Demonstration Plant Equipment Design and Scale-Up from Pilot Plant of a Leaching and Solvent Extraction Process

Germanium recovery from coal fly ash by hydrometallurgical procedures was studied at the pilot scale (5 kg of fly ash/h). Results were used to design the equipment of a demonstration-sized plant (200 kg of fly ash/h). The process is based on hydrometallurgical operations: firstly a germanium extraction from fly ash by leaching and a consequent Ge separation from the other elements present in the solution by solvent extraction procedures. Based on the experimental results, mass balances and McCabe-Thiele diagrams were applied to determine the number of steps of the solvent extraction stage. Different arrangements have been studied and a countercurrent process with three steps in extraction and six steps in elution was defined. A residence time of 5 min was fixed in both the extraction and elution stages. Volumetric ratios in extraction and stripping were: aqueous phase/organic phase = 5 and organic phase/stripping phase = 5, so a concentration factor of 25 is achieved. Mixers and decanters were completely defined. The maximum extracted and eluted germanium was estimated and a global efficiency of 94% was achieved. The cost-effectiveness of the equipment was estimated using the Lang factors

Non-dispersive extraction of ge(IV) from aqueous solutions by cyanex 923: Transport and modeling studies

Transport process of germanium from an aqueous solution containing oxalic acid and 100 mg/L Ge was studied. Cyanex 923 immobilized in a polytetrafluoroethylene membrane was employed as a carrier in a flat-sheet supported liquid membrane (FSSLM) system. The speciation of the germanium ion in the oxalic acid medium and related diagrams were applied to study the transport of germanium. The effective parameters such as oxalic acid, carrier concentration, and strip reagent composition were evaluated in this study. Based on the experimental data, the oxalic acid and carrier concentrations of 0.075 mol/L and 20% v/v were the condition in which the efficient germanium transport was achieved, respectively. The concentration range of 0.04–0.1 mol/L was selected for sodium hydroxide (NaOH) as a strip reagent providing the best efficiency to transport germanium through the supported liquid membrane (SLM) system. Furthermore, the permeation model was obtained to calculate the mass transfer resistance of the membrane (¿m) and feed (¿f) phases. According to the results, the values of 1 and 1345 s/cm were found for ¿m and ¿f, respectivelyPeer ReviewedPostprint (published version

Low environmental impact process for germanium recovery from an industrial residue

This paper focused on the germanium recovery from an Integrated Gasification with Combined Cycle fly ash (IGCC FA). The global process comprised the leaching of the IGCC fly ash with an aqueous solution containing tartaric acid, retention of the germanium-tartaric chelate onto a conventional anionic resin (IRA-900) and elution of germanium. The last step consisted of the germanium precipitation which was accomplished with tannic acid. The leaching experiments were performed with tartaric aqueous solutions and with the raffinate from the subsequent ion-exchange (IX) step. Raffinate from the IX step can be reintroduced in the process as leaching solution. When the contact between FA and leaching solution was maintained for 3 h at pH = 1, the Ge leaching efficiency achieved 86%. The effect of pH, resin dosage and tartaric acid dosage on the Ge retention onto the IRA-900 resin was investigated employing a centered composite rotatable design (CCRD) for experimental design and analysis of results. The retention of Ge-tartaric acid complex onto IRA-900 was optimized using design-expert software and the optimum predicted efficiency and loading capacity were 90–98% and 3.0–3.5 mg·g−1. The experimental affinities that IRA-900 showed for the elements extracted (leached) were: Ge >> Sb > V > Ni > As > Sn > B > Zn. Different eluting solutions were tested, and more than 90% of Ge elution was achieved with 2 M HCl. Final solutions contained Ge, Sb and V. Precipitation tests focused on the optimum pH for Ge precipitation adding tannic acid to the elution solutions. A 99.3% of Ge was precipitated from eluting solution, adding 33.3 g of tannic acid per g of Ge. V also precipitated in some extent along with Ge but the rest of elements practically remained in solution

Non-dispersive selective extraction of germanium from fly ash leachates using membrane-based processes

Non-dispersive selective extraction of Ge(IV) tartrates was carried out from simulated fly ash solutions containing heavy metals through supported liquid membranes (SLM). The optimum transport was obtained using a PTFE membrane containing Alamine 336 5%v/v in the condition of tartaric acid 2.76 mmol/L and HCl 1 mol/L in feed and strip phases, respectively. Under this condition, a hollow fiber (HF) SLM experiment was conducted. The results showed that this system could transport germanium from the feed to the strip phase so much faster than the flat sheet (FS) SLM system. The rate of transport through HFSLMs is comparable to dispersive extractions.Peer ReviewedPostprint (author's final draft

Germanium transport across supported liquid membrane with Cyanex 923: Mathematical modeling

