Studies on the Enrichment Feasibility of Rare Earth-Bearing Minerals in Mine Tailings

This Study Aimed to Investigate the Potential of Enrichment of Rare-Earth-Bearing Minerals in Historic Mine Tailing using the Froth Flotation Process. Characterization Studies Indicated that Tailings Contained 11,000 Ppm of Rare Earth Elements (REEs). the Major Mineral in the Tailings Was Apatite at ~84%, Which Was Associated with Iron Oxides (~16%). TESCAN\u27s Integrated Mineral Analysis (TIMA) Showed that Monazite Was the Main REE Mineral, and 69% of Monazite Was Locked in Apatite Grains. Characterization Studies Suggested that the Separation of REEs-Bearing Apatite from Iron Oxides is Possible using Froth Flotation, Wherein Apatite Was Floated and Iron Oxides Were Depressed. Zeta Potential Experiments Were Conducted to Understand the Behavior of the Main Minerals in the Feed When Selected Depressants of Iron Oxides Were Added. Depressants Included Corn Starch, Sodium Metasilicates, Polyacrylamide (PAM), Hybrid Polyacrylamide (HyPAM), and Chitosan. Zeta Potential Results Suggested that Chitosan and Polyacrylamide-Based Polymers Had the Strongest Adsorption on Magnetite at PH 7 and PH 9, Respectively, as Indicated by the Large Shift in the Zeta Potential of Magnetite Suspensions. Flotation Results Were Consistent with Zeta Potential Findings and Showed that Hy-PAM and Chitosan Had the Best Depression Efficiency of Iron Oxides at PH 9 and PH 7, Respectively

Probing Surface Characteristics of Rare Earth Minerals using Contact Angle Measurements, Atomic Force Microscopy, and Inverse Gas Chromatography

Rare earth minerals (REMs) such as bastnaesite, monazite, and xenotime are of considerable significance since they are the main commercial sources for rare earth elements (REEs) with cutting-edge applications. Fundamental understanding of surface properties of REMs is essential to identify the reactions taking place at different interfaces to develop more robust technologies for the recovery of REEs. The goal of this study is to provide a comprehensive investigation on the surface energy characteristics of bastnaesite and xenotime, as the primary sources of light and heavy rare earth elements, respectively. Crystal\u27s orientation of REMs was identified using surface X-ray diffraction analysis, whereas the morphology and elemental composition were characterized using scanning electron microscopy and energy dispersive spectra analyses. Wettability of REMs was studied using sessile drop contact angle measurement technique, and the surface energy and its constituents were evaluated using Fowkes, van Oss-Chaudhury-Good, Owens-Wendt-Rabel-Kaelble, Zisman, and Neumann models. Atomic force microscopy (AFM) was used to compare the local surface properties and work of adhesion of REMs by analyzing the force profile between the mineral surfaces and a n-type silicon tip. Inverse gas chromatography (IGC) was employed to study the surface energy heterogeneity of REM powders and evaluate the dispersive and Lewis acid-base interactions. Results indicated that the dispersion forces have a larger contribution to the surface energy of both REMs in comparison with the polar interactions. The surface energy values obtained using contact angle measurements were lower than those obtained using IGC, however, the IGC results seemed to be closer to reality since the contact angle results showed a strong dependence on probe liquids, roughness, and local properties of the surfaces. Contact angle measurements and AFM analysis indicated that bastnaesite had higher hydrophobic character, whereas the IGC analysis revealed that the surface energy of xenotime was lower than that of bastnaesite at higher surface coverages. Despite the shortcomings of each method, results showed that a combination of these techniques could provide a deeper understanding of surface energy and wetting behavior of minerals

Flotation Behavior of Complex Sulfide Ores in the Presence of Biodegradable Polymeric Depressants

In this study, chitosan polymer was tested as a potential selective green depressant of pyrite in the bulk flotation of galena (PbS) and chalcopyrite (CuFeS2) from sphalerite (ZnS) and pyrite (FeS2) using sodium isopropyl xanthate as a collector and 4-methyl-2-pentanol (MIBC) as a frother. Flotation tests were carried out in a D12-Denver flotation laboratory cell in the presence and absence of chitosan and/or sodium cyanide depressant which is commercially used as pyrite depressant in sulfide mineral flotation process. Flotation recoveries and concentrate grades (assay) were studied as a function of polymer concentration and flotation time. It was found that at 50 g/ton, chitosan depressed 5.6% more pyrite as compared to conventional depressant NaCN at its optimum dosage. Furthermore, the measured assay values of pyrite in concentrates dropped by ∼1.2% when NaCN depressant was replaced with chitosan polymer. Zeta potential measurements of galena, chalcopyrite, sphalerite, and pyrite suspensions before and after chitosan\u27s addition revealed that the polymer has preferential adsorption on pyrite minerals as compared to other sulfide minerals specially galena. Results obtained from this work show that chitosan polymer has a promising future as a biodegradable alternative to sodium cyanide for the purpose of depressing pyrite in sulfide minerals flotation

