ZnAl-SO4 Layered Double Hydroxide and Allophane for Cr(VI), Cu(II) and Fe(III) Adsorption in Wastewater: Structure Comparison and Synergistic Effects

Abstract

Owing to their structure, layered double hydroxides (LDHs) and allophane are nowadays considered as promising materials for application in different fields. The goal of this work is to compare the efficacy of allophane and ZnAl-SO4 LDH to remove, by adsorption, some cationic and anionic pollutants from industrial wastewater. Both compounds were synthesized via the co-precipitation route (direct method) followed by hydrothermal treatment, obtaining nanoscopic crystallites with a partially disordered turbostratic (ZnAl-SO4 LDH) or amorphous (allophane) structure. The characterization of the obtained compounds was performed by means of powder x-ray diffraction (PXRD), thermal gravimetry analysis (TGA), field emission scanning electron microscopy analysis (FESEM), and Fourier-transform infrared spectroscopy (FT-IR). The sorbents were tested using wastewater produced by a real metalworking plant and containing ionic species such as Cu(II), Fe(III) and Cr(VI), whose concentration was measured by means of inductively coupled plasma-optical emission spectrometry (ICP-OES). This investigation represents an alternative procedure with respect to standard protocols based on customarily made and artificially lab-produced wastewaters. Both sorbents and their combination proved to be efficient in Cr(VI) removal, irrespective of the presence of cations like Cu(II) and Fe(III). A synergistic effect was detected for Cu(II) adsorption in a mixed allophane/LDH sorbent, leading to a Cu(II) removal rate of 89.5%.

Highly Efficient Cd2+ Removal Using Tobermorite with pH Self-Adjustment Ability from Aqueous Solution

“…In recent decades, water demand has increased steadily due to population growth and industrial development [ 1 ]. Many parts of the world are now facing a water crisis, which may also be exacerbated by mismanagement of water resources [ 2 , 3 ].…”

“…The OH - released from tobermorite provides a desired alkaline environment, which can facilitate the combination of Ca 2+ and PO 4 3- to form hydroxyl calcium phosphate [ 25 ]. Considering its layered structure and ability to release Ca 2+ and OH - , tobermorite has the potential to become a functional adsorbent that removes Cd 2+ from wastewater efficiently and economically [ 1 ]. However, previous studies have commonly focused on synthesis and modification (mainly Al substitution) of tobermorite but rarely on its pH self-adjustment ability or Cd 2+ removal mechanism.…”

Novel MXene-Modified Polyphenyl Sulfone Membranes for Functional Nanofiltration of Heavy Metals-Containing Wastewater

“…With the rapid growth in nanotechnology and its outstanding applications, various novel nanoscale materials (0D, 1D and 2D) have simply found their way into water treatment applications. The nanoscale materials were extensively harnessed for versatile wastewater treatment applications as a standalone or nanocomposite adsorbents [ 28 ]. Their low cost, availability and promising potential to eliminate various contaminants have contributed to the circular economy [ 29 ].…”