Effect of pH in the synthesis of organo-clays for rare earths removal

Two montmorillonitic clays were modified with N-(methoxy-polyethylene glycol) ethylene diamine and tested as sorbents for removal of Rare Earths (REs) from aqueous solutions. Lanthanum was chosen as representing element of REs family and adsorption tests were performed with the aim of selecting a system with good uptake efficiency for the pollutant abatement in wastewaters. The effects of pH were studied and the properties ofthe obtained final materials were evaluated with simple model systems of the final application. The modified clays were characterized before and after the intercalation, combining the results ofX-ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FT-IR), whereas the solutions were analysed by means of Chemical Oxygen Demand to quantify the amount of intercalated polymer and by Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES) to quantify the metal ions concentration. The results showed that the organo-clays have been efficiently prepared while the characterization techniques showed that the intercalation mechanism was strongly dependent on the pH ofthe preparation procedure, affecting the protonation ofthe amino groups

Use of natural clays as sorbent materials for rare earth ions: materials characterization and set up of the operative parameters

Two mineral clays of the montmorillonite group were tested as sorbents for the removal of Rare Earths (REs) from liquid solutions. Lanthanum and neodymium model solutions were used to perform uptake tests in order to: (a) verify the clays sorption capability, (b) investigate the sorption mechanisms and (c) optimize the experimental parameters, such as contact time and pH. The desorption was also studied, in order to evaluate the feasibility of REs recovery from waters. The adsorption–desorption procedure with the optimized parameters was also tested on a leaching solution obtained by dissolution of a dismantled NdFeB magnet of a hard-disk. The clays were fully characterized after REs adsorption and desorption by means of X-ray powder diffraction (XRPD) and X-ray photoelectron spectroscopy (XPS); the liquid phase was characterized via Inductively Coupled Plasma–Optical Emission Spectroscopy (ICP–OES) analyses. The experimental results show that both clays are able to capture and release La and Nd ions, with an ion exchange mechanism. The best total efficiency (capture 50%, release 70%) is obtained when the uptake and release processes are performed at pH = 5 and pH = 1 respectively; in real leached scrap solutions, the uptake is around 40% but release efficiency is strongly decreased passing from a mono-ion system to a real system (from 80% to 5%). Furthermore, a strong matrix effect is found, with the matrix largely affecting both the uptake and the release of neodymium

Enhanced lanthanum adsorption by amine modified activated carbon

Rare earths are one of the most critical raw materials group. In an effort to develop an effective adsorbent for aqueous rare earths recovery, activated carbon (AC) was modified with pentaethylenehexamine. Both raw AC and modified activated carbon (MAC) were characterized by X-ray diffraction (XRD), FT-IR and surface area analyses. The set of experiments was carried out with lanthanum, selected as representing of rare earths family, and the impacts of reactive time and concentrations of lanthanum were evaluated. The aqueous lanthanum adsorptive kinetics and capacity were also determined. The strong improvement in the efficiency values detected by using modified carbons (uptake 100% until initial concentrations of about 2600 ppm and release over 95%) demonstrated that the coordination mechanism due to modifying agent is effective. MAC presented lower kinetics and more than double adsorptive capacity as compared with AC. Furthermore, the adsorbent can be used successfully at least four times after regeneration for the removal of lanthanum and seems to show a selective behaviour in equimolar solutions with copper as competitive ions. The overall results demonstrated the potential utility of modification for enhancement of performances of AC-based materials for rare earths removal from aqueous solutions

SOLID LIQUID EXTRACTION OF RARE EARTHS FROM AQUEOUS SOLUTIONS: A REVIEW

Rare Earths (REs) demand is constantly increasing in the global market because new technological applications exploit these materials for their unique properties. Since natural resources are located just in focused areas, lots of worldwide countries are arranging solutions to recover REs from end-of-life products. Currently each EU citizen produces about 17 kg of Waste Electrical and Electronic Equipment (WEEE) per year. These wastes are rich in precious and strategic metals and, in many cases, are characterized by higher REs contents than those of natural minerals. Accordingly, recycling can be considered a valuable opportunity: this perspective is known as "urban mining”. From a technological point of view, recycling of WEEE and recovering of metals can be divided into three major steps: disassembly, upgrading and refining. Regarding the refining, different methods have been proposed. Among the others, hydrometallurgical method has been reported to be one of the most interesting. Some of the few disadvantages are related to the step of metal ions removal from aqueous solution. REs separation has always represented indeed a critical challenge in traditional chemical processing because of the similar chemical and physical properties of these elements. Solvent extraction is usually the most used process to separate individual REs but solid-liquid extraction (SLE) presented as an alternative. This paper reviews the different SLE extraction systems proposed for REs separation with particular focus on the different kinds of solid sorbents used (resins, nanotubes, clays and modified clays, membranes, silica and ion-imprinted polymers) evaluating advantages and critical issues of the different systems

