Adsorption Features of Loess Calcareous Nodules to Heavy-Metal Ions in Aqueous Solution

Qi Li,Yanan Li

doi:10.3390/coatings11111314

Abstract

This paper explores the use of calcareous tuberculosis as an adsorbent and heavy-metal ions (Cu2+, Zn2+, Cd2+, and Pb2+) 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 Cu2+, Zn2+, and Pb2+ gradually declined with the increase in particle size, with no evident effect on Cd2+. In the meantime, with further increases in factors such as the adsorption time, adsorbent dosage, and temperature, the adsorption rates of Cu2+, Zn2+, Cd2+, and Pb2+ experienced gradual increases. The adsorption rates of Cu2+, Zn2+, and Cd2+ gradually declined with the increase in initial concentration of heavy-metal ions, whereas the adsorption rate of Pb2+ experience increased first and then declined. As the pH increased, the adsorption rate of Cd2+ experience increased first and then declined at a slow pace. The adsorption rates of Cu2+, Zn2+, and Pb2+ increased first and then decreased. The adsorption capacity of calcareous nodules toward the four heavy-metal ions was in the order of Pb2+ > Zn2+ > Cu2+ > Cd2+. 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 Pb2+, Zn2+, and Cu2+. Moreover, Cd2+ 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 Pb2+, Zn2+, Cu2+, and Cd2+ 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.

Highlights

Over recent years, with the rapid progress made in industrialization and urbanization, a large amount of wastewater containing heavy-metal ions such as Cu2+, Zn2+, Cd2+, and Pb2+ has been discharged into water ecosystems
In the Freundlich isotherm model, nonuniform surface adsorption played the dominant role in the adsorption of Zn2+ to calcareous nodules, mainly composed of silica
Zou et al adopted corn stalks to prepare biochar, conducted experiments on the adsorption effects of heavy metals including Cd2+ and Pb2+, and analyzed the capacity and efficiency of the biochar’s adsorption to heavy metals [3]. Their experimental results showed that the optimal adsorption condition for Cd2+ was reached when the pH value was set to 5, and the adsorption equilibrium amounted to 120 min

Summary

Introduction

With the rapid progress made in industrialization and urbanization, a large amount of wastewater containing heavy-metal ions such as Cu2+, Zn2+, Cd2+, and Pb2+ has been discharged into water ecosystems. The contamination of water bodies caused by heavy metals has become increasingly severe [1]. Identifying ways of purifying water and removing metal ions has become a research hotspot within the topic of environmental pollution [2]. The adsorption method is more applicable to various water bodies with a low concentration of heavymetal pollution, mainly due to the advantages of this method, such as fast treatment rate, simple operation, and optimal environmental coordination [3,4]. Illite, kaolinite, and montmorillonite feature an optimal adsorption effect on Cu2+, Zn2+, Cr3+, Cd2+, and Pb2+ in water [9]

Methods

Results

Discussion

Conclusion