chemical adsorption could occur. The results of Mulliken population suggested that the oxidation and reduction reactions of S atoms from the sulfidization agent were simultaneously involved in the adsorption process. This paper revealed the mechanism of surface sulfidization at an atomic level. It was expected that the study could provide a theoretical reference to improve the sulfidization roasting performance of massicot.

The present work studies the immobilization forms of lead in alkali-activated cementitious binders (AACBs) based on mine tailings. Through deconvolution of Pb 4f XPS spectra of the mine tailings-based binders, the immobilization forms of lead in network, and lead in silicate glass of PbO·3SiO2 and PbO·7SiO2 were first quantitatively presented. The 29Si NMR spectra of the binders synthesized with Pb(NO3)2 additions from 0 to 6% give the ratios of silicates involved in the formation of lead silicate glass, ranging from 0 to 10.56%. In addition, images of scanning electron microscope (SEM) equipped with X-ray microanalytical mapping and results of zeta potential measurements confirmed the immobilization forms in the mine tailings-based binders. It not only gives fundamentals for the solidification/stabilization (S/S) of mine tailings through alkaline activation process, but also enriches the understanding on the immobilization of heavy metals in AACBs.

The sulfidization mechanism of ZnO involving the interaction between S2 and zincite (10 1 ¯ 0) surface was investigated by density functional theory (DFT) calculations. The geometry structures and electronic properties of atoms at the zincite surface layers before and after S2 adsorption were thoroughly calculated. The results indicated that the oxygen atoms at the zincite surface were the dominating active site for the subsequent reaction. The S2 could easily adsorb on the surface of zincite with an adsorption energy of −2.27 eV, followed by dissociation of Zn–O bond. The density of sate (DOS) analyses presented that the S 3p orbital from the S2 and O 2p orbital at the mineral surface layer were obviously overlapped near the Fermi energy, suggesting that an intensive hybridization occurred between them. The Mulliken population results showed that both S atoms in S2 could not only be oxidized, but also be reduced, resulting in the generation of SO2 and ZnS. This study gave an insight into the interaction between S2 and zincite surface at an atomic level and further enriched the sulfidization mechanism of ZnO at a high temperature.

Surface sulfidization behavior of smithsonite at high temperature was investigated by X-ray powder diffractometer (XRD) along with thermodynamic calculation, X-ray photoelectron spectroscopy (XPS) and electron probe microanalysis (EPMA). The XRD and thermodynamic analyses indicated that the smithsonite was decomposed into zincite at high temperatures. After introducing a small amount of pyrite, artificial sulfides were formed at surface of the obtained zincite. The XPS analyses revealed that the sulfide species including zinc sulfide and zinc disulfide were generated at the zincite surface. The EPMA analyses demonstrated that the film of sulfides was unevenly distributed at the zincite surface. The average concentration of elemental sulfur at the sample surface increased with increasing of pyrite dosage. A suitable mole ratio of FeS2 to ZnCO3 for the surface thermal modification was determined to be about 0.3. These findings can provide theoretical support for improving the process during which the zinc recovery from refractory zinc oxide ores is achieved by xanthate flotation.

The extraction kinetics of lanthanum (III) from a chloride medium by bis(2-ethylhexyl) phosphate(HDEHP) and dimethylheptyl methyl phosphate(P350) in the presence of sulfonated kerosene are investigated using a Lewis cell. The effects of the stirring rate, temperature, and specific interfacial area on the extraction rate are investigated. The results show that the extraction process is controlled by diffusion and chemical reactions in the interfacial area rather than in the bulk phase. The apparent activation energy and the changes in the enthalpy, entropy, and Gibbs free energy of the extraction reaction are calculated using the Arrhenius equation and transition state theory. The rate equation derived from the experimental results is similar to that of the interface reaction model. A mass transfer model with a rate-control step is proposed. This study provides guidance and data support for an HDEHP-P350 system in industrial production applications.

