Purification of Materials Roman Boiko National University of Life and Environmental Sciences of Ukraine, Institute for Nuclear Research, Kyiv, Ukraine

Plan Introduction Classification of purification methods Standard methods of separation Special aspects of high-pure materials production

Introduction Basic statement: all materials could be divided into two groups, pure materials (or chemically individual compounds) and mixture. Wrong. All materials are mixtures Impurities could be divided in two group: Physical (or particle) – solids or liquids in gas, solids in liquids, mixture of solids Chemical – solved in host material molecules and ions Original source of all impurities is nature (subsoil resources, air)

Introduction All purification techniques are based on differences in chemical or physical properties of host material and impurities Chemicals – capability to interact giving new material with other properties Physical – physical form, size, melting point, boiling point, vapor pressure, solubility etc Disadvantages of different purification methods could be: low purity of the most common setups and additional chemicals low productive capacity low end-product yield

Purity grades There are a lot of different purity grades of chemicals in different countries and companies Sigma-Aldrich® standard product quality grades: Technical (purity may be <90%) ReagentPlus ® (purity is ≥95%) ACS reagent (American Chemical Society standards) puriss p.a., ACS reagent (exceeds ACS standards) % purity (defined as a percent purity) TraceSELECT ® (metal traces are below 0.01 ppm) TraceSELECT ® Ultra (trace impurities are below <0.1 ppb) Many chemicals are standardised for a field of utilization: Chromatography, Medicine, Food, Optics, Electronics etc Impossible to find chemicals with standardized radio-purity

Classification of purification methods Crystallization Sedimentation Filtration Distillation Sublimation Adsorption Extraction Zone melting Chromatography (Ion exchange) Electrodialysis Reverse osmosis Electrophoresis Electrolysis Others very specific methods

Separations based on phase equilibrium Gas-LiquidGas-SolidLiquid-LiquidLiquid-Solid Distillation (rectification) Adsorption Sublimation Filtration ExtractionCrystallization Sedimentation Filtration Adsorption Zone melting Ion exchange chromatography

Separations based on properties Initial material Chemical difference Adsorption, Sedimentation, Ion exchange chromatography Physical difference Distillation, Adsorption, Sublimation, Filtration, Extraction, Crystallization, Sedimentation, Zone melting, Final product Chemical purification or transformation Physical purification and separation

Filtration Separation of particle (physical) impurities of different sizes. A porous material is used to separate particles of different sizes. If the pore sizes are highly uniform, separation can be fairly sensitive to the size of the particles Filtration can be applied for separation of… a)solids from gases (e.g. air filtration in clean room) b)solids from liquids (always used together with recrystallization and sedimentation techniques) c)Screening as a kind of “filtration” different size solids through sieves

Filtration Porous materials for filtration: paper, glass, organic polymers, wool etc. Depending on physical properties of mixture and physical form of host material several filtration techniques are applied: Natural filtrationSuction (pressure) filtration

Crystallization A method of purification of solids that based on physical property, solubility. It is the most common laboratory technique Stages: Dissolving of solid substance in a proper solvent Crystallization Filtration Rinsing Drying Final product

Crystallization 1. Solvent should not interact with solid purified, dissolve solid well, be pure, be volatile (for some cases) 2. Crystallization is a solid phase formation from liquid solution. The formed solid usually has the same chem. formula as initial material. This process can be applied as a)cooling saturated solution b)solvent evaporation c)solvent substitution Cr. process has to be slow to obtain macro-crystalline precipitation. It can be accompanied by impurities co-precipitation: host crystals and impurities form isomorphous compounds, absorption on the surface of crystals, heterogeneous insertions of solution inside the crystals

Crystallization 3-4. Filtration and rinsing with different kind of liquids and solutions is applied to remove residual solution from crystalline sample a)pure initial solvent b)solvent that solves only impurities c)another kind of solvent to remove initial solvent d)solutions of different chemicals that decrease crystals’ solubility 5. Drying (annealing, calcination) is to be at lower temperature then decomposition

