Reclamation of an arsenic-bearing gypsum via acid washing and CaO-As stabilization involving svabite formation in thermal treatment

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

“…While due to the characteristics of amphoteric hydroxide, some HM species have dissolved out in the forms of Pb­(OH) 4 2– , Cr­(OH) 4 – , Cu 2 (OH) 2 2+ , and Zn­(OH) 4 2– , etc . − Meanwhile, Cr (VI) and As species in the forms of CrO 4 2– , HAsO 4 2– , and HAsO 3 2– anions are of high mobility. , When the pH of alkaline RM is neutralized via CaCl 2 ·2H 2 O addition, the interfacial OH – on Fe and Al (hydr)­oxides surface is consumed, enhancing its adsorption effect to HM species. , In this process, as the main component in RM, hematite plays an important role. The dissociative HM cations and hydrated metal ions, such as Pb 2+ , Cu 2+ , Zn 2+ , Cr 3+ , Pb­(H 2 O) 6 2+ , Zn­(H 2 O) 6 2+ , Cr­(H 2 O) 6 3+ , and [Cr­(H 2 O) 2 OH] 2+ could be adsorbed on the surface of hematite via proton exchange effect following eqs –. ,− In the view at the atom level, as shown in Figure a, according to the reported K-edge extended X-ray absorption fine structure (EXAFS) and DFT calculation studies, the monodentate mononuclear, bidentate, and more complicated tridentate corner-sharing binuclear surface complexes could be proposed. ,− Furthermore, Cr­(VI) anions should be adsorbed on hematite surface via forming inner-sphere monodentate mononuclear and bidentate binuclear surface complexes (Figure b). ,,− While as shown in Figure c, As­(III/V) anions would be immobilized as monodentate and bidentate complexes. − Notably, due to the vast Ca 2+ addition, As species could also be stably immobilized in the forms of insoluble Ca–As salt, such as typical Ca 3 (AsO 4 ) 2 and Ca 5 (AsO 4 ) 3 OH with K sp at 10 –21.14 and 10 –37.76 , which is regarded as a considerable As stabilization factor. − …”

Spatial Distribution and Migration Mechanisms of Toxic Elements in Farmland Soil at Nonferrous Metal Smelting Site

“…Numerous results have proven that the oxides of Fe and Mn have a good adsorption effect on TE [47][48][49]. CaO is also the most effective mineral for absorbing TE in soil [1,50,51]. Therefore, the spatial distribution of TE is intertwined with many factors, including soil clay, pH, TOC, CEC, Fe 2 O 3 , Mn, and CaO.…”

“Soil for Soil Remediation” Strategy Driven on Converting Natural Soils into Fe2O3-CAN-Type Zeolite Composites for Dual Ionic Heavy Metal-Contaminated Soil Remediation: Universality, Synergistic Effects, and Mechanism

“…6−8 For example, in the typical Cd(II)/As(III) co-contaminated areas of South China, the hazardous Cd(II) and As(III) in soils can be easily up-taken by crops and vegetables, which would further cause dangerous bioaccumulation problems and flow into the human body via the food chain, resulting in irreversible chronic diseases, cancers, and even death. 9,10 Furthermore, since the Cd(II) and As(III) species are present in soil in the forms of Cd 2+ cations and AsO 2 − anions, respectively, the traditional remediation materials dedicated to remediating mono ions are unable to achieve satisfactory synergistic dual ion remediation effects. 11 Therefore, developing novel soil remediation strategies together with cost-effective remediation materials with cation/anion dual ion capture capacity is highly demanded.…”

“…Soil environmental safety is critical to the sustainable development of global agriculture, graziery, and forestry . Worryingly, owing to industrial discharge activities of the manufacturing industry, power stations, smelting plants, and mineral processing in the past decades, high concentrations of heavy metals (HMs), such as Pb­(II), Cu­(II), Cr­(VI), Cd­(II), and As­(III), has been diffused into soil environments, resulting in severe soil contamination problems. − Among various types of polluted soils, the cation/anion-type HM co-contaminated soil is of significant pollution hazards with high remediation difficulties. − For example, in the typical Cd­(II)/As­(III) co-contaminated areas of South China, the hazardous Cd­(II) and As­(III) in soils can be easily up-taken by crops and vegetables, which would further cause dangerous bioaccumulation problems and flow into the human body via the food chain, resulting in irreversible chronic diseases, cancers, and even death. , Furthermore, since the Cd­(II) and As­(III) species are present in soil in the forms of Cd 2+ cations and AsO 2 – anions, respectively, the traditional remediation materials dedicated to remediating mono ions are unable to achieve satisfactory synergistic dual ion remediation effects . Therefore, developing novel soil remediation strategies together with cost-effective remediation materials with cation/anion dual ion capture capacity is highly demanded.…”