Showing 4 results for Desorption
M. Soleimani, M. Shahedi,
Volume 10, Issue 2 (7-2006)
Abstract
Isotherm curves are useful for the designing of dryer as well as controling of the seed moisture content during storage and drying process. To study the curves, this research was performed on the basis of two factorial experiments including three factors: (1) hybrid at two levels (Three Way Cross 647 and Single Cross 704) (2) temperature at 6 levels (from 5 to 55°C) and (3) Relative Humidity (RH) at 5 levels (from 10 to 90 percent) for the analysis of the adsorption and desorption phenomena. For maintaining RH at the above mentioned ranges, glycerol solutions with different concentrations were used. The results showed that the relationship between solutions concentration and their RH was non-linear and somewhat related to temperature. Also, statistical analysis displayed that for 3 factors of tepmerature , RH and hybrid, the effects on Equilibrium Moisture Content (EMC) in both adsorption and desorption phenomena were significant at α=1%. Comparisons of means showed that hybrid 704 had higher EMC values than did hybrid 647 under the same conditions, in other words, hybrid 704 produced lower aw than did hybrid 647 at the same moisture content. Fitting experimental values on non-linear models (Henderson, Chung-Pfost and Oswin) showed Oswin as the best model for adsorption and desorption curves for hybrid 704 and also for adsorption curve for hybrid 647 , but the best model for desorption curve for hybrid 647 was Chung-Pfost.
F. Alsadat Hodaee Koskkoee, H. Shariatmadari, M. Hamidrpour, M. Shirvani,
Volume 18, Issue 70 (3-2015)
Abstract
Sorption hysteresis in soil constituents has important environmental implications such as pollutant transport and bioavailability. This research was carried out to study sorption reversibility of cadmium (Cd) on natural zeolite. Sorption isotherms were derived by sorption of Cd (П) from solutions containing different concentrations of Cd in the range of 1 to 10 mg L-1 using a 24h batch equilibration experiment. Desorption of Cd(II) was studied with the clay samples initially treated with the metal loadings of 50 and 100% maximum sorption capacity (SCmax) during the sorption study. Sorption isotherms of Cd were well described by the Freundlich and Coble-Korrigan models (R2=0.96). Desorption isotherms of Cd from zeolite showed little deviation from sorption data indicating reversible sorption. On the other hand, the results revealed no hysteresis. The average amount of 71.75 % of the initially sorbed Cd was desorbed from zeolite after five successive desorption steps. Release of such a relatively high proportion of sorbed Cd indicates that zeolite is an effective sorbent for the repeated purification of polluted water and wastewater.
M. Piri, E. Sepehr,
Volume 19, Issue 72 (8-2015)
Abstract
Humic substances are the most important organic fractions in soils and have affinity towards trace metals. In order to evaluate the effect of humic acid on zinc (Zn) sorption and desorption by soil, a batch experiment was conducted with two soil samples which were different in clay and calcium carbonate contents. Three levels of humic acid (0, 200, 500 mg/L) and various Zn concentrations (0 to 450 mg/L) were applied at constant ionic strength (0.05 M NaCl). Adsorption data were fitted to Langmuir, Freundlich and Temkin equations. Freundlich equation fitted relatively better (R2= 0.86-0.98). Results showed that the application ofhumic acid increased both sorption and desorption of Zn in the two sample soils. Increasing of humic acid concentration increased maximum adsorption of Langmuir (qmax) up to 8-21% and Freundlich sorption capacity (Kf) up to 73-95%. All sorption parameters including Langmuir binding energy (KL), Freundlich intensity factor (n) and coefficients of Temkin equation (A, KT) were increased by adding humic acid, so that the above mentioned sorption parameters of S1 (with low clay and calcium carbonate) were lower than those of S2 (with high clay and calcium carbonate). Application of humic acid (500 mg/L) increased desorption of Zn (DTPA-Zn) from 511 to 711 mg/kg for S1 and 499 to 609 for S2.
E. Chavoshi, M. Afyuni , M. Ali. Hajabbasi,
Volume 19, Issue 73 (11-2015)
Abstract
The sorption and desorption of fluoride by soil can play an important role in the transport of fluoride in soil. The study was conducted on the soil from Isfahan University of Technology research station site (two depths of 0-30 and 30- 60 cm). Fluoride sorption reactions were examined by equilibrating 0, 2.5, 5, 10, 25, 50 and 100 mg L-1 NaF solution with soils for 23 hr. The desorption experiments were performed using 0.03 mol L-1 NaCL solutions immediately following the completion of sorption experiments. The sorption isotherms of F were well described by the Langmuir and Freundlich models. The n values for Freundlich isotherm were 0.57 and 0.55 for two depths of the studied soil, respectively. The kF values for Freundlich isotherm were 0.026 and 0.025 mg (1-n) Ln g-1 for two depths, respectively. Maximum monolayer sorption capacities (q max) were obtained to be 0.4 and 0.35 mg g-1 for 1 and 2 layers of the studied soil, respectively. The desorption isotherms of F were well described by the Freundlich model. The fitted model parameters’ (kF and n) values for desorption branches were larger than these values for sorption branches. Also, the results showed a positive hysteresis (ndesrb sorb and kdesorb >Ksorb). It seems fluoride sorption to be reversible.
