Removal Of Rare Earth Elements Research Articles

ГЕОХИМИЧЕСКИЕ ОСОБЕННОСТИ РУД И ВМЕЩАЮЩИХ ПОРОД ОРОГЕННОГО МАЛО-ТАРЫНСКОГО ЗОЛОТОРУДНОГО МЕСТОРОЖДЕНИЯ (ВЕРХОЯНО-КОЛЫМСКАЯ СКЛАДЧАТАЯ ОБЛАСТЬ, СЕВЕРО-ВОСТОК РОССИИ)

The paper presents the results of studying the distribution of major, rare, and rare earth elements in the terrigenous rocks, wall-rock metasomatites, and ore zones of the orogenic Malo-Tarynsky gold deposit (Upper Kolyma folded area, Northeast Russia). Hydromicatization, carbonatization, sulfidization, and silicification played an important role in the formation of metasomatites and ore zones leding to different mobility of macroelements with a predominance of acidic low-temperature carbonic-calcium metasomatism. Increase in the proportion of quartz in wall-rock metasomatites and ore zones involved the loss of the most of the rock-forming elements: К, Na, Al, Fe, Mg, and Тi, and Ca and CO2 were supplied. The ores and metasomatites of the deposit are characterized by As-Au-Sb-W geochemical specialization with low Bi, Co, Ni, Cr, Cu, and Zn and high Li, Ag, Cd, and Sc concentrations. The distribution spectra of REE contents in modified rocks are similar to that of REE in Upper Triassic host rocks showing some tendency to decreasing their amount. The removal of rare earth elements during the formation of metasomatites and ores was established. The values of the Eu/Eu* (0.61–0.88) and Ce/Ce* (0.6–1.3) anomalies indicate slightly reducing conditions of the ore formation with a limited involvement of oxidized meteoric water.

Evaluation of strong anion exchange hyper-crosslinked resin for lanthanum removal

In this study, strong anion exchange hyper-crosslinked resin was used for the removal of rare earth element, lanthanum. Poly (styrene-co-EDGMA-co-VBC) is a resin that was synthesized and used in this research. The objective of this research is to study the pH stability and to evaluate the resin for lanthanum removal by using the Solid Phase Extraction (SPE) batch method where the influent of lanthanum solution will be loaded to the designed column containing resin. The pH stability test of resin was studied at different pH (pH 2-5). The evaluation of resin for resin loading (0.5, 1.0, and 1.5 g) and concentration of lanthanum (10, 30, and 50 ppm) were investigated. From the experiment, the resin is stable in acid solution since there is no change in the functional group. The morphology surface using Scanning Electron Microscope (SEM) shows a rough surface and beads attach on the resin without porous on the surface of resin except the resin at the condition of 50 ppm of with 1.0g resin. The resin that performed at 50 ppm with 1.0 g was successful remove lanthanum for 26.7 ppm based on ICP-MS analysis. As a conclusion, this resin can be used for removal of lanthanum.

The role of Al13-polymers in the recovery of rare earth elements from acid mine drainage through pH neutralization

Rare Earth Elements (REE) are crucial to the development of new technologies, given their strategic importance, a wide range of actions has been implemented to ensure sustainable and affordable supplies. Acid Mine Drainage (AMD) besides being one of the major environmental issues faced by the mining industry is a naturally occurring process involving a considerable amount of REE. The recovery of REE from AMD, which is considered a secondary source, has been investigated worldwide over the past few years aiming at sustainability. The current work seeks to provide an understanding of the geochemistry of the REE in an AMD system and also of its respective treatment through pH neutralization, as a contribution to the development of novel REE recovery technologies. The approach proposed herein employed acid mine water and sediment sampling, ICP-OES, XRD, SEM-EDS, TEM, 27Al MAS-NMR and XPS analysis, BCR sequential extraction and geochemical modelling by PHREEQC. The results showed that the REE content in the AMD investigated is very high being Ln3+, LnSO4+ and LnF2+ the dominant species in the impoundments at pH ± 3.5. The neutralization of the AMD with an alkali agent promoted a high REE recovery and produced an amorphous precipitate containing 14% of REE oxides. This precipitate contains Al13-polymers and accounts for the REE removal when the pH is raised to 8, thus promoting adsorption and entrapment simultaneously. Sequential extraction revealed that the REE could be efficiently leached with the use of acetic acid, thus supporting novel and promising recovery technologies through co-precipitation processes.