Sedimentation A method that based on difference in chemical properties of material and impurities. It is very similar to crystallization. Crystals are formed under the chemical reactions, new compounds are precipitated. Stages: Preparation of initial solution Precipitating of host material Precipitating or co-precipitating of impurities Filtration, rinsing and drying of the sediment Filtration of the sediment Final product Recrystallization of the host material

Sedimentation 1. Preparation of initial solution almost the same as for crystallization method 2. Precipitation of host material. Additional chemicals have to be purer then final product. 3. Precipitation of impurities is usually used if there is high concentration of them and obtained compound completely insoluble. Co-precipitation is used at low concentration of impurities. Collector usually forms isomorphous crystals with impurities 4. Filtration, rinsing and drying are the same as for crystallization

Distillation A commonly used method for purifying liquids and separating mixtures of liquids into their individual components. It is based on difference in the boiling points of the components at any given temperature, the vapor pressure of the lower-boiling (lower BP) compound > the vapor pressure of the higher- boiling (higher BP) compound. Thus, the vapor above the liquid will be richer in the lower-boiling compound, compared to the relative amounts in the liquid phase.

Distillation Scheme of the distiller

Sublimation A specific method that based on a difference in vapor pressure of compounds that is separated. Sublimation is a “solid to gas” phase transition without liquid state. It is commonly performed in closed apparatus under the vacuum. Under reduced pressure, the solid volatilizes and condenses as a purified compound on a cold part.

Extraction A frequently used technique when organic compounds (mostly hydrophobic) are dissolved or dispersed in water, Phase A. An appropriate solvent) (sufficient to dissolve the organic compound, Phase B) is added to the aqueous phase, and the mixture is shaken well so that the organic compound is sure to be extracted by the organic solvent. The organic and aqueous layers are separated by means of a separatory funnel, and the organic compound is recovered from the organic layer by removing the solvent.

Extraction of Ce from Ce(NO 3 ) 4 solution Aqueous phase (1) is the acidic solution of Ce(NO 3 ) 4 Organic phase (2) is tributyl phosphate (TBP) Following selective reaction is occurring at shaking two liquids: Ce(NO 3 ) 4(aq) + nTBP (org) = [CenTBP](NO 3 ) 4(org) Tributyl phosphate (TBP) – aqueous phase2 – organic phase 20 Extraction

Zone melting A kind of recrystallization technique in which a narrow region of a crystal is molten, and this molten zone is moved along the crystal. the sample is made into the form of a thin rod. The temperature is several degree above melting point. The method is based on difference in solubility of impurities in liquid and in solid phases. The impurities are continuously concentrated in liquid phase.

Chromatography A method of separation that based on different behavior of components in their mixture between two phases, one stationary and the other mobile. Stationary phase Moving phase Physical or chemical adsorption take place on phase boundary Strength of adsorption for different component determines the velocity of their moving together with moving phase A A A A A A A A A B B B B B B B B B B

Chromatography Stationary Phase beginningend Moving phase AAAB B B criterionname mobile phaseliquid chromatography, gas chromatography mechanismadsorption chromatography, partition chromatography, ion exchange chromatography, gel chromatography stationary phasecolumn chromatography, thin layer chromatography, paper chromatography

Chromatography Ion exchange chromatography is widely used for separation of ionic substances from aqueous solution. Moving phase – different aqueous solution Stationary phase – organic polymer materials (resins) with active polar sites (functional groups) on the polymer chains. Cation exchanger: R-SO 3 H ↔ R-SO H + R-SO3H + Na + ↔ R-SO 3 Na + H + Anion exchanger: R-N(CH 3 ) 2 OH ↔ R-N(CH 3 ) OH - R-N(CH 3 ) 2 OH + Cl - ↔ R-N(CH 3 ) 2 Cl + OH -

Chromatography

High-pure materials production Requirements for purification processes: Clean area (laboratory with strong control of chemical wastes, Clean Room) Ultrapure chemicals (water, acids, …) and stuff (Teflon, plastic, quartz) Special setups for purification procedures and for analysis of low-level contamination Purity control

27 Thank you for attention