Leaching Process Of Rare Earth Research Articles

Extraction of Rare Earth and CaF2 from Rare Earth Calcium Thermal Reduction Slag by Using CaO Roasting–Acid Leaching Method

The rare earth calcium thermal reduction slag (RCS) generated during the production of heavy rare earth metal contains large amounts of rare earth and fluoride compounds. In this study, rare earth elements (REEs) and fluorine in the RCS were recovered by the CaO roasting–hydrochloric acid leaching method. Firstly, the thermodynamic feasibility of converting rare earth fluoride to rare earth oxides through CaO roasting was demonstrated. The influence of roasting conditions and leaching conditions on the leaching rate of the REEs was investigated. Optimal results, a 95.48% leaching rate of the REEs, were obtained under the following conditions: a CaO dosage of 15%, a roasting temperature of 1000 °C, and a roasting duration of 90 min. XRD, SEM, and EDS results revealed that during the calcination process, the REEs present in fluorite (CaF2) in isomorphic form were transformed into acid-soluble rare earth oxides; furthermore, the rare earth metallic in the RCS remained unchanged even after roasting. In the leaching process, rare earth metals and rare earth oxides are efficiently extracted, while CaF2 rarely dissolves. The leaching slag contained 97.31% CaF2 with a F recovery of 96.92%. The kinetics of the rare earth leaching process was analyzed, and the results show that the three-dimensional diffusion control at the phase interface of the kinetic model best fits the process. The calculated apparent activation energy for the leaching rate of REEs is 20.869 kJ/mol. Therefore, efficient comprehensive recovery of rare earth and fluorite from RCS can be achieved by using the CaO roasting–hydrochloric acid leaching method.

Leaching process assisted by cetyltrimethylammonium chloride for weathered crust elution-deposited rare earth ores: Leaching behavior, kinetic analysis and interfacial regulation

Magnesium salts are commonly employed as ammonium-free leaching agents in the extraction of weathered crust elution-deposited rare earth ores (WCE-REO). Nonetheless, these salts frequently face technical challenges, including relatively low leaching rates and inadequate permeability in the in-situ leaching process. In this study, cetyltrimethylammonium chloride (CTAC) was used as a novel leaching aid agent to improve the rare earth leaching process. The effects of CTAC and pH on the rare earth leaching behavior and permeability was investigated. The leaching kinetic model was established and the regulation mechanism by which CTAC interacts with clay mineral surfaces was revealed for rare earth leaching process enhanced by CTAC. The results indicate that the appropriate amount of CTAC can increase the permeation velocity by 1.16×10−4 cm·s−1. Moreover, the rare earth leaching rate increased from 83.75 % to 95.65 %, accompanied by a reduction in leaching equilibrium time under optimal conditions. However, a higher concentration of CTAC results in a lower permeation velocity due to the increasing viscosity and the hydrophilicity. The relatively low pH will affect permeability of composite leaching agent in the ore pillar, diminishing its beneficial impact on rare earth leaching. The kinetic equation, fitted by the shrinking core model, suggests that the leaching adheres to an internal diffusion control mechanism, underscoring mass transfer as the pivotal limiting factor in rare earth leaching. CTAC reduces surface tension and viscosity, facilitating the permeation of the leaching solution into the rare earth ore. Furthermore, CTAC can be adsorbed on the surface of rare earth mineral particles, increasing the contact angle of clay minerals, elevating the Zeta potential, and diminishing the thickness of the diffusion layer, thus promoting mass transfer during leaching. The results of atomic force microscopy (AFM) analysis shows that the appropriate amount of CTAC adsorbed on rare earth ores can decreases the thickness of the hydration film on the particles’ surface, further improving the mass transfer efficiency during the leaching process. The findings of this study offer new insights into the green and efficient extraction of rare earth resources from both theoretical and technical perspectives.