Experimental And Machine Learning Studies On Chitosan-Polyacrylamide Copolymers For Selective Separation Of Metal Sulfides In The Froth Flotation Process

The froth flotation process is extensively used for the selective separation of valuable base metal sulfides from uneconomic associated minerals. However, in this complex multiphase process, various parameters need to be optimized to ensure separation selectivity and peak performance. In this study, two machine learning (ML) models, artificial neural network (ANN) and random forests (RF), were used to predict the efficiency of in-house synthesized chitosan-polyacrylamide copolymers (C-PAMs) in the depression of iron sulfide minerals (i.e., pyrite) while valuable base metal sulfides (i.e., galena and chalcopyrite) were floated using nine flotation variables as inputs to the models. The prediction performance of the models was rigorously evaluated based on the coefficient of determination (R2) and the root-mean-square error (RMSE). The results showed that the RF model was able to produce high-fidelity predictions of the depression of pyrite once thoroughly trained as compared to ANN. With the RF model, the overall R2 and RMSE values were 0.88 and 4.38 for the training phase, respectively, and R2 of 0.90 and RMSE of 3.78 for the testing phase. As for the ANN, during the training phase, the overall R2 and RMSE were 0.76 and 4.75, respectively, and during the testing phase, the R2 and RMSE were 0.65 and 5.42, respectively. Additionally, fundamental investigations on the surface chemistry of C-PAMs at the mineral–water interface were conducted to give fundamental insights into the behavior of different metal sulfides during the flotation process. C-PAM was found to strongly adsorb on pyrite as compared to galena and chalcopyrite through zeta potential, X-ray photoelectron spectroscopy (XPS), and adsorption density measurements. XPS tests suggested that the adsorption mechanism of C-PAM on pyrite was through chemisorption of the amine and amide groups of the polymer

High-Performance Polymers for Separation and Purification Processes: An Overview

Separation and purification techniques are applied in many important fields, such as in the medical, chemical, metallurgical, environmental, and pharmaceutical industries. Recent advances in separation science and the urgent need for highly selective purification have necessitated a rapid progress with respect to the reagents, chemicals, and surfactants used in separation processes to attain a high efficiency and selectivity. Polymeric materials have attracted considerable interest, and they have been widely used as extractants, catalysts, and modifiers, in separation and purification processes. This review outlines the recent advances in the use of novel polymers, natural and synthetic, in different separation and purification techniques. Various separation techniques such as chromatography, crystallization, precipitation, distillation, electrophoresis, filtration, and mineral processing methods are discussed, and the polymers used in each method are described in terms of their properties, structure, and function. The application of polymers shows great promise in achieving a highly efficient separation, especially in the areas of membrane separation and water purification. The rational design of new multifunctional polymers with triggered functions presumably presents new opportunities for the development of advanced separation methods

Separation and Recovery of Rare Earth Elements using Novel Ammonium-Based Task-Specific Ionic Liquids with Bidentate and Tridentate O-Donor Functional Groups

In the present work, two novel ammonium-based functional ionic liquids (FILs) with oxygen donating groups: trioctyl(2-ethoxy-2-oxoethyl)ammonium dihexyl diglycolamate, [OcGBOEt][DHDGA], and tricaprylmethylammonium dihexyl diglycolamate, [A336][DHDGA] were synthesized and tested for the recovery and separation of rare earth elements from aqueous solutions. The synthesized FILs were characterized using nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR), high-resolution mass spectrometry (HRMS), thermal gravimetric analysis (TGA), disc scanning calorimetry (DSC) in addition to density and viscosity analysis. The extraction behavior of europium ions (Eu3+) in HNO3 solution was investigated in detail by changing key process parameters, including solution acidity, concentration of Eu3+ ions, extraction temperature, extraction time, and the type of organic diluent. Kinetic studies indicated that the extraction process was relatively fast with 97% of Eu3+ions recovered after 5 min using [OcGBOEt][DHDGA], whereas it took 15 min for [A336][DHDGA] system to reach 80% recovery. Extraction thermodynamics was evaluated by analyzing the effect of temperature on the extractability of Eu3+ ions in nitrate solution. Results indicated that the extraction reactions were favorable for both FILs. Back extraction studies indicated that ~99% of Eu3+ can be stripped off [OcGBOEt][DHDGA] and [A336][DHDGA] using 0.1 and 0.5 molL-1 HNO 3, respectively. Separation efficiencies of rare earth ions, including La3+, Pr3+, Nd3+, Sm3+, Eu3+, Tb3+, Dy3+, Y3+, Er3+, and Lu3+ were also investigated to examine the selectivity of the synthesized FILs. Results showed that both FILs have significant affinity to heavy rare earth elements, however, the separation efficiency of [A336][DHDGA] was superior to that of [OcGBOEt][DHDGA]

