Browsing by Issue Date, starting with "2019-09-13"
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- Hydrometallurgical approach for recovery of pgms from spent automobile catalytic convertersPublication . Piedras, Francisco Javier vega; Paiva, Ana Paula; Costa, Maria ClaraThe recovery of platinum-group metals (PGMs) from secondary sources, such as spent devices like automobile catalytic converters (ACC), has been gaining interest in the last decades due to their scarcity in the earth crust and their high demand. Their extended applications among different industries, together with their difficulty to be replaced by other materials, has created the urge to develop new technologies for PGMs recovery that can help with the supply requirements, while being environmentally friendlier than the existing processes. Hydrometallurgical techniques represent a possible strategy to recover PGMs and avoid the high energy consumption of smelting processes in pyrometallurgical plants. In this study, a hydrometallurgical approach was adopted, starting with a leaching step for the solubilization of the metals into an aqueous phase, employing the use of an oxidizing agent for the formation of metal chlorocomplexes, thus facilitating their dissolution; after this, the recovery of PGMs was intended by using a solvent extraction (SX) step with appropriate extractants, to transfer the selected metals into a more purified aqueous phase, from which the PGMs recovery and transformation into forms with commercial interest would be easier. Two spent ACCs were collected (H98 and I95), and their initial metal compositions were evaluated by an X-ray fluorescence (XRF) analysis. Two different elemental compositions were found, leading to a separate treatment of each sample. In the first stage of the work, the leaching process, the most relevant variables such as temperature (°C), acid concentration (M), L/S ratio (L/kg), time (h), stirring (min-1) and particle size (mm) were evaluated experimentally and through a factorial design methodology (FDM), to establish the individual and joint contributions of the relevant parameters to the leaching efficiency. As a result, the optimised conditions for the leaching of both catalyst samples were T= 60 ºC, [HCl]= 11.6M, L/S= 2L/kg, t= 3h, stirring= 250 min-1, and particle sizes Dp=0.397mm and Dp=0.409mm for H98 and I95, respectively. The FDM treatment showed that time represented the most determinant parameter in terms of leaching efficiency for the H98 sample. For the I95, time, temperature, acid concentration, and the pair time-temperature were the main interactions to be considered, according to the FDM, in order to obtain a higher efficiency of the leaching process. For the second step, the SX, four commercial compounds and/or mixtures (tributyl phosphate (TBP), Cyanex® 471X, trioctylphosphine oxide (TOPO) and Adogen® 464), and one ionic liquid (Cyphos® 101), were employed as extractants, using toluene as diluent. The concentrations of each extractant were calculated according to the concentration of the targeted metals in the solutions. The first part of the SX step was the development of a scheme for each sample using model solutions, prepared with the metals expected to be in higher concentrations in the real leaching solutions obtained. The results achieved with the model solutions showed that the appropriate SX scheme, when using traditional extractants, would involve an approximate 6M HCl concentration for the aqueous phases and the use of TBP to remove Fe(III) in the first extraction, followed by an extraction with Cyanex® 471X to remove Pd(II). In the third extraction, TOPO could be used to remove Pt(IV), and the final extraction could be carried out with Adogen® 464 to remove Rh(III). The above loaded organic phases were subjected to a stripping procedure, to transfer the metals to new aqueous phases and to evaluate the reusability of the organic solutions. The stripping agents chosen were: a 0.1M HCl solution to strip Fe(III) from TBP, a stabilized 1M Na2S2O3 solution to strip Pd(II) from Cyanex® 471X, and a 0.4M malonic acid solution to strip Pt(IV) from TOPO. Due to the low content of Rh(III) in the solutions, the decision of not stripping this metal from Adogen® 464 was taken. Regarding the application of the ionic liquid Cyphos® 101 for the SX of the model solutions, it was found that Pd(II), Pt(IV) and Fe(III) were quantitatively extracted from both 3M and 6M HCl solutions. Two stripping agents were tested, e.g., a 0.1M KSCN to remove Pt(IV), and a 0.1M CH4N2S in 5% v/v HCl to strip Pd(II). Finally, the SX schemes previously developed were tested in the real leaching solutions for each catalyst, and a completely different behavior was found. The extraction and stripping efficiencies were very low compared to the results from the model solutions. This unexpected behavior is attributed to the complexity of the real leaching solutions, to the large number of metals involved that were not considered for the composition of the modelsolutions, and to possible interactions of the extractants with those unanalysed metals
- Exploring agricultural waste as raw material for the production of bioflocculantsPublication . Kebede, Eyob Mulugeta; Costa, Ana M. Rosa da; Teixeira, Margarida RibauPlant derived materials can be applied in water clarification since they reduce the use of chemically based coagulants. This study aims to evaluate the use of powders (particle size ≤ 0.5 mm) of pine needles, spent coffee ground, almond shell and banana tree bark, as well as their extracts, as coagulants for municipal wastewater treatment, in order to remove turbidity. A representative model municipal wastewater was synthesized in the laboratory, presenting a turbidity ranging from 50 to 130 NTU. Jar-tests were performed using this model synthetic wastewater and either a commercial aluminum-based coagulant-flocculant, for comparison purposes, or the prepared materials. As results showed no turbidity removal, banana tree bark powder was physically and physico-chemically treated in order to obtain suspensions of cellulose microfibrils. Both the powder and the microfibrils were chemically modified by reaction with glycidyltrimethylammonium chloride (GTMAC). These materials were tested as coagulant-flocculants to check their potential on turbidity removal. Physico-chemically treated banana tree bark powder with particle size between 25 and 100 μm showed a modest result, with a turbidity removal efficiency of 36.5%. Finally, the GTMAC cationized cellulose microfibrils removed 78.8% of the synthetic wastewater turbidity. When this coagulant was tested in a real wastewater, the result was quite similar, as 79.7% of turbidity was removed.
