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Frontiers of Environmental Science & Engineering

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Front. Environ. Sci. Eng.    2024, Vol. 18 Issue (1) : 1    https://doi.org/10.1007/s11783-024-1761-1
REVIEW ARTICLE
Cr-containing wastewater treatment based on Cr self-catalysis: a critical review
Manshu Zhao1, Xinhua Wang1,2,3, Shuguang Wang1,2,3,4, Mingming Gao1,2,3()
1. School of Environmental Science and Engineering, Shandong University, Qingdao 266237, China
2. Shandong Key Laboratory of Environmental Processes and Health, Shandong University, Qingdao 266237, China
3. Shandong Key Laboratory of Water Pollution Control and Resource Reuse, Shandong University, Qingdao 266237, China
4. Weihai Research Institute of Industrial Technology of Shandong University, Weihai 264209, China
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Abstract

● Cr self-catalysis behaviors during Cr-initiated AOPs were described.

● Cr transformation in AOPs-based synergistic systems was reviewed.

● Discussed detection methods for active species related to Cr-initiated AOPs systems.

● This review provided insights into Cr self-catalysis and its applications.

Chromium (Cr), as a transition metal material with multiple redox states, has exhibited the catalysis toward Fenton-like reactions over a wide pH range. Although it is not sensible to add Cr reagents as catalysts due to its toxicity, it is highly promising to remediate Cr-containing wastewater through Cr-initiated advanced oxidation processes (Cr-initiated AOPs), which are clean and low-cost. Moreover, the widely concerned Cr-complexes, considered as obstacles in the remediation process, can be effectively destroyed by AOPs. Cr self-catalysis is defined as Cr species is both substrate and catalyst. However, the full understanding of Cr self-catalysis, including the generation of intermediates Cr(IV)/Cr(V), the synergetic effects with co-existing ions, and the accumulation of toxic Cr(VI), remains a challenge for the practical application of Cr-initiated AOPs. In this review, relevant researches on Cr self-catalysis during Cr-initiated AOPs are summarized. Specifically, the Cr-Fenton-like reaction, Cr substituted materials, and Cr-sulfite reactions are explored as key mechanisms contributing to Cr self-catalysis. Moreover, Cr transformation processes, including synchronously Cr removal, Cr redox reactions, and Cr(VI) accumulation, in AOPs-based synergistic systems are systematically analyzed. Detailed approaches for the detection of active species in AOPs-based systems are also presented. The primary objective of this review is to explore the application of AOPs for Cr-containing wastewater remediation based on Cr self-catalysis, and provide fundamental insights and valuable information for future research on Cr-initiated AOPs.
Keywords Self-catalysis      Cr-initiated AOPs      Cr transformation      Cr intermediates      Cr-containing wastewater     
Corresponding Author(s): Mingming Gao   
Issue Date: 01 August 2023
 Cite this article:   
Manshu Zhao,Xinhua Wang,Shuguang Wang, et al. Cr-containing wastewater treatment based on Cr self-catalysis: a critical review[J]. Front. Environ. Sci. Eng., 2024, 18(1): 1.
 URL:  
https://academic.hep.com.cn/fese/EN/10.1007/s11783-024-1761-1
https://academic.hep.com.cn/fese/EN/Y2024/V18/I1/1