Strengthening rare earth and inhibiting aluminum leaching in magnesium salt-acetic acid compound system from ion-adsorption type rare earth ore

The leaching process of rare earth (RE) from ion-adsorption type rare earth ore (IATREO) using ammonium salt or magnesium salt as leaching agents presents challenges to inefficient leaching of RE elements and simultaneous leaching of ion-exchangeable phase aluminum (Al). This paper introduced acetic acid (HAc) into the leaching process of IATREO, to enhance the leaching of RE elements and inhibit the leaching of ion-exchangeable phase Al. The results show that RE elements and HAc mainly existed in the form of REAc2+, with a relative proportion of approximately 15 %. The presence of the HAc-Ac- conjugate acid-base pair provided a buffer capacity. In the MgSO4-HAc compound system, column leaching was controlled by internal diffusion, and the supplementation of HAc decreased the activation energy of the RE leaching reaction to 7.11 kJ/mol while increasing the leaching rate. Besides, the HAc-Ac- buffer system increased the pH of the leaching process and promoted the hydrolysis of ion-exchangeable phase Al, thereby inhibiting its leaching. Single-factor experiments indicated that under the optimal conditions, the leaching efficiency of RE elements reached 98.40 %, while the leaching efficiency of Al was 66.61 %. Compared with the ammonium and magnesium salts leaching systems, the leaching efficiency of RE elements increased by more than 6 %, while the leaching efficiency of Al was reduced by 23.33 %. This paper plays an important role in promoting the efficient and green extraction of IATREO.

Leaching Behavior of Rare Earth Elements and Aluminum from Weathered Crust Elution-Deposited Rare Earth Ore with Ammonium Formate Inhibitor

In situ leaching of weathered crust elution-deposited rare earth ore usually uses ammonium sulfate as the leaching agent, which poses challenges such as low mass transfer efficiency, high consumption of the leaching agent and long leaching periods. In order to intensify the leaching process of rare earth elements and reduce the impurity of leaching accompanying rare earth, ammonium sulfate and ammonium formate were mixed as a novel compound leaching agent to treat weathered crust elution-deposited rare earth ore. The effects of ammonium formate concentration, liquid/solid ratio, leaching agent pH and leaching temperature on the leaching process of rare earth (RE) and aluminum (Al) were investigated and evaluated using the chromatographic plate theory. Results showed that ammonium formate could effectively enhance the mass transfer efficiency of rare earth and significantly inhibit the mass transfer efficiency of aluminum. Leaching agent pH has a greater impact on the mass transfer efficiency of aluminum. A higher leaching temperature could enhance the mass transfer efficiency of rare earth and aluminum by providing a driving force to overcome the resistance of diffusion. The optimum conditions for leaching rare earth and aluminum are 0.1 mol/L ammonium sulfate compounded with 0.032 mol/L ammonium formate, pH 4–8 of the leaching agent, 0.8:1 liquid:solid (mL/g) ratio and room temperature. Under this condition, the mass transfer efficiency of rare earth was improved, and the mass transfer efficiency of aluminum was significantly inhibited.

Research on the saturated/unsaturated seepage laws of ionic rare earth ore under different leaching conditions

The seepage law of the ionic rare earth leaching process plays an important role in the efficient development and utilization. The saturation permeation test of ionic rare earth under different leaching conditions was carried out using the variable head method, and the influence of type, concentration, and leaching path on the saturation permeability coefficient was revealed. The relationship between the water content and the matric suction of ionic rare earths under different leaching conditions was measured with the Geo-Experts pressure plate apparatus, and the soil-water characteristic curves under different leaching conditions were obtained. Based on the soil-water characteristic curve model, the unsaturated permeability coefficient function of ionic rare earths under different conditions was studied. The results show that the saturated-unsaturated permeability coefficients of ionic rare earths are pure water, 3% (NH4)2SO4, and 3% MgSO4, in descending order, when the type of leaching solution is different. For different concentrations of the leaching solution, when the concentration of (NH4)2SO4 increases from 2% to 5%, the saturated permeability coefficient first increases and then decreases. The matrix suction is an important factor affecting the unsaturated permeability coefficient when the ore body is unsaturated, and the unsaturated permeability coefficient decreases with the increase of the leaching solution concentration under the same matric suction. The seepage law is related to the leaching path, and the permeability coefficient increases when leaching at high concentrations followed by low concentrations, in reverse order, the permeability coefficient decreases. The research results can provide theoretical guidance for the design of injection parameters, and improve the theory of in-situ leaching.

