Effective removal of mercury from aqueous streams via electrochemical alloy formation on platinum

Retrieval of mercury from aqueous streams has significant environmental and societal importance due to its very high toxicity and mobility. We present here a method to retrieve mercury from aqueous feeds via electrochemical alloy formation on thin platinum films. This application is a green and effective alternative to traditional chemical decontamination techniques. Under applied potential, mercury ions in solution form a stable PtHg4 alloy with platinum on the cathode. A 100 nanometres platinum film was fully converted to a 750 nanometres thick layer of PtHg4. The overall removal capacity is very high, > 88 g mercury per cm3. The electrodes can easily be regenerated after use. Efficient and selective decontamination is possible in a wide pH range, allowing processing of industrial, municipal, and natural waters. The method is suited for both high and low concentrations of mercury and can reduce mercury levels far below the limits allowed in drinking water

Vanadium sustainability in the context of innovative recycling and sourcing development

This paper addresses the sustainability of vanadium, taking into account the current state-of-the-art related to primary and secondary sources, substitution, production, and market developments. Vanadium plays a critical role in several strategic industrial applications including steel production and probable widespread utilization in next-generation batteries. Confirming the importance of vanadium, the European Commission identified and formally registered this metal on the 2017 list of Critical Raw Materials for the European Union. The United States and Canada have also addressed the importance of this metal. Like the European economy, the American and Canadian economies rely on vanadium and are not globally independent. This recognized importance of vanadium is driving many efforts in academia and industry to develop technologies for the utilization of secondary vanadium resources using hydrometallurgical and pyrometallurgical techniques. In this paper, current efforts and their outcomes are summarized along with the most recent patents for vanadium recovery

Waste of batteries management: Synthesis of magnetocaloric manganite compound from the REEs mixture generated during hydrometallurgical processing of NiMH batteries

In the present study, rare earth elements (REEs, i.e., La, Ce, Nd, and Pr) were hydrometallurgically recovered in oxalate form with presence of very low concentration of Co, Al, Zn and Ni from solution after processing of spent Nickel metal hydride (Ni-MH) batteries. The recovered mixture was used as alternative source in the synthesis of magnetocaloric materials. In this study, a manganite sample with general formula ABO3 was selected to be prepared since it is relatively easy to synthesize and is tuneable by adjustment of the doping concentration. The conventional solid-state reaction method was used to prepare an orthorhombic structure of manganite with presence of REE2O3 and MnO2 as secondary phases reported from x-ray pattern at room temperature. The thermomagnetic measurements showed a PM to FM transition at 184 K in a 0.01 T magnetic field that shifts to 194 K by increasing the magnetic field to 1.8 T. The magnetocaloric properties were determined by calculating the isothermal entropy change and directly measuring the adiabatic temperature change. A reversible magnetocaloric effect was observed

Temperature and concentration dependence of the electrochemical PtHg4 alloy formation for mercury decontamination

New and improved methods to remove toxic mercury from contaminated waters and waste streams are highly sought after. Recently, it was shown that electrochemical alloy formation of PtHg4 on a platinum surface with mercury ions from solution can be utilized for decontamination, with several advantages over conventional techniques. Herein, we examine the alloy formation process in more detail by mercury concentration measurements using inductively coupled plasma mass spectrometry in batch measurements as well as electrochemical quartz crystal microbalance analysis both in batch and in flowing water with initial mercury concentrations ranging from 0.25 to 75000 \ub5g L−1 Hg2+. Results show that mercury is effectively removed from all solutions and the rate of alloy formation is constant over time, as well as for very thick layers of PtHg4. The apparent activation energy for the electrochemical alloy formation was determined to be 0.29 eV, with a reaction order in mercury ion concentration around 0.8. The obtained results give new insights that are vital in the assessment and further development of electrochemical alloy formation as a method for large scale mercury decontamination

Hydrometallurgical recovery of rare earth elements from flourescent lamp waste fractions

