Assessing the potential of red mud and dehydrated mineral mud mixtures as soil matrix for revegetation

The disposal of red mud (RM) and dehydrated mineral mud (DM) presents a significant challenge for the global alumina industry. This study proposes a novel disposal method for RM and DM, which uses mixtures of RM and DM as a soil matrix for revegetation in the mining area. RM mixed with DM effectively alleviated its salinity and alkalinity. X-ray diffraction analysis indicated that reduction of salinity and alkalinity may be due to the release of chemical alkali from sodalite and cancrinite. Applications of ferric chloride (FeCl3), gypsum, and organic fertilizer (OF) improved the physicochemical properties of the RM-DM mixtures. FeCl3 significantly reduced available Cd, As, Cr, and Pb content in the RM-DM, while OF significantly increased the cation exchange capacity, microbial carbon and nitrogen, and aggregate stability (p < 0.05). Micro-computed tomography and nuclear magnetic resonance analysis showed that amendment with OF and FeCl3 increased the porosity, pore diameter, and hydraulic conductivity in the RM-DM mixture. The RM-DM mixtures had low leaching of toxic elements, indicating low environmental risk. Ryegrass grew well in the RM-DM mixture at a ratio of 1:3. OF and FeCl3 significantly increased the ryegrass biomass (p < 0.05). These results suggested that RM-DM amended with OF and FeCl3 has a potential application in the revegetation of areas after bauxite mining.

Construction of arsenic selective chelating resin with iron precursor for removal of low-concentration arsenic: Breakthrough modeling and field deployment

The presence of exorbitant arsenic contamination in the aquatic environment causes astronomically immense health quandaries affecting millions of people, which may lead to death in the case of prolonged indigestion of arsenic-containing drinking water. Herein, we are reporting porous chelating resin with an iron precursor for the removal of arsenic ions from water. Weak acid cation resin was functionalized under varying experimental conditions to get a suitable resin with high arsenic uptake. The theoretical results revealed that the maximum Langmuir adsorption capacities of 3.27 mg g-1 and 1.13 mg g-1 were achieved for As(V) and As(III), respectively. The kinetics of adsorption followed the pseudo-second-order (PSO) model with a high determination coefficient (R2) of 0.9963 and 0.9895 for As(V) and As(III), respectively. The Adams-Bohart, Thomas, Yoon-Nelson, and Pore diffusion models were used to identify the breakthrough curve in the fixed bed adsorption column. The column performance improved with a larger bed height (55 cm), low concentration of influent (0.25 mg L-1), and low flow rate of influent (80 mL min-1). Under this condition, the breakthrough time and exhaustion time were 314 min and 408 min for As(V) and 124 min and 185 min for As(III), respectively.

Continuous fixation of dissolved arsenite from flooded soil by cooperating ferrihydrite with Geobacter sulfurreducens

The fixed arsenic in soil is easy to be released into the aquatic environment in the form of arsenite (As(III)) with high toxicity and mobility due to the eutrophication of environment under anaerobic conditions. However, As(III) is difficult to be fixed in situ continuously by traditional methods, especially for the most efficient fixation method by iron ores. Based on that Fe(II) could promote the fixation of As(III), this study investigated the possibility that Geobacter sulfurreducens (G. sulfurreducens) cooperates with ferrihydrite to fix released As(III) from flooded soil in a glass column continuously under anaerobic conditions. During 42 days of operation of reactors that simulated the actual flooded soil environment, the concentration of released As(III) in the reactor with adding G. sulfurreducens and ferrihydrite is always lower than that in reactors with adding ferrihydrite or no treatment. Compared with reactors without treatment, the accumulated content of released As(III) (2455.0 ± 313.1 μg) decreased by 39.4% in the reactor with adding G. sulfurreducens and ferrihydrite on the last day, while that in reactors with adding ferrihydrite only decreased by 11.6%, respectively. These were caused by the cooperation of G. sulfurreducens and ferrihydrite, which increased the relative abundance of iron-reducing microorganisms to inhibit metabolisms of As-reducing microorganisms, inhibited the quick release of As(III) from solid soil, and promoted the release of iron to accelerate the formation of stable secondary ores with As. This study could provide an environmentally friendly method to fix dissolved As(III) pollutants from soil continuously.

Structure and Population of Complex Ionic Species in FeCl2 Aqueous Solution by X-ray Absorption Spectroscopy

Technologies for mass production require cheap and abundant materials such as ferrous chloride (FeCl₂). The literature survey shows the lack of experimental studies to validate theoretical conclusions related to the population of ionic Fe-species in the aqueous FeCl₂ solution. Here, we present an in situ X-ray absorption study of the structure of the ionic species in the FeCl₂ aqueous solution at different concentrations (1–4 molL⁻¹) and temperatures (25–80 °C). We found that at low temperature and low FeCl₂ concentration, the octahedral first coordination sphere around Fe is occupied by one Cl ion at a distance of 2.33 (±0.02) Å and five water molecules at a distance of 2.095 (±0.005) Å. The structure of the ionic complex gradually changes with an increase in temperature and/or concentration. The apical water molecule is substituted by a chlorine ion to yield a neutral Fe[Cl₂(H₂O)₄]⁰. The observed substitutional mechanism is facilitated by the presence of the intramolecular hydrogen bonds as well as entropic reasons. The transition from the single charged Fe[Cl(H₂O)₅]⁺ to the neutral Fe[Cl₂(H₂O)₄]⁰ causes a significant drop in the solution conductivity, which well correlates with the existing conductivity models.

Corrosion mitigation of mild steel in hydrochloric acid solution using grape seed extract

Plant extracts have gained a lot of attention due to their ecofriendly nature for corrosion inhibition. In this study, we examined the inhibition performance of grape seed extract as an eco-environmental inhibitor for mild steel in hydrochloric acid medium. Electrochemical impedance spectroscopy, potentiodynamic polarization, and electrochemical noise techniques were employed to study mild steel's electrochemical behavior in the hydrochloric acid solutions containing grape seed extract. Results depicted that grape seed extract could successfully inhibit the corrosion of mild steel. Besides, water droplet contact angle, field-emission scanning electron microscopy coupled with energy dispersive spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscopy were utilized to study the surface of mild steel specimens after dipping in acidic solutions. Electrochemical impedance results showed a corrosion efficiency of about 88% in 300 ppm of grape seed extract. Also, results revealed more compact corrosion products with improved integrity in the presence of grape seed, which confirmed electrochemical test results.