1 / 9

Lecture 8 Adsorption - Desorption

Particle Sizes and Surface Area. Colloidal ( < 1 um)Pore sizes.- < 2 nm, micropores- 2-50 nm, mesopores- > 50 nm, macroporesSurface area increases rapidly as particle sizes decrease (see Table 10.1).. Terminology of Adsorption. GSOH: concentration of sorbing surface sites (mol sites/L)Ns: s

wan
Download Presentation

Lecture 8 Adsorption - Desorption

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

    1. Lecture 8 Adsorption - Desorption

    2. Particle Sizes and Surface Area Colloidal ( < 1 um) Pore sizes. - < 2 nm, micropores - 2-50 nm, mesopores - > 50 nm, macropores Surface area increases rapidly as particle sizes decrease (see Table 10.1).

    3. Terminology of Adsorption GSOH: concentration of sorbing surface sites (mol sites/L) Ns: surface site density (sites/m2) SA: surface area per weight of sorbent (m2/g) Cs: weight concentration of sorbent NA: Avogadro’s number SA and Ns of geological materials can be found in Table 10.2 CEC and AEC CEC (meq/100 g) = 0.1661 x Ns x SA

    4. The Freundlich Adsorption Isotherm Here x/m is concentration of sorbate on the sorbent; C is the aqueous concentration of sorbate. When n=1, K=(x/m)/C=Kd, which is distribution coefficient. Assumption: infinite supply of sorption sites.

    5. The Langmuir Adsorption Isotherm Here C is the aqueous concentration of sorbate; a and b are constants; Nmax is the maximum adsorption by solid (sorbent). Assumptions: - single layer coverage; - finite supply of sorption sites.

    6. Calculate Kd in Column Experiments Ci: initial concentration Cf: final concentration V: volume of solution passed through the column M: mass of sorbate in the column Column and batch experiment results usually do not agree.

    7. Surface Complexation Models (SCM) Consideration of solution speciation, aqueous activities, complexes. - Constant Capacitance Model (CC) - Diffuse Layer Model (DL) - Triple Layer Model (TL) See Fig.s 10.18 & 10.19 for differences among models. In the CC model and DL model, adsorption at the zero plane; In the TL model, adsorption can happen at both the zero plane and the beta plane.

    8. Most Important Concept HS+ is H+ at the solid surface pHPZNPC = 0.5 (pKa1+pKa2) Working examples 10.1 and 10.2 (p377-378).

    9. Reading & Homework Read 10.1.1, 10.1.2, 10.2.1, 10.2.2, 10.2.3, 10.2.4, 10.4.1, 10.4.2, 10.4.7, 10.5 Problems 2 & 9. Good Luck!

More Related