Microwave-assisted atmospheric alkaline leaching process and leaching kinetics of rare earth melt electrolysis slag.

This study focuses on the difficulty of converting fluorinated rare earth elements into hydroxylated rare earth elements in rare earth melt electrolysis slag (RMES) and proposes the use of a microwave-assisted atmospheric alkaline leaching method for the treatment of RMES. The leaching behavior of RMES under microwave-assisted atmospheric alkaline leaching was studied, and the optimal reaction conditions were determined. Under the conditions of a reaction temperature of 150 °C, initial NaOH concentration of 60 %, NaOH-to-slag mass ratio of 4:1, microwave power of 700 W, reaction time of 120 min, and stirring speed of 300 r/min, the conversion rate of fluorinated rare earths reached 99.17 %. The apparent rate equation of the microwave-assisted atmospheric alkaline leaching process was obtained by leaching kinetic analysis, and the apparent activation energy under this process was calculated to be 54.872 kJ/mol, which was 12.458 kJ/mol lower than that achieved when conventional heating was used for leaching (67.33 kJ/mol).

Study on adsorption of ammonia nitrogen by sodium-modified kaolin at calcination temperature.

Natural kaolin (NK) is not used as a material for removal of ammonia nitrogen in wastewater because of its low ammonia adsorption capacity. In this study, sodium-modified kaolin adsorbent (NaCK) with high ammonia nitrogen adsorption capacity was prepared by NaOH modification of calcined NK, which was developed to address this problem. The adsorption properties were evaluated by batch static adsorption test. The results showed that when the initial concentration of ammonia nitrogen was 10 mg/L, pH = 8, and dosage of adsorbent was 1 g/L, the adsorption capacity of NaCK-600 for ammonia nitrogen was the best, reaching 6.23 mg/g, which was 34.6 times higher than that of NK (0.18 mg/g). Batch static adsorption test combined with adsorption kinetics, adsorption isothermal, and characteristic data showed that NaCK prepared at different temperatures had different adsorption mechanisms. Batch static adsorption test data of NaCK-600 was in good agreement with the pseudo-second-order model and Langmuir model, and the main mechanism of its adsorption of ammonia nitrogen was the ion exchange of NH4+ and Na+ in NaCK. After the third cycle, the removal rate of NaCK-600 was still up to 76.44%, which indicates that NaCK-600 has considerable potential for removal of ammonia nitrogen in wastewater and provides a new way for the application of kaolin in removal of ammonia nitrogen.

[Preparation of Functional Attapulgite Composite and Its Adsorption Behaviors for Congo Red].

Heavy metal ion wastewater poses a serious threat to human health and the environment. The adsorption method is an important method to remove heavy metal ions from heavy metal wastewater. Magnetic attapulgite (ATP) composite nanomaterials with excellent adsorption properties were prepared by grafting the Fe3O4 nanoparticles and using 3-aminopropyl triethoxy silane (APTES) modification. The prepared ATP-Fe3O4-APTES materials were used as adsorbents and applied to the treatment of heavy metal ion wastewater. The structure and surface properties of the materials were characterized by FT-IR, XRD, SEM, TEM, and BET characterization, Zeta potential, and VSM. The effects of pH, adsorption time, adsorption temperature, and initial concentration of Pb2+ on the adsorption properties of the ATP-Fe3O4-PEI materials were investigated. The results show that the maximum adsorption capacity of the materials for Pb2+ was 129.32 mg·g-1 under optimum conditions. The adsorption process conformed to the pseudo second order kinetic model and Langmuir adsorption isotherm, which indicates that the adsorption of Pb2+ is a monolayer chemical adsorption and a spontaneous endothermic process. The driving force of adsorption mainly comes from the coordination between the amino group (-NH2) on the ATP-Fe3O4-APTES surface and Pb2+. These results indicate that the functionalized magnetic attapulgite adsorbent has good adsorption properties for heavy metal ions and is expected to be used in the treatment of heavy metal ion wastewater.

Volatilization of Zn and Pb and preparation of integrated micro-electrolysis filter from copper slag and its application for removing Cr(VI) from aqueous solution.