Novel Functionality of Lithium-Impregnated Titania as Nanocatalyst

The present work incorporates the synthesis of a multifunctional catalyst for the transesterification of waste cooking oil (WCO) to biodiesel and recovery of rare earth elements (REEs). For this purpose, TiO2 nanoparticles and TiO2 doped with lithium ions were prepared. The influence of lithium ions on the catalytic performance of TiO2 was attained by impregnation of the different molar ratios of lithium hydroxide to bare TiO2. Then each catalyst was screened for catalytic conversion of WCO to fatty acid methyl ester (FAME) and also for REEs recovery. All synthesized materials were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), Transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) analysis, and Hammett indicator for the basicity test. The obtained biodiesel was characterized by gas chromatography with mass spectrometry (GC-MS), 1H, and 13C nuclear magnetic resonance (NMR). Moreover, the physical parameters of the synthesized biodiesel were also determined. The REEs recovery efficiency of synthesized nanomaterials was investigated, and the percentage of REEs removal was determined by inductively-coupled plasma optical emission spectroscopy (ICP-OES).

Biological treatment removal of rare earth elements and yttrium (REY) and metals from actual acid mine drainage.

Actual acid mine drainage (AMD) containing a high concentration of sulfate (∼1,000 mg·L-1), dissolved metals, uranium, rare earth elements and yttrium (REY) was treated using a down-flow fixed-structured bed biological reactor (DFSBR). The reactor was operated in a continuous flow mode for 175 days and the temperature was maintained at 30 °C. The synthetic AMD was gradually replaced by the actual AMD in 20, 50 and 75% of the total medium volume. Sugarcane vinasse was used as the electron donor and the influent pH of the reactor was decreased from 6.9 to 4.6 until the system collapsed. REY elements and transition metals were removed from the actual AMD and precipitated in the down-flow fixed-structured bed reactor. Sulfate reduction achieved 67 ± 22% in Phase II and chemical oxygen demand (COD) removal was above 56% in Phases I and II. Removal of La, Ce, Pr, Nd, Sm and Y was higher than 70% in both Phases II and III while Fe, Al, Si and Mn were removed with efficiencies of 79, 67, 48 and 25%, respectively. The results highlighted the potential use of DFSBR in the treatment of AMD, providing possibilities for simultaneous sulfate reduction and metal and REY recovery in a single unit.

Ultra-High Performance of Hyper-Crosslinked Phosphate-Based Polymer for Uranium and Rare Earth Element Adsorption in Aqueous Solution.

In this work, a new type of hyper-crosslinked phosphate-based polymer (HCPP) polymerized by bis(2-methacryloxyethyl)phosphate has been developed for uranium and rare earth element (REE) extraction in an aqueous solution. The influence of the pH value, contact time, initial concentration, temperature, and competing ions on uranium adsorption of HCPP is investigated in detail. HCPP exhibits a maximum uranium adsorption capacity of up to 800 mg g-1 at pH = 6.0 and excellent selectivity toward uranium adsorption over coexisting ions, because of the high affinity between HCPP and uranium ions and dense phosphate groups on the backbone. It also demonstrates high adsorption performance in both simulated seawater with a high salt concentration and a real nuclear industrial effluent. Besides, the crosslinked network structure of HCPP endows this polymer with high chemical stability and reusability. Furthermore, the adsorption mechanism is probed by energy-dispersive spectroscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared measurements. It is confirmed that the adsorption of uranium on the adsorbent originates from the interaction between phosphate groups and uranium ions. Meanwhile, HCPP also displays high REE adsorption capacities. This work indicates that the phosphate-based HCPP could be utilized as a promising adsorbent for the effective removal of uranium and REEs from aqueous solution.

