Document Type : ORIGINAL RESEARCH ARTICLE
Authors
1 Department of Soil Science, Science and Research Branch, Islamic Azad University, Tehran, Iran
2 Department of Basic Science, Sari University of Agricultural Sciences and Natural Resources, Sari, Iran
Abstract
Four diverse chlorides layered double hydroxides with diverse ratios, i.e. Mg-Al (3:1), Mg-Al (4:1), Zn-Al (4:1), and Zn-Al (3:1) LDHs, were prepared to evaluate their efficiency and selectivity towards nitrate removal from aquatic solutions. A batch experiment was done at the initial nitrate concentration of 5-1000 mg/L, pH 5 to 12, and contact time of 5-180 min. Isotherms of nitrate adsorption on LDHs, soil and soil-LDH mixtures were studied. Kinetics of adsorption, temperature effect, nitrate adsorption in nitrate adsorption, simulated soil solution and desorption on Mg-Al-LDH (4:1) were measured. At an optimum speed of 250 rpm, pH value of 7 and adsorbent dosage of 2 g/L, the amounts of nitrate adsorption on Mg-Al- LDH (3:1) and Mg-Zn-LDH (3:1) and also on Mg-Al- LDH (4:1) and Mg-Zn-LDH (4:1) were obtained after 30 and 60 min, respectively. Isotherm studies indicated that nitrate adsorption on soil, soil-LDH mixture, and LDH fitted Langmuir linear isotherm. The highest nitrate adsorption on Mg-Al-LDH (4:1) and a mixture of soil-Mg-Al-LDH (4:1) were 188.67 and 107.52 mg/g, respectively. Among the studied kinetic equations for nitrate adsorption on Mg-Al-LDH (4:1), the pseudo-second-order with R2=0.998 had the best fitness. Negative values of ∆H in different nitrate concentrations indicated the exothermic process of nitrate adsorption on Mg-Al-LDH (4:1). In the presence of other anions, Mg-Al-LDH (4:1) removed nitrate preferentially. Moreover, Mg-Al-LDH (4:1) could exchange nitrate 20 times in different concentrations with no reduction in its adsorption capacity.
Graphical Abstract
Highlights
- LDH Mg-Al (4:1) has a higher nitrate adsorption capacity than Mg-Al (3:1), Zn-Al (4:1) and Zn-Al (3:1) LDHs;
- In the presence of carbonate, sulfate, phosphate and chloride anions in the simulated soil solution, Mg-Al-LDH (4:1) adsorbs nitrate as its preferential adsorption mechanism;
- Mg-Al-LDH (4:1) can exchange nitrates 20 times in different concentrations without reduction of nitrate adsorption capacity.
Keywords
Letters to Editor
[1] Letters that include statements of statistics, facts, research, or theories should include appropriate references, although more than three are discouraged.
[2] Letters that are personal attacks on an author rather than thoughtful criticism of the author’s ideas will not be considered for publication.
[3] Letters can be no more than 300 words in length.
[4] Letter writers should include a statement at the beginning of the letter stating that it is being submitted either for publication or not.
[5] Anonymous letters will not be considered.
[6] Letter writers must include their city and state of residence or work.
[7] Letters will be edited for clarity and length.
Send comment about this article