Effects of Ammonium Salts on Rare Earth Leaching Process of Weathered Crust Elution-Deposited Rare Earth Ores

In order to reveal the influence of ammonium salts on the rare earth leaching process of weathered crust elution-deposited rare earth ores, ammonium acetate, ammonium chloride, and ammonium sulfate were used as leaching agents. The effects of the leaching agent on the rare earth leaching efficiency and the expansion, dissolution, and transformation behavior of clay minerals in the rare earth leaching process were studied. The results showed that rare earth leaching efficiency followed the order ammonium acetate > ammonium chloride > ammonium sulfate, with values of 90.60%, 85.96%, and 84.12%, respectively. The swelling ratio of clay mineral followed the order ammonium acetate < ammonium chloride < ammonium sulfate; the clay mineral swelling ratio was 2.09% when ammonium acetate was the leaching agent. Thermogravimetric analysis showed that the interlayer water content was the lowest when ammonium acetate was used as the leaching agent. Under the conditions of different leaching agents, the clay mineral contents changed from illite and halloysite to smectite and kaolinite. When ammonium acetate was used as the leaching agent, the relative conversion of illite was 1.49%, and that of smectite was only 0.17%. SEM analysis showed that the clay minerals expanded and dissolved obviously when ammonium chloride and ammonium sulfate were used as the leaching agents. Meanwhile, the clay mineral layered structure was relatively complete when ammonium acetate was used as the leaching agent. Therefore, when ammonium acetate was used as the leaching agent, it had the least effect on the swelling, dissolution, and transformation of clay minerals. This can provide a theoretical basis for the safe production of weathered crust elution-deposited rare earth ore, and for the screening of green and efficient leaching agents.

Enhancing leaching efficiency of ion adsorption rare earths by ameliorating mass transfer effect of rare earth ions by applying an electric field

Improving the seepage of leaching solution in the ore body and strengthening the mass transfer process of rare earth ions during in-situ leaching are two critical methods to improve the leaching efficiency of rare earth. In this study, 2 wt% MgSO4 solution was used for the indoor simulated column leaching experiment on rare earth samples and an electric field was applied at both ends of the samples. Then the effects of different intensities, initial application time and duration of the electric field on the rare earth leaching system and its mechanism were investigated. The results show that compared with the single MgSO4 solution leaching, applying an electric field with a strength of 6 V/cm can save the leaching time of 30 min and increase the flow velocity of the rare earth leachate by 26.98%. Under the optimal conditions of applying an electric field with a strength of 6 V/cm for 20 min to the leaching system after 10 min of the rare earth leachate flowing out, the leaching efficiency of sample increases from 81.20% to 86.05% with the increase of 4.85%. The mechanism analysis shows that when a direct current electric field is applied to the rare earth leaching system, rare earth ions rapidly change from disorderly movement with the seepage into faster and directional movement. In addition, the seepage of the leaching solution is also improved due to the increase of the cross-sectional area of the seepage channel, the polarized water molecules migrate directionally by force from the negative pole, and the movement of the hydrogen is generated by the electrolytic water. More importantly, based on the principle of in-situ leaching process, the layout of injection holes and deflector holes in this process provides a natural site for the electrode layout of the electric field. With the simple equipment and the operation, the rare earth leaching process with the applied electric field has high feasibility in industrial application.