A mathematical model was developed to monitor the facilitated transport of germanium(IV) from oxalic acid solutions through a flat sheet supported liquid membrane (FSSLM) containing four trialkylphosphine oxides (Cyanex 923). The FSSLM modeling was based on the extraction constant (Kext) calculated from the liquid-liquid extraction (LLX) modeling. The LLX model presented a reliable calculation of the extraction constant (Kex= 2.057×103 L/mol4). The FSSLM model was solved using Matlab® software according to extraction constant, Fick's law, and diffusional principles. The model predicts the overall mass transfer coefficient (Korg) to be 3.84 cm/s. Using this value, diffusion coefficients (Dm) for various Cyanex 923 concentrations of 0.126, 0.252, 0.378, 0.505, 0.631 and 0.757 mol/L are found to be 8.50×10-4, 4.30×10-4, 1.87×10-4, 5.87×10-5, 2.57×10-5, 2.09×10-5 cm2/s, respectively. The results show that the diffusion rate of the current study is approximately more than that of similar FSSLM systems containing Cyanex 923 used to transport various metals. The modeling values are in good agreement with the experimental data, showing the good reliability of the mathematical model.Peer ReviewedPostprint (author's final draft

A comprehensive review on the applications of coal fly ash

Coal fly ash, an industrial by-product, is derived from coal combustion in thermal power plants. It is one of the most complex anthropogenic materials, and its improper disposal has become an environmental concern and resulted in a waste of recoverable resources. There is a pressing and ongoing need to develop new recycling methods for coal fly ash. The present review first describes the generation, physicochemical properties and hazards of coal fly ash at the global level, and then focuses on its current and potential applications, including use in the soilamelioration, construction industry, ceramic industry, catalysis, depth separation, zeolite synthesis, etc. Finally, the advantages and disadvantages of these applications, themode of fly ash utilizationworldwide anddirections for future research are considered

A review of the alumina recovery from coal fly ash, with a focus in China

Coal fly ash, an industrial by-product, is derived from coal combustion in thermal power plants. It is one of the most complex and abundant of anthropogenic materials and its improper disposal has become an environmental concern and resulted in a waste of recoverable resources. Coal fly ash is rich in alumina making it a potential substitute for bauxite. With the diminishing reserves of bauxite resources as well as the increasing demand for alumina, recovering alumina from fly ash has attracted extensive attentions. The present review first describes the alumina recovery history and technologies, and then focuses on the recovery status in China. Finally, the current status of fly ash recycling and directions for future research are considered

The influence of Ferro-silicon addition on the reduction and sulfurization of co, cu and Ge- bearing smelter slag with carbon and calcium Sulfate

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New challenges and applications of supported liquid membrane systems based on facilitated transport in liquid phase separations of metallic species

The linear economic model based on "take-make-dispose" has become unsustainable, revealing the necessity of shifting towards a circular economy (CE) approach, in which secondary raw materials play a key role in closing material cycles. In this context, industrial effluents with metallic content, are considered a potential secondary source for these elements, the lack of the availability of the appropriate technology being the main barrier when implementing circular economy principles at industrial scale. In this regard, supported liquid membrane (SLM) systems based on facilitated transport may be decisive. Thus, the objective of this research paper is to show the potential of facilitated transport systems to foster the transition to a more sustainable management of industrial metallic effluents. To accomplish that, three different applications of supported liquid membrane systems in acidic industrial effluents will be presented: a) Zn/Fe separation, b) Ni/Cd separations and c) Removal of hexavalent Cr. Additionally, the recovery and separation of two different critical raw materials, i.e. Li and rare earth elements will be discussed. Although facilitated transport systems have been successfully applied to both, Zn/Fe and Ni/Cd separation, as well as to hexavalent Cr removal, further work should be done for the successful recovery and separation of Li and rare earths with supported liquid membrane systems, especially in terms of selectivity improvement and validation with real industrial effluents.Financial support from the Spanish Ministry of Science, Innovation and Universities under the projects PID2020-115409RB-I00 and RTI2018-093310-B-I00 are gratefully acknowledged

A Novel Method of using Iron Nanoparticles from Coal Fly Ash or Ferric Chloride for Acid Mine Drainage Remediation

Iron nanoparticles (nano Fe) were extracted from coal fly ash (CFA) or ferric chloride (FeCl3) and used for acid mine drainage (AMD) remediation. Characterization was achieved by X-ray diffraction (XRD), X-ray fluorescence, scanning electron microscopy-energy dispersive spectroscopy (SEM–EDX), high resolution transmission electron microscopy (HRTEM), and the Braunaer–Emmet–Teller (BET) surface area determination. The HRTEM indicated good dispersion of the characteristic bead-like structure of nano Fe. It was also observed that the nano Fe were mainly in the zero-valent oxidation state, as denoted by the characteristic peak at ≈ 44.7° in the XRD analysis; it was accompanied by the generally accepted oxide layer around the particles, which was confirmed by the appearance of a core–shell structure in the HRTEM micrographs. The BET surface areas of the nano Fe extracted from the CFA or FeCl3 were recorded to be 34.7 or 88.8 m2/g, respectively. The nano Fe lowered the concentration of most of the monitored contaminants, with the percentage removal ranging from 17 to 99%. The pH of the AMD after treatment with nano Fe obtained from CFA or FeCl3 increased to 5.74 or 6.01, respectively, from 3.49, the electrical conductivity decreased to 0.18 or 0.13 Ω/m, respectively from 0.57 Ω/m, while the total dissolved solids was decreased to 447 or 384 mg/L, respectively, from 1683 mg/L. The water quality of the treated AMD is suitable for Category 4 industrial use, per the Dept. of Water Affairs and Forestry\u27s limits