Recovery and reuse of materials is important for a circular economy. In recent years the recovery of critical metals from end-of-life products has received increased attention. Various streams, e.g. permanent magnets, nickel metal hydride batteries and fluorescent lamps are considered targets for the recovery of rare earth elements (REEs). The last can be a source of up to six different REEs: europium and yttrium (primarily), as well as lanthanum, cerium, terbium and gadolinium (secondarily). Because fluorescent lamps use mercury to generate light, a decontamination step needs to be carried out prior to processing discarded products for REEs recovery. This is often carried out using thermal treatment (up to 800 \ub0C) but this method has some drawbacks, e.g. energy consumption and the fact that it is not best suited for waste streams containing high amounts of moisture.Hydrometallurgical methods for the decontamination of fluorescent lamp waste fractions and subsequent recovery of the REEs contained are presented in this study. A selective leaching process followed by separation of metals using solvent extraction was developed. Mercury was leached in a first stage using iodine in potassium iodide solutions. Further processing of the mercury in solution was investigated using various techniques, e.g. ion exchange, reduction and solvent extraction. In a second leaching step, impurity metals, e.g. calcium, barium, etc., were selectively leached from the REEs with nitric acid solution by making use of their fast dissolution kinetics. Further leaching, carried out with more concentrated acidic solutions for longer time, led to the dissolution of the REEs. Partial leaching selectivity between yttrium + europium and the other four REEs was achieved by controlling the leaching time, acid concentration and temperature.A group separation of the REE ions in solution was carried out using solvent extraction with Cyanex 923, a commercial mix of trialkyl phosphine oxides. Testing of the process at laboratory pilot scale in mixer-settlers showed promising results, leading to a final product consisting of a yttrium/europium-rich solution. Over 99% of the REEs present in lamp leachates were extracted and stripped, respectively, in a mixer-settler system comprised of three extraction stages and four stripping stages. The metals were then further separated using Cyanex 572, a novel phosphorus-based chelating extractant aimed at the separation of individual REEs. Selective separation of yttrium and europium was achieved by controlling the equilibrium pH (pHeq) during extraction. Yttrium was extracted at pHeq = 0 and europium at pHeq = 1. Rare earth oxides were prepared via oxalic acid precipitation and thermal treatment of the obtained oxalates at 800 \ub0C. A mixed REE oxide (99.96% REEs, with 94.61% yttrium, 5.09% europium and 0.26% others) was synthetized from the strip product after extraction with Cyanex 923. Yttrium oxide (99.82%) and europium oxide (91.6%) were synthetized from the strip products after extraction with Cyanex 572

Leaching and solvent extraction of rare earth metals from fluorescent lamp waste

With the rapid advancement of technology, the demand for elements such as rare earth metals (REMs) has increased considerably during the last decade. Many countries are facing problems securing sustainable supplies, a fact acknowledged in many publications. Due to the ever-growing demand and supply problems, REMs are now considered to be some of the most critical elements. This has focused attention towards their recovery from end-of-life products and industrial waste streams, with fluorescent lamps being one of the main targets. However, despite the research published, large scale applications are scarce, mainly due to the lack of sustainable processes.The research presented here is aimed at developing a sustainable hydrometallurgical process for the treatment of fluorescent lamp waste, with the goal of recovering the REMs and mercury that these lamps contain.In comparison to other efforts in this field, these investigations were carried out using real waste samples originating from a discarded lamp processing facility. The complexity of the material (a mercury contaminated mix of glass, metallic and plastic parts, phosphors, remaining electronics and other impurities) and the nature of the initial process (crushing of mixed lamps followed by containment of elemental mercury via oxidation) make already proposed methods a challenge and make additional research necessary. This is due to the fact that many of the methods described in the literature have not been optimized for real or complex waste streams; parts of the published studies were performed on a laboratory scale, using clean lamps, artificial mixtures that resemble real samples or pure commercial phosphors.Cerium, europium, gadolinium, lanthanum, terbium, and yttrium were the REMs identified in the material. Leaching of metals was investigated using different solutions (pure water, ammonium chloride, acetic acid, nitric and hydrochloric acid) and parameters (temperature, ultrasound-assisted digestion, solid-to-liquid ratio, and leaching agent concentration). An increased acid concentration and increased temperature, and ultrasound-assisted digestion improved the leaching efficiency for most of the investigated elements. Solvent extraction experiments were carried out using a commercial mix of trialkylphosphine oxides (Cyanex 923), in order to assess the extraction potential of REMs and the advantages/disadvantages for possible industrial scale-up. Separation of heavier elements (such as terbium, yttrium, europium and gadolinium) from lighter ones (like cerium and lanthanum) is possible due to larger separation factors

Leaching and solvent extraction of rare earth metals from fluorescent lamp waste

With the rapid advancement of technology, the demand for elements such as rare earth metals (REMs) has increased considerably during the last decade. Many countries are facing problems securing sustainable supplies, a fact acknowledged in many publications. Due to the ever-growing demand and supply problems, REMs are now considered to be some of the most critical elements. This has focused attention towards their recovery from end-of-life products and industrial waste streams, with fluorescent lamps being one of the main targets. However, despite the research published, large scale applications are scarce, mainly due to the lack of sustainable processes.The research presented here is aimed at developing a sustainable hydrometallurgical process for the treatment of fluorescent lamp waste, with the goal of recovering the REMs and mercury that these lamps contain.In comparison to other efforts in this field, these investigations were carried out using real waste samples originating from a discarded lamp processing facility. The complexity of the material (a mercury contaminated mix of glass, metallic and plastic parts, phosphors, remaining electronics and other impurities) and the nature of the initial process (crushing of mixed lamps followed by containment of elemental mercury via oxidation) make already proposed methods a challenge and make additional research necessary. This is due to the fact that many of the methods described in the literature have not been optimized for real or complex waste streams; parts of the published studies were performed on a laboratory scale, using clean lamps, artificial mixtures that resemble real samples or pure commercial phosphors.Cerium, europium, gadolinium, lanthanum, terbium, and yttrium were the REMs identified in the material. Leaching of metals was investigated using different solutions (pure water, ammonium chloride, acetic acid, nitric and hydrochloric acid) and parameters (temperature, ultrasound-assisted digestion, solid-to-liquid ratio, and leaching agent concentration). An increased acid concentration and increased temperature, and ultrasound-assisted digestion improved the leaching efficiency for most of the investigated elements. Solvent extraction experiments were carried out using a commercial mix of trialkylphosphine oxides (Cyanex 923), in order to assess the extraction potential of REMs and the advantages/disadvantages for possible industrial scale-up. Separation of heavier elements (such as terbium, yttrium, europium and gadolinium) from lighter ones (like cerium and lanthanum) is possible due to larger separation factors