Effects of Salinity and pH on Clay Colloid Aggregation in Ion-Adsorption-Type Rare Earth Ore Suspensions by Light Scattering Analysis

Ion-adsorption-type rare earth ores (IREOs) are an indispensable strategic resource. Rare earths can be extracted from IREOs by means of in situ leaching, which is strongly influenced by the migration of clay components. In order to clarify the effect of the interaction between mineral particles on the rare earth leaching process, the aggregation of IREO colloids was investigated in suspension after NaCl concentration and pH value were disturbed based on a light scattering method. The results show that IREO colloids are prone to unstable aggregation, which can be affected by salinity and pH in suspension. Combined with the analysis of the surface acid–base properties and the zeta potential of the IREO colloids, the long-range electrostatic attraction between mineral heterogeneous charge surfaces plays a leading role in the interaction between mineral particles. In suspension, electrolyte concentration and pH can adjust the strength of the electrostatic force and the force field overlapping between the surface double electric layers to influence the aggregation of the IREO colloids. The above conclusion can enrich and supplement the rare earth extraction theory, which has a certain guiding significance for green exploitation of IREOs.

Simulation of an Ionic Rare Earth Leaching Process Based on the Darcy Law-Chemical Reaction Engineering-Transfer of Dilute Substance Coupling

The basic principle of in situ leaching is chemical mining. The process of in situ leaching is to inject leaching solution into the ore body, and the leaching solution is spread in the pores of the mountain. The process is completed by the coupling action of the liquid seepage field and ion exchange reactions. In the production process, only one injection of liquid can be carried out in a certain stope, so it is impossible to improve the injection process and leaching effect through field practice. By simulating the in situ leaching process of rare earth ions, this paper builds the test stope true three-dimensional numerical model and simulates the leaching process of rare earth ore under the coupling of seepage control, ion exchange, and dilute material transfer in porous media. The migration rule of RE3+ and Mg2+ in stopes was analyzed to evaluate the leaching effect. It is of great significance to increase the recovery rate of rare earth ore.

Insight into leaching of rare earth and aluminum from ion adsorption type rare earth ore: Adsorption and desorption

Clay minerals are inferred to be the primary host materials for ion-exchangeable rare earth in ion adsorption type rare earth ore (IAREO). During the rare earth leaching process, the adsorption and desorption reactions of the cations controlling the leaching process continue to occur at the clay minerals-leaching agent solution interface. In order to understand the leaching mechanism and behavior of rare earth and co-leached aluminum, adsorption, competitive adsorption, and desorption experiments were carried out using kaolin as a typical clay mineral. The powerful electrostatic attraction and concentration driving forces facilitate the adsorption of cations. The adsorption ability and competitive adsorption ability of cations depend on their charge, hydration radius, and hydrolysis properties, and decrease in the order of La3+, Y3+, Al3+, Mg2+, and NH4+. The desorption of rare earth and aluminum is positively affected by the concentration-driving force exerted by high concentrations of Mg2+ and NH4+, with the order of the desorption ability being opposite to the adsorption ability. However, unspecified interactions between clay mineral particles enhanced by high-concentration desorbents, especially by Mg2+ than NH4+, will adversely affect desorption reactions, which result in lower desorption efficiencies of rare earth and aluminum obtained with magnesium sulfate compared to those obtained with ammonium sulfate at high concentrations. Solid-phase Al(OH)3 generated at a high peak aluminum concentration leads to a considerably delayed aluminum efflux, thereby partially separating the rare earth from aluminum during the actual column leaching process. To advance the mining technology of IAREO by selectively improving the rare earth leaching efficiency with minimal leaching agent consumption, higher charged cations with concentrations limited to suitable levels should be preferred as leaching agents.

Efficient leaching process of rare earth, alkali and alkaline earth metals from phosphogypsum based on methanesulfonic acid (MSA) as green & eco-friendly lixiviant.

