Amna Solvent Extraction PDF

# Methods of Extraction ## Counter Current Extractions - Multistage technique consisting of series of tubes. Separation is done on bases of density difference. - Denser phase enters from the top, while the lighter phase enters from the bottom (counter current). Separation is based on distribution...

# Methods of Extraction ## Counter Current Extractions - Multistage technique consisting of series of tubes. Separation is done on bases of density difference. - Denser phase enters from the top, while the lighter phase enters from the bottom (counter current). Separation is based on distribution ratio. e.g. Mixer settler - Less time to set. - Less mixing chances, efficient method. - Multiple tubes used. - Multi analyte extract. - In industries, continuous extraction used, then due to mixing problems, counter current then used. ## Process of Extraction Systems - By chelate extraction - By Solvation - By ion-pair formation - By Synergic extraction ## Methods of Extraction ### Batch Extractions - This extraction occurs either in a single step or in stages to extract analytes from a sample. The feed solution is added in parts. - When one process is completed, the solvent and extracted substances are removed, and a new batch begins. - It’s used in laboratories for smaller-scale extraction. e.g. separating funnel ### Continuous Extractions - In this, the solvent is constantly added, that passes through the mixture continuously. - As the solvent flows, it extracts the analyte. - The process keeps going without stopping. - It's more efficient for large-scale processes. e.g. Soxhlet extractor. ## Chelate Extraction - Example: Extraction done by the formation of chelates and structure with specific methods. ## Solvation and Solution - Solvent molecules surround and interact with solute molecules. This interaction stabilizes the solute particles in the solvent and facilitates dissolution. - Forces such as H-Bonding, ion-dipole interactions and Van der Waals forces aid in the process. - If water is the solvent, the process is called hydration. - **Extractability of neutral or organic solutes:** - **Non-Chelateds:** Bulky cations or anions - Aggregate - Extracted by system. e.g. Phuasch + MnO₄ = Phuasl + MnO₄^- - **Chelated:** Solubility in organic solvents, making them readily extractable: - Fe (o-Phe)₃ 2ClO₄ - BuN₄ VO₂(Ox)₂ - **Oxonium systems:** Oxygen containing solvents with strong coordination with oxonium cation - Extracted in slight acidic medium e.g. [(C₂H₅O)₂]H (H₂O) FeCl₃. ## Estimation - Estimation in fruits, vegetables - Examples: - 8-hydroxyquinoline - Nickel Estimation - Di1G - Nickel Estimation - 1-Nitroso-2-Naphthaliron - Estimation - Cupferron - Capturing strength (maximum donor atoms) - Copper Estimation - Strength of Chelating agent - Electronegativity of donor atoms: - High E-N - Maximum - Small ring size - It reduces steric effect. Carbon or benzene ring is arranged well. - Ring Size: Either singly, doubly charged, stability (φ) systems. - Nature of Metal ion - Ionization potential (5-6 member system) - Resonance or steric effect: if E-N is low & resonance is high then chelating agent resonates itself and does not capture metal ion. - Best chelating is that which gives resonance stability to complex after incorporating metal ion. ## Major Applications of S.E in Industries 1. Hydrometallurgy 2. Extraction of U²³⁵ & U²³⁸ in Nuclear Power Plants. 3. Biofuel separation. 4. Waste water treatment. - Metal Anionic complexes in strong acid can be extracted in such solvents: ((C₂H₅)₂O).HO.FeCl₃ - Solvent extraction differs from traditional extraction methods in several ways, including: - It uses less solvent. - It's more efficient than others. - It can be repeated multiple times without adding fresh solvent. - It's automated and less labor intensive. - It's faster than others. - S.E. (Soxhlet extractor) limited to boiling solvents because solvent vaporization and condensation are essential to the process. - Soxhlet extractor is time-consuming because it involves repeatedly washing a solid sample with solvent over a long period of time. (12-24 hours) - **Spray column** is the oldest technique for solvent extraction. - **Solvent extraction** is not a membrane separation technique. - **Extractable complexes** - **Ion-association system** - Extraction of charged species from aqueous solutions is not possible unless it is neutralized by chelation or association with other ionic species of opposite charge to form a complex which is electrically neutral. At least one of the ions should contain a bulky hydrophobic group to aid extraction. - Non-chelated complex - These include simple ionic extraction systems in which bulky cations or anions are extracted as pairs or aggregates without further coordination by solvent molecules e.g. Fe(oph)₃²⁺, BuN₄⁺ UO₂(OX)₂^2-, PhuAsl + MnO₄^- = PhuASTyNO + ct^-. - They are more stable and neutral, which enhances their extractability. - Chelated: Solubility in organic solvents making them readily extractable: - Fe (o-Phe)₃ 2ClO₄ - BuN₄ VO₂(Ox)₂ - Oxonium systems: Oxygen containing solvents with strong coordination with Oxonium cation - Extracted in slight acidic medium. e.g. [(C₂H₅O)₂]H (H₂O) FeCl₃. ## MCQs - **Dispersed phase:** Refers to the phase that is distributed throughout another dispersing medium (salutes). - **Major problem of settler is emulsification in mining:** When agitation is very intense the size of the particle reduces to 1 to 1.5um. - **S.E. is a quantative separation of a compound:** - Compared with other separation methods, S.E. gives a better separation effect than chemical precipitation and a higher degree of selectivity and faster mass transfer than ion exchange methods. - Compared with distillation, S.E. has advantages such as low energy consumption, larger production capacity, fast action, easy continuous operation, and ease of automation. - **Effect of resonance on chelate formations:** - Resonance delocalizes the electron density over a ligand and metal ion, strengthening the metal-ligand bond. - If aromatic ligands like 8-hydroxyquinoline benefit from resonance, forming highly stable chelates. - **Steric effect** - Bulky group on a ligand or near metal ion creates spatial hindrances, preventing proper coordination, reducing the strength of chelation. ## Industrial effluents - Safe for reuse, promoting environmental sustainability. - **Biogas Extractions:** S.E. separates methane from raw biogas. By using solvents like amine solutions or Selexol (non-toxic, high B.P. solvent model of the dimethyl ethers of polyethylene glycol (DEPG)) CO2 and other impurities are removed, producing high-purity methane for renewable energy applications, reducing reliance on fossil fuel. - **Pharmaceutical:** S.E. is used to isolate & purify active pharmaceutical ingredients (APIs) & intermediates and biomolecules. It separates drugs from fermentation broths, crude extracts or reaction mixtures. - **Biochemistry:** It extracts proteins, lipids and nucleic acids, by leveraging their solubility difference like DNA extraction with phenol-chloroform or lipid isolation using hexane, ensuring high-purity products for research and production. - **Nuclear power plants:** S.E. is employed to separate uranium isotopes, particularly U235 & U238, which are crucial for nuclear fuel. Processes like PUREX method uses tributyl phosphate (TBP) dissolve in kerosene to extract uranium and plutonium from spent nuclear fuel. This process not only supplies enriched uranium to reactors but also helps to manage radioactive waste - **Biofuel separation:** The biofuel industry uses solvent extraction for purifying biodiesel (biofuel, made from vegetable oils and animal fat, used in pure form as biofuel additive to reduce the level of particulates, carbon monoxide and hydrocarbons from diesel-powered vehicles) and bioethanol (alcohol, made from carbohydrates fermentation, used in pure form as a gasoline additive to increase octane and improve vehicle emissions). It removes impurities such as glycerol, water and catalysts from biodiesel and separates ethanol from fermentation broths. For instance, hexane is used to extract lipids from algae for biodiesel production. - **Wastewater treatment:** Wastewater treatment, S.E. effectively removes hazardous substances like heavy metals (Chromium, Cadmium) and organic pollutants from industrial effluents, ensuring treated water safe for reuse, promoting environmental sustainability - **Solute, reducing risk of contamination in downstream processing:** - **Synergic attractions:** It is the use of multiple extractants that work together to enhance solute transfer into the organic phase. It increases extraction efficiency and often improves the stability of extracted complexes. e.g. Crown-II with picrolomic acid and benzo-15-crown-5. - **Variation of oxidation state:** Changes in oxidation state of a solute alter its chemical behavior and extractability. So, it should be stabilized. e.g. Fe³⁺ changes its oxidation state and becomes Fe²⁺, which is easily extracted than Fe³⁺. It is stabilized by adding SO₂^-. - **Industrial applications of solvent extraction:** - Hydrometallurgy: Hydrometallurgy, it's used to extract and refine metals from ores or recycled materials. Metal ions are typically dissolved in an aqueous solution and selectively transferred to an organic solvent using specific extractants. e.g. Copper is extracted using Lix reagent while rare earth metals are separated for high-tech applications, offering cost-effective and energy-efficient alternatives to pyrometallurgy that does extract metals from ores and other materials, it involves changes physical and chemical properties of