Removal of Chromates and Sulphates by Mg/Fe LDH and Heterostructured LDH/Halloysite Materials: Efficiency, Selectivity, and Stability of Adsorbents in Single- and Multi-Element Systems

Abstract

Industrial wastewaters often contain mobile and toxic anions that cannot be removed by precipitation techniques and most known adsorbents. Layered double hydroxides (LDH) are excellent scavengers of anions; however, their use in real applications is of minor importance owing to their swelling behavior and high cost of production. The performed research shows the possibility of obtaining Mg/Fe LDH using natural magnesite. Moreover, heterostructured LDH/halloysite materials were synthesized. The adsorption efficiency of these materials was very high in both single- and multi-element systems, confirming the LDH selectivity. This was with the exception of wastewaters containing a high concentration of chlorides, which clearly hampered the removal of Cr(VI) and S(VI). The measurements indicated that LDH dissolution took place to a small extent (<10 wt%). The LDH/halloysite materials showed lower efficiency than the raw LDH; however, the clay presence has several benefits in terms of future applications: (i) it significantly reduces the pH, especially in contrast to the calcined LDH, which enables the reuse or safe disposal of purified water; (ii) it reduces swelling of the composite, which opens the possibility for applications in column adsorption; (iii) it induces dual adsorption properties through additional cation adsorption; and (iv) it substantially lowers the price of the adsorbent.

Ironmaking and Steelmaking Slags as Sustainable Adsorbents for Industrial Effluents and Wastewater Treatment: A Critical Review of Properties, Performance, Challenges and Opportunities

“…The findings from these and several other studies clearly demonstrate the potency of LDH-based adsorbents in the removal of anions and cations from both single-and multi-solute solutions [136,[168][169][170][171][172][173][174][175][176]. In particular, the findings highlight the potential to utilise ironmaking and steelmaking slags as low-cost, high-value feedstocks in the synthesis of novel LDH-based adsorbents for treating industrial effluents and wastewaters.…”

“…Layered double hydroxides (LDHs) belong to a class of nanostructured and lamellar-structured anionic clay minerals consisting of positively charged metal hydroxide sheets, exchangeable counter ions and water molecules in the hydrotalcite-like interlayers [136,[168][169][170][171][172][173][174]. The general formula of an LDH can be expressed as [M 2+ 1-x M 3+ x (OH) 2 ] x+ (A n-) x/n • mH 2 O, where M 2+ and M 3+ represent divalent and trivalent metal cations such as Mg 2+ and Al 3+ , respectively; A nrepresents an intercalated anion for charge compensation; x is the charge density (c.a.…”

“…0.25 < x <0.33); and m is the number of interlayer water molecules [136,168,170,172]. Due to the ubiquitous structural and physicochemical properties such as interlayer anion-exchange ability, easy accommodation of cations in the hydroxide layer and strong basicity, LDHs have attracted widespread attention as novel adsorbents in the treatment of industrial effluents and wastewaters [136,[168][169][170][171][172][173][174][175][176][177].…”

A Comparative Study on Color Stability of Anthocyanin Hybrid Pigments Derived from 1D and 2D Clay Minerals

“…The bending vibration of H 2 O was located at around 1630 cm −1 . The peaks at about 1100–1000 cm −1 and 475–800 cm −1 were originated from the Si-O bending and stretching vibrations of the tetrahedral sheets, while the bands of octahedral Al-Al-OH bending vibrations were found at around 910 cm −1 [46,47]. The absorption bands at 3500–2900 cm −1 and at 1735 cm −1 of the extracted ACN corresponded to the O-H groups stretching vibration and the C=O groups bending vibration, respectively (Figure 2b).…”

Synthesis of MgFe Layered Double Hydroxide from Iron-Containing Acidic Residual Solution and Its Adsorption Performance

“…From the multitude of Me 2+ /Me 3+ LDH types, much focus has been directed toward the Mg 2+ /Fe 3+ pair. A literature search revealed that Mg/Fe-LDH has been used for phosphate removal from aqueous solutions [9][10][11]; as adsorbent materials of various heavy metals, such as Cr, As, Pb, Zn, Cu, Se, Sb, and so forth [12][13][14][15][16]; for treatment of aqueous solutions contaminated with different reactive dyes [17][18][19]; or as a catalyst [20][21][22]. Presently, there is a focus on obtaining cheaper adsorbent materials that still retain properties similar to those obtained from pure chemicals.…”