The leaching of rare earth elements (REEs) from secondary resources is exponentially increasing to supply the widespread range of high-tech applications of these elements including phosphors lighting materials, catalysis and permanent magnets. Phosphate fertilizer byproducts including phosphogypsum (PG) were identified as a potential alternative resource of REEs, not only to face the expansion of market demand, but also to achieve a sustainable management of REE resources. This study reports the leaching of REEs from PG using methanesulfonic acid (MSA) as a green organo-sulfonic acid in comparison with other acids such as p-toluenesulfonic acid (PTSA) and hydrochloric acid (HCl). MSA achieved the highest leaching efficiency of 78% with low solubility of PG under the operating conditions of 3 M, solid to liquid ratio (S/L) of 1/8, 120 min and 25 °C. The optimized leaching process was also modeled using shrinking core theory to assess the kinetics behavior of the system and to enable the determination of the predominant mechanisms. It was demonstrated that the leaching is governed by a product layer diffusion-controlled model with an activation energy of 2.73 kJ mol-1. The cleaned PG after leaching could greatly meet the quality requirements of the building materials industry.

Inhibition on the swelling of clay minerals in the leaching process of weathered crust elution-deposited rare earth ores

Rare earths are mainly adsorbed on the clay minerals as ion-exchangeable phase which could be extracted by the ion-exchange method in weathered crust elution-deposited rare earth ore. The clay minerals would swell after adsorbing electrolyte solution during the rare earth leaching process, which would easily lead to the occurrence of landslides and other geological disasters. In this study, to alleviate the expansion of the clay minerals, swelling kinetics curves of the ore samples in the three anti-swelling agents: urea, NH4Cl and NH4NO3 were investigated. Synergy effects of these three anti-swelling agents in binary and ternary systems were also studied. Results showed that the lowest swelling ratio was obtained in the urea/ NH4Cl/NH4NO3 system: 3% wt NH4Cl and NH4NO3 with mass ratio: 7:3 and 6% wt urea at the optimum value of pH 5.0. The Swelling ratio of clay minerals increased with the increase of the temperature in the ternary system. Additionally, swelling kinetics equation δ = A•e-B/t of the clay minerals in different anti-swelling agents were also determined by mathematical regression analysis. The SEM, TG, FTIR and XRD analysis of rare earth tailing leached by ternary system verified the anti-swelling function of urea in the leaching process.

Effects of Ion Characteristics on the Leaching of Weathered Crust Elution-Deposited Rare Earth Ore.

To reveal the ion-exchange mechanism in the leaching process of weathered crust elution-deposited rare earth ores with different leaching agents, the effects of a variety of cations and anions at different concentrations on the leaching process were investigated, including Al3+, Fe3+, Ca2+, Mg2+, Na+, K+, and Cl−, , and . Meanwhile, the relationships between different concentrations of cations and anions and leaching efficiency were investigated, as was the relationship between different concentrations of cations and anions and zeta potential. The effect of different ions on the swelling of clay minerals during leaching process was also investigated. The results shown that was the most affected electrolyte cation in terms of rare earth leaching efficiency during the leaching process of weathered crust elution-deposited rare earth ore among three different cationic valence states, and the leaching efficiency was 86.93% at the optimal leaching concentration. The influence of the three anions on the leaching efficiency of rare earth was , and the leaching efficiency of rare earth were 83.21, 81.52, and 80.12% at the optimal leaching concentration, respectively. The had the greatest effect on the zeta potential of weathered crust elution-deposited rare earth ore, and the zeta potential was −18.1 mV at the optimal leaching concentration. Additionally, the order of the effect of three anions on zeta potential was . Combined with the effect on the rare earth leaching process, anions and cations were considered separately, and and Cl− were selected; the relationship between the rare earth leaching efficiency and zeta potential conforms to the follow equations: :Y = −0.48X2 – 13.51X – 1.58, R2 = 0.98133 and Cl−:Y= −1.22X2 – 17.64X + 23.29, R2 = 0.99010. It was also found in the swelling experiment of the weathered crust elution-deposited rare earth ore that the swelling ratio of clay minerals was the lowest when the cation and anion were and Cl− and the swelling ratios were 1.874 and 2.015%, respectively.

