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)2PO4(1), Mg-Al(OH)2PO4PF6(2), Ca-Al(OH)2SO4(3), and Ca-Al(OH)2PO4PF6(4), were prepared by the coprecipitation method followed by mild hydrothermal processing at 60°C. Mg2+and Ca2+in solution with Al3+were titrated with NaOH over 3–5 h to yield Mg-Al and Ca-Al layered double hydroxides, respectively, incorporating PO43−, PO43−PF6−, and SO42−anions in the interlamellar spaces. The 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). The SEM micrographs of Mg-O-Al-OH and Ca-O-Al-OH layers intercalated with PO43−and/or [PO4PF6]4−anions are similar consisting of uniform nanospheres with an average size of 100 nm, while the M-O-Al-OH layer of compound3, intercalated with SO42−anions, consists of hexagonal nanoplate crystals. In the infrared spectra, the characteristic absorption band for water molecules was observed in all the compounds. The XRD pattern showed thatd012andd104peaks of M-Al-PO4LDHs corresponding to interplanar spacing of 3.4804 and 2.5504 Å, respectively, shifted to higher 2θvalues for the M-Al-PO4PF6system, which indicates a decrease in the interlamellar spacing as PF6−was incorporated along with PO43−anion. The XRD pattern for Ca-Al-SO4LDHs was quite different, showing the presence of low-angle peaks at 2θ = 11.68 and 14.72°. The results of the column adsorption studies showed that there was a significant removal of Ca2+by all the compounds under investigation with an efficiency of 84–99%. However, compounds1and2remove Fe2+effectively with the efficiency of 98.73 and 99.77%, respectively; compounds3and4were shown to have little or no effect.