materials, allowing for valuable metals. ## Stripping - Stripping is the process of removing extracted solutes from the organic phase back into the aqueous phase. - Efficient stripping ensures the recovery of solute for further processing, influencing the overall extraction cycle. - Commonly used in colorimetric or radioactive methods. e.g. EDTA. - **Salting-out agent:** A salt added to the aqueous phase to reduce the solubility of solutes in water, enhancing its transfer to the organic phase. It aids in extraction efficiency. e.g. Ammonium salts are weaker reagents (they are convenient (extracted in the aqueous phase) while Ammonium and Calcium salts are best). - **Metal complexing agents:** - They selectively bind interfering ions, preventing them from reacting with extractants, thus ensuring purity of the analyte. e.g. fluorides, citrates, tartrates, cyanides, EDTA. - **Backwashing:** It is the washing of the organic phase with the aqueous solution to remove impurities or the quantity of extracted solute. ## Chelate, Solvation, Ion pair, Synergic - **Advantages:** - **Chelates:** Selective for simple molecules, highly effective for challenging extraction, cost-effective. - **Solvation:** Simple for effective species - Trace level, cost-effective. - **Ion Pair:** Enhanced efficiency - Effective at molecules, species - Effective for challenging extraction - **Synergic:** Effective at molecules, species, enhanced efficiency - Cost-effective. - **Limitations:** - **Chelates:** Limited to ions that form neutral or near neutral combinations, requires stable chelates, weakly for polar species, molecules. So is complex. - **Solvation:** Limited to ions that form neutral or near neutral combinations, Requires stable chelates, Weakly for polar species, molecules. - **Ion Pair:** Not effective for neutral combination. - **Synergic:** Requires a combination of extractants. - **Factors affecting extraction efficiency:** - **Choice of solvents:** The organic solvent used for extraction is chosen on the basis of the degree of miscibility, safety, toxicity, flammability, effective separation, reactivity and availability. A suitable solvent enhances solute transfer, increases the distribution coefficient and improves separation efficiency. - **Acidity of the aqueous phase:** The acidity of the aqueous phase affects the ionization of solutes and extractants’ reaction, allowing control of the formation of extractable species e.g., Fe(oph)₃²⁺. - **pH:** The pH variation directly influences metal complexes. - **Coordination complexes:** e.g. Extraction using carboxylic and sulfonic acid for organometallic compounds. ## Comparisions - **Chelate:** Ideal for selective extraction, involves forming combined charges, utilizes 2 extractants, forms stable neutral soluble complex with counterions, that work together to improve the metal ion complex for extraction. - **Solvation:** Simple for effectiveness and selectivity, utilizes neutral molecules. targets only ions that form neutral complex. - **Ion Pair:** Simple for easy transfer to the organic phase and selectivity. It should contain bulky hydrophobic groups to aid extraction. - **Synergic:** Target molecule target ion, Metal ion + chelating agent + extractant = counterion, neutral (primary ligand & secondary ligand), neutral metal complex, neutral ion pair, organic solvents. - **Organic solvents:** Oxygenated, mineral acids, chelates, CCl₄, chlorofromO-solvents. - **Solvents:** - Alcohols or ketones - Ionic compounds - Metal ions - Mostly metal or weakly-polar compounds - Transition or weakly-polar compounds - **Selectivity:** - High selectivity - Moderate selectivity - High selectivity (improved by the combined effect of 2 extractants) - **Heavy metals:** Moderate effect - Target solubility selecting - Loosened counterions - Specific considerations. ## Solvation extraction: - It’s a separation technique that relies on the solubility of neutral molecules or complexes in a solvent. It involves forming a neutral, soluble complex between the target compound and a neutral complexant, which allows the target to dissolve in an organic solvent, while ions, which are already soluble in the aqueous phase, remain in the aqueous phase. - **Extracts:** Neutral molecules with bulky hydrophobic groups using organic solvents like alcohols, ketones, ether esters. - e.g., Extraction of uranium with tributyl phosphate from nitric acid. - Extraction of iodine with diethyl ether from HI. ## Synergic extraction - It is a specialized technique where two or more extractants (solvents or ligands) work together to enhance the efficiency or selectivity of solvent extraction beyond what either could achieve alone. It involves using two or more ligands to bind to the target metal ion, forming a complex that is more stable than the individual complexes. - One ligand may complex with the metal