Leaching Process of Weathered Crust Elution-Deposited Rare Earth Ore With Formate Salts.

To strengthen the rare earth leaching process and weaken the hydration of clay minerals for preventing landslides, it is of great importance to adopt a green and sustainable leaching agent in the industry. In this work, the leaching process of weathered crust elution-deposited rare earth ores with formate salts (ammonium formate, potassium formate, and sodium formate) was investigated. The effects of formate salts on the linear swelling ratio and zeta potential of the clay minerals were studied. The experimental results showed that ammonium formate could effectively recover the rare earth elements from weathered crust elution-deposited rare earth as well as inhibit the leaching of impurity aluminum. At room temperature, when the ammonium formate concentration was 1% wt, the leaching efficiencies of rare earth and aluminum were 87 and 37%, respectively. Compared with traditional inorganic ammonium salts, the inhibition effect of impurity aluminum was obvious. In addition, the results of the linear swelling ratio in the clay minerals showed that the inhibit ability of formate salts on the hydration of clay minerals enhanced with the increase of the formate concentration, and the order of the inhabitation on the clay minerals followed: 1% ammonium formate > 1.5% potassium formate > 2.5% sodium formate > distilled water. Based on the double layer theory, ammonium formate and potassium formate could effectively compress clay mineral particles to avoid water intake, which could increase the interaction between clay mineral particles and greatly reduce the electronegative property of the clay minerals, so as to effectively reduce the surface hydration of clay minerals to decrease the swelling of rare earth ore. The results of this experiment have important and practical significance in guiding the prevention of landslides, promoting the in-situ leaching technology, and effectively protecting the ecological environment in mining areas.

Leaching Process and Mechanism of Weathered Crust Elution-Deposited Rare Earth Ore

The leaching processes and mechanisms of weathered crust elution-deposited rare earth (RE) ores with ammonium sulfate were investigated for their high efficiency and low consumption exploitation. The leaching process is a typical reversible heterogeneous ion exchange reaction in liquid–solid systems. The raw ore and leached tailings were analyzed by SEM and FTIR. Results indicated that no dissolution or structural changes of the ores occurred during the leaching process. The migrations of RE3+, Al3+, and $$ {\mathrm{NH}}_4^{+} $$ in the leaching process were studied under various liquid–solid ratios. With increasing liquid–solid ratio, the content of $$ {\mathrm{NH}}_4^{+} $$ adsorbed on clay mineral by physical effect decreased, $$ {\mathrm{NH}}_4^{+} $$ adsorbed by ion-exchange increased, and the content of exchanged RE and Al increased until reaching equilibrium. The adsorption capacity of the RE ores for $$ {\mathrm{NH}}_4^{+} $$ remained about 0.61–0.63 mg/g. It was difficult to desorb $$ {\mathrm{NH}}_4^{+} $$ from RE ores with washing water alone. The leaching mechanism of Al was the same as RE, but the leaching of Al slightly lagged behind RE. At the optimal liquid–solid ratio of 0.4:1, the leaching efficiencies of RE and Al were 95.51% and 90.99%, respectively, and 56.65% of $$ {\mathrm{NH}}_4^{+} $$ remained in the leachate. After impurity removal and RE precipitation, the leachate can be reused by replenishing fresh leaching agent. The aim of this study is to enhance the leaching process of RE, restrain the leaching of impurities, and decrease the consumption of leaching agents.

