Comparative Study of Copper Adsorptivity and Selectivity toward Zeolites

The objectives of the study were to find the type and species of zeolite which gives optimum adsorption of copper, provide an explanation of the mechanism involved in the adsorption process and establish the selectivity sequence among zeolites. Adsorption of Cu onto zeolites and mont-morillonite as a reference was conducted at an initial Cu concentration range of 0 - 0.60 mM in the presence of 100 mM NH4NO3 at initial pH of 5. Langmuir and Freundlich models were used in analyzing the equilibrium data and a selectivity sequence derived from the Langmuir calculation was A4 > faujasite X > modernite > Na-P1 ≈montmorillonite ≈faujasite Y > clinoptilolite. Zeolites A4 and faujasite X had high adsorptive capacities of 1429 mmol·kg﹣1 and 909 mmol·kg﹣1, respectively. Zeolite A4 has the highest CEC among all the samples (6150 mmol·kg﹣1), and the adsorption capacity of Cu was largely influenced by the CEC of the samples. The adsorption mechanism was based on the exchange of Cu from solution with mostly Na which was the main exchangeable cation available. These results are important in selecting the most effective and suitable adsorbent for Cu removal from polluted environments.

Decrease in Cation Exchange Capacity of Zeolites at Neutral pH: Examples and Proposals of a Determination Method

Cation exchange capacity (CEC) is an important characteristic of zeolites, especially when they are used as adsorbents in the aqueous system. However, no international standard method exists for the determination of CEC of zeolites. We determined CEC of Linde-type A and Na-P1 type zeolites at various pH (4 to 10) with a simple method, where Na+-saturated zeolites were prepared, and then various amounts of HCl were added. CEC was simply calculated by subtracting the amount of Na+ in the final supernatant from the content of Na+ of the Na+-saturated zeolites. CEC of the zeolites decreased with decreasing pH and with decreasing Na+ concentration of the final supernatant. The concentration of Na+ of the supernatant, CEC of the zeolites began to decrease at weakly alkaline or neutral pH, and that of the Linde-type A zeolite became about half at pH around 6. When CEC was plotted against pH-pNa;where pNa is negative logarithm of the activity of Na+;CEC of each zeolite was expressed by a curve. It indicates that the CEC or the amount of Na+ retention is univocally determined by the ratio of activities of Na+ and proton.

pH Dependence of Lead Adsorption on Zeolites

The adsorption of Pb on zeolites A4, X, Y and mordenite was studied at various initial pH with the purpose of assessing the pH dependence of Pb adsorption. The adsorption was conducted using 0 - 0.6 mM Pb(NO3)2 in the presence of 100 mM NH4NO3 and pH adjustment done using HNO3. The coexisting NH4NO3 served as a representative of other cations available in nature. The study was conducted at initial solution pH ranging from 3 - 5. Adsorption results were analyzed using Langmuir isotherm analysis. Adsorption was noted to be dependent on pH with increasing adsorption as pH increased from 3 - 5 for zeolites A4, X and Y. The adsorption of Pb on mordenite on the other hand did not show any dependence on pH since it was almost constant within the studied pH range. The adsorptive capacities were 2500, 2000, 588 and 179 mmol·kg-1 for A4, X, Y and mordenite, respectively. The results of this study can be used in designing or planning for the clean-up of polluted water using adsorption techniques. An important attribute of these findings was that the samples studied were shown to have the capacity of removing even very low concentration of Pb, a property which is hardly achievable by most adsorbents.

Mechanism of Diazinon Adsorption on Iron Modified Montmorillonite

The study was carried out with the objective of developing suitable and sustainable low cost adsorbent materials for diazinon, an organophosphate pollutant used as a pesticide. Montmorillonite modified with iron was used. Two different types of iron-montmorillonite, each having different contents of iron and synthesized with different pH and levels of Fe hydrolysis were used. One was denoted “Fe-modified” and the other denoted as “FeOH-modified”. The color of the samples changed from greyish green to light-reddish brown after the modification. X-ray diffraction and physical observations were used for characterization of the samples. The d-spacing of the samples was greater than 15 ?, indicating the formation of iron hydroxides in the interlayer space of montmorillonite. The amount of adsorption was calculated from the difference between the initial and the final concentration of diazinon. The adsorption data were analyzed using the Langmuir adsorption isotherms. The amounts of diazinon adsorbed were 58.8 and 54.1 mmolkg-1 for Fe-modified and FeOH-modified respectively. The steep rise in their adsorption isotherms indicated the possibility of adsorption for low level of diazinon in polluted water.

Mutual Adsorption of Lead and Phosphorus onto Selected Soil Clay Minerals

Mutual adsorption of lead (Pb) and phosphorus (P) at pH 5 onto three soil clays materials (kaolinite, montmorillonite, and allophane) was studied to know interaction of the anion and the cation at surface of the clays. Adsorption of Pb was determined on montmorillonite, kaolinite and allophane with the following pretreatments;1) untreated clay (control), 2) phosphate treated clay (P-clay) and 3) clay pre-treated with both P and Pb (P-Pb-clay). Adsorption of P was determined on montmorillonite, kaolinite and allophane with the following pretreatments;1) control 2) Pb treated clay (Pb-clay) and 3) P-Pb-clay. The adsorption of Pb on the untreated clays was in the order: montmorillonite > allophane > kaolinite. On allophane and kaolinite Pb adsorption was in the order P-clay > P-Pb-clay > control. For montmorillonite, the trend was: P-Pb-clay = control > P-clay. Phosphorus adsorption was in the order Pb-clay = P-Pb-clay > control for montmorillonite and kaolinite, Pb-clay > control > P-Pb-clay for allophane. The findings suggested that pre-treatment with phosphate increases Pb adsorption on kaolinite and allophane, and decrease on montmorillonite, while pretreatment with Pb increases phosphate sorption on all clays, and both Pb and P increased adsorption on montmorillonite and kaolinite and decrease on allophane.