Fig.1  (A) Cr cycle in Cr-Fenton-like reaction. (B) Schematic representation of complex chemistry between Cr and H2O2. Copyright 2021, American Chemical Society (Watwe et al., 2021). (C) Cr species changes with pH. (D) A unit cell of magnetite. Copyright 2012, Elsevier (Liang et al., 2012). (E) Diagram of Cr occupying the magnetite octahedral position points. Copyright 2013, Elsevier (Liang et al., 2013). (F) The kinetics of •OH generation in the heterogeneous Fenton systems catalyzed by magnetite. Copyright 2014, Elsevier (Zhong et al., 2014). (G) Schematic illustration of the synergy in SA-Cr/PN-g-C3N4 + H2O2 + Vis system for producing of the radical species. Copyright 2021, John Wiley and Sons (Chen et al., 2021).
Material composition Application BET specific surface area (m2/g) Degradation of pollutants pH Time Chemical dose Ref.
Fe3–xCrxO4 Heterogeneous Fenton 110 (about) 10 mg/L PNP: about 17% 6.5 1400 min Catalyst: 0.5 g/L, H2O2: 10 mmol/L Zhong et al. (2014)
Fe3–xCrxO4 Heterogeneous UV/Fenton 110 (about) 20 mg/L TBBPA: about 98% 6.5 300 min Catalyst: 0.5 g/L, H2O2: 10 mmol/L Zhong et al. (2014)
Fe3–xCrxO4 (x = 0.00, 0.18, 0.33, 0.47, and 0.67) Heterogeneous Fenton 27.84, 61.94, 88.60, 76.71, 111.92 0.2 mmol/L MB: 59.3%, 71.3%, 87.0%, 95.2%0.2 mmol/L AOII: 48.6%, 81.6%, 86.4%, 89.6% 7.0 MB: 200 minAOII: 240 min Catalyst: 1.0 g/L,H2O2: 80 mmol/L Liang et al. (2012)
Fe3–xCrxO4 (x = 0.00, 0.07, 0.26, 0.42, and 0.51) Heterogeneous Fenton 31, 49, 64, 72, 81 (about) TOC: 7%, 24%, 17%, 7.5% (about) 6.0 60 min Catalyst: 4.29 g/L,H2O2: 0.3 mol/L Magalhaes et al. (2007)
SA-Cr/PN-g-C3N4 Heterogeneous Fenton 40–50 10 mg/L BPA: over 98.8% 3.0–11.0 70 min Catalyst: 0.2 g/L,30% H2O2: 0.5 mL in 30 mL Chen et al. (2021)
Cr-doped PKU-1 aluminoborate Catalytic oxidation of styrene by H2O2 – 1 mmol styrene: 58.0% (in DMF) – 10 h Catalyst: 30 mg, H2O2: 3 mmol Chen et al. (2019)
LaCr0.5Cu0.5O3 Heterogeneous Fenton-like 38.38 TOC: 92% (optimum condition) 3.0 3 h Catalyst: 1 g/L Jain et al. (2022)
Cr-doped CeO2 Photocatalysis 455 0.3 mmol/LAO7: 89% – 6 h Catalyst: 10 mg Arul et al. (2015)
Tab.1  Decontamination performance of Cr substituted materials as heterogeneous catalysts
Process description Target pollutant Optimal operating conditions Time (min) Performance Cr(VI) accumulation Ref.
Pyrite/H2O2-precipitation Cr(III) complexed by various ligands (citrate, EDTA, oxalate, and tartrate) Catalyst dosage: 4g/LH2O2: 20 mmol/L, pH0 = 3, precipitation pH = 7.0 60 > 90% Cr removal in 30 min Less than 0.5 mg/L in 60 min Ye et al. (2018)
Fenton-like reaction-adsorption Cr(III)-citrate Catalyst dosage: 8 g/LH2O2: 15.16 mmol/L,pH = 10 60 Residual total Cr: 0.73 mg/LTOC: 3.20 mg/L 0.36 mg/L Liu & Yu (2022)
Electro-Fenton-alkaline precipitation Cr-complex (malonate, malate, citrate, EDTA) Catalyst dosage: 0.2 mmol/LEF: pH = 3Alkaline precipitation pH: 7–7.1 60 Cr-complex: 67%–71% N.D. Jiang et al. (2020)
Fenton-alkaline precipitation Cr(VI) Catalyst dosage: 0.7 g/LMolar ratio Fe2+/H2O2 = 2.4Fenton pH = 4Alkaline precipitation pH: 7 50 Cr: 99.99% – Jafari et al. (2013)
Reduction-Fenton reaction Cr(VI) and 4-chlorophenol Catalyst dosage: 0.4 g/LH2O2: 9.79 mmol/L, pH = 3 240 Cr(VI): 100%TOC: 37% – Xiao et al. (2017)
Heterogeneous photo-Fenton Cr(VI) and tetracycline hydrochloride Catalyst dosage: 0.4 g/LH2O2: 10 mmol/L, pH = 3.81 150 TC: 97.5%COD: 80.0%Cr(VI): 98.1% – Guo et al. (2020)
Photo-Fenton Rhodamine B (RhB) and Cr(VI) Catalyst dosage: 0.3 g/LH2O2: 1.0 mmol/L, pH = 6.5 10 RhB/Cr(VI): almost 100% by 10-NiFeOx – Xiao et al. (2022)
Photothermal-assisted photocatalytic-Fenton-like Cr(VI) and tetracycline hydrochloride Catalyst dosage: 0.2 g/LH2O2: 200 60 TC: 90.56%Cr(VI): 96% 100% reduction of Cr(VI) (1 min) Liu et al. (2022a)
Electro-Fenton Cr(VI) Voltage: 30 VH2O2: 50 mL/L,pH = 3 25 Cr(VI): 97% – Rahmani et al. (2015)
Electro-Fenton Cr(VI) and humic acids Catalyst dosage: 5.0 g/L40 mA, pH = 3 8 h TOC: beyond 90%Total Cr: 90% Completely reduced Huang et al. (2017)
