Morpholine-Based Gemini Surfactant: Synthesis and Its Application for Reverse Froth Flotation of Carnallite Ore in Potassium Fertilizer Production

Basic magnesium sulfate@TiO2 composite for efficient adsorption and photocatalytic degradation of 4-dodecylmorpholine in brine

More than 70% of the potash fertilizer globally is produced by the froth flotation process, in which 4-dodecylmorpholine (DMP) serves as a reverse flotation agent. As the potash fertilizer production rapidly rises, the increased DMP levels in discharged brine pose a threat to the production of high-value chemicals. In this paper, composite particles of basic magnesium sulfate@TiO2 (BMS@TiO2) were prepared using a simple and mild loading method. These particles were utilized for the adsorption and photocatalytic degradation of DMP in brine. Compared with normal powdered materials, the granular BMS@TiO2 in this study can be easily separated from liquid, and the degradation intermediates will not enter the brine without causing secondary pollution. BMS@TiO2 consists of 5·1·7 phase (5Mg(OH)2·MgSO4·7H2O) whisker clusters embedding 2.3% TiO2. The adsorption equilibrium of DMP on BMS@TiO2 particles was achieved through hydrogen bonding and pore interception with the adsorption capacity of approximately 5 mg g-1 after 6 h. The photodegradation efficiency of DMP adsorbed on BMS@TiO2 reached about 92% within 16 h, which is compared with that of pure TiO2 nanoparticles. Additionally, excellent stability and recyclability of BMS@TiO2 were also observed in five cycle tests of adsorption and photocatalytic degradation of DMP, and the possible photocatalytic degradation pathways and mechanism of DMP are proposed following molecular electrostatic potential analysis. This work provides a sustainable and environmentally friendly approach for eliminating organic micropollutants from water environments.

Perspectives on cultivation and harvesting technologies of microalgae, towards environmental sustainability and life cycle analysis

The development of algae is seen as a potential and ecologically sound approach to address the increasing demands in multiple sectors. However, successful implementation of processes is highly dependent on effective growing and harvesting methods. The present study provides a complete examination of contemporary techniques employed in the production and harvesting of algae, with a particular emphasis on their sustainability. The review begins by examining several culture strategies, encompassing open ponds, closed photobioreactors, and raceway ponds. The analysis of each method is conducted in a systematic manner, with a particular focus on highlighting their advantages, limitations, and potential for expansion. This approach ensures that the conversation is in line with the objectives of sustainability. Moreover, this study explores essential elements of algae harvesting, including the processes of cell separation, dewatering, and biomass extraction. Traditional methods such as centrifugation, filtration, and sedimentation are examined in conjunction with novel, environmentally concerned strategies including flocculation, electro-coagulation, and membrane filtration. It evaluates the impacts on the environment that are caused by the cultivation process, including the usage of water and land, the use of energy, the production of carbon dioxide, and the runoff of nutrients. Furthermore, this study presents a thorough examination of the current body of research pertaining to Life Cycle Analysis (LCA) studies, presenting a perspective that emphasizes sustainability in the context of algae harvesting systems. In conclusion, the analysis ends up with an examination ahead at potential areas for future study in the cultivation and harvesting of algae. This review is an essential guide for scientists, policymakers, and industry experts associated with the advancement and implementation of algae-based technologies.

Synthesis and stability of switchable CO2-responsive foaming coupled with nanoparticles

CO₂-responsive foaming has been drawing huge attention due to its unique switching characteristics in academic research and industrial practices, whereas its stability remains questionable for further applications. In this paper, a new CO₂-switchable foam was synthesized by adding the preferably selected hydrophilic nanoparticle N20 into the foaming agent C₁₂A, through a series of analytical experiments. Overall, the synergy between cationic surfactants and nanoparticles with a contact angle of 37.83° is the best. More specifically, after adding 1.5 wt% N20, the half-life of foam is 14 times longer than that of pure C₁₂A foam. What’s more, the C₁₂A-N20 solution is validated to own distinctive CO₂-N₂ switching features because very slight foaming degradations are observed in terms of the foaming volume and half-life time even after three cycles of CO₂-N₂ injections. This study is of paramount importance pertaining to future CO₂ foam research and applications in energy and environmental practices.