Removal of rare earth elements from a U/RE ingot via a reaction with UCl3

A chemical equilibrium experiment was conducted to remove rare earth (RE) elements from a U/RE ingot using UCl3 as an oxidant. Upon analysis, the RE and uranium in the prepared U/RE ingot formed discrete matrixes and were not well mixed. The reaction with UCl3 resulted in the complete removal of the RE matrix from the U/RE specimen, and an increased concentration of RE chloride and a drastically reduced concentration of UCl3 in the LiCl–KCl molten salt. The results of this study will be used to improve the process for transuranic waste treatment in pyroprocessing.

Fractionation of rare earth elements (REEs) and actinides (U and Th) originating from acid thermal water during artificial and natural neutralization processes of surface waters

Abstract In the Tamagawa geothermal area of Akita Prefecture, northern Japan, Obuki spring discharges a large amount of thermal water (∼9000 L/min), which is chloride-rich and acidic (pH 1.2). We have investigated changes in the physico-chemical nature and fractionation mechanisms of rare earth elements (REEs) including Y and actinides (Th and U) in the Shibukuro and Tama rivers into which acid thermal water from the Obuki spring discharges. The geochemical behavior of these elements is shown to be mainly controlled by pH-dependent sorption onto ferric and/or aluminum oxy-hydroxides (HFO and HAO). HFO is formed around pH > 3. In the upstream region, where pH is less than 4, dissolved Th is removed due to precipitation of Th(SO4)2(s). Whereas, under pH condition greater than 4, remaining dissolved Th is nearly completely sorbed onto suspended HFO, where hydroxyl species of Th are thermodynamically significant. Then, the Th(SO4)2(s) and HFO-sorbed Th are nearly completely removed in an upstream man-made lake. Dissolved U is also removed mainly by sorption onto HFO, where hydroxyl species of UO2 are predominant. A considerable portion of U is also trapped in the sediments of this lake. On the other hand, removal of REEs is nearly negligible until the lake. This is the first fractionation among REEs and actinides caused by pH-dependent sorption, and the order of removal from river water is Th > U ≫ REEs. The remaining dissolved U and REEs in the river waters are transported farther downstream. At pH values of >6, suspended HAO is effectively formed, and the second fractionation among REEs and U occurs. During the second fractionation, REEs are removed by HAO, whereas U largely remains as a dissolved species in river water under higher pH conditions. Lighter REEs, such as La and Ce, tend to remain in the river waters compared to the other REEs including Y. The predominant chemical species for UO2 during the second fractionation are carbonate complex species, and relative proportions of hydroxyl species drastically decreases, resulting in prevention of U sorption onto HAO.

Study on the carbamoyl phosphine oxide moiety functionalized mesoporous graphene for the removal of rare earth elements

We successfully synthesized the carbamoyl phosphine oxide moiety functionalized mesoporous graphene (CMPO–AMG) for the removal of rare earth elements (REE). For this purpose, amine-functionalized mesoporous graphene (AMG) was fabricated by hydrothermal treatment of graphene oxide, ammonium hydroxide and triblock copolymer (pluronic P123). Followed by, AMG was modified using carbamoyl phosphine oxide moiety (CMPO, triethylphosphonoacetate), known as forming strong chelate with REE, through amide bonding between amine in prepared AMG and ester of triethylphosphonoacetate. The physicochemical characterizations of the obtained CMPO–AMG have been carried out systematically by powder X-ray diffraction, field emission scanning electron microscopy, fourier transform-infrared spectroscopy, X-ray photoelectron spectroscopy and N2 adsorption–desorption isotherms. To evaluate the adsorption performance of the CMPO–AMG for REE, we performed preliminary adsorption test, using lanthanum(III) ion as a model ion for REE and the time-dependent adsorption capacity was studied by using inductively coupled plasma-mass spectroscopy.

Water mass transformation in the Barents Sea inferred from radiogenic neodymium isotopes, rare earth elements and stable oxygen isotopes

