adsorption model

1、1Ideal experiment designParameters may affect adsorptionSolution: pH, Eh, temperature, ion strength, competing or interaction with other ions, adsorbent dose, adsorbate concentration, contacting time.Adsorbent: surface functional groups, surface area, pHzpc, elemental composition, morphology, pore s

2、tructure, particle size distribution, and other physical and chemical property.Adsorbate: coordination number, ionic radius, electro negativity, standard reduction potential, species in solution, and other physical and chemical property. 2Ideal experiment designAdsorption kinetics experimentExperime

3、nts can be done under different adsorbate concentrations, adsorbent dose, temperature, pH, etc.Sampling interval is increased from the beginning to the endTime (h, d)Amont adsorbed (mmol/g)Different adsorbate concentrationAdsorbent doseTemperaturepH3Ideal experiment designAdsorption isotherm or equi

4、librium experimentExperiments can be done under different temperature, pH, ionic strength.Vary adsorbate concentration to adsorbent dose ratio (establish one and change another one) Sample after equilibrium (established parameter)Equilibrium concentration (mmol/L)Amount absorbed (mmol/g)Different te

5、mperaturepHIonic strength4Adsorption kinetics experimentAdsorption modellingZero order kinetic modelPseudo first order kinetic modelPseudo second order kinetic modelTime (h, d)Amount adsorbed (mmol/g)Time (h, d)Amount adsorbed (mmol/g)Time (h, d)Amount adsorbed (mmol/g)0tdqkdt1()tetdqk qqdt22()tetdq

6、k qqdt0tqk t1(1)k tteqqe221teettqk qq; ;tt is the adsorption time q is the amount of adsorbate adsorbed at time t012;,.eq is the amont adsorbed at equilibrium kkkthe adsorption rate constantareMohan, 20115Adsorption modellingAdsorption isotherm or equilibrium experiment01eeeQ bCqbCLangmuir isotherms

7、Freundlich isotherms1/neFeqK Cqe is the amount of solute adsorbed per unit weight of adsorbent (mg g-1), Ce is the equilibrium concentration of solute in the bulk solution (mg L-1). Q0 is the monolayer adsorption capacity (mg g-1) and b is the constant related to the free energy of adsorption (b e-G

8、/RT) and represents the affinity of adsorbate and adsorbent. G is the free energy, K is the Langmuir constant same as b. The sign of G can be used to indicate the feasibility of adsorption process and the spontaneous nature of adsorption.qe is the amount of solute adsorbed per unit weight of adsorbe

9、nt (mg g-1), Ce is the equilibrium concentration of solute in the bulk solution (mg L-1). KF is the constant indicative of the relative adsorption capacity of the adsorbent (mg g-1) and 1/n is the constant indicative of the intensity of the adsorption.lnGRTK 6Adsorption modellingAdsorption isotherm

10、or equilibrium experimentLangmuir isothermsFreundlich isothermsThe adsorption capacity (Q0) of adsorbent can be calculated.“Sorption extends infinitely as adsorbate concentrations increase.”(Langmuir, 1918; Freundlich, 1906; Appelo & Postma, 2005)Equilibrium concentration (mmol/L)Amount absorbed

11、 (mmol/g)Equilibrium concentration (mmol/L)Amount absorbed (mmol/g)Q07Adsorption modellingAdsorption isotherm or equilibrium experimentRedlich-Peterson modelToth isotherm model1RPeePeKCqa CRedlich and Peterson, 1959; Allen, 2004 qe is the amount of solute adsorbed per unit weight of adsorbent (mg g-

12、1), Ce is the equilibrium concentration of solute in the bulk solution (mg L-1). KRP, aRP and are Redlich-Peterson constants and the exponent, , lies between 0 and 1.qe is the amount of solute adsorbed per unit weight of adsorbent (mg g-1), Ce is the equilibrium concentration of solute in the bulk s

13、olution (mg L-1). KT, B, are the Toth constants.1/(1)TeeeK CqBCR-P model can be used to represent adsorption equilibria over a wide concentration range.Toth model is derived from potential theory and is applicable to heterogeneous adsorption.8Adsorption modellingAdsorption isotherm or equilibrium ex

14、perimentTempkin modelSlips or Langmuir-Freundlich isotherm model(ln)eeRTqACbAllen, 2004; Vijayaraghavan, 2006; Mohan, 2011qe is the amount of solute adsorbed per unit weight of adsorbent (mg g-1), Ce is the equilibrium concentration of solute in the bulk solution (mg L-1). R, A, T and b are Tempkin

15、constants.qe is the amount of solute adsorbed per unit weight of adsorbent (mg g-1), Ce is the equilibrium concentration of solute in the bulk solution (mg L-1). KLF, aLF, and nLF are the Slips constants.1LFLFnLFeenLFeKCqa CTempkin considered the effects of some indirect adsorbate/adsorbent interact

16、ions and suggested that because of these interactions the heat of adsorption of all the molecules in the layer would decrease linearly with coverageAt low adsorbate concentrations it effectively reduces to the Freundlich isotherm. At high adsorbate concentrations, it predicts a monolayer sorption ca

17、pacity characteristic of the Langmuir isotherm9Adsorption modellingAdsorption isotherm or equilibrium experimentRadke-Prausnitz model1eeeabCqabCMohan, 2011qe is the amount of solute adsorbed per unit weight of adsorbent (mg g-1), Ce is the equilibrium concentration of solute in the bulk solution (mg

18、 L-1). a, b and are Radke-Prausnitz constants.10Adsorption modellingThermodynamic parameters01 22211000()lnTTKHRTTKHGST Mohan, 2011G is the free energy, K is the Langmuir constant same as b. The sign of G can be used to indicate the feasibility of adsorption process and the spontaneous nature of adsorption.lnGRTK K1 and K2 are the Langmuir constants same as b1 and b2 corresponding to te