Abstract
The increasing threat of chloride ions (Cl−) has led researchers to explore efficient removal technologies. Sewage treatment with a double-layer hydroxide/oxide (LDH/LDO) is receiving increasing attention. In this work, Mg-Al LDO adsorbents were produced by the calcination of the Mg-Al LDH precursor, which was constituted by improved coprecipitation. The influence of calcination temperature, calcination time, adsorbent dosage, Cl− initial concentration, contact time, and adsorption temperature on Cl− elimination was investigated systematically. The experimental results showed that a better porous structure endowed the Mg-Al LDO with outstanding adsorption properties for Cl−. The adsorption process was well matched to the pseudo-second-order kinetics model and the Freundlich model. Under optimal conditions, more than 97% of the Cl− could be eliminated. Moreover, the removal efficiency was greater than 90% even after 11 adsorption–desorption cycles. It was found that the electrostatic interaction between Cl− and the positively charged Mg-Al LDO laminate, coupled with the reconstruction of the layer structure, was what dominated the Cl− removal process.
Highlights
Cl− concentration in this wastewater is much greater than 2000 mg L−1, even up to 10,000 mg L−1 [3]
At present, being dependent on the first-level water discharge requirements of the salt chemical industry, the Cl− content must be kept below 300 mg L−1
The adsorbents used were produced by the calcination of the Mg-Al LDH precursor, which was fabricated by improved coprecipitation implemented at room temperature [45]
Summary
Large quantities of chloride wastewater are generated by the metallurgical and chemical industries [1,2]. LDHs, known as hydrotalcites, are a class of two-dimensional anionic intercalation materials with a bimetallic hydroxide laminate and exchangeable intercalation anions [13] They are widely applied in adsorption, catalysis [14–16], energy storage [17,18], biology [19], medicine release [20–22], heavy metal ions [23,24], and functional materials [25–28]. Their laminate elements are characteristically available in variable types and various proportions; changeable interlayer anions and controllable sizes bring more possibility in terms of application of the materials [30,31] Anions such as NO3 − can be exchanged with CO3 2− , SO4 2− , and Cl−. The influence of different calcination temperatures, calcination time, adsorbent doses, Cl− initial concentration, contact time, and adsorption temperatures on Cl− removal efficiency was explored These findings were used to clarify the adsorption law and the adsorption mechanism of Mg-Al LDO on Cl− in water. Stability and reusability of LDO materials were studied
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