Comparison of Two Types of Modified Zeolites and the Key Factors for Cd(II) Adsorption Processes in Micropolluted Irrigation Water

Abstract

Zeolites were modified by high-temperature roasting and chitosan loading, respectively. As a result, activated zeolite and chitosan-loading natural zeolite were obtained. They were used for the treatment of the micro-polluted irrigation water quality simulated by a low concentration (100 μg/L) of Cd(II) contamination. The static adsorption experiments showed that two types of modified zeolites were cost-effective and had high removal efficiency for low concentrations of Cd(II). The removal rates were 95.8% and 92.06%, respectively. The static adsorption experiments investigated the effects of modified zeolite dosage, pH, initial concentration of the solution, and adsorption time on the removal efficiency of cadmium ions. The dynamic adsorption experiments discussed the influence of factors such as dynamic adsorption medium type, influent filtration rate, and adsorbent amount on adsorption efficiency in the adsorption column. The dynamic adsorption experiments adopted intermittent operation to simulate the characteristics of micro-polluted irrigation water. The optimal operating conditions were determined as follows: single activated zeolite filter column or mixed medium (activated zeolite: chitosan loading natural zeolite = 4:1), filtration rate of 6 m/h, filter column height of 500 mm, adsorbent dosage of 30 g. The removal rate was more than 99.5%. The adsorption experiments were represented by Langmuir and Freundlich isotherm models. The adsorption results indicated that the adsorption of modified zeolite showed a better correlation with the Langmuir isotherm model than the Freundlich isotherm model. The adsorption process was described by pseudo-first-order and pseudo-second-order kinetic models, with the pseudo-second-order kinetic model being the predominant mechanism. The average concentration of Cd(II) in the effluent after filtration was 0.41 μg/L, which was far lower than the 0.01 mg/L stipulated in the standard for irrigation water quality (GB5084-2021), and met the requirements of the irrigation water quality standard. Activated zeolite and chitosan-loaded natural zeolite are good adsorbent materials that have broad application prospects in the treatment of micro-polluted irrigation water containing low concentrations of Cd(II).