Grinding plays an important role in the beneficiation process. Different grinding media can determine the size distribution, shape, and even the surface properties of the produced material. However, comprehensive research related to the effect of grinding media on the flotation performance of cassiterite is lacking. In the current study, the effects on the flotability of the products obtained by grinding with ceramic and stainless steel media were investigated using micro-flotation, laser particle size distribution analysis, inductively coupled plasma optical emission spectroscopy (ICP-OES), chemical element analysis, zeta potential measurements, field emission scanning electron microscopy-energy dispersive spectroscopy (FESEM-EDS), and X-ray photoelectron spectroscopy (XPS). The micro-flotation results demonstrate that the flotability of stainless steel ground cassiterite surpasses that of ceramic. The laser particle size distribution test reveals that the two grinding media do not have a strong impact on the particle size distribution. The ICP-OES and chemical element analysis results identify the higher iron content in the samples and pulp of stainless steel ground cassiterite as the principle influencing factor. The zeta potential analysis indicates that the dissolved iron ions absorbed on the cassiterite surface results in a positive shift of the mineral surface potential. This not only reduces electrostatic repulsion but also increases the active sites of salicylhydroxamic acid (SHA) chemisorption. FESEM-EDS results demonstrate the rougher surface and higher iron content of the stainless steel ground cassiterite compared to the ceramic ground cassiterite, thereby increasing the SHA adsorption. The stainless steel grinding cassiterite was observed to alter the chemical environment of Fe species on the cassiterite surface via XPS analysis, with Fe2+ exhibiting a stronger reactivity and stability towards SHA compared to Fe3+. Thus, the stainless steel media ground cassiterite demonstrates an improved flotability performance compared to the ceramic equivalent.

Waste rocks were obtained during the mining, and were identified as a solid waste. The waste rocks were mostly stockpiled due to lack of economic value, resulting in a large occupation of land and secondary pollution risks. Considering that the waste rocks mainly consisted of clay minerals, it was firstly speculated that the waste rocks might be used as a novel adsorbent to treat the beneficiation wastewater containing arsenic and fluorine. In the study, the compositions of waste rocks were studied by chemical analysis, XRD and SEM-EDS, and the stability of heavy metals in the waste rocks was examined by dissolution experiments. The optimum modification reagents and adsorption parameters were determined by a batch of experiments. Adsorption mechanisms were revealed by adsorption kinetics, adsorption isotherms, SEM, N2 adsorption-desorption isotherms, zeta potentials and XPS. The removal ratios of arsenic and fluorine in the beneficiation wastewater reached 98.13% and 86.13%, respectively. The interlayer spacing and average pore size of the waste rocks increased after the modification. In addition, zeta potentials moved from negative to positive, leading to the increase in adsorption capacity of the waste rocks. The data of adsorption experiments was well fitted by nonlinear pseudo-second-order kinetics and Langmuir isotherm, indicating that the adsorption was controlled by chemisorption and was a monolayer adsorption process. The adsorption of arsenic and fluorine on the waste rocks referred to the ligand exchange and electrostatic adsorption. It was a promising method to achieve the clean utilization of waste rocks and the sustainable development of mining.

This paper systematically analyzed the effects of Fe(II) ions on the cassiterite surface to promote the adsorption of salicylhydroxamic acid (SHA). The interaction behavior and mechanisms re investigated using micro-flotation experiments, adsorption experiments, zeta potential measurements, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The micro-flotation tests revealed that the Fe(II) ions had a strong activation effect on the cassiterite, and the recovery reached the maximum at pH values of 7–8. The results of the adsorption experiment showed that the adsorption capacity of SHA on the mineral surface significantly improved after Fe (II) ion activation; this result was confirmed by the zeta potential test. In addition, the zeta potential results indicated that the positively charged Fe species absorbed on the cassiterite surface led to positive changes in the mineral surface potential and an increase in the number of active sites, thereby increasing the SHA adsorption. The XPS and FTIR results demonstrated that the Fe(II) ions activated the cassiterite through the interaction of terminal oxygen atoms with Fe species on the cassiterite surfaces, and redox reactions and displacement reactions occurred between Fe2+ and Sn4+. SHA was chemisorbed on the cassiterite surface, allowing the anions to react readily with the Fe species to form Fe-SHA complexes. Therefore, the Fe(II) ion-activated cassiterite surfaces enhanced the strength and stability of the SHA chemisorption. Based on the results, an adsorption model of the Fe(II) ion-activated cassiterite surface in the SHA system was established.

