Colloid chemistry - Chapter 6: Adsorption on Liquid - Solid inferface - Ngo Thanh An

Nội dung text: Colloid chemistry - Chapter 6: Adsorption on Liquid - Solid inferface - Ngo Thanh An

1. 1. Characterization of phenomenon
2. 2. Classification of adsorption isotherm
3. 2. Classification of adsorption isotherm
4. 3. 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
5. 3. Ion exchange
6. 3. Ion exchange • 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.
7. 3. Ion exchange • synthetic aluminosilicates having the general formula: Al2O3×(SiO2)x(Na2O)x×(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.
8. 3. Ion exchange • 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
9. 3. Ion exchange