Synthesis and properties of CaAl-layered double hydroxides of hydrocalumite-type

Abstract

CaAl-layered double hydroxides (CaAl-LDHs) with various carbonate ion contents are essentially formed in Bayer liquors during the causticisation step in alumina production. Under well-defined conditions hemicarbonate is formed, which is beneficial in the process of retrieving both Al(OH) − 4 and OH − ions. In the current work, Ca2Al-LDHs with various carbonate contents were prepared by the co-precipitation procedure and the products were dried in different ways. Structural information was obtained by a variety of methods, such as X-ray diffractometry (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). Elemental maps were constructed through a combination of SEM images and EDX measurements. The targeted CaAl-hydrocalumites were successfully synthesised. It was found that the method used for drying did not influence the basal spacing although it significantly altered the particle sizes.

Optimisation of the synthesis parameters of mechanochemically prepared CaAl-layered double hydroxide

“…e l s e v i e r . c o m / l o c a t e / c l a y the preparation of these materials are the co-precipitation (Tóth et al, 2014) and the urea hydrolysis methods. The co-precipitation method is a solution-phase chemical method, in which aqueous solutions of M(II) and M(III) cations are used as precursors.…”

“…Their most important and most commonly used feature is that the interlayer (intercalated) anions can be replaced by other, even large organic or inorganic anions (Reichle, 1986;Khan and O'Hare, 2002;Sipiczki et al, 2012). LDHs containing Ca(II) and Al(III) can be found in nature as a mineral called hydrocalumite (Brown and Gastuche, 1967), and can also be synthesised (Tóth et al, 2014). The structure of these materials was studied and characterised thoroughly in the literature (Rousselot et al, 2002).…”

Perchlorate‐Intercalated Layered Double Hydroxide of Ca and Al: Synthesis, Structure Refinement, and Reversible Dehydration

“…Six of the seven coordination sites of Ca 2+ are occupied by hydroxyl ions of the metal hydroxide layer, and the seventh coordination is satisfied by an intercalated water molecule (ii) To facilitate the seventh coordination, the Ca 2+ ion is displaced to an acentric position along the three fold axis of the crystal resulting in a puckering of the plane of the metal ions. (iii) The composition of the hydrocalumites is invariant at [Ca 2+ ]/[M 3+ ] = 2 (M = Al, Fe, Sc),, whereas this ratio is known to vary in the range 2–4 in the case of LDHs comprising other divalent cations , . An attempt made to synthesize Ca‐rich phases in the [Ca‐Al‐Cl] LDH system yielded a mix of the 2:1 LDH and Ca(OH) 2.…”

Placing Ni(II) Ions in Various Positions In/On Layered Double Hydroxides: Synthesis, Characterization and Testing in C–C Coupling Reactions

“…Layered double hydroxide (LDH) has several advantageous features facilitating wide range of applications possibilities. These are the large variety of salts, which can be applied for their preparation, the relative ease of their synthesis, the numerous methods available for this, the anion-exchange property-among the negatively charged layers having two metal ions most frequently, interlayer anions maintain charge neutrality [1]-, thus the possibility of post-synthetic modification [2][3][4][5].…”