Yu Junxia

Kinetics of thermal decomposition of lanthanum oxalate hydrate

Abstract Lanthanum oxalate hydrate La 2 (C 2 O 4 ) 3 ·10H 2 O, the precursor of La 2 O 3 ultrafine powders, was prepared by impinging stream reactor method with PEG 20000 as surfactant. Thermal decomposition of La 2 (C 2 O 4 ) 3 ·10H 2 O from room temperature to 900 °C was investigated and intermediates and final solid products were characterized by FTIR and DSC-TG. Results show that the thermal decomposition process consists of five consecutive stage reactions. Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) methods were implemented for the calculation of energy of activation ( E ), and the results show that E depends on α, demonstrating that the decomposition reaction process of the lanthanum oxalate is of a complex kinetic mechanism. The most probable mechanistic function, G (α)=[1−(1+α) 1/3 ] 2 , and the kinetic parameters were obtained by multivariate non-linear regression analysis method. The average E -value that is compatible with the kinetic model is close to value which was obtained by FWO and KAS methods. The fitting curve matches the original TG curve very well.

Process optimization of rare earth and aluminum leaching from weathered crust elution-deposited rare earth ore with compound ammonium salts

Abstract In order to intensify the leaching process of rare earth (RE) and reduce the impurities in the leachate, ammonium chloride (NH 4 Cl) and ammonium nitrate (NH 4 NO 3 ) were mixed as a compound leaching agent to treat the weathered crust elution-deposited RE ore. Effects of molar ratio of NH 4 Cl and NH 4 NO 3 , ammonium (NH 4 + ) concentration, leaching agent pH and flow rate on the leaching process of RE were studied and evaluated by the chromatographic plate theory. Leaching process of the main impurity aluminium (Al) was also discussed in detail. Results showed that a higher initial ammonium concentration in a certain range could enhance the mass transfer process of RE and Al by providing a driving force to overcome the resistance of diffusion. pH almost had no effects on the mass transfer efficiency of RE and Al in the range of 4 to 8. The relationship between the flow rate and height equivalent to a theoretical plate (HETP) could fit well with the Van Deemter equation, and the flow rate at the lowest HETP was determined. The optimum conditions of column leaching for RE and Al were 1:1 (molar ratio) of NH 4 Cl and NH 4 NO 3 , 0.2 mol/L of ammonium concentration, pH 4–8 of leaching agent and 0.5 mL/min of flow rate. Under this condition, the mass transfer efficiency of RE was improved, but no change was observed for Al compared with the most widely used ammonium sulfate. Moreover, the significant difference value (around 20 mL) of retention volume at the peak concentration between RE and Al provided a possibility for their separation. It suggested the potential application of the novel compound leaching agent (NH 4 Cl/NH 4 NO 3 ). It was found that the relative concentration of RE in the leachate could be easily obtained by monitoring the pH of leachate.

Column leaching process of rare earth and aluminum from weathered crust elution-deposited rare earth ore with ammonium salts

In order to better understand the leaching process of rare earth (RE) and aluminum (Al) from the weathered crust elution-deposited RE ore, the mass transfer of RE and Al in column leaching was investigated using the chromatographic plate theory. The results show that a higher initial ammonium concentration in a certain range can enhance the mass transfer process. pH of leaching agent in the range of 2 to 8 almost has no effect on the mass transfer efficiency of RE, but plays a positive role in the mass transfer efficiency of Al under strong acidic condition (pH<4). There is an optimum flow rate that makes the highest mass transfer efficiency. The optimum leaching condition of RE is the leaching agent pH of 4–8, ammonium concentration of 0.4 mol/L and flow rate of 0.5 mL/min. The mass transfer efficiencies of RE and Al both follow the order: (NH4)2SO4

Leaching hydrodynamics of weathered elution-deposited rare earth ore with ammonium salts solution

Abstract In order to reveal the permeability rule of leaching agent solution and the effects of anions in the leaching process of weathered crust elution-deposited rare earth (RE) ores, the effects of ammonium concentration, temperature, particle size and porosity on the permeability were discussed in detail with (NH 4 ) 2 SO 4 , NH 4 Cl and NH 4 NO 3 as the leaching agent. It was found that the permeation velocity of ammonium salts increased linearly with the increase of hydraulic gradient. The seepage of ammonium salts solution in the RE ores followed Darcys law and displayed a laminar flow. The properties of the leaching agent solution and RE ores were the main factors that affect the permeability of RE ores. With the decrease of ammonium concentration and increase of temperature, the viscosity of solution decreased and the permeability coefficients of RE ores increased. And the effects of temperature on the viscosity and permeability were larger than ammonium concentration. The permeability of RE ores became worse with the decrease of particle size and porosity, and the particle size played a more important role compared with porosity. The permeability coefficient of RE ores increased and the viscosity of ammonium salts solution decreased in the order of (NH 4 ) 2 SO 4 , NH 4 Cl and NH 4 NO 3 , implying that the penetrating power of anions increased in the order of SO 4 2– , Cl − and NO 3 − . The results may play a vital role in improving the permeability of weathered crust elution-deposited RE ores.

