24 Questions
What is the distribution ratio D of Cu in the given system?
6
What is the percentage extraction of Cu in the given system?
75%
What is the mass balance equation for multistage extraction?
Va xo + Vo yn+1 = Va xn + Vo y1
What is the assumption made in deriving the operating line equation?
yn+1 = 0 and xn = 0
What is the equation for the fraction remaining after n stages of extraction?
xn / xo = (E - 1)^n
What is the graphical procedure used to analyze multistage extraction systems?
McCabe-Thiele Diagram
What is the definition of the extraction factor E?
E = D × (Vo / Va)
What is the relationship between the distribution ratio D and the extraction factor E?
D = E
What is the primary advantage of using Counter Current Extraction in industrial leaching processes?
It can deliver the highest possible concentration in the extract.
What is the assumption made in the mass balance equation for Single Batch Counter Current Extraction?
There is no volume change on mixing.
What is the expression for the extraction factor E in terms of V0 and Va?
E = V0 y1 / Va x1
What is the equation for the fraction extracted in a Single Batch Counter Current Extraction process?
V0 y1 / Va x0 = E (E + 1)
What is the purpose of the decanting step in the extraction process?
To allow the phases to coalesce and separate.
What is the distribution ratio in a Single Batch Counter Current Extraction process?
y1 / x1
What is the expression for the mass balance in a Single Batch Counter Current Extraction process?
Va x0 + V0 y0 = Va x1 + V0 y1
What is the concentration of Cu in the leach liquor in the worked example?
4g/l
What is the main purpose of drawing 'steps' between the operating line and the equilibrium curve in a McCabe-Thiele Diagram?
To calculate the number of theoretical stages required for extraction
What is the effect of not attaining equilibrium conditions on the extraction process?
It requires more stages in practice than the ideal analysis
What is the main factor that affects the equilibrium curve in a McCabe-Thiele Diagram?
All of the above
What is the purpose of an extraction isotherm in a McCabe-Thiele Diagram?
To plot the metal extraction in the aqueous and organic phases
What is the main advantage of using a mixer-settler or a series of mixer-settlers in solvent extraction?
It is well established with hundreds of operating units
What is the effect of partial miscibility of the solvents on the separation process?
It requires more stages in practice
What is the main purpose of a McCabe-Thiele Diagram?
To predict the number of theoretical stages necessary to achieve given levels of extraction
What is the main advantage of using a column as a solvent extraction equipment?
It can be agitated or pulsed
Study Notes
Solvent Extraction
- The final concentration of Cu in the oil phase and aqueous phase are 6g/l and 1g/l respectively, with volumes of 4 and 8 litres respectively.
- The distribution ratio (D) is 6g/l / 1g/l = 6.
- The percent extraction is 100(6 × 4 / (4 × 8)) = 75%.
Multistage Extraction
- Fresh solvent and metal in fresh solvent plus metal in aqueous solution equals metal in loaded phase plus metal in raffinate.
- Va xo + Vo yn + 1 = Va xn + Vo y1.
- Assuming metal content in fresh solvent and barren solution is near zero, Va y1 = (xo - xn) / Vo.
Operating Line
- y1 = (xo - xn) / Vo.
Fraction Remaining
- After n stages, xn / xo = (E - 1) / (E^n + 1).
McCabe-Thiele Diagram
- A graphical procedure used to analyze systems, where each phase coalesces and separates by decanting.
- Rarely used in commercial processes due to large solvent volume and low solute concentration.
Counter Current Extraction
- Frequently used in industrial leaching to deliver high concentrations in the extract and minimize solvent needed.
- The solvent phase becomes concentrated as it contacts the solute-rich solid in a stagewise fashion.
- The raffinate becomes less concentrated in soluble material as it moves toward the fresh solvent stage.
Single Batch Counter Current Extraction
- A process where fresh solvent and fresh feed are used, with equilibrium reached in each stage.
- A mass balance is calculated as Va x0 + V0 y0 = Va x1 + V0 y1.
Mass Balance
- Metal in fresh solvent plus metal in aqueous solution equals metal in loaded phase plus metal in raffinate.
- Va (xo - x1) = V0 (y1 - y0) = V0 y1 (when y0 = 0).
- Extraction factor (E) = V0 / Va.D, and fraction extracted = E / (E + 1).
Worked Example
- A copper leach liquor containing 4g/l of Cu is subjected to solvent extraction using LIX 84 dissolved in kerosene.
- The number of theoretical stages (n) is found by drawing steps between the operating line and the equilibrium curve.
McCabe-Thiele Diagram
- Consists of an extraction isotherm and the operating line drawn on the same diagram.
- Enables prediction of the number of theoretical stages necessary to achieve given levels of extraction in a counter-current process.
Extraction Isotherm
- Obtained by plotting metal extraction in the aq phase (x-axis) and the organic phase (y-axis).
- The equilibrium isotherm is specific for every particular system and changes with temperature, pH, and concentrations of extractant or metal.
Calculate the distribution ratio and percent extraction of Cu in an oil and aqueous phase system, given the concentrations and volumes of the phases.
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