Nearly half the inflow of warm and saline Atlantic Water (AW) to the Arctic Ocean is substantially cooled and freshened in the Barents Sea, which is therefore considered a key region for water mass transformation in the Arctic Mediterranean (AM). Numerous studies have focused on this transformation and the increasing influence of AW on Arctic climate and biodiversity, yet geochemical investigations of these processes have been scarce. Using the first comprehensive data set of the distributions of dissolved radiogenic neodymium (Nd) isotopes (expressed as ɛNd), rare earth elements (REE) and stable oxygen isotope (δ18O) compositions from this region we are able to constrain the transport and transformation of AW in the Barents Sea and to investigate which processes change the chemical composition of the water masses beyond what is expected from circulation and mixing.Inflowing AW and Norwegian Coastal Water (NCW) both exhibit distinctly unradiogenic ɛNd signatures of −12.4 and −14.5, respectively, whereas cold and dense Polar Water (PW) has considerably more radiogenic ɛNd signatures reaching up to −8.1. Locally formed Barents Sea Atlantic Water (BSAW) and Barents Sea Arctic Atlantic Water (BSAAW) are encountered in the northeastern Barents Sea and have intermediate ɛNd values resulting from admixture of PW containing small amounts of riverine freshwater from the Ob (<~1.1%) to AW and NCW. Similar to the Laptev Sea, the dissolved Nd isotope composition in the Barents Sea seems to be mainly controlled by water mass advection and mixing despite its shallow water depth. Strikingly, the BSAW and BSAAW are marked by the lowest dissolved REE concentrations reported to date for the AM reaching 11 pmol/kg for Nd ([Nd]), which in contrast to the Nd isotopes, cannot be attributed to the admixture of REE-rich Ob freshwater to AW or NCW ([Nd] = 16.7, and 22 pmol/kg, respectively) and instead reflects REE removal from the dissolved phase with preferential removal of the light over the heavy REEs. The REE removal is, however, not explainable by estuarine REE behavior alone, suggesting that scavenging by (re)suspended (biogenic) particles occurs locally in the Barents Sea. Regardless of the exact cause of REE depletion, we show that AW transformation is accompanied by geochemical changes beyond those expected from water mass mixing.This article is part of a special issue entitled: “Cycles of trace elements and isotopes in the ocean – GEOTRACES and beyond” - edited by Tim M. Conway, Tristan Horner, Yves Plancherel, and Aridane G. González.

ГЕОХИМИЯ РЕДКОЗЕМЕЛЬНЫХ ЭЛЕМЕНТОВ В ИЗВЕСТНЯКАХ ТОРГАШИНСКОЙ СВИТЫ И СОДЕРЖАЩИХСЯ В НИХ ФЛЮИДОЛИТАХ, АРГИЛЛИЗИТАХ И КАЛЬЦИТОВЫХ ОНИКСАХ (ВОСТОЧНЫЙ САЯН)

The Purpose of the paper is to study the features of rare-earth element (REE) geochemistry in limestones and post-sedimentation products including fluidolites, argillisites and calcite onyxes of the carbonate stratum of the Torgashino limestone deposit. Methods. The mass-spectrometry method with inductively coupled plasma is used for studying the REE behavior. The tests have been carried out in the multiple-access center “Analytical Center for Natural Systems Geochemistry” of the Tomsk State University. Results. The features of REE geochemistry are considered in the Torgashino suite limestones and fluidolites, argillisites and calcite onyxes contained in them. The distribution spectra of REE, Eu (Eu/Eu*), Ce (Ce/Ce*), light REE / heavy REE and other have been studied. Conclusions. Argillisites penetrating carbonate strata are characterized by the input of all REE while limestones and low-temperature hydrothermal formations in the form of calcite onyx have been formed in the presence of removal of both lanthanides and heavy REE. The analysis of REE distribution allows to make a conclusion on the different nature of argillisites which are the product of the fluidization explosive process and Torgashino suite limestones, which these processes were imposed on.

Rare Earth Elements Geochemistry and Nd Isotopes in the Mississippi River and Gulf of Mexico Mixing Zone

