Nanostructured zeolites for heavy metals removal from wastewater

Introduction Zeolites used in wastewater treatment are efficient because of multiple reasons such as:  ability to lose and gain water reversibly and to exchange some of their constituent elements without a major change of... [ view full abstract ]

Introduction

Zeolites used in wastewater treatment are efficient because of multiple reasons such as:  ability to lose and gain water reversibly and to exchange some of their constituent elements without a major change of structure, high efficiency for retaining various compounds in their structure since will provide a high accessibility of them into the structure and at the active sites (adsorption), etc. 

The purpose of this research was the study of ZSM-5 type zeolite for wastewater depollution by removal of two heavy metals (Pb²⁺ and Cd²⁺). After the synthesis, Na- ZSM-5 zeolites and its corresponding hybrid Na-ZSM-5-chit were characterized X-ray diffraction and transmission electron microscopy (TEM). 

Methods

The reagents used for the synthesis of Na-ZSM-5 and Na-ZSM-5chit were: sodium silicate (28% SiO₂, 8% Na₂O and 64% H₂O), aluminium nitrate (Al (NO₃)₃^. 9H₂O), tetrapropyl-ammonium hydroxide (TPAOH), cetyltrimethyl-ammonium bromide (CTAB) and chitosan, obtained from Sigma Aldrich.

Results and discussion

The XRD of the synthesized pristine powder depicted in Figure 1 reveal the presence of the MFI (mordenite framework inverted) structure that is typical for ZSM-5. The structure of ZSM-5 contains pentasil units bonded by bridges of oxygen forming pentasilchains which can be seen in Figure 2. 

The morphology of the obtained zeolites materials was investigated by TEM analysis(Figure 3 a and b) show that the sample particles have elongated shape like plaques with an average size of 220 nm. The chitosan polymer looks as a shell on the Na-ZSM-5particles.

Adsorption studies were performed by mixing 0.1 g of each sample (Na-ZSM-5 and Na-ZSM-5-chit) with 100 mL mixed solution of Pb(II) and Cd(II),respectively at room temperature (21.5°C). The mixed solutions (100 mL) of Pb(II)and Cd(II) had the same concentrations: 10, 25, 50 and 100 mg/L of each metal.

Was observed that Na-ZSM-5 and Na-ZSM-5-chit are available to remove Pb(II) and Cd(II) from acidic wastewater (almost 50% efficiency), with the highest result in case Pb (over 55%), only after 15 minutes.

The removal efficiency for Pb(II) decrease as follows Na-ZSM-5 >Na-ZSM-5-chit. For Cd(II), the removal tendency is Na-ZSM-5-chit>Na-ZSM-5.