In this study, copper slag was treated by carbothermal reduction technology for preparing an integrated micro-electrolysis filter (IMEF) and recovery of Zn and Pb. The influence of roasting conditions on the volatilization of Zn and Pb, and on the performance of IMEF in removing Cr(VI) from water were studied. The results showed that increasing the roasting temperature, time, and dosage of coal facilitated the generation of zero-valent iron (ZVI) and volatilization of Zn and Pb. The IMEF, roasted at 1150 °C for 40 min with 25% anthracite, had the best reduction effect on Cr(VI), and the volatilization efficiencies of Zn and Pb were 97.38% and 96.77%, respectively. The prepared IMEF had a porous structure with a porosity of 75.20%. A great number of nano/micro-sized ZVI particles were generated on the surface of silicate pore, and had super reactivity. The removal of Cr(VI) was promoted by increasing IMEF dosage and solution temperature, and decreasing the pH of the Cr(VI) solution. The IMEF presented good mechanical strength and excellent long-term performance in removing Cr(VI). Cr(VI) was reduced into Cr(III) and then mineralized to FeCr2O4 during reaction.

Density Functional Theory and XPS Studies of the Adsorption of Cyanide on Chalcopyrite Surfaces.

In this work, both the density functional theory (DFT) calculation and X-ray photoelectron spectroscopy (XPS) were conducted to investigate the depression mechanisms of cyanide on the flotation performance of chalcopyrite. The density functional theory calculation results showed that cyanide could be adsorbed on a chalcopyrite (112) surface spontaneously, which preferably occurred on the surface Fe-Fe hollow site. Both C and N atoms of cyanide could bond with Fe atoms of the chalcopyrite (112) surface, while the interaction of Fe-C bond was more intense, where the Fe 3d orbital donated electrons to the hybrid sp orbital of a C atom forming a back-donating bond. XPS analysis indicated that the chemical interaction between cyanide and surface Fe atoms occurred, resulting in the generation of a hydrophilic iron-cyanide complex on the chalcopyrite surface, which deteriorated the flotation performance of chalcopyrite.

Facile preparation of chitosan modified magnetic kaolin by one-pot coprecipitation method for efficient removal of methyl orange.

Chitosan modified magnetic kaolin (CS/kaolin/Fe3O4) composite was prepared by a facile one-pot coprecipitation method and used for the removal of methyl orange (MO) from aqueous medium. Under alkaline condition, Fe3O4 nanoparticles were deposited on the kaolin layer by in-situ growth method and chitosan was deposited on the kaolin layer by pH-precipitation method. With the modification of CS, adsorption sites for anionic species were introduced onto the adsorbent. The prepared CS/kaolin/Fe3O4 could remove more than 94 % of MO and showed a high saturated adsorption capacity of 349.7 mg/g. The adsorption process was controlled by film diffusion and well described by Langmuir model. The thermodynamic studies indicated that the adsorption process was exothermic in nature. Furthermore, the adsorbent exhibited satisfactory recycle ability. The results suggested that the modification with CS broadened the application scope of kaolin in anionic species removal and the CS/kaolin/Fe3O4 composite could be a promising adsorbent for wastewater treatment.

The role of reagent adding sequence in the NH4+-N recovery by MAP method.

Ammonium-nitrogen (NH4+-N) recovery from high concentration of NH4+-N-containing wastewater by struvite (MgNH4PO4·6H2O, MAP) precipitation method has been realized, but whether NH4+-N recovery under different reagent adding sequence of NaOH, solid Mg salt and P salt can generate different effects, remains ambiguous. In view of the problem, four modes to add reagents were investigated in detail on the formation of struvite. The results show that the Mode IV (M-IV, i.e. using 50% NH4+-N wastewater to dissolve completely the Mg salt and the P salt, respectively and then simultaneously poured into a beaker to mix the solution evenly and adjust the pH to 9.5.) has the highest NH4+-N recovery efficiency (90.80%) and the maximum mass of precipitates (896 mg) because of the more amount of alkali and initial seed formation. From the morphology of the obtained precipitates, it can be seen that sample M-IV is more loose and porous than the others. XRD patterns show that the four products under the different modes basically agree with the standard MAP.

Behavior and mechanism of low-concentration rare earth ions precipitated by the microbial humic-like acids.

The disposal of bulky low-concentration rare earth solutions (usually ≤ 200 mg L-1) is difficult and it can easily lead to the waste of rare earth resources. The precipitant separation method is a simple and effective technique that is commonly used for rare earth recovery, but the application of biological component precipitants is rarely reported. In this study, the effects of the precipitation of low concentrations of rare earth ions by excess sludge humic-like acids were evaluated. Scanning electron microscopy with energy-dispersive spectroscopy (SEM/EDS) and infrared (IR) spectroscopy revealed that the addition of humic-like acids to low-concentration rare earth solutions could produce a flocculent precipitate. The precipitation rate was more than 89%. The content of rare earth metals such as Nd, Y, and La in the rare earth precipitate reached 23.72%, and the elution rate of 1.25 mol L-1 hydrochloric acid was 90.50%. It was concluded that the humic-like acids might contain many functional groups capable of adsorbing rare earth ions. It was inferred that the possible mechanism might be that rare earth ions were precipitated by a series of net catch, ion exchange, and adsorption processes. These findings provide a reference for the future recovery of rare earth resources.