Rare earth elements (REE) concentrations were measured in surface waters collected across the salinity gradient in the Mississippi River estuary (i.e., Mississippi River plume, MRP), which includes the near-shore portion of the Louisiana Shelf. In addition, the neodymium (Nd) isotope compositions of two river water samples, and the acid leachable fractions of the associated suspended particulate matter (SPM), were quantified to compare Mississippi River water, and SPM with Gulf of Mexico waters. Despite the spatial limitations associated with sampling due to the size of the Mississippi River system, this study provides some important insights into the REE geochemistry of the MRP. The Mississippi River and its estuarine waters are enriched in the heavy REE (HREE) compared to the light REE (LREE) when normalized to shale composites. All water samples from the estuary also exhibit substantial negative Ce anomalies. In contrast to the majority of other estuaries investigated, removal of REE in the low salinity reaches of the Mississippi River estuary is less substantial. For example, approximately 50% of the river borne Nd is removed in the low salinity region (S < 10) of the Mississippi River estuary compared to the estimated global average of ca. 70% removal of Nd for estuaries worldwide. We propose that the relatively low REE removal in the Mississippi estuary reflects the high pH (~8) of the Mississippi River, where REE complexation with carbonate ions and natural organic ligands act to stabilize REE in solution. The Nd isotope composition of Mississippi River water near its outflow to the Gulf of Mexico is eNd(0)= -10.5. The acid leachable fraction of the associated SPM is more radiogenic (-9.95 ≤ eNd(0) ≤ -9.77), and closer to the generally more radiogenic Gulf of Mexico (eNd(0) = -9.0). Sequential extraction of the Mississippi River bank sediment reveals substantially different Sm/Nd ratios for the operationally defined fractions of the sediment, which suggests variations in Nd isotope compositions between the labile fractions and the bulk sediment.

N- and O- ligand doped mesoporous silica-chitosan hybrid beads for the efficient, sustainable and selective recovery of rare earth elements (REE) from acid mine drainage (AMD): Understanding the significance of physical modification and conditioning of the polymer

Silica-chitosan hybrid beads were synthesized via three different methods to investigate the selective recovery of REE from AMD. The influence of amino/non-amino silanes, high molecular weight/high viscous chitosan and N-/O- based ligands were studied and their effects on REE removal efficiencies were analyzed. The adsorption efficiencies of three various groups of modified beads were inspected with respect to feed pH, in a single and a multi-component system, and their affinities towards the light and heavy rare earth elements (LREE/ HREEs) were interpreted to understand the intra-series REE separation behavior. The focus of the study was mainly directed towards utilizing these fabricated beads for the recovery of valuable REEs from the real AMD obtained at three different sampling depths which was found rich in iron, sulfur and aluminum. Moreover, the selectivity of the beads towards REEs improved with silanized and ligand immobilized gels and their impacts on REE recovery in the presence of competing ions were successfully presented in this paper. Also, the synthesized beads showed rapid REE adsorption and recovery within a process time of 5 min. Group II adsorbents, synthesized by forming silica-chitosan hybrid beads followed by PAN/acac modifications, showed superiority over the other groups of adsorbents.

Rare earth element geochemistry characteristics of seawater and porewater from deep sea in western Pacific

Deep-sea sediments contain high concentrations of rare earth element (REE) which have been regarded as a huge potential resource. Understanding the marine REE cycle is important to reveal the mechanism of REE enrichment. In order to determine the geochemistry characteristics and migration processes of REE, seawater, porewater and sediment samples were systematically collected from the western Pacific for REE analysis. The results show a relatively flat REE pattern and the HREE (Heavy REE) enrichment in surface and deep seawater respectively. The HREE enrichment distribution patterns, low concentrations of Mn and Fe and negative Ce anomaly occur in the porewater, and high Mn/Al ratios and low U concentrations were observed in sediment, indicating oxic condition. LREE (Light REE) and MREE (Middle REE) enrichment in upper layer and depletion of MREE in deeper layer were shown in porewater profile. This study suggests that porewater flux in the western Pacific basin is a minor source of REEs to seawater, and abundant REEs are enriched in sediments, which is mainly caused by the extensive oxic condition, low sedimentation rate and strong adsorption capacity of sediments. Hence, the removal of REEs of porewater may result in widespread REE-rich sediments in the western Pacific basin.