RECOVERY OF VALUABLE METALS FROM ELECTRONIC SCRAPS BY CLAYS AND ORGANO-CLAYS: STUDY ON BI-IONIC MODEL SOLUTIONS

The demand of valuable metals as precious metals and rare earths is constantly increasing in the global market, as many and different technological applications exploit these materials because of their unique properties. Since natural resources are located just in focused areas, an interesting possibility could be the recovery of metals from Waste Electrical and Electronic Equipments (WEEE). The aim of this work is to evaluate the recovery potentialities of clays and organo-clay based systems towards the metals contained in the solutions of electronic scraps dissolved in strong acid, by preliminary tests on bi-ionic model solutions. Lanthanum has been chosen as representative of the rare earths while copper has been considered since it is by far the most used metal in electronics. The considered sorbents are a montmorillonitic clay and two polyamine based organo-clays. Uptake and release processes have been carried out in order to assess the performances of these solids and to evaluate the uptake and release mechanisms. The results showed that the cationic exchange is the prevailing mechanism in the case of pristine materials, while both coordinating effect due to amino groups and cationic exchange occur in the case of modified clays, respectively accounting for copper and lanthanum uptake. Furthermore the pH was found having a great influence in both the adsorption and desorption phenomena

LANTHANUM UPTAKE BY CLAYS AND ORGANO-CLAYS: EFFECT OF THE POLYMER

Two natural smectite clays (STx-1b and SWy-2) were studied as solid sorbents for uptake and release of lanthanum. Since the obtained global efficiencies of lanthanum recovery were about 30-35%, the same considered natural clays were modified by intercalating a PEGylated ethylene diamine having chelating properties, in order to evaluate a possible improvement effect of the polymer. The pristine and the organo-clays were characterized by XRD analyses while the amounts of intercalated polymer and captured lanthanum were estimated respectively by COD and ICP-OES analyses. The results showed that pristine clays and modified clay had similar lanthanum uptake efficiencies while modified clays presented a better behaviour towards release processes, ensuring a recovery global efficiency of 43%

Recovery of rare earths and precious metals from waste electrical and electronic equipment by acid leaching and immobilized chelating agents

A natural smectite mineral clay (STx-1b) was modified by intercalating different concentrations of Pentaethylenehexamine (PEHA) with the final aim of synthesizing new solid materials for the recovery of valuable metals, in particular Rare Earths (REs), from Waste Electrical and Electronic Equipment (WEEE). The modified clays were then contacted with a model solution of Lanthanum (chosen as representing element of REs family). Finally, release tests were performed on the different samples in order to verify the organo-clay capability not only to capture but also to recover metal ions. The results showed that the experimental procedure was appropriate to intercalate the polymer in the clay for every initial polymer concentration considered. Furthermore, the obtained organo-clays were effective in both uptake (efficiencies up to 99 %) and release processes (efficiency around 80 % contacting with acid solutions). The organo-clay system with polymer content of 0.4 mmolpolymer/gclay was selected as that of choice to guarantee the highest global process efficiency, ensuring a Lanthanum recovery of 80 %. The adsorbed and released metal ions were calculated by ICP-OES while the amounts of intercalated polymer were estimated by COD (Chemical Oxygen Demand) analysis of the residual amounts in solution and deduced by difference. All the solid materials were characterized by X-ray diffraction (XRD)

Rare Earths (La, Y, and Nd) Adsorption Behaviour towards Mineral Clays and Organoclays: Monoionic and Trionic Solutions

Metals from electric and electronic waste equipment (WEEE) can be recovered by dissolution with acids followed by liquid–liquid extraction. A possible alternative to liquid–liquid extraction is liquid–solid adsorption, where sorbents efficiency is the key factor for process efficiency. In this respect, aim of this paper is the study of the behaviour of two solid sorbents for the recovery of Rare Earths (REs)—in particular, La, Nd, and Y—from scraps of end-of-Life (EOL) electronic equipment. Two solid matrices were considered: a pristine montmorillonite clay and a modified-montmorillonite clay intercalated with a commercial pentaethylen-hexamine. The capture ability of the solids was tested towards single-ion La, Nd, and Y solutions and a multi-element solution containing the three ions. Before and after the uptake step, samples of both the solid and liquid phases were analysed. For both sorbents, at lower metal initial concentrations, the ions were captured in similar amount. At higher concentrations, pure clay showed a high total uptake towards La ions, likely due to surface interactions with clay sites. The organoclay preferentially interacts with Nd and Y. Considering the presence of the polyamine, this behaviour was related to ion coordination with the amino groups. The capture behaviour of the two sorbents was related to the different physicochemical properties of the ions, as well as to the ionic radius

Environmental impacts of a hydrometallurgical process for electronic waste treatment: A life cycle assessment case study

The recovery of precious metals through hydrometallurgical techniques is one of the most active research areas on recovery of metals from electronic scraps. In this perspective, a pilot plant was designed for the treatment of small WEEE (Waste Electrical and Electronic Equipment) via hydrometallurgy. The process is based on two different leaching steps, in nitric acid and in aqua regia, followed by electrodeposition processes, to mainly recover copper, silver and gold. Two adsorption steps were also carried out to recover nickel and tin.The goal of the present study is to assess the environmental impacts associated with the designed hydrometallurgical treatment of the small WEEE through Life Cycle Assessment (LCA) methodology. The approach considered is cradle-to-gate, i.e., from the collected WEEE entering the collection centre to the secondary metals obtained from the hydrometallurgical treatment.Results obtained by SimaPro software and CML-IA method show that the nitric acid leaching contributes mostly to the impacts of the hydrometallurgical process (from 40% to 80%), followed by the adsorption steps. From an environmental perspective, the latter can still be improved at the design phase by increasing the lifetime of the sorbents