Probing the hydrophobic mechanism of N-[(3-hydroxyamino)-propoxy]-N-octyl dithiocarbamate toward bastnaesite flotation by in situ AFM, FTIR and XPS

A review of flotation reagents for bastnäsite-(Ce) rare earth ore

Given the indispensability and immense value of rare earth elements for scientific and technological advancements in the 21st century, extracting high-quality rare earth resources from nature has become a global priority. Bastnäsite-(Ce) is one of the known rare earth minerals with high rare earth content and wide distribution, which occupies a pivotal position in human life and high-end production activities, making its efficient development and utilization crucial. In recent years, research on separating bastnäsite-(Ce) from gangue minerals has focused on the flotation process, with flotation reagents playing a critical role in achieving effective separation. This paper provides a detailed summary of current research on the behavior of bastnäsite-(Ce) flotation agents on minerals, their interaction with mineral surfaces during flotation separation, and outlines future prospects for further research.

Selective recovery of Cu(II) from strongly acidic wastewater by zinc dimethyldithiocarbamate: Affecting factors, efficiency and mechanism

The selective recovery of copper from strongly acidic wastewater containing mixed metal ions remains a significant challenge. In this study, a novel reagent zinc dimethyldithiocarbamate (Zn(DMDC)₂) was developed for the selective removal of Cu(II). The removal efficiency of Cu(II) reached 99.6% after 120 min reaction at 30°C when the mole ratio Zn(DMDC)₂/Cu(II) was 1:1. The mechanism investigation indicates that the Cu(DMDC)₂ products formed as a result of the displacement of Zn(II) from the added Zn(DMDC)₂ by Cu(II) in wastewater, due to the formation of stronger coordination bonds between Cu(II) and the dithiocarbamate groups of Zn(DMDC)₂. Subsequently, we put forward an innovative process of resource recovery for strongly acidic wastewater. Firstly, the selective removal of Cu(II) from actual wastewater using Zn(DMDC)₂, with a removal efficiency of 99.7%. Secondly, high-value CuO was recovered by calcining the Cu(DMDC)₂ at 800°C, with a copper recovery efficiency of 98.3%. Moreover, the residual As(III) and Cd(II) were removed by introducing H₂S gas, and the purified acidic wastewater was used to dissolve ZnO for preparation of valuable ZnSO₄·H₂O. The total economic benefit of resource recovery is estimated to be 11.54 $/m³. Accordingly, this study provides a new route for the resource recovery of the treatment of copper-containing acidic wastewater.

New insights into the aggregation and disaggregation between serpentine and pyrite in the xanthate flotation system

HYPOTHESIS

In xanthate flotation system, the aggregation of serpentine on sulfide minerals significantly weakened their floatability. And it was generally assumed that the electrostatic attraction was of the dominant driver for coating of serpentine slimes. In this paper, the hydrophobic interaction between the "talc-like" cleavage plane of serpentine and the xanthate-hydrophobized surface of sulfide minerals was proposed as the dominated driver.

EXPERIMENTS

To evaluate the aggregation of serpentine on pyrite surface, a novel experimental protocol was designed, and the aggregation behavior and mechanism in the absence and presence of sodium isobutyl xanthate (SIBX) were explored through in situ optical microscope, micro-flotation, contact angle, zeta potential and FT-IR. Afterwards, the disaggregation mechanism of 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP) to the aggregates of serpentine on pyrite surface was revealed.

FINDINGS

The electrostatic attraction facilitated the slight aggregation of serpentine slimes on bare pyrite surface. The hydrophobic interaction between the "talc-like" plane of serpentine and SIBX-covered pyrite significantly promoted the aggregation between them, which remarkably weakened the floatability of pyrite. The attendance of HEDP anions reversed the surface potential of the octahedral Mg-O layers of serpentine from the positive into the negative, thus to prevent the aggregation of the HEDP-anchored serpentine with the SIBX-covered pyrite via the strong electrostatic repulsion between them. As a result, the disaggregation as well as SIBX flotation separation of pyrite from serpentine was realized. This investigation also provided new insights into the aggregation and disaggregation between serpentine and sulfide minerals during froth flotation.

Removal of Hg2+ in wastewater by grafting nitrogen/sulfur-containing molecule onto Uio-66-NH2: from synthesis to adsorption studies

