Precipitation of (Mg/Fe-CTAB) - Layered double hydroxide nanoparticles onto sewage sludge for producing novel sorbent to remove Congo red and methylene blue dyes from aqueous environment

Abstract

Preparation of new sorbent from precipitation of nano-sized (Mg/Fe-CTAB)- layered double hydroxide (LDH) on the surfaces of sewage sludge byproduct to remove the anionic and cationic dyes was the focal point of this work. The presence of nanoparticles and enlarged of interlayers by CTAB intercalation have increased the sludge surface area from 5.34 to 10.32 m²/g. The CTAB mass 0.03 g/50 mL, sludge dosage 1 g/50 mL and (Mg/Fe) molar ratio 2 were the best preparation conditions required to obtain effective sorbent with efficiencies exceeded 93% for MB and CR dyes. These efficiencies were obtained under operational conditions for batch study of 0.5 g coated sludge per 50 mL colored dye solution, initial pH 3 (for CR) and 12 (for MB), and time 3 h for 10 mg/L dyes at 200 rpm. Models of Langmuir and pseudo second-order have a high capability in the representation of sorption records with maximum capacities of adsorption 163.6 and 132.6 mg/g for CR and MB dye, respectively. The X-ray diffraction analysis proved that the calcite occurred mainly at 2θ = 29.8° while quartz corresponded to the 21, 26.6, 36.4, 36.9, 50.1, 60.01 and 68.4°. Characterization tests showed that nano-sized particles of magnesium/iron were precipitated on the sludge due to the formation of hydrotalcite-like compounds with an increase in the percentages of Mg and Fe from 0.87 and 1.36 to 4.25 and 3.03%, respectively. The results showed that the electrostatic attraction, intra-particle diffusion and hydrogen bonding were predominant mechanisms for removal of CR and MB onto coated sludge.

Keywords: CTAB surfactant; Congo red; Contamination; Layered double hydroxide; Methylene blue; Treatment.