Adsorption Features of Loess Calcareous Nodules to Heavy-Metal Ions in Aqueous Solution
This paper explores the use of calcareous tuberculosis as an adsorbent and heavy-metal ions (Cu<sup>2+</sup>, Zn<sup>2+</sup>, Cd<sup>2+</sup>, and Pb<sup>2+</sup>) as adsorbates, and the influence of varying levels of particle size, adsorption time, p...
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| Autores principales: | , |
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| Formato: | article |
| Lenguaje: | EN |
| Publicado: |
MDPI AG
2021
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| Materias: | |
| Acceso en línea: | https://doaj.org/article/0175833b94b5474c86cd899c01a5e1cf |
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| Sumario: | This paper explores the use of calcareous tuberculosis as an adsorbent and heavy-metal ions (Cu<sup>2+</sup>, Zn<sup>2+</sup>, Cd<sup>2+</sup>, and Pb<sup>2+</sup>) as adsorbates, and the influence of varying levels of particle size, adsorption time, pH, adsorbent dosage, and initial concentration of heavy metals is studied through an experiment of single heavy-metal adsorption. In addition, the impact of the temperature and other factors on the adsorption of heavy-metal ions by calcareous nodules is analyzed to identify the optimal conditions for the adsorption of heavy-metal ions by calcareous nodules. As shown by the research findings, the adsorption rates of Cu<sup>2+</sup>, Zn<sup>2+</sup>, and Pb<sup>2+</sup> gradually declined with the increase in particle size, with no evident effect on Cd<sup>2+</sup>. In the meantime, with further increases in factors such as the adsorption time, adsorbent dosage, and temperature, the adsorption rates of Cu<sup>2+</sup>, Zn<sup>2+</sup>, Cd<sup>2+</sup>, and Pb<sup>2+</sup> experienced gradual increases. The adsorption rates of Cu<sup>2+</sup>, Zn<sup>2+</sup>, and Cd<sup>2+</sup> gradually declined with the increase in initial concentration of heavy-metal ions, whereas the adsorption rate of Pb<sup>2+</sup> experience increased first and then declined. As the pH increased, the adsorption rate of Cd<sup>2+</sup> experience increased first and then declined at a slow pace. The adsorption rates of Cu<sup>2+</sup>, Zn<sup>2+</sup>, and Pb<sup>2+</sup> increased first and then decreased. The adsorption capacity of calcareous nodules toward the four heavy-metal ions was in the order of Pb<sup>2+</sup> > Zn<sup>2+</sup> > Cu<sup>2+</sup> > Cd<sup>2+</sup>. When the particle size was set to 0.25 mm, the adsorption time was set to 120 min, and the dosage was set to 0.6 g, the calcareous nodules included Pb<sup>2+</sup>, Zn<sup>2+</sup>, and Cu<sup>2+</sup>. Moreover, Cd<sup>2+</sup> was able to achieve stronger adsorption capacity, with the adsorption rate able to reach 83.33%, 77.78%, 73.81%, and 81.93% of its maximum level. Therefore, as the particle size of the heavy-metal ions decreased, the adsorption capacity generally became stronger. As the adsorption time increased, the temperature and the amount of adsorbent also increased. The optimal pH value for the adsorption of calcareous nodules toward Pb<sup>2+</sup>, Zn<sup>2+</sup>, Cu<sup>2+</sup>, and Cd<sup>2+</sup> was found to be 7, 6, 5, and 8, respectively, and the optimal temperature was 50 °C. In summary, calcareous nodules are a natural, low-cost, and effective adsorbent. |
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