Adsorption of Scandium and Neodymium on Biochar Derived after Low-Temperature Pyrolysis of Sawdust

The objective of this study was to investigate the adsorption of two rare earth elements (REEs), namely scandium (Sc) and neodymium (Nd), on biochar produced after low temperature pyrolysis (350 °C) of wood sawdust. The biochar was characterized with the use of several analytical techniques, namely X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric (TG) analysis, while the pH at point of zero charge (pHPZC) was also determined. The experimental conditions were: absorbent concentration 1–10 g·L−1, REE concentration in solution 20 mg·L−1, contact time for equilibrium 24 h, temperature 25 °C and stirring speed 350 rpm. The efficiency of biochar was compared to that of a commercial activated carbon. Geochemical modelling was carried out to determine speciation of Nd and Sc species in aqueous solutions using PHREEQC-3 equipped with the llnl database. The experimental results indicated the potential of low temperature produced biochar, even though inferior to that of activated carbon, to adsorb efficiently both REEs. The equilibrium adsorption data were very well fitted into the Freundlich isotherm model, while kinetic data suggested that the removal of both REEs follows the pseudo-second order kinetic reaction. Finally, the most probable adsorption mechanisms are discussed.

Ligand immobilized novel hybrid adsorbents for rare earth elements (REE) removal from waste water: Assessing the feasibility of using APTES functionalized silica in the hybridization process with chitosan

This experimental study was aimed at checking the potential of employing commercially available amino functionalized silica gels in synthesizing the ligand immobilized hybrid materials rather than the conventional method of utilizing Tetraethyl orthosilicate (TEOS) precursors for the removal of REE from the waste water. The parameters used for the optimization of the synthesis process included the influence of silanes (3-Aminopropyl triethoxysilane APTES/methyltrimethoxy silane MTM), types of ligands (1 – (2-Pyridylazo) 2-naphthol (PAN) and acetylacetone (Acac)), molecular weight and degree of deacetylation of chitosan. Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), Brunauer Emmett and Teller (BET) and Zeta potential (ZP) analysis were employed to understand the surface characterization of the hybridized adsorbents. The adsorption of La3+, Sc3+ and Y3+ was investigated further in detail using the hybridized PAN adsorbent to understand the effect of initial solution pH, contact time, temperature and initial adsorbate concentration. Single/multi-component system was studied through batch adsorption tests to assess the affinity towards target REEs and the intra series adsorption behavior of light/heavy REEs was also inspected.

Short-term variability of dissolved rare earth elements and neodymium isotopes in the entire water column of the Panama Basin

The distribution of dissolved rare earth elements (REEs) and neodymium isotopes (εNd) in the open ocean traces water mass mixing and provides information on lithogenic inputs to the source regions of the water masses. However, the processes influencing the REE budget at the ocean margins, in particular source and sink mechanisms, are not yet well quantified. In this study the first dissolved REE concentrations and Nd isotope compositions of seawater from the Panama Basin (RV Meteor cruise M90) in the Eastern Equatorial Pacific (EEP) are presented. The EEP is characterized by one of the world's largest oxygen minimum zones (OMZs). It is dominated by high particle fluxes that are expected to enhance the removal of REEs from the water column by scavenging.The measured REE concentrations peak at the surface indicating high lithogenic input, which is supported by shale-normalized REE patterns in surface waters and highly radiogenic εNd signatures ranging between +1.4 and +4.3, the latter value constituting the most radiogenic value measured for seawater to date. In contrast, intermediate and deep water REE concentrations are low compared to other Pacific Basins and suggest enhanced removal via scavenging associated with high particle fluxes. The εNd signatures of intermediate and deep waters are less radiogenic than surface waters ranging between −1.4 and +1.3 but significantly more radiogenic than source water masses in the EEP. The εNd signatures consequently do not reflect mixing of intermediate and deep water masses entering the Panama Basin but can only be explained by lithogenic inputs originating from source rocks with highly radiogenic Nd isotope signatures such as the Central American Volcanic Arc (εNd=+3 to +10). Our data demonstrate significant surface input via continental particles, which are partially dissolved in the water column and thereby release REEs and particularly radiogenic Nd isotope signatures to the subsurface ocean. Data obtained from a re-occupied station in the southern Panama Basin for the first time shows that these processes can partially reset water mass Nd isotope and REE signatures of the entire water column proximal to continental sources on time scales of a few years.

