Ion-adsorption Rare Earth Ores Research Articles

Extraction mechanism and separation behaviors of low-concentration Nd3+ and Al3+ in P507–H2SO4 system

In order to clarify the solvent extraction and separation behaviors of rare earths and impurity of Al during the extraction and enrichment of low-concentration leach solution of ion-adsorption rare earth ore, the extraction mechanism and separation behaviors of Nd3+ and Al3+ in the Nd2(SO4)3–Al2(SO4)3 mixed solution using P507 were studied in this work. The extraction of Nd3+ and Al3+ follows the cation exchange mechanism. With the increase of the equilibrium pH, βNd/Al in the extraction of the Nd2(SO4)3–Al2(SO4)3 mixed solution using P507 is always higher than that in the extraction of single Nd2(SO4)3 and Al2(SO4)3 solutions. It can be attributed to the fact that the extraction of Nd3+ using P507 is much faster than that of Al3+, and Al3+ is more prone to be hydrolyzed at lower pH. βNd/Al in the extraction of the Nd2(SO4)3–Al2(SO4)3 mixed solution decreases gradually with the increase of mixing time within the equilibrium pH range of 1.5–1.9. The extraction of Nd3+ using P507 is much faster than that of Al3+, but the stability of Al3+-loaded organic phase is better than that of Nd3+-loaded organic phase, thus Nd3+ in the Nd3+-loaded organic phase is gradually replaced by Al3+ in the aqueous phase with the increase of mixing time.

Adsorption of hydrated [Y(OH)2]+ on kaolinite (001) surface: Insight from DFT simulation

Yttrium (Y) is a crucial rare earth element, and it is found in the ion-adsorption rare earth ore of Jiangxi province, China, at a percentage of up to 64.9%. This study used density functional theory calculations to investigate the adsorption behaviour and bonding mechanisms of the Y ion on the surface of kaolinite (001). Understanding these would be beneficial for its mineralisation processing and exploitation. [Y(OH)2(H2O)7]+ was studied as the initial adsorption structure with the lowest binding energy of −1629.19 kJ/mol in an aqueous system. The adsorption models were divided into outer-layer and inner-layer adsorption models based on the adsorption energy and bonding mechanisms. It was found that [Y(OH)2(H2O)7]+ preferred to adsorb on the Al-OH surface with inner-layer adsorption mainly via the coordination bond of Y–Os, and through hydrogen bonds for outer-layer adsorption. In the outer-layer adsorption, the adsorption energy of [Y(OH)2(H2O)7]+ on the Al-OH surface was higher than that on the Si–O surface because of the steric hindrance effect of the H in the hydroxyl of the Al-OH surface. The Mulliken bond populations of Y–Os for inner-layer adsorption showed that it was primarily dominated by the bonding orbital.

Ion-adsorption rare earth ores of China

Geology and geochemistry of China’s ion-adsorption rare earth ores are discussed. The structure and material constitution of Lognan, Huashan, Guposhan and Heling deposits are compared. The weathered layer structure, as well as the distribution, differentiation and occurrence forms of rare earth elements (REE) in the weathered layer are described. The prospecting indicators and criteria of readily dissociated adsorbed REE ore are identified to find this type ores in the territory of Russia. The weathered layer enclosing ion-adsorption rare earth ore features specific differentiation of REE. General composition of such ores is governed by the composition of the primary rare earth mineralization in mother granites. If granites contain much yttrium and heavy lanthanides, then ion-adsorption rare earth ore contain also much yttrium and heavy lanthanides. Regarding differentiation of REE, yttrium and heavy lanthanides mainly concentrate in the middle, most clayey part of the weathered layer, while cerium accumulates in subsurface lateritic soil. The prime feature of ion-adsorption rare earth ore is the prevalence of readily dissociated REE, which can reach a quantity of 80% and more but not less than a half. The rest REE concentrate in relict rock-forming minerals and accessories. The quantitative estimation of adsorption form of REE is necessary for the geological and economic appraisal of a deposit. It is assumed that the quantity of readily soluble REE should be not less than 0.05–50% of the total content. Russia has many regions with such geotectonic environment. It is required to explore ion-adsorption rare earth ore occurrences in these regions.

Leaching behaviors of calcium and magnesium in ion-adsorption rare earth tailings with magnesium sulfate

Abstract The leaching behaviors of calcium and magnesium in the rare earth tailings leached with magnesium sulfate using deionized water, CaCl2 solution and lime water were investigated. Experimental data indicated that magnesium in the tailings was easy to be leached out since most of the magnesium was in the form of water-soluble phase. Most of calcium in the lime water was electrostatically adsorbed on the clay mineral of the tailings, and the water-soluble magnesium was also gradually converted into exchangeable phase because of back-adsorption of Mg2+ on the clay mineral with increasing the pH values. When the liquid-to-solid ratio was 0.80, the contents of readily-available magnesium and calcium were 104.4−207.6 and 201.7−1426.3 mg/kg, respectively, which could meet the requirements for plants. These results suggest a promising route for the environmental remediation of ion-adsorption rare earth ore after in-situ leaching.

