Competitive mechanism and influencing factors for the simultaneous removal of Cr(III) and Zn(II) in acidic aqueous solutions using steel slag: Batch and column experiments
“…In addition, the 250 mL glass vessels were covered by parafilm to avoid contact to air. Because OH – is the only ligand to complex dissolved Cr(III), the precipitated Cr(III) solid is expected to exist as Cr(OH) 3(s) with a maximum dissolved Cr(III) concentration of 0.1 μg/L at pH 7 based on the solubility product constant of Cr(OH) 3(s) ( K sp = 6.3 × 10 –31 ) . Furthermore, control experiments with pure Cr(OH) 3(s) solid exhibited a much lower rate constant for Cr(VI) formation via HOCl oxidation (i.e., 0.2 × 10 –3 vs 1.67 × 10 –3 L·m –2.…”
In drinking water distribution systems, the oxidation of zerovalent chromium, Cr(0), in iron corrosion scales by chlorine residual disinfectant is the dominant reaction to form carcinogenic hexavalent chromium, Cr(VI). This study investigates inhibitive corrosion control strategies through adjustments of chemical water parameters (i.e., pH, silicate, phosphate, calcium, and alkalinity) on Cr(VI) formation through oxidation of Cr(0) (s) by free chlorine under drinking water conditions. The results show that an increase in pH, silicate, alkalinity, and calcium suppressed Cr(VI) formation that was mainly attributed to in situ surface precipitation of new Cr(III) solids on the surface of Cr(0) (s) , including Cr(OH) 3(s) , Cr 2 (SiO 3 ) 3(s) , CrPO 4(s) , Cr 2 (CO 3 ) 3(s) , and Cr 10 Ca(CO 3 ) 16(s) . The Cr(III) surface precipitates were much less reactive with chlorine than Cr(0) (s) and suppressed the Cr redox reactivity. The concentration of surface Cr(III) solids was inversely correlated with the rate constant of Cr(VI) formation. Adding phosphate either promoted or inhibited the Cr(VI) formation, depending on the phosphate concentration. This study provides fundamental insight into the Cr(VI) formation mechanisms via Cr(0) oxidation by chlorine and the importance of surface precipitation of Cr(III) solids with different corrosion control strategies and suggests that increasing the pH/alkalinity and addition of phosphate or silicate can be effective control strategies to minimize Cr(VI) formation.
“…In addition, the 250 mL glass vessels were covered by parafilm to avoid contact to air. Because OH – is the only ligand to complex dissolved Cr(III), the precipitated Cr(III) solid is expected to exist as Cr(OH) 3(s) with a maximum dissolved Cr(III) concentration of 0.1 μg/L at pH 7 based on the solubility product constant of Cr(OH) 3(s) ( K sp = 6.3 × 10 –31 ) . Furthermore, control experiments with pure Cr(OH) 3(s) solid exhibited a much lower rate constant for Cr(VI) formation via HOCl oxidation (i.e., 0.2 × 10 –3 vs 1.67 × 10 –3 L·m –2.…”
In drinking water distribution systems, the oxidation of zerovalent chromium, Cr(0), in iron corrosion scales by chlorine residual disinfectant is the dominant reaction to form carcinogenic hexavalent chromium, Cr(VI). This study investigates inhibitive corrosion control strategies through adjustments of chemical water parameters (i.e., pH, silicate, phosphate, calcium, and alkalinity) on Cr(VI) formation through oxidation of Cr(0) (s) by free chlorine under drinking water conditions. The results show that an increase in pH, silicate, alkalinity, and calcium suppressed Cr(VI) formation that was mainly attributed to in situ surface precipitation of new Cr(III) solids on the surface of Cr(0) (s) , including Cr(OH) 3(s) , Cr 2 (SiO 3 ) 3(s) , CrPO 4(s) , Cr 2 (CO 3 ) 3(s) , and Cr 10 Ca(CO 3 ) 16(s) . The Cr(III) surface precipitates were much less reactive with chlorine than Cr(0) (s) and suppressed the Cr redox reactivity. The concentration of surface Cr(III) solids was inversely correlated with the rate constant of Cr(VI) formation. Adding phosphate either promoted or inhibited the Cr(VI) formation, depending on the phosphate concentration. This study provides fundamental insight into the Cr(VI) formation mechanisms via Cr(0) oxidation by chlorine and the importance of surface precipitation of Cr(III) solids with different corrosion control strategies and suggests that increasing the pH/alkalinity and addition of phosphate or silicate can be effective control strategies to minimize Cr(VI) formation.
“…4 d presents the formation of FZHx composite material. According to the literature, the solubility product constants of Zn(OH) 2 and Fe(OH) 3 were determined as 6.8 × 10 -17 [27] and 2.8 × 10 -39 [28] , respectively. Fig.…”
Reducing the recombination efficiency of photo-induced carriers has been found as an effective means to improve the degradation of antiviral agents. Given that the Lorentz forces can cause the abnormal charge to move in the opposite direction, external magnetic field improved α-Fe
2
O
3
/Zn
1-x
Fe
x
O heterojunctions (FZHx) were developed to remove increasing antiviral agents that were attributed to the COVID-19 pandemic under visible light. The characterization of the mentioned FZHx in the external magnetic field indicated that FZHx had perfect photocatalytic activity for degrading antiviral agents. In the external magnetic field, the quantities of photo-generated carriers and free radicals (•OH and •O
2
-
) derived from FZHx increased significantly, which improved antiviral agent removal by 30.0%. Though the band structure (α-Fe
2
O
3
) is unlikely to change due to some orders of magnitude weaker of Zeeman energy in magnetic fields, which insignificantly impacts photocatalytic performance. However, this study proposed a strategy of negative magnetoresistance effects and heterojunctions to facilitate the separation and transfer of photo-induced carriers in magnetic fields. Based on the proposed strategy, spin oriented electrons were selected and accumulated on the conduction band, which contributed to the degradation of antiviral agents. Overall, this study presented novel insights into the improved degradation performance of antiviral agents by applying Fe-based heterojunctions in an external magnetic field.
“…The presence of hydrogen oxides on the surface of slag has the ability to diffuse into the slag surface [98] due to small masses [99] and then can immobilize PTEs on the slag surface [100]. Moreover, PTEs exchange with the silicate and ferrite present on the slag surface and can be immobilized within the slag matrix [101]. The PTE ions present in the soil solution gradually enter the slag due to the absorption gradient.…”
Section: Mechanism Of Slag Interaction With Potentially Toxic Elements In Soilmentioning
Potentially toxic element (PTE) pollution is a major abiotic stress, which reduces plant growth and affects food quality by entering the food chain, and ultimately poses hazards to human health. Currently, the use of slag in PTE-contaminated soils has been reported to reduce PTEs and toxicity in plants. This review highlights the role of slag used as a fertilizer for better crop production and sustainable agricultural development. The application of slag increased the growth, yield, and quality of crops under PTE toxicity. The mechanisms followed by slag are the immobilization of PTEs in the soil, enhancement of soil pH, changes in the redox state of PTEs, and positive changes in soil physicochemical and biological properties under PTE toxicity. Nevertheless, these processes are influenced by the plant species, growth conditions, imposition length of stress, and type of slag used. The current review provides an insight into improving plant tolerance to PTE toxicity by slag-based fertilizer application and highlights the theoretical basis for applying slag in PTE-contaminated environments worldwide.
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