Although numerous studies on the flotation depression of sphalerite by calcium have been reported, certain issues warrant further investigation. Previous research works did not examine the role that the iron content of iron-bearing sphalerite plays in calcium depression and did not obtain direct and convincing microscopic evidence of calcium adsorption to support the depression of calcium-containing ions on iron-bearing sphalerite’s flotation. In this paper, the effects of iron content and the presence of calcium on iron-bearing sphalerite’s flotation depression under high alkalinity environment are studied using flotation tests, adsorption amount measurements, surface extraction, zeta potential measurements, time-of-flight secondary-ion mass spectrometry (TOF-SIMS) and density functional theory (DFT) calculations. The results show that increasing iron content or the presence of calcium will lead to an increase in the degree of flotation depression and will reduce the adsorption of copper and xanthate. Increasing iron content will cause the surface of iron-bearing sphalerite to adsorb more metal hydroxides (especially iron hydroxide) and calcium. The TOF-SIMS results confirmed the trend of calcium adsorption at the atomic level. DFT calculations show that the adsorption energy of CaOH+ on the surface of iron-substituted sphalerite is lower than that on the surface of ideal sphalerite. The following conclusions can be obtained through analysis of the aforementioned: Increase in the adsorption of hydroxides (especially iron hydroxide) and calcium significantly hinder the adsorption of copper and xanthate, and increase the hydrophilicity of high-iron sphalerite surface, which ultimately leads to an increase in the degree of flotation depression of high-iron sphalerite with increasing iron content.

Salicylhydroxamic acid (SHA) has been widely used as collector in cassiterite flotation, and α-terpineol (AT) and methyl isobutyl carbinol (MIBC) are common frothers in mineral flotation. The effects of AT and MIBC on cassiterite flotation have rarely been reported, which severely limits our understandings of the role of frother in cassiterite flotation. Here, comparative studies between AT and MIBC in affecting cassiterite flotation using SHA as collector were conducted through micro-flotation tests. Micro-flotation tests showed that the averaged value of the recovery of cassiterite with AT was 10% higher than that with MIBC at the same concentration. To unveil the mechanisms of enhancement effects of AT on the flotation of fine cassiterite particles, zeta potential measurements, contact angle measurements and surface tension measurements were conducted. Zeta potential of cassiterite surface shifted to more negative value in the presence of SHA, and the nonionic reagents, AT and MIBC, could not affect the surface potential of cassiterite. Contact angle measurements showed AT could adsorb on the surfaces of cassiterite particles, and therefore the hydrophobicity of particles was increased. In addition, there was a synergistic behavior between SHA and AT on cassiterite surface due to co-adsorption, and the cassiterite surface was more hydrophobic in the SHA/AT solution. Less surface tension and smaller bubble size were obtained in the SHA/AT solution compared to SHA/MIBC solution. These two combining effects, i.e. increasing the hydrophobicity of cassiterite particles and reducing the single bubble size, are beneficial to the flotation of cassiterite, which explains higher recoveries in cassiterite flotation when AT is used as frother and SHA as collector.

The incidence of aflatoxin M1 (AFM1) contamination in milk and milk products is a serious health hazard for human worldwide. Thus, the global monitoring of AFM1 in raw milk has been ongoing for decades. In this review, the occurrence of AFM1 in raw milk has been summarized worldwide in 32 countries date from 97 references over the past decade. The data from 28 references demonstrated that a great risk related to high AFM1 concentrations (above 500 ng/L) in raw milk exist in several countries. Furthermore, to minimize health risks associated with ubiquitous exposure to AFM1 contamination in milk, several detoxification methods have been tested to lessen the transfer of aflatoxins from feed (7.3–112 μg/kg) to milk (190–1920 ng/L). Although most of them could lessen the concentrations of AFM1 in milk (76–1840 ng/L), these methods are still substandard relative to the EU limit (50 ng/L). The limitation of detoxification approaches in milk might suggest that comprehensive solutions should be implemented containing the standardization of legitimately harvest, storage, and lifetime of feedstuff, the application of detoxification methods, the establishment of official monitoring and regulatory limits, and so on.