The remediation of heavy metal deserves to be on the agenda, with the adsorbent design bearing the brunt of it. In this study, the molecule (4, 6-diamino-2-mercaptopyrimidine, DMP) containing thiol (-SH) and amino (-NH₂) functional groups was grafted onto Uio-66-NH₂, and a composite metal-organic framework nanomaterial (Zr(NH₂)-DMP) was synthesized via a facile post-modification scheme. The morphological characteristics and structural features of the modified adsorbent were characterized by XRD, FT-IR, FE-SEM, EDS, BET, and XPS. The characterization results verified that the post-modification scheme was successfully achieved. The adsorption experiments were carried out to investigate the removal performance of the Zr(NH₂)-DMP towards Hg²⁺ under different influencing parameters. The maximum adsorption capacity of 389.4 mg/g was obtained, and the adsorption equilibrium was achieved within 30 min at pH 6 at room temperature. Adsorption thermodynamic study indicated that the adsorption process was exothermic and spontaneous. The Zr(NH₂)-DMP exhibited excellent selectivity for Hg²⁺, and also has the potential to remove Cu²⁺, Fe²⁺, and Zn²⁺ ions. The introduction of Cl^- inhibited the removal of Hg²⁺ due to the formation of mercuric chlorides (removal efficiency reduced from 97.8 to 95.6%). The removal efficiency of up to 86.7% was obtained after four cycles. The Langmuir isotherm and Pseudo-second kinetic were more suitable for fitting the adsorption process of Hg²⁺ by Zr(NH₂)-DMP. The main removal mechanism could be attributed to the chelation between Hg²⁺ (soft acid) and nitrogen/sulfur (soft base) elements. These findings convinced that the successful synthesis of Zr(NH₂)-DMP provides an option for Hg²⁺ removal from wastewater.

Oxygen Vacancy-Mediated Activates Oxygen to Produce Reactive Oxygen Species (ROS) on Ce-Modified Activated Clay for Degradation of Organic Compounds without Hydrogen Peroxide in Strong Acid

The treatment of acid wastewater to remove organic matter in acid wastewater and recycle valuable resources has great significance. However, the classical advanced oxidation process (AOPs), such as the Fenton reaction, encountered a bottleneck under the conditions of strong acid. Herein, making use of the oxidation properties of CeAY (CeO₂@acid clay), we built an AOPs reaction system without H₂O₂ under a strong acid condition that can realize the transformation of organic matter in industrial wastewater. The X-ray photoelectron spectroscopy (XPS) proved that the CeAY based on Ce³⁺ as an active center has abundant oxygen vacancies, which can catalyze O₂ to produce reactive oxygen species (ROS). Based on the electron spin-resonance spectroscopy spectrum and radical trapping experiments, the production of •O₂^- and •OH can be determined, which are the essential factors of the degradation of organic compounds. In the system of pH = 1.0, when 1 mg CeAY is added to 10 mL of wastewater, the degradation efficiency of an aniline solution with a 5 mg/L effluent concentration is 100%, and that of a benzoic acid solution with a 100 mg/L effluent concentration is 50% after 10 min of reaction. This work may provide novel insights into the removal of organic pollutants in a strong acid water matrix.

Improving Rare-Earth Mineral Separation with Insights from Molecular Recognition: Functionalized Hydroxamic Acid Adsorption onto Bastnäsite and Calcite

Enhancing the separation of rare-earth elements (REEs) from gangue materials in mined ores requires an understanding of the fundamental interactions driving the adsorption of collector ligands onto mineral interfaces. In this work, we examine five functionalized hydroxamic acid ligands as potential collectors for the REE-containing bastnäsite mineral in froth flotation using density functional theory calculations and a suite of surface-sensitive analytical spectroscopies. These include vibrational sum frequency generation, attenuated total reflectance Fourier transform infrared, Raman, and X-ray photoelectron spectroscopies. Differences in the chemical makeup of these ligands on well-defined bastnäsite and calcite surfaces allow for a systematic relationship connecting the structure to adsorption activity to be framed in the context of interfacial molecular recognition. We show how the intramolecular hydrogen bonding of adsorbed ligands requires the inclusion of explicit water solvent molecules to correctly map energetic and structural trends measured by experiments. We anticipate that the results and insights from this work will motivate and inform the design of improved flotation collectors for REE ores.

Efficient removal of uranium from wastewater using pig manure biochar: Understanding adsorption and binding mechanisms

In this work, three kinds of biochars (PMBC-H₂O, PMBC-PP and PMBC-HP) with excellent adsorption performance were obtained by carbonizing pig manure pre-treated with different agents. These biochars had the ordered mesoporous structures and possessed abundant active functional groups on their surface. The adsorption behaviors of the biochars towards U_VI under various conditions were evaluated by batch experiment. The results showed that KMnO₄ and H₂O₂ could enormously improve the adsorption performance of PMBC to U_VI. After KMnO₄ and H₂O₂ pretreatment, the maximum adsorption capacities of PMBC-PP (979.3 mg/g) and PMBC-HP (661.7 mg/g) were about 2.6 and 1.8 times higher than that of PMBC-H₂O (369.9 mg/g), respectively, which was much higher than previously reported biochar-based materials. Obviously, KMnO₄ pretreatment leaded to a higher enhancement than that of H₂O₂. The removal mechanism of U_VI on PMBC-PP was discussed in-depth. The interaction between U_VI species and PMBC-PP was mainly ascribed to the abundant active sites on the surface of PMBC-PP. In a word, conversion of pig manure pre-treated with KMnO₄ into biochar not only demonstrates that PMBC-PP has great potential in the treatment of actual uranium-containing wastewater, but also provides a method for the rational utilization of pig manure to reduce the pollution.