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Cationic surfactants have the best synergy with NPs with a contact angle of 37.83°

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The foam stability increased with the increase of NPs concentration

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CO₂/N₂ can control the foaming properties of C₁₂A-N20 solution and are reversible

Flotation surface chemistry of water-soluble salt minerals: from experimental results to new perspectives

The flotation separation of water-soluble salt minerals has to be conducted under the condition of saturation in brines which represents a challenging but exciting topic of colloid and surface chemistry. Despite several proposals on explaining the success of this industrial application for many decades, our understanding of the flotation separation is still far from complete yet, owing to the complexity of the highly selective collection of salt crystals by air bubbles in brines. Here, we thoroughly review the experimental results for halogen, oxyanion, and double salts and match them with the proposed theories on the flotation of soluble salts to identify the agreed and disagreed cases. The experimental results show that the flotation of these salts varies from collectors (surfactants applied to control the crystal hydrophobicity) to collectors and is strongly affected by the brine ion composition and pH conditions. We find some exceptional flotation results that cannot be simply explained by the crystal surface charge and wettability. Furthermore, we outline several disputes and discrepancies between the experiments and the theories when different collectors are applied. Apart from the extensive consideration of surface hydration, the presence of external ion species exhibits ubiquitous effects on the surface properties of salt crystals and the colloidal properties of collectors. We conclude that the interactions between salt ions, water molecules, collectors, and salt crystals must be considered more thoroughly, and the activity of collectors at the air-liquid interface should also be the focus. Advanced techniques such as molecular dynamics simulation, atomic force microscopy, X-ray photoelectron spectroscopy, and sum-frequency generation spectroscopy are expected to be promising research tools for future studies.

A Review of Energy Consumption in the Acquisition of Bio-Feedstock for Microalgae Biofuel Production

Microalgae biofuel is expected to be an ideal alternative to fossil fuels to mitigate the effects of climate change and the energy crisis. However, the production process of microalgae biofuel is sometimes considered to be energy intensive and uneconomical, which limits its large-scale production. Several cultivation systems are used to acquire feedstock for microalgal biofuels production. The energy consumption of different cultivation systems is different, and the concentration of culture medium (microalgae cells contained in the unit volume of medium) and other properties of microalgae vary with the culture methods, which affects the energy consumption of subsequent processes. This review compared the energy consumption of different cultivation systems, including the open pond system, four types of closed photobioreactor (PBR) systems, and the hybrid cultivation system, and the energy consumption of the subsequent harvesting process. The biomass concentration and areal biomass production of every cultivation system were also analyzed. The results show that the flat-panel PBRs and the column PBRs are both preferred for large-scale biofuel production for high biomass productivity.

Resveratrol Alleviates the KCl Salinity Stress of Malus hupehensis Rhed

Applying large amounts of potash fertilizer in apple orchards for high apple quality and yield aggravates KCl stress. As a phytoalexin, resveratrol (Res) participates in plant resistance to biotic stress. However, its role in relation to KCl stress has never been reported. Herein we investigated the role of Res in KCl stress response of Malus hupehensis Rehd., a widely used apple rootstock in China which is sensitive to KCl stress. KCl-stressed apple seedlings showed significant wilting phenotype and decline in photosynthetic rate, and the application of 100 μmol Res alleviated KCl stress and maintained photosynthetic capacity. Exogenous Res can strengthen the activities of peroxidase and catalase, thus eliminating reactive oxygen species production induced by KCl stress. Moreover, exogenous Res can decrease the electrolyte leakage by accumulating proline for osmotic balance under KCl stress. Furthermore, exogenous Res application can affect K⁺/Na⁺ homeostasis in cytoplasm by enhancing K⁺ efflux outside the cells, inhibiting Na⁺ efflux and K⁺ absorption, and compartmentalizing K⁺ into vacuoles through regulating the expression of K⁺ and Na⁺ transporter genes. These findings provide a theoretical basis for the application of exogenous Res to relieve the KCl stress of apples.

Probing the Interaction Mechanism between Benzohydroxamic Acid and Mineral Surface in the Presence of Pb2+ Ions by AFM Force Measurements and First-Principles Calculations

Probing the interaction mechanism between organic molecules and material surfaces in the presence of metal ions is of great importance in many fields, such as mineral flotation. The collectability of benzohydroxamic acid (BHA) to a spodumene (LiAl(SiO₃)₂) mineral surface during mineral flotation could be enhanced with the addition of metal ion activators-Pb²⁺ ions. Pb²⁺ ions could be added as either Pb-BHA complex formed by premixing Pb²⁺ ions and BHA molecules at a given ratio or sequential addition of Pb²⁺ ions and BHA molecules. However, the complete understanding of the interaction mechanisms (e.g., adhesion) between BHA and the spodumene mineral surface in the presence of Pb²⁺ ions remains very limited. In this study, atomic force microscopy (AFM) was used to measure the intermolecular forces between BHA and the spodumene mineral surface in aqueous solutions. A BHA model molecule, that is, N-hydroxy-4-mercaptobenzamide (MBHA), was synthesized to prepare a BHA-functionalized AFM probe for force measurements. Two model systems (i.e., a Pb-BHA complex interacting with the spodumene mineral surface (model I) and BHA with a Pb²⁺-activated spodumene surface (model II)) were investigated for comparing the role of Pb²⁺ in BHA-mineral adhesion. The adhesion measured for model I (23.7 mN/m) is much higher than that of model II (12.5 mN/m), as further supported by the adsorption energies obtained from density functional theory (DFT) calculations. The calculation results showed a higher adsorption energy for model I (∼188.58 kJ/mol) than model II (∼128.16 kJ/mol), which is due to the better spodumene flotation recovery for the Pb-BHA complex as a collector than the sequential addition of Pb²⁺ and BHA. This work provides useful information on the intermolecular interactions between chemical additives and mineral surfaces in complex mineral flotation processes, and the methodology can be readily extended to other related interfacial processes such as membrane technology, water treatment, oil production, and bioengineering processes.

