Adsorption & ion exchange: Definition: Process in which solute molecules (adsorbate) become attached to a solid surface (adsorbent) under the attracting influence of surface forces. It is primarily a surface phenomena TVM 4145 Vannrenseprosesser TorOve Leiknes

Adsorption processes in water treatment Activated carbon most used in water treatment PAC: Powder activated carbon GAC: Granular activated carbon In Out GAC Sand 8 PAC TVM 4145 Vannrenseprosesser TorOve Leiknes

 T A A2  T A  T Adsorption processes: Mass transport from bulk liquid phase to the surface of solid material. 1. Physical adsorption: Van der Waals forces Hydrogen binding Hydrophobic binding  T 2. Chemical adsorption: A A2  T A 3. Exchange adsorption:  T TVM 4145 Vannrenseprosesser TorOve Leiknes

Adsorption equilibrium: adsorption rate  desorpsjon rate q C q = mass adsorbed weight of adsorbent Langmuir og Freundlich developed equilibrium isotherms TVM 4145 Vannrenseprosesser TorOve Leiknes

 1-   = q/Qo KA(1-)C KA(1-)C = KD KD  (KA C+ KD) = KA C Langmuir Isotherm (1916): Assumptions: 1. Given a set number of adsorption sites 2. Each site can only hold one molecule 3. All sites have the same binding energy  1-  = q/Qo At equilibrium:  KA(1-)C KA(1-)C = KD KD  (KA C+ KD) = KA C TVM 4145 Vannrenseprosesser TorOve Leiknes

Substitute f and rewrite; q C 1/C 1/q Freundlich Isoterm : TVM 4145 Vannrenseprosesser TorOve Leiknes

Adsorption kinetics: 1 Transport mechanisms: 2 3 4 Transport mechanisms: 1. convection in the bulk liquid 2. Molecular diffusion (film diffusion) 3. Pore diffusion 4. Adsorption rate In evaluating the adsorption mechanisms one must distinguish which of the respective transport mechanisms is limiting for the process. TVM 4145 Vannrenseprosesser TorOve Leiknes

q C* Cb Cb r r Film diffusion: Pore diffusion: =0 TVM 4145 Vannrenseprosesser TorOve Leiknes

99% of surface area is inside the pore structure Activated carbon: Surface area ca. 600-1500 m2/g pyrolysis Pore radius: 1 nm to 25 nm 99% of surface area is inside the pore structure PAC - powder, d < 0,1 mm GAC - granular, d = 0,42 - 2,38 mm TVM 4145 Vannrenseprosesser TorOve Leiknes

Ion exchange Reversible exchange process of ions Q, Co Q, C Reversible exchange process of ions between the liquid phase and a natural or artificial ion exchange media TVM 4145 Vannrenseprosesser TorOve Leiknes

Ion exchange media: Struktur: Matrix (polystyrene cross-linked with divinylbenzene) Struktur: Gel media - varierende grad av kryssforbindelser der matrisen fylles med væske Macroporøse medier - strukturen har porer Isoporøse medier - uniform porstørrelser Micro media - pulverisert media TVM 4145 Vannrenseprosesser TorOve Leiknes

Ved hardhets fjerning: Bytte mekanismer: Ingen ionebytting Ionebytting B- A- Ved hardhets fjerning: TVM 4145 Vannrenseprosesser TorOve Leiknes

For bytting av ioner med lik ladning er likevektskonstanten Likevektsforhold: Separasjonsfaktor: For bytting av ioner med lik ladning er likevektskonstanten og separasjonsfaktoren den samme TVM 4145 Vannrenseprosesser TorOve Leiknes

Ionebyttemassens selektivitet fremgår av likevektskonstanten Ionebyttemasser vise forskjellig bytte evner på ioner; Sulfoniske media (-SO3-)  Fe+ > Al3+ > Ca2+ Karboxylat media (-COO-)  H+ > Ca2+ > Mg2+ > K+ > Na+ Ionebyttemassens selektivitet fremgår av likevektskonstanten der X er fraksjon av ioner i de respektive faser TVM 4145 Vannrenseprosesser TorOve Leiknes

Ionebytter isoterm : XA XB Ks>1 Ks<1 1.0 TVM 4145 TorOve Leiknes 1.0 XA XB Ks>1 Ks<1 TVM 4145 Vannrenseprosesser TorOve Leiknes

”Break through” kurver: 1.0 CB=0 CB= CBo Full fjerning Delvis fjerning Faktorer som påvirker driften: 1. Temperatur 2. Media størrelse (diameter) 3. Gjennomstrømningsmengde 4. Selektivitetskoeffisienten TVM 4145 Vannrenseprosesser TorOve Leiknes

+ Utnyttelsesgrad: Calculation: Utnyttelsesgrad = CB/CBo CB/CBo CB/CBo 1.0 CB/CBo Calculation: 1.0 1.0 CB/CBo CB/CBo Utnyttelsesgrad = + TVM 4145 Vannrenseprosesser TorOve Leiknes

Typical arrangement: Operation: Q : 16-50 m3/h.m2 QB QC0 QR Regeneration: QB : 12-15 m3/h.m2 tB : 20 min QR: 4 m3/h.m2 h > 0.8m QC QR QB TVM 4145 Vannrenseprosesser TorOve Leiknes