Preparation of Modified Montmorillonite and Its Application to Rare Earth Adsorption

Abstract

Montmorillonite, the major clay mineral in the tailings of weathered crust elution-deposited rare earth ores, was modified as an excellent adsorbent to enrich rare earth ions from solutions. It was demonstrated that 5% H 2 SO 4 could be used as a modifier to effectively enhance the adsorption capacity of montmorillonite after modifying for 3 h with a liquid:solid ratio of 40:1 at 90 • C. A superior modified montmorillonite over montmorillonite on adsorption performance was analyzed by the XRD, FT-IR, SEM, and BET (Specific Surface Area and Pore Diameter Analysis). The adsorption behaviors of La 3+ and Y 3+ on modified montmorillonite were fitted well with the Langmuir isotherm model and their saturated adsorption capacities were 0.178 mmol/g to La 3+ and 0.182 mmol/g to Y 3+ , respectively. Furthermore, (NH 4 ) 2 SO 4 as a common leaching agent in weathered crust elution-deposited rare earth ores, were successfully used as the eluent to recover the adsorbed rare earth ions. and edges and this is responsible for giving superior activity to Mt as an adsorbent [12]. Mt is formed by negatively charged silicate layers (about 1 nm) connected by electrostatic interaction. It belongs to the 2:1 clay minerals, the basic structure unit of which is composed of two silica tetrahedrons with an interlayer of aluminum oxygen octahedron. The atoms in this interlayer, which are common to both sheets, become oxygen instead of hydroxyl [13]. The isomorph substitution of Al 3+ by Si 4+ in the tetrahedral sheet and by Mg 2+ or Zn 2+ in the octahedral sheet results in a net negative charge on the clay surface, which makes it gain the ability to absorb certain cations. Moreover, Mt invariably contains exchangeable cations and anions held to the surface. The prominent cations and anions found between the sheets are K + , Na + , Mg 2+ , Cl − etc., and these ions are easily exchanged by other lower valence ions, which mainly carries out between the crystal layers and shows no effect on the Mt structure [14]. Adsorption of cations onto Mt involves two distinct mechanisms: (1) an ion exchange reaction at permanent charge sites, and (2) formation of complexes with the surface hydroxyl groups [15]. However, the industrial application of Mt is limited due to the crystal structure and negative charge of natural clays and interlayer impurity defects [16]. Single modifications of Mt through acid activation, inorganic salts, and cationic surfactant or polymer activation have attracted considerable interest and the adsorption capability of clay minerals can be successfully improved through modification [17].In industry, the RE concentration of leachate from weathered crust elution-deposited RE ores is approximately 0.2-2.0 g/L [11]. Although the precipitation and extraction are used to recycle RE, there is still some residual RE in the liquor with the concentration approximately below 0.15 g/L. To some extent, a large amount of RE resources is wasted. Therefore, the reuse of dumped tailings to enrich and recover RE in low-concentration solution is ...

Fabrication, Characterization and Evaluation of an Alginate–Lignin Composite for Rare-Earth Elements Recovery

“…Wang et al [ 37 ] studied the adsorption behaviour of Nd(III) ions using o-carboxymethyl chitosan entrapped by silica. They reported that the adsorption capacity of o-carboxymethyl chitosan was significantly improved by support on SiO 2 and reached 53.04 mg/g at 328 K. The montmorillonite was prepared, modified and applied to adsorb La(III) and Y(III) by Liu et al [ 38 ]. The maximum adsorption capacities for the modified montmorillonite were 0.178 mmol/g for La(III) and 0.182 mmol/g for Y(III).…”

Sorption Behaviors of Light Lanthanides(III) (La(III), Ce(III), Pr(III), Nd(III)) and Cr(III) Using Nitrolite

“…The Montmorillonite was modified by hexadecyl trimethyl ammonium bromide (HDTMA) and sodium diethyl dithiocarbamate (DDTC). The maximum of sorption capacity for La(III) was 0.178 mmol/g and was higher than for Nitrolite [33].…”

Removal of Fluorine from RECl3 in Solution by Adsorption, Ion Exchange and Precipitation

“…With the change of the environ-ment of the solution system, especially at higher temperatures, RE 2 (CO 3 ) 3 was able to be hydrolyzed into RECO 3 (OH), and CO 2 was released again, which also indicates that the pores of the mixed phase may be caused by the release of CO 2 [20,21]. In this process, the porous surface of tRECO 3 (OH) has a strong adsorption effect on F − in the solution, and the adsorbed F − replaces OH − on the RECO 3 (OH) surface by ion exchange [22][23][24][25][26][27][28][29][30]. Finally, tREFCO 3 is generated on the RECO 3 (OH) surface.…”