Abstract
Divalent europium ions were produced from trivalent lanthanide solution by using a flow-through porous graphite electrode. The reduction of Eu(III) was investigated by varying the composition of electrolyte, flow rate and applied current in an electrochemical system with recycle. Increasing the ratio of lanthanide to europium content and the flow rate favoured the rate of reduction and improved the efficiency. High current efficiency was obtained by applying high current. Evolution of hydrogen and reoxidation of the reduced europium caused reduction in the current efficiency.A mathematical model was developed to describe the electrochemical system, the values obtained from the model computation compared closely with experimental results.
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Abbreviations
- a :
-
specific surface area of the electrode (cm2 cm−3)
- A :
-
geometrical cross-sectional area of the electrode (cm2)
- C(x,t) :
-
reactant concentration at electrode positionx and instant timet (mol cm−3)
- C′ :
-
product concentration (mol cm−3)
- E 0 :
-
electrode potential (V)
- f :
-
ratio factor
- F :
-
Faraday's constant (96 487 C mol−1)
- i :
-
subscript noted as initial state
- I a :
-
applied cell current (A)
- I l :
-
limiting current (A)
- J :
-
mass flux from bulk electrolyte to electrode (mol cm−2s−1)
- k :
-
rate constant of the zero order reaction (mol cm−3 s−1)
- k a :
-
apparent mass transfer coefficient,k m a (s−1)
- K m :
-
mass transfer coefficient (cm s−1)
- L :
-
electrode thickness (cm)
- Q :
-
flow rate of electrolyte (cm3s−1)
- R :
-
chemical reaction rate (mol cm−3 s−1)
- R t :
-
conversion factor,R t = 1 - exp (-k mαAL/Q)
- T :
-
superscript noted as total Eu
- TRE :
-
total rare earths (lanthanides) concentration (M)
- t :
-
instant time (s)
- u :
-
electrolyte flow velocity,u=Q/A (cm s−1)
- V :
-
volume of reservoir (cm3)
- x :
-
geometrical location of the electrode
- ε:
-
porosity of the electrode
- \(\bar \eta\) :
-
overall mean current efficiency, (Equation 11)
- τ:
-
residence time,V/Q (s)
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Hung, T.M., Lee, C.J. Electrochemical reduction of Eu(III) using a flow-through porous graphite electrode. J Appl Electrochem 22, 865–871 (1992). https://doi.org/10.1007/BF01023731
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DOI: https://doi.org/10.1007/BF01023731