Solvent Extraction Techniques

Solvent Extraction

• Solvent extraction is a method that separates chemical substances in a mixture or solution.
• It achieves this by transferring a specific component from one liquid phase to another based on its solubility.
• The process targets retrieving one or more desired constituents from a mixture.
• It's also useful for mixture purification and removing interfering elements.

Types of Mixtures

• Solid in Liquid Mixtures

• Homogenous: Components uniformly distributed

• Evaporation: Removing solvent through heating

• Distillation: Separating components by boiling point differences

• Centrifugation: Separating components by density differences

• Heterogenous: Components unevenly distributed

• Sedimentation/Gravitation: Separation based on density differences

• Filtration: Separating solids from liquids

• Magnetic Separation: Separating magnetic components

• Fractional Distillation: Separating miscible liquids using a more effective distillation technique

• Liquid in Liquid Mixtures

• Homogenous: Components uniformly distributed

• Simple/Fractional Distillation: As described in homogenous solid-liquid mixtures, this involves heating and condensing liquid(s) based on differing boiling points

• Chromatography

• Electrophoresis

• Heterogenous: Components unevenly distributed

• Partitioning: Separating components through separation funnels

Solvent Extraction Process

• A process for separating compounds based on their differing solubilities in different liquids.
• Relevant properties of compounds impacting solubility include polarity, size, mass, density as well as chemical similarities and differences

Quality Considerations

• Quality of the extracted material is essential in many industries, including:
• Mining
• Food processing
• Research labs

Solvent Extraction Example

• Separation of Benzoic acid and p-methoxyphenol.
• The process involves:
• Mixing the mixture in a separating funnel.
• Adding saturated sodium bicarbonate solution.
• Shaking and equilibrating the funnel.

Aqueous Solvents

• Factors to consider when choosing aqueous solvents:

• Purity

• Suitable additives to improve the desired characteristics

• Ensuring the analyte becomes less hydrophilic and more hydrophobic through dissolution

• Different solvents (acids, bases, high-ionic strength solutions, complexing/ion-pairing/chiral agents) needed for various purposes

Organic Solvents

• Factors to consider when choosing organic solvents:
• Immiscibility: Unmixable with water and other solvents
• Density
• Volatility
• Toxicity
• Polarity: matching desired component/s
• Cost

Solvent Extraction Theory

• Solvent extraction is based on the selective transfer of solute.
• The extraction process relies on the differential solubility of components in the different phases.
• Distribution/partition coefficients (KD) are key parameters determining the equilibrium distribution of the solute between two immiscible phases.
• The process is governed by the Nernst partition law

Extraction Efficiency

• Efficiency depends on the distribution ratio (D) and the relative volumes of the liquid phases.
• Calculations determining the extent of extraction, including multi-stage extractions
• Percentage extraction calculations

Selectivity in Extraction

• Partial extraction of other components alongside the targeted one may occur.
• The separation factor (β) helps determine separation efficiency between components.

Extraction of Uncharged Metal Chelates

• Use of organic solvents to extract uncharged metal chelates.
• The reagent needs to behave as a weak acid.
• The presence of hydrophobic groups reduces the aqueous solubility of the complex.

Extraction of Ion-association Complexes

• Extracting charged components by neutralizing the charge with chelation or by association with other ions.
• Formation of stable complexes essential for achieving extraction.

Methods of Extraction

• Batch Extraction: Simplest method; mixing phases, allowing separation, repeating as needed.

• Continuous Extraction: Recycled solvent, more efficient for smaller distribution ratios, requires more complex apparatus