ion while another ligand stabilizes this complex through secondary bonding interactions. This method can significantly reduce the amount of solvent required, improving selectivity and efficiency. - e.g. Extraction of uranium with tributyl phosphate (TBP) as well as 2-thonoyl- trifluoroacetone (TTA). - **Advantages:** - High selectivity: Highly selective for specific targets, very effective for treating radioactive waste, very efficient, handles large volumes of solutions. - Versatility: Different chelating agents can be chosen to target specific metals making the process adaptable to various applications. - **Limitations:** - Potential emulsifications - Risk of forming stable complexes - Can complicate separations. ## Ion Pair formation extractions - Ion pair formation extraction relies on the ability of a positively charged ion to associate with a counterion to form a neutral ion pair complex, allowing it to be extracted into the organic phase. - The counterion is a critical component in this process and its selection is a critical parameter as it must be compatible with solubility properties, along with the target ion, stability, and solubility properties. - Large organic ions - like quaternary ammonium sulfates (for anionic targets) or alkyl sulfonates (for cationic targets) - are commonly used. Non-polar or weakly polar organic solvents dissolve neutral ion pair complexes well, making extraction more efficient. - Examples: Vanadium and Scandium with Trioctylamine from mineral acid. - **Advantages:** - Selective extraction - Highly selective because specific counterions can be chosen to target particular ionic species - Effective for ionic species - Ideal for extracting charged compounds, i.e. ionic drugs, dyes, or certain metal complexes. - **Disadvantages:** - Potential emulsifications - Risk of forming stable emulsions, which can complicate separations. ## Chelates Extraction - It's a method to selectively separate metal ions from a solution using organic ligands called chelating agents. - It is a molecule with multiple binding sites that can form strong bonds with organic ligands. - “Chelates” comes from the Greek word “chela” which refers to the way these organic ligands grab metal ions, forming a ring-like structure that stabilizes the metal within the complex. - This process is particularly useful in fields like analytical chemistry, environmental science, metallurgy, and water treatment where it is often essential to isolate or remove specific metals. - **Steps:** - **Addition of a chelating agent:** The chelating agent is added to the aqueous solution containing metal ions. The agent binds to specific metal ions, forming stable complexes, i.e., the formation of a ring-shaped metal ion and chelating agent complex. - **Formation of the chelate complex:** Metal ions and chelating agent form a ring-shaped structure. This complex is non-polar, making it soluble in an organic solvent. - **Extraction into organic solvents:** The non-metal-chelate complex is then extracted into an organic solvent, separating it from other ions in water. - **Examples:** - Extraction of uranium by 8-hydroxyquinoline in chloroform. - Extraction of iron by cupferron in CCl₄ solvent. - **Density difference: The principle of separation in a mixer settler is density difference** - Heavy heavier or lighter phases refers to the phase that is distributed throughout another dispersion containing solutes (organic solvent) - aqueous phase (continuous phase) - **Major proble of settler in mixing:** When agitation is very intense, the size of the particle reduces to 1 to 1.5um. - **Advantages of using a mixer settler:** - Efficiency/Efficient methods. It allows thorough extraction without needing a large amount of solvent. - Continuous process: Same solvent is reused, saving resources. - Isolation of derived oils. - Oils having limited solubilities are extracted by it. - **Disadvantages:** - Long extraction time. - Large amount of solvent used. - Poor extraction of lipids and their compounds. - High, sensitive compounds degrade due to continuous heating. - Solvent vapors escape from the system if not well-sealed. - **Mixer settler:** It's a type of equipment used in liquid-liquid extraction to separate components based on their solubility in different solutes. - It comprises two compartments: - Mixer compartments: This is where mixing of those liquid phases occurs. It usually contains an agitator to ensure mass transfer between them before the two phases are allowed to settle. - Settler compartments: After mixing, the phases are allowed to settle. This compartment is designed to facilitate the separation of two liquid phases based on their densities, i.e., solvent extraction is used for distillation purposes. - **Expansion adaptor:** Controls pressure to prevent liquid’s backflow. - **Condensers:** It cools the