Mixed Oxide Layered Double Hydroxide Materials: Synthesis, Characterization and Efficient Application for Mn2+ Removal from Synthetic Wastewater.

Cristina Modrogan,Oanamari Daniela Orbuleț,Violeta Purcar,Simona Cǎprǎrescu,Eugeniu Vasile,Annette Madelene Dǎncilǎ

doi:10.3390/ma13184089

Abstract

Magnesium–aluminum (Mg-Al) and magnesium–aluminum–nickel (Mg-Al-Ni) layered double hydroxides (LDHs) were synthesized by the co-precipitation method. The adsorption process of Mn2+ from synthetic wastewater was investigated. Formation of the layered double hydroxides and adsorption of Mn2+ on both Mg-Al and Mg-Ni-Al LDHs were observed by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy Dispersive Spectrometry (EDX) analysis. XRD patterns for prepared LDHs presented sharp and symmetrical peaks. SEM studies revealed that Mg-Al LDH and Mg-Al-Ni LDH exhibit a non-porous structure. EDX analysis showed that the prepared LDHs present uniformly spread elements. The adsorption equilibrium on these LDHs was investigated at different experimental conditions such as: Shaking time, initial Mn2+ concentration, and temperatures (10 and 20 °C). The parameters were controlled and optimized to remove the Mn2+ from synthetic wastewater. Adsorption isotherms of Mn2+ were fitted by Langmuir and Freundlich models. The obtained results indicated that the isotherm data fitted better into the Freundlich model than the Langmuir model. Adsorption capacity of Mn2+ gradually increased with temperature. The Langmuir constant (KL) value of Mg-Al LDH (0.9529 ± 0.007 L/mg) was higher than Mg-Al-Ni LDH (0.1819 ± 0.004 L/mg), at 20 °C. The final adsorption capacity was higher for Mg-Al LDH (91.85 ± 0.087%) in comparison with Mg-Al-Ni LDH (35.97 ± 0.093%), at 20 °C. It was found that the adsorption kinetics is best described by the pseudo-second-order model. The results indicated that LDHs can be considered as a potential material for adsorption of other metallic ions from wastewater.

Highlights

Pollution of water bodies by metals has received increasing public attention due to the importance of metals in industrial processes and their potential toxicity towards humans and in aquatic environments [1]
Results reveal that layered double hydroxides (LDHs) present structural and chemical characteristics that make them potential materials for use as storage matrices for slow P release
Zhao et al [17] designed and fabricated NiMn layered double hydroxide (NiMn LDH) microcrystals grafted on a carbon nanotube (CNT) backbone by an in situ growth route

Summary

Introduction

Pollution of water bodies by metals has received increasing public attention due to the importance of metals in industrial processes and their potential toxicity towards humans and in aquatic environments [1]. In the earth’s crust, manganese is frequently associated with iron. Manganese oxides can be reduced with coal in furnaces at high temperatures or in electric furnaces. Pure manganese can be obtained by aluminothermy, by electrolysis of MnSO4 concentrated solution or by sodium dislocation of MnF2 or MnCl2 [2,3]. The sources of manganese pollution are: Siderurgy, an alloying element with other metals such as iron (Fe), nickel (Ni), copper (Cu) and aluminum (Al); manufactures of dry batteries, glass and products from the ceramics industry, chemical industry and paint industry. Wastewaters from industries, mainly the steel manufacturing industry (about 95%), are the main sources of manganese pollution, along with the processing and exploitation of ores [2,3]

Methods

Results

Conclusion