The Use of Chitosan as a Green Depressant of Silicates in Phosphate Flotation

The application of green reagents as process aids in the froth flotation process is of crucial importance in order to reduce the environmental impacts. In this study, chitosan polymer was used as a green depressant of silicates in the direct flotation of phosphate minerals. Zeta potential measurements were used to examine the electrical properties of mineral surfaces in the presence and absence of chitosan polymer to understand the behavior of the flotation feed. Flotation recoveries and concentrates\u27 grade of phosphates were studied as a function of chitosan\u27s dosage, pulp\u27s pH, and flotation time. The flotation recoveries of phosphate minerals in the presence of chitosan polymer were compared with the recovery values obtained when commercial silicates dispersant (sodium silicate) was applied. Results indicated that in the presence of 300 g/ton of chitosan polymer, the recovery of phosphate minerals was ~70% as compared to ~40% when the same dosage of sodium silicate dispersant was used. Results suggested that chitosan can be used as a green and sustainable depressant of silicate minerals in phosphate flotation process under specific conditions

Adsorption Characteristics of Chitosan Grafted Copolymer on Kaolin

Efficient destabilization of colloidal dispersions is the top challenge facing solid-liquid separation processes. In this study, an in-house synthesized environmentally friendly graft copolymer, chitosan-graft-polyacrylamide (chi-g-PAM), was investigated as a potential flocculant of fine kaolin dispersions. Chi-g-PAM was successfully prepared by combining the properties of synthetic monomer (acrylamide) and natural polymer (chitosan) using ceric ammonium nitrate as an initiator. The physical and chemical characteristics of the copolymer were analyzed using Fourier-transform infrared (FTIR), scanning electron microscopy (SEM), X-ray powder diffraction (XRD) and Zetasizer Nano ZS in order to identify the active adsorption sites in the polymer structure.The performance of chi-g-PAM as a flocculant was evaluated by treating 5 wt% kaolin despersion (d50 and mean diameter of 6.63 and 9.24 μm, respectively) with different dosages of the polymer and calculating the initial settling rates (ISR). The flocculation mechanism and the adsorption capacity were investigated using zeta potential and total organic carbon (TOC) measurements. Results showed that ISR increased with increasing chi-g-PAM dosages before reaching maximum values at corresponding optimal ones; then, the settling rate slightly decreased. Chi-g-PAM showed a better flocculation and settling behavior (ISR 24.84 m/h) as compared to chitosan (ISR of 7.2 m/h) at optimun dosages and performed similar to commercial PAM (ISR of 25.92 m/h). Reliable correlation of zeta potential measurement and adsorption isotherms obtained from TOC mesaurements demonstrated that bridging and charge neutralization were the dominant adsorption mechanisms involved. The experimental adsorption data were analyzed using Langmuir and Freundlich models. The best fit was obtained using the Langmuir isotherm model with a correlation coefficient value of 0.991 as compared with 0.895 for the Freundlich model. The TOC method has proven to be suitable and feasible for explaining the adsorption mechanism and determination of the adsorbed amount of chi-g-PAM on kaolin

Adsorption of Organic-Inorganic Hybrid Polymers on Kaolin from Aqueous Solutions

Adsorption of two in-house synthesized organic-inorganic hybrid polymers, Al(OH)3-polyacrylamide (Al-PAM) and Fe(OH)₃-polyacrylamide (Fe-PAM) on kaolin and corresponding flocculation of fluid fine kaolin suspensions were investigated. For comparison, a commercial anionic flocculant (partially hydrolyzed polyacrylamide or known as H-PAM) was also examined. The flocculation dynamics of fine kaolin suspensions were determined using an on-line focused beam reflectance measurement (FBRM) probe. As an example of applications, flocculation of a laboratory oil sands extraction tailings sample was studied. A quartz crystal microbalance with dissipation (QCM-D) was used to determine adsorption kinetics of the polymers on silica and alumina as representative of T- and O-basal planes of kaolin. Al-PAM, Fe-PAM and H-PAM were shown to be excellent flocculant of kaolin suspensions, with H-PAM being less effective and more sensitive to overdosing. The flocculation performance was greatly influenced by proper mixing. Strong flocculation of kaolin suspension by Al-PAM and Fe-PAM is attributed to their ability to adsorb on both basal planes of kaolin, in contrast to relatively weak flocculation of kaolin by H-PAM which adsorbs only on positively charged aluminum oxy-hydroxyl basal planes. The electrostatic attraction or repulsion is identified as a critical parameter in determining polymer adsorption and hence corresponding flocculation of kaolin suspensions. © 2014 Elsevier B.V