Specific ion binding interactions in potash flotation

As the main resource of potash fertilizer, high grade of sylvite (KCl) is mainly separated from halite (NaCl) in soluble potash ores using flotation. An effective flotation collector determines the separation efficiency of sylvite. However, the collector adsorption mechanism is still the subject of much debate due to high ions concentration in the flotation pulp. This paper studies the hydration status of KCl, the flotation behavior of KCl and NaCl with lauric acid and the interfacial water structure of the soluble salts to provide further insights into the fundamental mechanisms at play. The contact angle measurements and laboratory micro-flotation experiments have shown that both the hydration status of KCl and the flotation soluble salts with lauric acid were dependent on the solution composition. Specifically, it was determined that the addition of Na-ions had an adverse effect on the hydrophobicity of KCl crystals. Both KCl and NaCl can be floated with lauric acid. However, flotation of NaCl is greatly enhanced with the addition of K-ions whereas the flotation of KCl is suppressed with the addition of Na-ions. Sum frequency generation (SFG) measurements have found, most strikingly, more disordered water molecules dominating the "structure maker" salt surfaces in a saturated NaCl solution. "Collins Concept" is employed to explain the specific ion binding behaviors in the flotation pulp.

Sandwich membranes based on PVDF-g-4VP and surface modified graphene oxide for Cu(II) adsorption

UV photo-preactivation/thermally-induced grafting was employed for grafting 4-vinylpyridine (4-VP) on polyvinylidene fluoride (PVDF), and graphene oxide (GO) was modified with 4'-carboxy-2,2':6',2"-terpyridine (CTPy). Then sandwich PVDF-g-4VP/GO-CTPy/polytetrafluoroethylene (PTFE) membrane was fabricated for adsorption of Cu (II) as a model. The membrane formation, static adsorption thermodynamics, kinetics and dynamic adsorption/desorption were studied. The results showed that, the addition of polyethylene glycol (PEG 4000) as porogen can significantly increase the porosity and adsorption capacity of the membranes. The adsorption could be well described by the Langmuir model and pseudo-second-order kinetic model. The breakthrough volume and saturated volume increased with rising GO-CTPy contents. The adsorption capacity of sandwich membranes was much higher than that of mixed matrix membranes. The sandwich membrane also exhibited excellent reusability in dynamic adsorption/desorption cycles, demonstrating great potential in adsorption of trace Cu (II).

Gemini surfactant: A novel flotation collector for harvesting of microalgae by froth flotation

Froth flotation has been proved to be a promising approach for commercial scale harvesting of microalgae. However, all the surfactants used in the microalgae flotation harvesting process are conventional monomeric surfactants contain a single similar hydrophobic group in the molecule, which results in a low harvesting efficiency. In this work, a novel Gemini surfactant, N,N'-bis(cetyldimethyl)-1,4-butane diammonium dibromide (BCBD) was prepared, and originally recommended as a collector for froth flotation harvesting of Chlorella vulgaris from culture medium. The performance of BCBD was compared with the results acquired using its conventional monomeric surfactant cetyl trimethyl ammonium bromide (CTAB). The bench-scale flotation results showed that BCBD had excellent collecting power for Chlorella vulgaris. Achieving the obviously superior flotation harvesting performance (flotation recovery increased by 21.4% and enrichment ratio increased by 22.9), the dosage of Gemini type BCBD collector is five times less than that of monomeric CTAB collector.

Surface Features of Fluorapatite and Dolomite in the Reverse Flotation Process Using Sulfuric Acid as a Depressor

The surface features of fluorapatite (FA, Ca5(PO4)3F) and dolomite (CaMg(CO3)2) conditioned with sulfuric acid (H2SO4) were examined through flotation experiments, contact angle tests, time-of-flight secondary ion mass spectrometry (TOF-SIMS), and FTIR experiments. The flotation and contact angle results suggested that oleate insufficiently adsorbed onto the H2SO4-treated FA surface such that the FA surface remained hydrophilic. However, using oleate as a collector, the recovery and hydrophobicity of H2SO4-treated dolomite were satisfactory. TOF-SIMS and FTIR studies indicated that sulfate anion bound with Ca atoms on the FA surface, which hindered oleate adsorption onto the FA surface. Meanwhile, sulfate anion and oleate species appeared on the dolomite surface, thereby generating a hydrophobic dolomite and also a satisfactory recovery.