Use of Nanostructured Layered Double Hydroxides as Nanofilters in the Removal of Fe²⁺ and Ca²⁺ Ions from Oil Wells

Abstract

Four new metal-aluminum layered double hydroxides (LDHs), Mg-Al(OH) 2 PO 4 (1), Mg-Al(OH) 2 PO 4 PF 6 (2), Ca-Al(OH) 2 SO 4 (3), and Ca-Al(OH) 2 PO 4 PF 6 (4), were prepared by the coprecipitation method followed by mild hydrothermal processing at 60°C. Mg 2+ and Ca 2+ in solution with Al 3+ were titrated with NaOH over 3-5 h to yield Mg-Al and Ca-Al layered double hydroxides, respectively, incorporating PO 4 3− , PO 4 3− PF 6 − , and SO 4 2− anions in the interlamellar spaces. e isolated compounds were characterized with the help of XRD, IR, and SEM/EDAX, and their ability to remove scale-forming ions from the aqueous system was studied with the help of atomic absorption spectroscopy (AAS). e SEM micrographs of Mg-O-Al-OH and Ca-O-Al-OH layers intercalated with PO 4 3− and/or [PO 4 PF 6 ] 4− anions are similar consisting of uniform nanospheres with an average size of 100 nm, while the M-O-Al-OH layer of compound 3, intercalated with SO 4 2− anions, consists of hexagonal nanoplate crystals. In the infrared spectra, the characteristic absorption band for water molecules was observed in all the compounds. e XRD pattern showed that d 012 and d 104 peaks of M-Al-PO 4 LDHs corresponding to interplanar spacing of 3.4804 and 2.5504Å, respectively, shifted to higher 2θ values for the M-Al-PO 4 PF 6 system, which indicates a decrease in the interlamellar spacing as PF 6 − was incorporated along with PO 4 3− anion. e XRD pattern for Ca-Al-SO 4 LDHs was quite different, showing the presence of lowangle peaks at 2θ � 11.68 and 14.72°. e results of the column adsorption studies showed that there was a significant removal of Ca 2+ by all the compounds under investigation with an efficiency of 84-99%. However, compounds 1 and 2 remove Fe 2+ effectively with the efficiency of 98.73 and 99.77%, respectively; compounds 3 and 4 were shown to have little or no effect.

Nano/Micro-Structured Materials: Synthesis, Morphology and Applications

“…Khansi et al [7] synthesized four metal-aluminum layered double hydroxides (LDHs): Mg-Al(OH) 2 PO 4 , 1, Mg-Al(OH) 2 PO 4 PF 6 , 2, Ca-Al(OH) 2 SO 4 , 3 and Ca-Al(OH) 2 PO 4 PF 6 , 4, by co-precipitation method followed by mild hydrothermal processing at 60°C. In Figure 1, we present the SEM micrographs of the as-synthesized LDHs.…”

“…The synthesized nanostructured zinc and calcium phosphonates were applied in the removal of scale-forming ions from aqueous solution. A similar procedure reported for LDHs [7] was used. Small amount of glass wool was first introduced into the syringe followed by 0.2 g of the nanoparticles.…”

“…The presence of such contaminants as polycyclic aromatic hydrocarbons (PAHs), poly chlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane (DDT) and heavy metals like mercury, lead and manganese poses risk to both human health and the aquatic biota [3]. Functionalized magnetic metal oxide nanoparticles [4,5], silver nanoparticles as well as nanostructured layered double hydroxides have proven useful in the remediation of toxic waste in the water environment, inhibition of bacterial and fungi activities [6] and removal of scale forming ions from oil wells [7].…”

“…(a) SEM micrograph of Mg-Al(OH) 2 PO 4 , 1; (b) SEM micrograph of Mg-Al(OH) 2 PO 4 PF 6 , 2; (c) SEM micrograph of Ca-Al(OH) 2 SO 4 , 3; (d) SEM micrograph of Ca-Al(OH) 2 PO 4 PF 6 , 4. Source: Khansi et al[7].…”

“…Results for the removal of Fe 2+ and Ca 2+ ions from aqueous solutions by compounds 1-4. Source: Khansi et al[7].…”