It is inevitable for the presence of dissolved ions, especially inorganic cations or anions, in the process water of an industrial flotation system. They could alter the chemistry of a flotation system and interfere with the interaction between minerals and reagents. The purpose of this study was to identify the relationship between anion distribution in the process water and the flotation performance of a typical industrial iron ore concentrator when the process conditions were stable. An effort was also made to understand how the anions affect the flotation properties of the iron ore through a series of water chemical analyses by Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES), ore sample analysis by X-ray Diffraction (XRD), bench flotation tests by using the industrial iron ore, micro-flotation tests by using pure quartz, and zeta potential measurement. The data from water chemical analyses indicated that sulfate ion concentrations in the process water, especially from the roughing stage, are more relevant to the SiO2 content and Fe recovery in concentrate than chloride ion. This can be explained by the results from flotation tests, suggesting that the anions at higher valence tend to have more significant influences on lowering the SiO2 content. But it substantially depends on anion concentration, pulp pH, and type of metal ions. At 8.5–9.2, SO42− ions have promotive effects on the recovery of the quartz pre-modified by FeCl2, or FeCl3 in the water. This is probably due to a shift towards acidic direction on the zeta potential of quartz surfaces in the presence of sulfate ions. These anions, however, have negative effects on the quartz recovery with the occurrence of Ca2+ ions. The precipitation of CaSO4 on the mineral surfaces could be attributed to it.

Centrifugal high gradient magnetic separation (CHGMS) concentrates fine weakly magnetic minerals at a high selectivity, which was achieved through a magnetic matrix dynamically rotating in a magnetic field. In this work, the highly selectivity capture mechanisms of magnetic wires rotating in uniform and alternating magnetic fields were comparatively described, including their magnetic field distributions and the magnetic forces required for the capture of the wires to magnetic particles. The capture mechanism was experimentally verified with a primary ilmenite concentrate assaying 13.04% TiO2, which was produced from pulsating HGMS process. It was found that the dynamically rotating wire was able to achieve significantly improved capture selectivity, in comparison with the static (quasi-static) one; for instance, when the rotation speed of the 3.0 mm wire was increased from 15 (quasi-static) to 120 rpm (dynamic) in the uniform magnetic field, the grade of captured ilmenite particles was significantly improved from 15.98% to 23.86% TiO2. In addition, the capture characteristics of rotating wire was related to the build-up pattern of centrifugal high gradient magnetic field; for instance, when the 3.0 mm wire rotated at 120 rpm and 40 mm radius, the wire in the alternating magnetic field produced a magnetic product with a high TiO2 grade of 29.86% at the expense of slightly reduced capture mass weight, and this grade was significantly superior to that (23.72% TiO2) produced from the uniform magnetic field. The conclusions from this investigation would provide valuable foundations for the development and application of CHGMS method.

Froth flotation of high-iron marmatite particles activated by ammoniacal copper(II) solution has been studied in this work. This study was performed on single marmatite mineral of 76–125 μm in size and 20% iron content by using micro-flotation. The results have shown that ammoniacal copper(II) solution effectively activated high-iron marmatite particles in the flotation with xanthate as the collector, being much better than copper sulfate, a traditional activator for sphalerite and marmatite flotation. Also, the maximum activation by ammoniacal copper(II) solution in the flotation appeared around pH 9, compared with pH 13–14 by copper sulfate. Therefore, the substitution of ammoniacal copper(II) solution for copper sulfate in high-iron marmatite flotation would increase the separation efficiency and would allow large savings on the consumptions of lime and xanthate. Based on the species distribution diagram for copper(II)–ammonia system, it has been found that the activation of ammoniacal copper(II) solution in high-iron marmatite flotation might be originated from copper(II)–ammonia complexes, CuNH 3 2 + and Cu ( NH 3 ) 2 2 + , through the adsorption on the mineral surface.

CD133+ tumor cells are responsible for the initiation, propagation and recurrence of tumors, which raises the question of how to effectively target CD133+ tumor cells. Arsenic trioxide (As2O3) has considerable efficacy in treating solid tumors with induction of apoptosis. Here, we found that purified CD133+ gallbladder carcinoma cells are highly resistant to conventional chemotherapy. However, As2O3 effectively induces CD133+ gallbladder carcinoma cells apoptosis. Treatment with As2O3 reduces CD133 expression at transcriptional levels. Furthermore, the ectopic expression of CD133 attenuated the apoptotic effect of As2O3 on cells through activation of AKT signaling pathways. Collectively, As2O3 effectively targets CD133 in gallbladder carcinoma, providing a new mechanism of As2O3-induced cell apoptosis and a better understanding of drug resistance in gallbladder carcinoma.