| The so-called biosorption is a combinative function of biology materials to removal the pollutant including dyes. In this paper we selected agricultural by-product of cereal chaff and waste materials of Phoenix Tree's leaves as biosorbent, and selected methylene blue(MB) and congo red(CR) as adsorbate. Both batch operation and fixed bed column are adopted in experiment.Adsorption of the objective MB and CR by chaff and leaves strongly depends on pH, contact time, initial concentration of the adsorbate and adsorbent dosage. The result is that with the pH value increasing at the range from 2 to 4.5, the adsorption quantity of cereal chaff and phoenix tree's leaves binding MB increases .When the value of pH increases from 4.5 to 10, the adsorption quantity is approximately constant. With the pH value increasing at the range from 3 to 4.3, the adsorption quantity of cereal chaff and phoenix tree's leaves binding CR increases. When the value of pH increases from 4.3 to 6, the adsorption quantity is approximately constant. Afterwards, with the value of pH increased, the adsorption quantity is drop. Higher removing for MB and CR are observed with temperature increasing. The maximum adsorption quantities of cereal chaff and phoenix tree's leaves binding MB and CR is 20.3 mg·g-1 (298 K), 80.9 mg·g-1 (295 K), respectively. The maximum adsorption quantities of cereal chaff and phoenix tree's leaves binding CR are 3.90 and 7.33 mg·g-1 at 299 K, respectively. Adsorption behavior of cereal chaff absorb MB can be approximately described with the Langmuir and Koble-Corrigan equation, while for CR the Freundlich and Koble-Corrigan equation are better. Adsorption behavior of phoenix tree's leaves binding MB and CR can be approximately described with the Langmuir, Koble-Corrigan and Temkin equation. The positive values of△H°suggest the endothermic nature of the adsorption of MB and CR on adsorbents. The negative values of△G°at various temperatures indicate the feasibility of the process and spontaneous nature of the adsorption.The kinetics of MB and CR adsorption consist of two phases: an initial rapid phase and a slower second phase. The pseudo-second-order model is the best choice among all the kinetic models to describe the adsorption behavior of MB and CR onto cereal chaff and phoenix tree's leaves. The adsorption rates have found to be adsorbate concentration and temperature dependent. The activation energy of adsorption (Ea) of cereal chaff binding MB is determined as 30.5 kJ·mol-1 and 26.4 kJ·mol-1 at 30 mg-L-1 and 50 mg·L-1, respectively. The activation energy of adsorption (Ea) of cereal chaff absorb CR is determined as 21.4 kJ·mol-1 and 24.0 kJ·mol-1 at 13 mg·L-1 and 21 mg·L-1, respectively. The activation energy of adsorption (Ea) of phoenix tree's leaves absorb MB is determined as 23.5 kJ·mol-1 at 130 mg·L-1,The activation energy of adsorption (Ea) of phoenix tree's leaves absorb CR is determined as 9.71 kJ·mol-1 and 18.0 kJ·mol-1 at 39 mg·L-1 and 72 mg·L-1, respectively. It can be concluded from adsorption thermodynamics and kinetics constants that chemical adsorption be predominant during adsorption process. Cereal chaff and phoenix tree's leaves are confirmed to be two good adsorbents for removal of MB and CR.Rice husk column for MB, CR adsorption and phoenix tree's leaves column for MB adsorption from solution are studied. The effects of experimental conditions such as pH value, flow rate, initial concentration, bed depth and the coexistences salt ion etc., are discussed. The Thomas model and BDST model are applied to adsorption at different flow rate, different bed depth and different initial concentration to predict the breakthrough curves and to obtain the characteristic parameters of the column. The higher initial concentration and bed depth, lower flow rate are benefited to enhance the adsorption efficiency and the adsorption quantity of equilibrium. The Thomas model and BDST model are found suitable for describing the dynamic behavior of the biosorption process of MR and CR on the biosorbent column.The characteristics of cereal chaff and leaves are studied by thermogravimetry analysis(TGA), differential thermal analysis(DTA) and Fourier—Transform Infrared Analysis spectroscopy(FTIR). The IR spectroscopy of the biomass is mainly composed of the adsorption of carbohydrates, lignin, cellulose etc. |
