Browsing by Author "Melka, Alemu Bejiga"
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- A new application of solvent extraction to separate copper from extreme acid mine drainage producing solutions for electrochemical and biological recovery processesPublication . Nobahar, Amir; Melka, Alemu Bejiga; Pusta, Alexandra; Lourenço, João P.; Carlier, Jorge; Costa, Maria ClaraOver the last decade, AMD waters have gained more attention as a potential source of metals due to the emerging need to recover or recycle metals from secondary resources. Metals recovery supports sustainability and the development of a circular economy with benefits for resource conservation and the environment. In this study, five extractants (Acorga M5640, LIX 54, LIX 622, LIX 622 N, and LIX 864) diluted (15% (v/v)) in Shell GTL with 2.5% (v/v) octanol were compared and evaluated for Cu recovery from an extreme AMD sample (5.3 +/- 0.3 g/L Cu) collected at the inactive Sao Domingos Mine in the Iberian Pyrite Belt of Portugal. Of the five extractants, Acorga M5640 showed the best selective efficiency. Further tests showed that 30% (v/v) of this extractant was able to selectively extract approximate to 96.0% of the Cu from the AMD in one extraction step and all of the remaining Cu (to below detection) in three steps. Among the different stripping agents tested, 2 M sulfuric acid was the most efficient, with approximate to 99% of the Cu stripped, and the recyclability of the organic phase was confirmed in five successive cycles of extraction and stripping. Furthermore, contact time tests revealed that the extraction kinetics allows the transfer of approximate to 97% of the Cu in 15 min, and aqueous to organic phase ratios tests demonstrated a maximum loading capacity of approximate to 16 g/L Cu in the organic phase. Raising the concentration of Cu in the stripping solution (2 M sulfuric acid) to approximate to 46 g/L through successive striping steps showed the potential to recover elemental Cu using traditional electrowinning. Finally, a biological approach for Cu recovery from the stripping solution was evaluated by adding the supernatant of a sulfate-reducing bacteria culture to make different molar ratios of biogenic sulfide to copper; ratios over 1.75 resulted in precipitation of more than 95% of the Cu as covellite nanoparticles.
- 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.
- Zinc recovery from an extreme copper-free acid mine drainage: studying the prior separation of ferric iron by solvent extraction using AliCy and/or alkalinizationPublication . Nobahar, Amir; Melka, Alemu Bejiga; Marín-Beltrán, Isabel; Neves, Luiz; Costa, Maria Clara; Dias Carlier, JorgeZn recovery attempts from a copper-free extreme Acid Mine Drainage with similar to 53 g/L Fe and similar to 2 g/L Zn revealed Fe co-extraction in solvent extraction with 0.9 M D2EHPA or a mixture of 0.72 M D2EHPA and 0.18 M Cyanex 272, and simultaneous precipitation of Fe during zinc sulfide recovery through biogenic sulfide addition. Therefore, alkalinization, solvent extraction with the self-prepared ionic liquid AliCy diluted in kerosene, and combinations of both these methods were studied for the separation of ferric iron (Fe3+) from such water, prior to Zn recovery. The most efficient strategy tested was a solvent extraction cycle with AliCy followed by alkalinization of its aqueous raffinate to pH 3.25 or 3.5. As a result of this approach, similar to 92% of Fe3+ is separated by SX and the remaining is removed by precipitation, with just similar to 12% or similar to 17% Zn losses, respectively. Afterwards, the highest Zn recovery from water resulting from such combination of processes was achieved by precipitation through addition of biogenic sulfide at pH = 3.5. The obtained precipitates are nanoparticles of Wurzite and Sphalerite (ZnS) of sizes between 2 to 22 nm agglomerated into larger structures. This work shows for the first time the potential of AliCy to separate Fe3+ from acidic multimetallic solutions, a known contaminant of several metal recovery processes.