Microbial communities in rare earth mining soil after in-situ leaching mining

In-situ leaching technology is now widely used to exploit ion adsorption rare earth ore, which has caused serious environmental problems and deterioration of mining soil ecosystems. However, our knowledge about the influences of mining operation on the microbiota in these ecosystems is currently very limited. In this study, diversity and composition of prokaryote and ammonia-oxidizing microorganisms in rare earth mining soil after in-situ leaching practice were examined using quantitative Polymerase Chain Reaction (qPCR) and Illumina high-throughput sequencing. Results showed that in-situ leaching mining considerably impacted microbial communities of the mining soils. The abundances of bacterial, archaeal, and ammonia-oxidizing archaea (AOA) were significantly and negatively correlated with ionic rare earth elements (REEs), while their diversities were relatively stable. Total rare earth elements (TREEs) and ammonium were the strongest predictors of the bacterial community structure, and organic matter was the key factor predicting the variation in the archaeal community. Chloroflexi, Proteobacteria, Acidobacteria, and Actinobacteria were the most abundant bacterial phyla, and archaeal communities were dominated by Thaumarchaeota. Phylogenetic analysis indicated that unclassified Thaumarchaeota and Crenarchaeota were the predominant AOA groups. The non-detection of ammonia-oxidizing bacteria (AOB) and the abundance of AOA indicated that archaea rather than bacteria were predominantly responsible for ammonia oxidation in the mining soil. Network analysis demonstrated that positive interactions among microorganisms could increase their adaptability or resistance to this harsh environment. This study provides a comprehensive analysis of the prokaryotic communities and functional groups in rare earth mining soil after mining operation, as well as insight into the potential interactive mechanisms among soil microbes.

Removal of thorium and uranium from leach solutions of ion-adsorption rare earth ores by solvent extraction with Cextrant 230

The removal of radioactive elements thorium and uranium from the leach solution of ion-adsorption rare earth ores by aluminum sulfate was studied using di(2-ethylhexyl) [N-(2-ethylhexyl)aminomethyl] phosphonate (Cextrant 230, L).The extraction of thorium, uranium, rare earths, aluminum and other elements was investigated in detail, especially for uranium. The extracted complex was inferred to be UO2SO4·2L, in which phosphoryl oxygen atom of Cextrant 230 was involved in the coordination of UO22+. The thermodynamic parameters, such as ΔH, ΔG, ΔS were calculated. The negative value of ΔH suggests that the extraction of U(VI) by Cextrant 230 is an exothermic process. The extraction capacities of 5% (v/v) Cextrant 230 for Th(IV) and U(VI) were determined to be 4.08 g/L and 6.16 g/L, respectively. The loaded U(VI) and Th(IV) can be stripped using common inorganic acids. By just one stage extraction, the concentrations of thorium and uranium in the simulated leaching solution decreased obviously from 2.73 mg/L and 0.82 mg/L to <0.1 mg/L.

Investigation on the radiation decontamination of lanthanum oxide during its production from ion-adsorption rare earth ores in China

A systematic study on radiation decontamination in lanthanum oxide production from ion-adsorption rare earth ores in China was conducted. The distribution characteristics of radiation levels during the production process was clarified, and effective measures for radiation decontamination were proposed. The results showed that during the lanthanum oxide production process, radiation would be separated from lanthanum and enter the production wastewater along with calcium, which is easily decontaminated through sodium carbonate precipitation. The percentage decontamination of calcium was close to and less than those of total α and total β, and it could be used for evaluating the percentage decontamination of radiation to ensure that the radiation level is controlled at a low level, as required in practice, instead of waiting for 140 days to analyse the values of total α and total β. Under the optimal condition of maintaining the terminal pH at 8.0–10.0, 99.66% of total α and 99.56% of total β in the production wastewater were decontaminated, and the radiation level of total α and total β could be drastically decontaminated to much lower than the national discharge standard of China, GB8978-1996 (total α < 1.0 Bq/L and total β < 10.0 Bq/L).

Ultrasound-assisted leaching of rare earths from the weathered crust elution-deposited ore using magnesium sulfate without ammonia-nitrogen pollution

The in situ leaching process of China's unique ion-adsorption rare earth ores has caused severe environmental damages due to the use of (NH4)2SO4 solution. This study reports that magnesium sulfate (MgSO4) as a leaching agent would replace (NH4)2SO4 by ultrasonically assisted leaching to deal with the ammonia-nitrogen pollution problem and enhance leaching process. At leaching conditions of 3wt% MgSO4 concentration, 3:1L/S ratio and 30min, the total rare earth leaching efficiency reaches 75.5%. Ultrasound-assisted leaching experiments show that the leaching efficiency of rare earths is substantially increased by introducing ultrasound, and nearly completely leached out after two stage leaching process. Thus, ultrasonic-assisted leaching process with MgSO4 is not only effective but also environmentally friendly, and beneficial to leach rare earths at laboratory scale.

Recovery of rare earth from ion-adsorption rare earth ores with a compound lixiviant

The present research investigates the use of ammonium nitrate and ammonium sulfate as a compound lixiviant, and ammonium acetate as an inhibitor for aluminum in the recovery of rare earth elements from ion-adsorption rare earth ores. It is previously shown that rare earth ions, adsorbed physically on ion-adsorption rare earth ores, could be easily recovered via an ion exchange mechanism with inorganic monovalent salt solutions. A standardized desorption procedure was established to systematically investigate the effects of elution conditions such as compound lixiviant concentration, ammonium nitrate/ammonium sulfate molar ratio, particle size, elution flow rate, pH and inhibitor concentration on the leaching of rare earth and aluminum. It was determined that the leaching rate of rare earth exceeded 80% under the optimum elution conditions: particle size <74μm, compound lixiviant concentration 2.0%, ammonium nitrate/ammonium sulfate molar ratio 4:1, pH 5.5, ammonium acetate concentration 0.05%, elution flow-rate 0.5ml/min and room temperature. At these conditions, the inhibition rate of aluminum exceeded 80%.