Lanthanides removal from mine water using banana peels nanosorbent

This study focuses on the performance of nanostructured banana peels in lanthanide-laden mine water treatment. Specifically, nanostructure formation via mechanical milling, characterization in detail and application of this sorbent media in rare earth elements (REEs) removal from synthetic and real mine water are thoroughly investigated. The sorbent samples were characterized by transmission electron microscopy, Brunauer–Emmett–Teller, X-ray diffraction and Fourier transform infrared analyses, while the amount of REEs adsorbed was analysed using inductively coupled plasma optical emission spectroscopy. Results revealed that the particle and crystallite sizes were reduced from <65,000 to <25 nm and 108 to 12 nm, respectively, as the milling progressed. Furthermore, the fracture of particles resulted in a surface area increment from 1.07 to 4.55 m2 g−1. Through Fourier transform infrared analysis, the functional groups responsible for the coordination and removal of metal ions were found to be carboxylic group (at absorption bands of 1730 cm−1) and amine groups (889 cm−1). The Langmuir maximum adsorption capacity was 47.8 mg g−1 for lanthanum and 52.6 mg g−1 for gadolinium. Meanwhile, results revealed that banana peels have a high affinity for Sm, Eu, Nd, Pr, Gd, Tb and Lu compared to other lanthanides present in the mine water samples. The results obtained so far indicate that nanostructured banana peel is a potential adsorbent for REEs removal from mine water. However, for any application, the water matrix to be treated substantially influences the choice of the sorbent material.

Synthesis of mesoporous and microporous amine and non-amine functionalized silica gels for the application of rare earth elements (REE) recovery from the waste water-understanding the role of pH, temperature, calcination and mechanism in Light REE and Heavy REE separation

The aim of this research project was to investigate the impact of surface modified silica for the purpose of rare earth elements (REE) recovery from both artificial and real waste water. The four silanes used for the functionalization of silica gels during the course of study were 3-Aminopropyl triethoxysilane (APTES), 3-Aminopropyl trimethoxysilane (APTMS), Trimethoxymethylsilane (MTM) and Chlorotrimethylsilane (TMCS). The analysis of silica gel surfaces was conducted using Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Brunauer Emmett Teller (BET) and Zeta potential measurements to better understand about the surface modification of the gels. The important yardstick for experimental analysis is the comparative REE removal efficiency of the silica gels in real and artificial waste water and how the trend of Light REE (LREE) and Heavy REE (HREE) removal changes with the effect of temperature and the presence of other competing ions. In addition, the influence of particle size, the effect of pH, the significance of calcination post silanization in the process of the selective REE removal as well as the silica leaching in both real and test waste water conditions has also been studied and addressed. The most effective results were observed for mesoporous silica gel A, with a particle size of 15–20μm, in most of the cases for both calcined and non-calcined adsorbents. Amino-functionalized APTES/APTMS silica gels demonstrated the most impressive behavior among the four adsorbents in all the cases. However, the calcination seems to have affected the performance of such gels in the removal of the target elements.

Chemically immobilized and physically adsorbed PAN/acetylacetone modified mesoporous silica for the recovery of rare earth elements from the waste water-comparative and optimization study

This study was aimed at the investigation of Rare Earth Element (REE) recovery from aqueous solution by silica gels with 1-(2-Pyridylazo) 2-naphthol (PAN) and acetyl acetone (Acac) modifications. The two different methods of silica gel chelation, such as chemical immobilization with the help of silane coupling agents (3-aminopropyl triethoxysilane (APTES) and 3-aminopropyl trimethoxysilane (APTMS) in this study) and direct physical adsorption onto the silica surface, is compared in terms of their REE removal efficiency. A comparative analysis between adsorption of different REEs for different silica gels is performed and the influence of parameters such as pH, contact time, temperature and initial concentration has been reported. The effect of calcined adsorbents on the adsorption process is also investigated. Characterization studies on silica gels by Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD) and zeta potential analysis are performed to better understand the relation between physical/chemical attributes of the adsorbents and their impact on the adsorption process. The experimental results are evaluated and optimal conditions for REE adsorption are identified. Chemically immobilized gels demonstrated immense potential for all the REE under study except Sc, for which, physically loaded gels seemed to be more efficient. The removal of REEs could be achieved at lower pHs by chemically immobilized PAN/Acac gels, making it suitable for many practical applications. The amine functionalized gels before chemical immobilization step were compared with PAN/Acac chemically immobilized gels in single as well as multi element system and the significance of chemical immobilization after amine functionalization is also stated.