Equilibrium uptake, isotherm and kinetic studies of Cd(II) adsorption onto iron oxide activated red mud from aqueous solution

Fabrication of core-shell structured magnetic nanocellulose base polymeric ionic liquid for effective biosorption of Congo red dye

Ionic liquids are considered to be a class of environmentally friendly compounds as combination of them with bioresource polymeric substances such as; cellulose, constitute emerging coating materials. Biosorption by polymeric ionic liquids exhibits an attractive green way that involves low cost and irrespective of toxicity. As a result, a novel polymeric ionic liquid has been developed by the reaction of one step synthesized Fe3O4-cellulose nanohybrid, epichlorohydrin and 1-methylimidazole and employed as a green sorbent for efficient biosorption of Congo red dye. Effective parameters on dye removing as well as their interactions were determined with response surface methodology (RSM). Congo red adsorption showed fast equilibrium time (11min) with maximum uptake of 131mgg(-1). Isotherm study revealed that Langmuir adsorption model can better describe dye adsorption behavior. Regeneration of the sorbent was performed with a mixture of methanol-acetone-NaOH (3.0molL(-1)) solution.

Composites based on PET and red mud residues as catalyst for organic removal from water

In this study, we obtained a composite based on carbon/iron oxide from red mud and PET (poly(ethylene terephthalate)) wastes by mechanical mixture (10, 15 and 20wt.% of PET powder/red mud) followed by a controlled thermal treatment at 400°C under air. XRD analyses revealed that the α-Fe2O3 is the main phase formed from red mud. TPR analyses showed that the iron oxide present in the composites undergoes reduction at lower temperature to form Fe(2+) species present in Fe3O4, indicating that the iron oxide in the composite can exhibit greater reactivity in the catalytic processes compared to the original red mud. In fact, catalytic tests showed that the composites presented higher capacity to remove methylene blue dye (MB), presenting about 90% of removal after 24h of reaction. The MB removal was also monitored by mass spectrometer with ionization via electrospray (ESI-MS), which demonstrated the occurrence of the oxidation process, showing the formation of MB oxidation products. The stability of the composites was confirmed after four reuse cycles. The results seem to indicate that PET carbon deposited over the iron oxide from red mud promotes adsorption of the contaminant allowing its contact with the iron atoms and their consequent reaction.

Removal of phosphate and chromium(vi) from liquids by an amine-crosslinked nano-Fe3O4 biosorbent derived from corn straw

A magnetic biocomposite based bio-sorbent (corn straw) was prepared after in situ co-precipitation with Fe²⁺ and Fe³⁺ solutions and amine functionalization.

Adsorption of phosphate on surface of magnetic reed: characteristics, kinetic, isotherm, desorption, competitive and mechanistic studies

A magnetic biocomposite was prepared by Fe₃O₄in situ co-precipitation and amine functionalization processes by using virgin reed as starting material.

Lanthanide metal–organic frameworks as selective microporous materials for adsorption of heavy metal ions

Four microporous lanthanide metal–organic frameworks (MOFs), namely Ln(BTC)(H₂O)(DMF)_1.1 (Ln = Tb, Dy, Er and Yb, DMF = dimethylformamide, H₃BTC = benzene-1,3,5-tricarboxylic acid), have been used for selective adsorption of Pb(ii) and Cu(ii).

Adsorption of Cd(II) by Mg-Al-CO3- and magnetic Fe3O4/Mg-Al-CO3-layered double hydroxides: Kinetic, isothermal, thermodynamic and mechanistic studies

Understanding the adsorption mechanisms of metal cations on the surfaces of solids is important for determining the fate of these metals in water and wastewater treatment. The adsorption kinetic, isothermal, thermodynamic and mechanistic properties of cadmium (Cd(II)) in an aqueous solution containing Mg-Al-CO3- and magnetic Fe3O4/Mg-Al-CO3-layered double hydroxide (LDH) were studied. The results demonstrated that the adsorption kinetic and isotherm data followed the pseudo-second-order model and the Langmuir equation, respectively. The adsorption process of Cd(II) was feasible, spontaneous and endothermic in nature. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy were used to explain the adsorption mechanisms. The characteristic XRD peaks and FTIR bands of CdCO3 emerged in the LDH spectra after Cd(II) adsorption, which indicated that the adsorption of Cd(II) by LDHs occurred mainly via CdCO3 precipitation, surface adsorption and surface complexation. Furthermore, the magnetic Fe3O4/Mg-Al-CO3-LDH can be quickly and easily separated using a magnet before and after the adsorption process.

Use of red mud (bauxite residue) for the retention of aqueous inorganic mercury(II)

The effectiveness of the oxide-rich residue from bauxite refining (red mud) to remove inorganic Hg(II) from aqueous solutions was assessed. The aspects studied comprised the kinetics of the process (t = 1 min-24 h), the effect of pH (3.5-11.5), the interacting effect between salt concentration (0.01-1 M NaNO3) and pH and the Hg(II) sorption isotherm. Hg leaching from spent red mud was evaluated using the toxicity characteristics leaching procedure (TCLP) method. The sorption of Hg(II) onto red mud was very fast, with most of Hg(II) (97.0-99.7%) being removed from 0.5-50 μM Hg solutions in few minutes. The kinetic process was best described by Ho's pseudo-second order equation, pointing to chemisorption as the rate controlling step. Hg(II) sorption efficiency was very high (% removal between 93.9 and 99.8%) within all the studied pH range (3.5-11.5) and added Hg concentrations (5 and 50 μM), being optimal at pH 5-8 and decreasing slightly at both lowest and highest pH. The effect of background electrolyte concentration suggests specific sorption as the main interaction mechanism between Hg(II) and red mud, but the increasing non-sorbed Hg concentrations at low and high pH for higher electrolyte concentrations also revealed the contribution of an electrostatic component to the process. The sorption isotherm showed the characteristic shape of high affinity sorbents, and it was better described by the Redlich-Peterson and Freundlich equations, which are models that assume sorbent heterogeneity and involvement of more than one mechanism. The estimated Hg(II) sorption capacity from the Langmuir equation (q m ~9 mmol/kg) was comparable to those of some inorganic commercial sorbents but lower than most bio- or specifically designed sorbents. The leachability of retained Hg(II) from spent red mud (0.02, 0.25 and 2.42 mmol Hg/kg sorbed concentration) was low (0.28, 1.15 and 2.23 μmol/kg, respectively) and accounted for 1.2, 0.5 and 0.1% of previously sorbed Hg, indicating that Hg(II) is tightly bound by red mud once sorbed.