Dual Ions Neutralized and Stabilized Red Mud for Chromium(VI) Polluted Soil Remediation

Abstract

Both alkaline heavy metal (HM) contaminated red mud (RM) recycling and Cr­(VI) polluted soil remediation are severe hazardous environmental problems. Herein, we developed a novel integrated approach to neutralize and stabilize the hazardous RM via the introduction of Ca2+ and Cl– dual ions. When 3% CaCl2·2H2O is added, the pH of RM is reduced from 11.0 to 8.9, and the Pb, Cr, Zn, Cu, and As leaching concentrations from RM are suppressed lower than the environmental standards of China and the World Health Organization (Pb, Cr, Zn, Cu < 0.50 mg/L; As < 10 μg/L). Detailed mechanism studies reveal that the pH neutralization is attributed to the novel OH– flocculation effect ascribing to Ca2+ charge neutralization and Cl– promoted proton neutralization. Furthermore, as the pH decreases, the HM adsorption capacity of RM is enhanced, achieving stable HM immobilization. The treated RM can be further employed to remediate Cr­(VI) contaminated soil (Cr concentration 570 ppm; treated RM weight percentage in soil 5.0%), which can suppress 56.0% Cr mobility in soil and 68.4% bioaccumulated Cr in the harvested vegetables. Overall, this work demonstrates an ecofriendly “waste-to-soil remediation” strategy to solve both the solid waste and soil pollution problems.

Stable Aggregate Formation and Microbial Diversity Resilience in Soil Formation of Bauxite Residue: Roles of Extracellular Polymeric Substances Secreted by Penicillium oxalicum

“…Compared with organic−alkaline mineral complex adsorption by proteins, the autopeak intensity responsible for carboxylate and hydrogen bond at 1002 and 3500 cm −1 were strengthened in that adsorption by polysaccharides. According to the rules for the explanation of the peak in 2D-FTIR-correlation spectroscopy maps of polysaccharides and proteins, 51,52 our results indicated that the spectral changes followed the order 1002 (carboxyl groups) > 3500 (hydrogen bond) > 1650 (peptide) > 650 (phosphatide) cm −1 and 1002 > 650 > 3500 > 1650 cm −1 , respectively. This may attribute to the selective adsorption was depended on functional groups' properties.…”

Multi-Walled Carbon Nanotubes Modified NiCo2S4 for the Efficient Photocatalytic Reduction of Hexavalent Chromium

“…Among them, inorganic anions, such as NO3 − , Cl − , SO4 2− , and PO4 3− , may have two inhibitory effects: the first is the competitive adsorption of ions and pollutant molecules to the active sites on the TiO2 surface, leading to a decrease in the photocatalytic efficiency. The second is that anions can react with the photogenerated holes, thus reducing the amount of oxides that degrade the pollutant molecules [12,63]. We investigated the effect The separation rate of photogenerated electron-hole pairs is an essential factor affecting the photocatalytic activity of a photocatalyst.…”

“…Thus, the reduction of Cr(VI) to Cr(III) is considered to be a critical step in the treatment of wastewater containing Cr(VI) [8][9][10]. In addition, Cr(VI) can quickly enter food chains and destroy human enzyme systems through ingestion, inhalation, or skin contact, which poses a considerable threat to human health [11,12]. Studies have shown that releasing potentially carcinogenic, highly toxic, and non-degradable Cr(VI) into the environment can cause health problems such as pulmonary gland obstruction, epidermal irritation, hepatitis, and cancer [11,13,14].…”

Sustainable Approaches for Wastewater Treatment: An Analysis of Sludge-Based Materials for Heavy Metal Removal from Wastewater by Adsorption

“…A study on the removal of heavy metals by iron ore sludge found that it can be used as a promising adsorbent for the simultaneous removal of heavy metals (As 2+ , Mn 2+ , Zn 2+ , Cd 2+ , and Pb 2+ ) in water, which was described as chemical adsorption by kinetic studies [67]. Red mud is an industrial by-product from the alkaline refining process that has been used for adsorption owing to the small particle size and large surface area [84]. Bai et al found that red mud effectively removes Pb 2+ , Cd 2+ , and Cu 2+ , with a maximum removal efficiency of 94.5%, 92.8%, and 78.1%, respectively [85].…”