Preparation Behavior of the Mg–Fe Hydrotalcite by Urea Method and Its Cr(VI) Sorption Property

Abstract

The hydrotalcite of Mg6Fe2(OH)16CO3 x 4.5H2O were synthesized using urea method by adjusting the initial pH and urea amount in the reaction solution. The results showed that the co-precipitation of Mg2+ with Fe3+ cations formed Mg-Fe LDH occurring at pH 8.48-9.35. The pH played a crucial role in the Mg-Fe LDH precipitation by controlling urea/Fe3+ molar ratio in the reaction solution at 105 degrees C. The optimized urea/Fe3+ molar ratio was 12.0, where the relative yield of the Mg-Fe LDH was 80.0% and the Mg-Fe LDH was highly crystalline with small particle sizes (1-2 μm). The affinity of the Mg-Fe mixed oxide (Mg-Fe LDO) with Cr(VI) was studied as a function of contact time, initial pH, temperature of the solutions and calcined time of Mg-Fe LDH. The adsorption conditions were optimized using response surface methodology. The maximum adsorption capacity of 38.86 mg/g was achieved at 85 min with the conditions of initial pH 5.5, temperature 55 degrees C and calcined time 4 h. It was concluded that the Mg-Fe LDO can be used as an adsorbent to removal Cr(VI) in aqueous solutions.

Layered double hydroxides and LDH-derived materials in chosen environmental applications: a review

“…Therefore, urea enables an efficient pH control and the formation of mono-dispersed LDH materials with high crystallinity through a low-cost method (Adachi-Pagano et al 2003;Yang et al 2004;Zeng et al 2009a;Xu et al 2016;Park et al 2018). The purity and crystallinity of hydrotalcite phases can also be optimized by tuning the M II :M III molar ratio, the urea concentration, and the ageing time (Costantino et al 1998;Zeng et al 2009a;Berber et al 2013;Montañez et al 2014;Zhang et al 2014;Bian et al 2016;Xu et al 2016;Park et al 2018). As an exemple, Berber et al (2013) identified the optimal synthesis conditions to obtain uniform and highly crystalline hydrotalcite particles by using a urea/metallic cation molar ratio of 2, and 12h of ageing time at 120°C.…”