vaporized solvent, converting it back to liquid. - **Cooling water inlet and outlet:** It allows cold water to circulate around the condenser, keeping it cool for effective consideration. - **The working of SOxhlet extractor in a distillation path:** The solvent in the extraction pot is heated, and vapors move up the distillation path, condenses in the condenser, and then drips into Soxhlet thimble containing a sample. As the solvent fills the thimble, it extracts the compound from solid. When it reaches a certain level, the siphon drains the path, containing analyte, the solvent and dissolves analyte compounds back into the heating flask. **Soxhlet Extractor:** - It’s a laboratory apparatus that extracts compounds from a solid material using a solvent. It's useful when a compound has limited solubility in a solvent and requires a large amount of that solvent otherwise the extraction will be incomplete & inefficient. The main purpose is for efficient and continuous extraction of compounds from solid materials. - It utilizes many components including a magnetic stirrer to ensure uniform heating and continuous stirring of the solvent in the extraction pot, an extraction pot, a distillation path, Soxhlet thimble, a porous container, siphon inlet tube, and a condenser - each with essential roles in the process. **Other important notes:** - **Diluents:** These are inert solvents added to primary solvents to adjust properties like viscosity or density in the extraction process. They're vital in helping optimize the extraction system for improved selectivity and easier handling. - **Selectivity of a solvent:** - The solvent should have a high extraction capacity and affinity for the target compound to maximize extraction efficiency. - It should preferentially dissolve the desired substance over others to improve purity. - It should have low viscosity, enabling easier handling, faster phase separation, and better mixing. - The solvent should be immiscible with the extraction medium (usually water) to facilitate phase separation. - Sufficient density difference: A notable density difference between the solvent and the other phase promotes easy separation after extraction. - **Other requirements for a solvent:** - Non-toxic - Non-reactive - Non-explosive - Easily available - Low cost. - **Solvents used in solvent extraction:** - Volatile solvents: These are liquids that evaporate quickly at room temperature due to their low boiling point. - Hexane: Used for aliphatic hydrocarbons. - Benzene: Used for aromatic hydrocarbons. - Ether: Used for polar compounds (having high electron negativity difference) containing Oxygen. - Ethyl acetate: A versatile solvent having efficiency of extraction of a wider range of non-polar to polar compounds. - **Dichloromethane:** A versatile solvent, having efficiency of extraction of wider range of non-polar to polar compounds. - **Difference of solvent extraction and other extraction techniques**: - Solvent extraction separates components based on their differing solubilities in two immiscible liquids, often used in complex matrices (biological, environmental, industrial samples) where other methods like filtration or crystallization are ineffective. - **Purpose of solvent extraction in analytical chemistry:** - **Separation:** Separates components based on their differing solubilities in two immiscible liquids, often used in complex matrices (biological, environmental, industrial samples) where other methods like filtration or crystallization are ineffective. - **Enrichment:** Pre-concentrate analytes present at low concentration. This is crucial for improving detection limits in techniques like chromatography, spectroscopy or mass spectrometry. - **Matrix interference:** It helps isolate target analytes from complex sample matrices, reducing interference from other substances that could affect the accuracy of analytical measurements. - **Differentiation of chemical species:** It allows for the separation of different chemical species based on their solubilities difference. - **Advantages of solvent extraction:** - Simple apparatus used. - Simple and quick separation. - Rapid and quick results. - Convenient and easy to tackle. - Wide scope applications. - **Partition coefficient:** It’s a quantitative description of the distribution of a solute between two immiscible phases. - **Nernst Distribution Law:** It further describes the distribution of solutes between two immiscible solvents. It states that at equilibrium, the ratio of solute concentrations in two solvents is constant, provided the solutes do not associate or dissociate in either phase. - **pH effects:** The distribution of ionic species in acidic or basic environments is influenced by pH of the solution. Nonionizable compounds will exhibit different solubilities at pH levels, enabling selective extractions.