Effect of a novel compound on leaching process of weathered crust elution-deposited rare earth ore

The leaching process of weathered crust elution-deposited rare earth ore is a typical noncatalytic heterogeneous reaction in liquid–solid systems. In order to intensify the leaching process of rare earth and reduce the impurity leaching accompanying with rare earth, ammonium sulfate and ammonium formate were mixed as a novel compound leaching agent, in which ammonium formate was used as an inhibitor for aluminum, as well as an aid agent to speed up rare earth leaching. Effects of ammonium formate concentration, liquid/solid ratio, leaching agent pH and leaching temperature on the leaching process of rare earth and aluminum were investigated, and then were systematically evaluated by the leaching kinetic theory. It is found that ammonium formate could effectively enhance the leaching rate of rare earth and significantly inhibit the leaching efficiency of aluminum. Leaching agent pH has a greater impact on the leaching efficiency of aluminum, and no effects on that of rare earth. A higher leaching temperature in the tested range could enhance the leaching rate of rare earth and aluminum, but it will largely increase the production cost. The optimum conditions of leaching rare earth and aluminum are 0.1 mol/L ammonium sulfate compounded with 0.032 mol/L ammonium formate, 1:1 liquid:solid (mL/g), pH 5.0 ∼ 8.0 and room temperature. At these conditions, the leaching efficiency of rare earth and aluminum are 92.97% and 37.79% respectively. Moreover, the leaching equilibrium time for rare earth was 320 min shorter than the traditional leaching process by the ammonium sulfate, confirming an acceleration from this novel compound on the leaching of rare earth, especially for the difficult-to-infiltrate weathered crust elution-deposited rare earth ore. The leaching results are well fitted with the shrinking core model with apparent activation energy of 15.83 kJ/mol for RE and 9.60 kJ/mol for Al in the temperature range of 283 ∼ 323 K, indicating a diffusion controlled reaction, and the reaction orders are 1.06 for RE and −1.77 for Al.

Lattice Boltzmann model for simulation on leaching process of weathered elution-deposited rare earth ore

The lattice Boltzmann model with coupled chemical reaction was proposed to simulate the ion exchange process of rare earth leaching and verified by comparison with both empirical correlation of mass transfer coefficient and unreacted-core shrinking model. By simulation, the zonation phenomenon of leaching reagent in the leaching column was presented, and the breakthrough curve of leaching reagent was obtained. When t=50 s, there existed the saturated and exchange zones, and the leaching reagent concentration decreased gradually from 20 to 9.3 g/L. In accordance with the breakthrough curve, the breakthrough capacity of ion-type rare earth ore and the adsorbed ion concentration of leaching reagent were derived, the time of t=25 s was the breakthrough point of ammonium ion in leaching reagent and the breakthrough capacity of the rare earth ore was 125 g/L. Besides, the chemical kinetics parameters used for the solute transfer process of rare earth leaching were obtained by the simulation and then were used to determine the rate-limiting steps of rare earth leaching process.

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<NH4Cl<NH4NO3, implying the complexing ability of anion.

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

In order to intensify the leaching process of rare earth (RE) and reduce the impurities in the leachate, ammonium chloride (NH4Cl) and ammonium nitrate (NH4NO3) were mixed as a compound leaching agent to treat the weathered crust elution-deposited RE ore. Effects of molar ratio of NH4Cl and NH4NO3, ammonium (NH4+) 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 NH4Cl and NH4NO3, 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 (NH4Cl/NH4NO3). It was found that the relative concentration of RE in the leachate could be easily obtained by monitoring the pH of leachate.

Leaching characteristics of ion-adsorption type rare earths ore with magnesium sulfate

Magnesium sulfate was proposed to be leaching agent to deal with the ion-adsorption type rare earths ore to reduce or even eliminate ammonia–nitrogen emissions. The effects of temperature, particle size and stirring speed on rare earth leaching process and the leaching behaviors of the single rare earth element were investigated in order to reveal the rare earth leaching characteristics. Besides, the comparison of leaching effects between magnesium sulfate and ammonium sulfate was also studied. The results showed that the rare earth leaching process could be well described with inner diffusion control model and the apparent activation energy was 9.48 kJ/mol. The leaching behaviors of the single rare earth element were brought into correspondence with rare earths. Moreover, when the concentration of leaching agent was 0.20 mol/L, the rare earth leaching efficiency could all reach above 95% and the leaching efficiency of aluminum impurities could be restrained by 10% using magnesium sulfate compared with ammonium sulfate.