Sequestration of orthophosphate by Ca2Al-NO3 layered double hydroxide – Insight into reactivity and mechanism

Pretreatment by recyclable Fe3O4@Mg/Al-CO3-LDH magnetic nano-adsorbent to dephosphorize for the determination of trace F− and Cl− in phosphorus-rich solutions

“…, the interlayer anion choice will play a key role. Based on LDHs, there are some good options to use the Cl À anion, 17,20,[22][23][24]31 or NO 3 À anion, 19,21,32 or Cl À and SO 4 2À anions 25 as the interlayer anion. They can be used to adsorb PO 4 3À effectively, but their adsorption efficiencies are inevitably affected by carbon dioxide (CO 2 ) or carbonate (CO 3 2À )…”

Atomic Level Understanding of Orthophosphate Adsorption by Magnesium Aluminum-Layered Double Hydroxides—A Multitechnique Study

“…In-situ powder X-ray diffractograms were recorded with a Philips X'Pert Pro diffractometer using CuKα radiation (λ = 1.5405 Å) over the 3-75 ° 2θ range at an accelerating voltage of 40 kV, a current of 30 mA and a scan speed of 2 °min −1 using the XRD flow cell described elsewhere. 29 FT-IR and Raman spectroscopy: FT-IR spectra were recorded from 4000-400 cm -1 on a Nicolet-5700 spectrophotometer by the KBr pellet method. The pellet was made by grinding approx.…”

“…The formation of phosphate minerals, e.g. newbeyrite, 27,49 bobierite, 27,67 aluminum phosphate, 36 calcium phosphates 29,68 and iron phosphates, 26 have been detected by 31 P SSNMR and PXRD after exposure of LDH to phosphate. Magnesium phosphate minerals were the predominant phase identified from adsorption experiment with a starting pH of 7 and a final pH of 12 except for a broad resonance in the region 0-5 ppm, tentatively assigned to phosphate affiliated with the MgAl-LDH.…”

“…The relative contribution from the suggested mechanisms is essential to design an efficient and recyclable filter material but have to our knowledge not been quantified. PXRD has extensively been used to probe intercalation of phosphate in the interlayer, seen as a shift of the (00 l ) reflections toward low 2θ values and always associated with a loss in crystallinity. ,,,,,,, Moreover, PXRD clearly shows that the CaAl-LDH structure is destroyed upon exposure to phosphate, resulting in the formation of calcium phosphates such as brushite (CaHPO 4 ·2H 2 O) and hydroxyapatite (Ca 5 (PO 4 ) 3 (OH)). ,, However, it has also become evident that the presence of amorphous phases are not detected by PXRD , and sorption to the LDH surface cannot be probed by PXRD. Furthermore, the LDH used for phosphate adsorption are normally prepared by coprecipitation at constant pH or at increasing pH using thermal hydrolysis of urea (the so-called “urea method”) .…”

Stability of magnetic LDH composites used for phosphate recovery

“…h [37]. Pi sorption to hydrocalumite-type CaAl and CaFe LDH showed ready dissolution of LDH and formation of Ca5(PO4)3OH and Ca(HPO4)•2H2O precipitates in non-buffered solutions [24,38]. MgFe-CO3 LDH dissolved completely with formation of MgHPO4•3H2O in 24h when exposed to very high Pi concentrations (> 1 M) at pH 7, demonstrating that not only the pH but also the high Pi concentration could also stimulate the dissolution of LDH [39].…”