Colloid chemistry chapter 6 adsorption on liquid solid inferface

COLLOID CHEMISTRY Chapter – Adsorption on L-S surfacce Dr Ngo Thanh An Characterization of phenomenon Classification of adsorption isotherm Classification of adsorption isotherm Classification of adsorption isotherm Classification of adsorption isotherm Classification of adsorption isotherm Ion exchange • Ion exchange process means an exchange of ions between an electrolyte solution and a solid (ionite) • In most cases the term is used to denote the processes of purification, separation, and decontamination of aqueous and other ion containing solutions with solid polymeric or mineral ion exchangers • This process is also called ion exchange adsorption, because it takes place at the solid/liquid interface • Ion exchanger – an inorganic or organic solid substance containing ions which can be replaced by the ions from solution whose electric charge is of the same kind Ion exchangers are either cation exchangers that exchange positively charged ions (cations) or anion exchangers that exchange negatively charged ions (anions) • There are also amphoteric exchangers that are able to exchange both cations and anions simultaneously • Typical ion exchangers are ion exchange resins (functionalized porous or gel polymer), zeolites, montmorillonite, clay, etc… Ion exchange • In respect of the chemical structure of the exchanger: ⇒ inorganic ⇒ organic • In respect of the exchanger origin: ⇒ natural ⇒ semisynthetic ⇒ synthetic Ion exchange Ion exchange Natural ion-exchanger • Their application is smaller than that of the synthetic ones because of their worse physicochemical properties in comparison to those of the synthetic ones • They were used to soften water (zeolites - hydrated aluminosilicates of calcium and sodium) ã The general formula of zeolites: (Me2+,Me2+)O; Al2O3ìnSiO2ìmH2O ã This group includes such minerals as: analcime (analcite), chabazite, natrolite, skolecite and others Ion exchange Natural ion-exchanger • The basic structural elements of zeolites are tetrahedrons of SiO4 and AlO4 which form 4-or 6-element rings • The aluminosilicate skeleton possesses an excess of negative charge which is compensated by Me+ or Me2+ ions • The ions are not built-in the crystal structure • Therefore they can migrate and be exchanged by other ions from solution • This group of natural ion exchangers includes montmorillonite and glauconite as well as some soils The soils are amphoteric ion exchangers 3 Ion exchange Semi-synthetic ionic exchanger • These are natural exchangers which have been chemically treated, e.g sulfonated coals obtained by treatment with concentrated sulphuric acid or oleum • They are known commercially as: Zoe-Karb-H, Permutyt, Wofatyt-Z, Eskarbo-H 3 Ion exchange Synthetic ion exchangerrs ã synthetic aluminosilicates having the general formula: Al2O3ì(SiO2)x(Na2O)xì(H2O)z, synthetic resins • Synthetic resins are the most commonly used exchangers They are mechanically resistant substances, insoluble in water and some organic solvents, like alcohols, ethers, hydrocarbons • They can exchange ions because of the presence of active groups in their matrix • The resins are obtained by polimerization, copolimerization or polycondensation of appropriate monomers whose functional groups can dissociate 3 Ion exchange Synthetic ion exchangerrs • An ion-exchange resin is in the form of small (1–2 mm diameter) beads, usually white or yellowish • The material has a highly developed structure of pores on the surface of which there are sites with easily trapped and released ions • Ion-exchange resins are widely used in different separation, purification, and decontamination processes • The most common examples are water softening and water purification 3 Ion exchange Synthetic ion exchangerrs • • • • • • • • • The resin ionite general formula can be written: Cationic resin: R–A–M+ Anionic resin: R–B+X– Where: R – the polimer matrix, A– – the covalently bonded with the matrix anionic group, for example acidic, –COO– ; M+ – the ionically bonded cation with A which can dissociate, e.g H+ or metal cation; B+ – the covalently bonded with the matrix cationic group, e.g =N2+, X– – ionically bonded anion with B which can dissociate, e.g OH– One polymer molecule can have many functional groups Hence ionite is a polyelectrolyte whose ions can dissociate Ion exchange Ion exchange Ion exchange process