Ultrasound-Enhanced Catalytic Ozonation Oxidation of Ammonia in Aqueous Solution.

Excessive ammonia is a common pollutant in the wastewater, which can cause eutrophication, poison aquatic life, reduce water quality and even threaten human health. Ammonia in aqueous solution was converted using various systems, i.e., ozonation (O3), ultrasound (US), catalyst (SrO-Al2O3), ultrasonic ozonation (US/O3), ultrasound-enhanced SrO-Al2O3 (SrO-Al2O3/US), SrO-Al2O3 ozonation (SrO-Al2O3/O3) and ultrasound-enhanced SrO-Al2O3 ozonation (SrO-Al2O3/US/O3) under the same experimental conditions. The results indicated that the combined SrO-Al2O3/US/O3 process achieved the highest NH4+ conversion rate due to the synergistic effect between US, SrO-Al2O3 and O3. Additionally, the effect of different operational parameters on ammonia oxidation in SrO-Al2O3/O3 and SrO-Al2O3/US/O3 systems was evaluated. It was found that the ammonia conversion increased with the increase of pH value in both systems. The NH3(aq) is oxidized by both O3 and ·OH at high pH, whereas the NH4+ oxidation is only carried out through ·OH at low pH. Compared with the SrO-Al2O3/O3 system, the ammonia conversion was significantly increased, the reaction time was shortened, and the consumption of catalyst dosage and ozone were reduced in the SrO-Al2O3/US/O3 system. Moreover, reasonable control of ultrasonic power and duty cycle can further improve the ammonia conversion rate. Under the optimal conditions, the ammonia conversion and gaseous nitrogen yield reached 83.2% and 51.8%, respectively. The presence of tert-butanol, CO32-, HCO3-, and SO42- inhibited the ammonia oxidation in the SrO-Al2O3/US/O3 system. During ammonia conversion, SrO-Al2O3 catalyst not only has a certain adsorption effect on NH4+ but accelerates the O3 decomposition to ·OH.

Preparation of micro-electrolysis material from flotation waste of copper slag and its application for degradation of organic contaminants in water.

Flotation waste of copper slag (FWCS) was used as a raw material for the preparation of a micro-electrolysis material (MEM) through a carbothermal reduction process. The performance of MEM was evaluated for the degradation of organic contaminants in water. The effects of preparation conditions on the performance of MEM were investigated. Results showed that the MEM prepared under the conditions of calcination temperature of 1100 °C, calcination time of 60 min, and coal dosage of 25% presented the best performance for degrading methyl orange (MO). The decolorization process was enhanced by increasing the MEM dosage, decreasing the initial pH of the solution, and raising the solution temperature. Moreover, the MEM presented good capability for the degradation of methylene blue, eosin Y, and acid fuchsin. X-ray diffraction (XRD) analysis showed that increasing the roasting temperature was beneficial to the formation of zero-valent iron (ZVI). Scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) showed that micro-sized ZVI particles were formed in the MEM, and they contained a small amount of copper element. Meanwhile, the mechanism analysis showed that a redox reaction of the MEM and MO occurred, the azo bond of MO was destroyed, and sulfanilic acid was generated.

Low-temperature conversion of ammonia to nitrogen in water with ozone over composite metal oxide catalyst.

As one of the most important water pollutants, ammonia nitrogen emissions have increased year by year, which has attracted people's attention. Catalytic ozonation technology, which involves production of ·OH radical with strong oxidation ability, is widely used in the treatment of organic-containing wastewater. In this work, MgO-Co3O4 composite metal oxide catalysts prepared with different fabrication conditions have been systematically evaluated and compared in the catalytic ozonation of ammonia (50mg/L) in water. In terms of high catalytic activity in ammonia decomposition and high selectivity for gaseous nitrogen, the catalyst with MgO-Co3O4 molar ratio 8:2, calcined at 500°C for 3hr, was the best one among the catalysts we tested, with an ammonia nitrogen removal rate of 85.2% and gaseous nitrogen selectivity of 44.8%. In addition, the reaction mechanism of ozonation oxidative decomposition of ammonia nitrogen in water with the metal oxide catalysts was discussed. Moreover, the effect of coexisting anions on the degradation of ammonia was studied, finding that SO42- and HCO3- could inhibit the catalytic activity while CO32- and Br- could promote it. The presence of coexisting cations had very little effect on the catalytic ozonation of ammonia nitrogen. After five successive reuses, the catalyst remained stable in the catalytic ozonation of ammonia.