Recovery of metals from Deep Eutectic Solvents Stylianos Spathariotis This project has received funding from the European Union's EU Framework Programme for Research and Innovation Horizon 2020 under Grant Agreement No 721385 https://etn-socrates.eu/
Circular economy of metals M M x+ Thermodynamics of species stability Redox depends on: Ligand type (Applied) potential and concentration MY Metal concentration Y = O, S, As, Te, Se etc Temperature, Stirring 2
SOCRATES project • Project aims to gain value from metallurgical residues • My project is to extract and recover metals from waste using DESs • Electrodeposition and cementation to reduce metal ions https://www.youtube.com/watch?v=9ilrNeKG4D8 3
Deep eutectic solvents Hydrogen bond donor Quaternary ammonium salt Urea – common fertiliser Choline chloride – vitamin in chicken feed HBDs are INEXPENSIVE (£1/kg) Non – toxic Non – flammable Biodegradable Versatile (>10 5 ) Acids, Amides, Alcohols Ethaline 200 Dissolution of salts, metal oxides, polar organics, amino Choline chloride acids, enzymes, surfactants + Ethylene glycol Chem. Comm., 2003, 70 4 JACS, 2004, 126, 9142 Chem. Rev., 2014,114, 11060-82
Electrodeposition Cu Ag Sn Fe Pb Ni • Reversible metals can be electrowon easily with high Co Zn current efficiency • Non-reversible/oxophillic metals – deposition is very dependent on concentration, stirring and temperature Low current efficiency due to film formation. 5 5
Factors affecting metal deposition Zn in Ethaline Temperature Stirring Metal concentration 4 o C 25 0.3M 2 o C 80 3 0 0.1M 0.05M 2 0 2 ) 2 ) 2 ) J (mA/cm J (mA/cm J (mA/cm -1 1 -2 0 -2 -1 Unstirred -4 500 rpm 1000 rpm -2 -3 -6 -1.5 -1.0 -0.5 0.0 -1.5 -1.0 -0.5 0.0 0.5 -1.5 -1.0 -0.5 0.0 E (V) vs Ag/AgCl E (V) vs Ag/AgCl E (V) vs Ag/AgCl Changing experimental parameters can make metals behave in a more reversible way and increase deposition efficiency 6
Cementation Redox potentials Metal in E /V ethaline Cu 2+ + e - ⇌ Cu + 0.39 Fe 3+ + e - ⇌ Fe 2+ 0.29 Zn 2+ Ag + + e - ⇌ Ag 0 -0.15 Zn Cu + + e - ⇌ Cu 0 -0.42 Fe 2+ + 2e - ⇌ Fe 0 -0.59 Ni 2+ + 2e - ⇌ Ni 0 -0.62 M Co 2+ + 2e - ⇌ Co 0 -0.64 Sn 2+ + 2e - ⇌ Sn 0 M n+ -0.64 Pb 2+ + 2e - ⇌ Pb 0 -0.73 Zn 2+ + 2e - ⇌ Zn 0 -1.12 Wide range of metals able to be cemented with sustained deposition 7
Cementation on Zn 0.05 Concentration (M) 0.04 Cementation is a pseudo first order process (diffusion controlled) 0.03 Aqueous cementation → pH < 4 to prevent passivation Fe DES cementation → neutral pH Co 0.02 Ni Sn Ag 0.01 Cu 0 2 4 6 8 10 Time (h) Oxidation of Zn is so fast, it pits the surface and the Ag reduced metal falls off the substrate as a powder. 20 Ag 15 Sn k/ 100 s -1 10 Cu Fe Pb 5 Cementation with Zn not driven solely by thermodynamics Ni Potentially side reactions occur e.g. passivation 0 Co 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 8 E / V
Cementation on Cu Cementation works better on metals which do not passivate Ag 5 mM Substrate S a = 0.45 µm S a = 0.34 µm Cu C A Separated cementation mechanism Ag 20 mM Ag 50 mM S a = 0.50 µm S a = 0.84 µm 9
Metal recovery from Jarosite Electrochemical dissolution of 500 g Jarosite at the anode Recovered by electrowinning & cementation Metal Removal (%) Fe: 63 Pb: 71 Zn: 80 10
Metal recovery from complex mixtures Initial atomic ratio 25 Fe : 1 Pb : 15 Zn Cementation Electrodeposition Ethaline + Oxalic acid Ethaline + Oxalic acid Fe : Zn : Pb Fe : Pb 0.2 : 0.02 : 1 0 : 1 Complexing agents can enhance selectivity 11
Conclusions ✓ DESs can be used for metal deposition ✓ Electrodeposition and cementation are linked to reversibility ✓ Temperature, stirring and metal concentration affect deposition ✓ Efficiency of non reversible metals is low due to passivation ✓ Complexing agents can enhance selectivity ✓ Potentially useful for secondary metal recovery for high value elements e.g. PCBs 12
Acknowledgments This project has received funding from the European Union's • European Union EU Framework Programme for Research and Innovation Horizon 2020 under Grant Agreement No 721385 https://etn-socrates.eu/ • Materials group • Socrates group Interested in my work? Contact me ! st.spatha@gmail.com
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