Kinetic, isotherm, and mechanism investigations of the removal of nitrate and nitrite from water by the synthesized hydrotalcite Mg-Al

摘要

The objective of this work is to test the effectiveness of hydrotalcite as an adsorbent for the retention of nitrate and nitrite ions and to study the influence of various reaction parameters such as pH, adsorbent dose, contact time and initial ion concentration. Hydrotalcites (HTx) of different Mg/Al ratios (x was Mg/Al ratio; 2, 3, 4) were synthesized by the co-precipitation method at constant pH and characterized by X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR). The results obtained indicate that hydrotalcite (HT3) allows good retention of nitrate and nitrite ions with no pH adjustment. Adsorption increases with decreasing mass of the adsorbent and increases with increasing initial concentration of nitrate and nitrite ions. When the Mg/Al ratio changes from 2 to 4; the electrical charge density between layers weakens; the inter-layer spacing increases and the material shows greater adsorption capacity. The equilibrium isotherm showed that the Langmuir model provided a better fit to the experimental data than the Freundlich model for nitrates and nitrites. The adsorption capacity of HT3 for nitrates and nitrites was found to be 6.92 mg/g and 9.26 mg/g, respectively. The XRD analysis after adsorption showed that materials that had undergone nitrate and nitrite ions adsorption, maintain the hydrotalcite structure.