Removal of copper(II) from aqueous solution with rape stalk modified by citric acid

ABSTRACT In this paper, rape stalk was modified with citric acid (CA) to prepare copper ion biosorbent. The modified rape stalk (MRS) was characterized by Fourier transforms infrared (FTIR), zeta potential, and thermogravimetric analysis (TGA). The effects of various parameters like initial Cu2+ concentration, contact time, initial pH, and temperature on adsorption capacity were studied. The adsorption capacity of MRS at 298 K was 69.84 mg/g, far higher than 18.24 mg/g for native rape stalk (NRS). The adsorption mechanism was also evaluated in terms of kinetics and thermodynamics. The adsorption equilibrium data was well described by the Langmuir isotherm model. The adsorption process followed the pseudo-second-order rate kinetics. Thermodynamic study showed spontaneous and endothermic nature of the adsorption process. The ion exchange of the adsorption mechanism was affirmed. MRS could be a potentially low-cost and green adsorbent for removal of Cu2+ from aqueous solution. GRAPHICAL ABSTRACT

Effect of HNO 3 concentration on a novel silica-based adsorbent for separating Pd(II) from simulated high level liquid waste

A new kind of silica-based (Crea + TODGA)/SiO2-P adsorbent with high selectivity adsorption for palladium (Pd) was synthesized to examined the applicability for partitioning process of high level liquid waste (HLLW). Adsorption behavior of Pd(II) towards (Crea + TODGA)/SiO2-P adsorbent and stability of adsorbent against HNO3 solution were investigated by batch method. The degradation parts of (Crea + TODGA)/SiO2-P dissolved in liquid phase were estimated by total organic carbon (TOC) analyzer. (Crea + TODGA)/SiO2-P adsorbent showed good selectivity adsorption for Pd(II) and reached equilibrium within 24 hr. The adsorption ability of (Crea + TODGA)/SiO2-P for Pd(II) and the content of TOC leaked decreased with the increasing of HNO3 concentration. In 3 M HNO3, the average of Kd values were 85.03 cm3/g and 26.10 cm3/g after contact time one to 28 days at 298 K and 323 K, respectively. While the content of TOC leaked from the adsorbent after 28 days were 1095 ppm (298 K) and 2989 ppm (323 K), respectively. Therefore, the adsorbent showed good stability at 298 K after contact with nitric acid for a long time. All results indicated (Crea + TODGA)/SiO2-P can be proposed as an applicable and efficient absorbent for separation of Pd(II) in 3 M HNO3 at 298 K.

Synthesis of carboxyl-introduced chitosan with C2 amine groups protected and its use in copper (II) removal

A route for the formation of carboxyl-introduced chitosan (CI-CS) with C2 amine groups protected (CIAP-CS) was investigated to improve copper (II) adsorption. First, the C2 amine groups of the chitosan (CS) were protected via a Schiff-base reaction by benzaldehyde. Then the product was obtained by the introduction of pyromellitic dianhydride to the C6 hydroxyl groups on CS via epichlorohydrin. The last product was obtained by removing the Schiff base with dilute hydrochloride solution. CI-CS without C2 amine groups protected was directly synthesized as well. The adsorbents were characterized by Fourier transform infrared (FTIR), X-ray diffraction (XRD) and X-ray photoelectron spectrometer (XPS). The adsorption properties for copper (II) were investigated. FTIR spectroscopy and XPS clearly showed that most of the amine groups in CS were converted to -N = CH2 groups after the benzaldehyde treatment and that no cross-linking reactions with CS were involved; the HCl treatment after the cross-linking reaction effectively released nitrogen atoms protected into the form of the primary amine again. The results confirm that the CIAP-CS cross-linked with the new method had significantly greater adsorption capacities than the CI-CS cross-linked directly with CS. Mechanism study revealed that the increased adsorption performance is attributed to the large number of primary carboxyl and amine groups available on the surfaces of the CIAP-CS. The adsorption mechanism is based on ion exchange and chelating action, and the adsorption process is mainly chemisorption.

Polyamine chitosan adsorbent for the enhanced adsorption of anionic dyes from water

ABSTRACT A simple synthesis route for amine protected-introduced-released chitosan (APIR-CS) was investigated to improve the adsorption of anionic dyes. The C2 amine groups of the chitosan (CS) were initially protected via a Schiff-base reaction by benzaldehyde. They were then synthesized by the introduction of ethylenediamine into C6 hydroxyl groups on CS via epichlorohydrin. The final product was obtained after removal of the Schiff base with dilute hydrochloride solution. Amine-introduced chitosan (AI-CS) was directly synthesized at the C2 amine groups. The adsorbents were characterized by FTIR, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). For Congo red (CR) and methyl orange (MO), most of the amine groups in CS were converted to–N˭CH2 groups after the benzaldehyde treatment. Hydrochloric acid treatment after the cross-linking reaction released protected nitrogen atoms into the form of the primary amine again. APIR-CS had significantly greater adsorption capacities than AI-CS. The increased adsorption performance was attributed to the large number of primary amine groups on the surfaces. The adsorption mechanism was based on electrostatic interaction, while the adsorption process was mainly physisorption. GRAPHICAL ABSTRACT