Hydrometallurgical recovery of rare earth elements from flourescent lamp waste fractions

Recovery and reuse of materials is important for a circular economy. In recent years the recovery of critical metals from end-of-life products has received increased attention. Various streams, e.g. permanent magnets, nickel metal hydride batteries and fluorescent lamps are considered targets for the recovery of rare earth elements (REEs). The last can be a source of up to six different REEs: europium and yttrium (primarily), as well as lanthanum, cerium, terbium and gadolinium (secondarily). Because fluorescent lamps use mercury to generate light, a decontamination step needs to be carried out prior to processing discarded products for REEs recovery. This is often carried out using thermal treatment (up to 800 \ub0C) but this method has some drawbacks, e.g. energy consumption and the fact that it is not best suited for waste streams containing high amounts of moisture.Hydrometallurgical methods for the decontamination of fluorescent lamp waste fractions and subsequent recovery of the REEs contained are presented in this study. A selective leaching process followed by separation of metals using solvent extraction was developed. Mercury was leached in a first stage using iodine in potassium iodide solutions. Further processing of the mercury in solution was investigated using various techniques, e.g. ion exchange, reduction and solvent extraction. In a second leaching step, impurity metals, e.g. calcium, barium, etc., were selectively leached from the REEs with nitric acid solution by making use of their fast dissolution kinetics. Further leaching, carried out with more concentrated acidic solutions for longer time, led to the dissolution of the REEs. Partial leaching selectivity between yttrium + europium and the other four REEs was achieved by controlling the leaching time, acid concentration and temperature.A group separation of the REE ions in solution was carried out using solvent extraction with Cyanex 923, a commercial mix of trialkyl phosphine oxides. Testing of the process at laboratory pilot scale in mixer-settlers showed promising results, leading to a final product consisting of a yttrium/europium-rich solution. Over 99% of the REEs present in lamp leachates were extracted and stripped, respectively, in a mixer-settler system comprised of three extraction stages and four stripping stages. The metals were then further separated using Cyanex 572, a novel phosphorus-based chelating extractant aimed at the separation of individual REEs. Selective separation of yttrium and europium was achieved by controlling the equilibrium pH (pHeq) during extraction. Yttrium was extracted at pHeq = 0 and europium at pHeq = 1. Rare earth oxides were prepared via oxalic acid precipitation and thermal treatment of the obtained oxalates at 800 \ub0C. A mixed REE oxide (99.96% REEs, with 94.61% yttrium, 5.09% europium and 0.26% others) was synthetized from the strip product after extraction with Cyanex 923. Yttrium oxide (99.82%) and europium oxide (91.6%) were synthetized from the strip products after extraction with Cyanex 572

Perspectives for the recovery of critical elements from future energy-efficient refrigeration materials

Rare earth elements (REEs) are the core of many future-sustainable technologies. One example is magnetocaloric refrigeration, an emerging field essential for the efficient use of energy. Future adoption of this technology will require adequate processing of end-of-life units and production residues. Currently, REEs have very high supply risk, and their recovery rates are below 1%. So far, their recovery from magnetocaloric materials has not been addressed. This work reports on a leaching and solvent extraction process to recover REEs from genuine magnetocaloric materials comprising cerium, iron, lanthanum, manganese and silicon. Leaching was studied using nitric, hydrochloric and sulfuric acid solutions, with optimizations in terms of temperature, acid concentration and solid-to-liquid ratio. Recovery of REEs from nitric, hydrochloric, and sulfuric acid leachates was investigated with three types of solvating extractants: tributyl phosphate (TBP), trioctylphosphine oxides (Cyanex 923) and tetraoctyl digylcol amide (TODGA). Extraction was most effective from nitric acid media. Very good extraction selectivity between REEs and non-REEs was achieved with TODGA. Cyanex 923 showed better extraction efficiency than TBP, and performed best in aliphatic diluents. A separation factor of 3.3 between cerium and lanthanum was achieved with 1 mol/L Cyanex 923 in Isopar L