- Recovery of metals from highly concentrated acid mine drainage by liquid-liquid extractionPublication . Melka, Alemu Bejiga; Costa, Maria Clara; Carliar, JorgeThe growing consciousness and anxiety about the environment have motivated in the recent years extensive research aiming to develop new efficient technologies for the acid mine drainage (AMD) remediation. Such type of pollution is considered of serious concern because of its acidic nature (pH ranges around 2–4), and high concentrations of metals and sulfate. The AMD collected from the inactive São Domingos mine, Portugal for this work has the following concentrations of: 55.2 ± 0.4g/L Fe, 2.60 ± 0.03g/L Zn, 6.2 ± 0.1g/L Al, 4.60 ± 0.07g/L Cu and 123.9 ± 0.2mg/L Mn and 157.2 ± 3g/L of SO42-. The recovery of largely used metals such as, copper, zinc and iron, from this type of highly concentrated AMDs is still eco-unfriendly and expensive, thus new recovery strategies should be investigated. In this study, liquid-liquid extraction (LLE) process, involving commercial industrially known extractants and new extractants were tested for the recovery of copper, iron and zinc from the AMD collected at São Domingos mine. Accordingly, the extraction of copper by ACORGA M5640 and the subsequent stripping of the metal with H2SO4 solution were optimized. The results revealed that copper can be extracted from such AMD by 30% (v/v) ACORGA M5640 diluted in Shell GTL, making an 8/1 ratio of its active compound (5-nonyl-2-hydroxy-benzaldoxime) to copper ions, with an efficiency of 96 ± 3%. Copper was then efficiently stripped (95 ± 2%) from the metal loaded organic phase with a 2M H2SO4 solution. This organic phase has excellent reuse performance and can be recycled at least 5 times, according to this work and potentially much more times. Its maximum loading capacity of copper from AMD was determined to be 16.15 g/L and the accumulation of copper in the stripping solution in successive cycles reached 46 ± 3 g/L. After copper extraction, iron was successfully extracted from AMD 94 ± 2%) by an ionic liquid diluted in kerosene containing ions from Aliquat 336 and from Cyanex 272 (ALiCY) both in a 3/1 ratio to iron ions to prevent further iron co-extracted with zinc. Complete stripping of Fe (96 ± 2%) was achieved using also a 2M H2SO4 solution. As an alternative, it was confirmed that iron can be simply removed from AMD by adjusting the pH to values between 5 and 6. Concerning the subsequent recovery of zinc, 52 ± 2% was extracted using a synergistic mixture of 80% D2EHPA and 20% Cyanex 272 (with 18/1 and 4.5/1 ratios to zinc ions, respectively) diluted in kerosene with 3% Tributyl phosphate (TBP), and 99 ± 2% of this metal was then stripped from such organic phase once again with 2M H2SO4.
- Recovery of zinc from metal-plating industrial wastewaters by liquid-liquid extractionPublication . Sathityatiwat, Suthapat; Costa, Maria Clara; Carliar, JorgeThe extraction of zinc(II) from zinc-plating wastewater by liquid-liquid extraction was studied using the commercial extractants di-(2-ethylhexyl)phosphoric acid (D2EHPA) and bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex® 272), as well as the ionic liquids, Trihexyltetradecylphosphonium bromide (Cyphos® 102), Trihexyltetradecylphosphonium decanoate (Cyphos® 103) and Trihexyltetradecylphosphonium bis(2,4,4- trimethylpentyl)phosphinate (Cyphos® 104), diluted in organic solvents. First, the commercial extractants and the ionic liquids with the most potential were selected based on the results from diluents, modifiers and stripping solution screening tests. Then, the optimization of extraction and re-extraction (stripping) conditions for each extractant was achieved either by effluent pretreatment (pH adjustment) to remove iron prior to liquid-liquid extraction or by adjusting the extractant-to-zinc ratio. Afterwards, one commercial extractant and one ionic liquid were selected for further evaluation based on the following parameters: reusability, contact time (kinetic studies), and loading capacity. Of the two commercial extractants, the most promising results were obtained with 20% (w/w) D2EHPA in kerosene and 3% (v/v) TBP (tributyl phosphate) as the modifier after a contact time of only five minutes. The extraction efficiency for zinc was 98%, with coextraction of iron which can be resolved by pre-treating the effluent to pH 5.5 to precipitate iron prior to liquid-liquid extraction. Selective stripping of zinc from the loaded organic phase was achieved using 0.6 M H2SO4. Under these optimized conditions, the reusability of the organic phase was successfully tested in three cycles of zinc extraction and re-extraction without loss of efficiency. Regarding ionic liquids, 0.08 M Cyphos® 102 in kerosene exhibited superior selectivity for zinc extraction (83%), with little to no co-extraction of iron. Despite this high efficiency, an issue of insolubility of Cyphos® 102 in the diluent was observed, with the ionic liquid being in a layer below kerosene. This insolubility issue made decantation difficult, which affected the reusability of the extraction system. However, the issue can be solved with the addition of 3% (v/v) decanol as modifier, but resulting in the decrease in zinc extraction efficiency to 40%. A raise of the concentration to 0.24 M Cyphos® 102 in kerosene with 3% (v/v) decanol allowed a 95% extraction efficiency of zinc with no insolubility being observed. On the other hand, the stripping of zinc from this loaded organic phase was obtained using a high concentration of HNO3 of 2M. Nevertheless, the problem of reusability of the organic phase remained, whereby zinc extraction decreased to 54% and re-extraction decreased to 5% in the second cycle. Therefore, time and effort need to be devoted to future studies to evaluate the application of Cyphos®102 in liquid-liquid extraction of zinc from zinc-plating wastewaters.