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

Abstract

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.

The synergistic hydration mechanism and environmental safety of multiple solid wastes in red mud-based cementitious materials

“…The leaching concentration of Hg in a sample soaked for 15 days appeared to show an inflection point, which was related to the fact that Hg was initially adsorbed on the surface of the hydration product and then existed freely in the leaching solution. The adsorption of Hg in RM was rapid, and the adsorption kinetic process was best described by Ho’s pseudo-second-order equation (Rubinos David and Teresa 2015 ). Pb and As could replace Ca in hydration products, while Cr and Cd could be wrapped in the layered structures of the hydration products (Liu et al 2009 ).…”

High‐efficiency preparation of Fe–Al based flocculants from red mud by microwave selective carbothermic reduction and magnetic separation

“…The adsorption of lead ions and disperse blue 2BLN in water by modified red mud was elaborated, and the maximum adsorption capacity were determined to be 27 mg/g and 45 mg/g 14,15 . The adsorption of mercury in water was researched using red mud as an adsorbent, and its adsorption concentration was found to be close to that of inorganic commercial adsorbent 16 . Previous literature has revealed the optimum adsorption capacity of red mud as adsorbent for various cations, including Cd 2+ (108.6 mg/g), Cr(VI) (22.7 mg/g), Cu 2+ (67.2 mg/g), Pb 2+ (173.4 mg/g), and Zn 2+ (133.0 mg/g) 17,18 .…”

“…14,15 The adsorption of mercury in water was researched using red mud as an adsorbent, and its adsorption concentration was found to be close to that of inorganic commercial adsorbent. 16 Previous literature has revealed the optimum adsorption capacity of red mud as adsorbent for various cations, including Cd 2+ (108.6 mg/g), Cr (VI) (22.7 mg/g), Cu 2+ (67.2 mg/g), Pb 2+ (173.4 mg/g), and Zn 2+ (133.0 mg/g). 17,18 However, it was pointed out that massive iron oxide in red mud not only consumes much sodium hydroxide but also gives rise to a lower utilization rate of hydrochloric acid due to direct acid leaching.…”

Characterization of Indoor Molds after Ajka Red Mud Spill, Hungary

“…Red mud is a caustic (pH > 12.8-13.0) material consisting of Fe 2 O 3 (40-45%), Al 2 O 3 (10-15%), SiO 2 (10-15%), CaO (6-10%), TiO 2 (4-5%), and Na 2 O (5-6%) in hydrated forms [2]. Minor or trace elements in this material can be K, Cr, As, Hg, V, Ni, Ba, Cu, Mn, Pb, Zn, Zr, Y, Sc, Ga, etc., and even 232 Th and 238 U, which have radioactivity about 10-fold above the soil background [3][4][5][6][7][8]. On the 4th of October 2010 the dam of red mud reservoir number X (ten) of the Ajkai Timföldgyár Zrt.…”