Tab.2  The synergistic effects of Fenton for Cr removal in wastewater
Fig.2  (A) Possible catalytic mechanism of light-iron oxalate system. Copyright 2020, Elsevier (Zhou et al., 2020). (B) Possible catalytic mechanism of Fe-R composite. Copyright 2020, Elsevier (Guo et al., 2020). (C) Possible catalytic mechanism of simultaneous removal RhB/Cr(VI) in the 10-NiFeOx/H2O2/visible light system. Copyright 2022, Elsevier (Xiao et al., 2022). (D) Possible catalytic mechanism of CuOx/γ-Al2O3/H2O2/light system. Copyright 2022, Elsevier (Liu et al., 2022a). (E) Possible catalytic mechanism of removal of HAs and Cr(VI) by electro-Fenton process. Copyright 2017, Elsevier (Huang et al., 2017).
Fig.3  (A) Plausible mechanism for treatment of Cr(III)-citrate complex by pyrite/H2O2/precipitation. Copyright 2018, American Chemical Society (Ye et al., 2018). (B) Plausible mechanism for tannin-Cr(III) removal by Fenton oxidation. Copyright 2020, Elsevier (Ma et al., 2020). (C) Removal efficiency of Cr according to pH in Fenton oxidation. Copyright 2013, IWA Publishing (Jafari et al., 2013). (D) Plausible mechanism for •OH induced flocculation. Copyright 2023, Elsevier (Zhao et al., 2023). (E) Plausible mechanism for Cr-Fenton-like-flocculation reaction. Copyright 2022, Elsevier (Lu et al., 2022). (F) Heterogeneous alkaline regions in Cr flocs. Copyright 2022, Elsevier (Lu et al., 2022).
Fig.4  (A) Schematic diagram illustrating principle of photocatalyst. Copyright 2020, Elsevier (Long et al., 2020). (B) Schematic illustration of the concurrent photocatalysis and adsorption for Cr removal under simulated sunlight irradiation. Copyright 2017, Elsevier (Li et al., 2017). (C) Mechanisms of electrocoagulation process. Copyright 2017, Elsevier (An et al., 2017). (D) An electrocoagulation process using Fe electrodes. Copyright 2016, American Chemical Society (Pan et al., 2016). (E) Schematic diagram of the removal of Cr(VI) by NiO-X/NF electrodes. Copyright 2020, Elsevier (Wang et al., 2020). (F) Schematic diagram of electrocoagulation reactor using Fe and Al electrocoagulation. Copyright 2020, Elsevier (Kim et al., 2020). (G) Experimental set-up and schematic diagram of the electrocoagulation reactor. Copyright 2016, Elsevier (Lu et al., 2016).
Process description Target pollutant Optimal operating conditions Time (min) Performance Cr(VI) accumulation Ref.
Synergy of adsorption and photo-catalysis Cr(VI) Catalyst dosage: 30 mg (50 mL) 120 Cr(VI): 100% – Wang et al. (2017b)
Synergistic PANI@ZFCN nanocomposite Cr(VI) and phenol Catalyst dosage: 200 mg (20 mL) 120 Cr(VI): 97.8%Phenol: 85.1% – Patnaik et al. 2018)
UV/Fe(III) + OH system Cr(III)-citrate Fe(III) dosage = 0.8 mmol/LInitial pH = 3.0Precipitation pH = 7.0 40 Cr(III)-citrate: 96.54%TOC: ~60% < 0.06 mg/L Ye et al. (2017)
Synergy of photocatalytic reduction and adsorption Cr(VI) [Mn3O4] = 0.15 g/LMn3O4@ZnO:Mn3O4 = 2:1pH = 6.0 70 Total Cr: 96% – Li et al. (2017)
Adsorption-photocatalytic processes Cr(VI) Catalyst dosage: 2 g/LpH = 3 30 Cr(VI): 98.1% – Dorri et al. (2022)
A combination of electrocoagulation and photocatalysis 2,4,6-trichlorophenol and Cr(VI) Anode: titanium dioxide (TiO2) coated on aluminum platesCathode: stainless steel 316 plate15 V DC electric voltagepH = 7 240 2,4,6-trichlorophenol: 58%Cr(VI): 100%390 PtCo Remazol Red dye: 97% – Sharfan et al. (2018)
Electrocoagulation Cr(VI) Working electrode: NiO-X/NFCounter electrode: platinum flakeReference electrode: saturated calomel electrodeApplied potential of 0.97 VpH = 4 20 Cr(VI): 99.5% – Wang et al. (2020)
Electrocoagulation Cr(VI) Electrode: Fe/FeJ = 0.73 mA/cm2pH = 6 50 Cr(VI): 95.76% – Lu et al. (2016)
Electrocoagulation Heavy metal (Cu, Ni, Zn, and Cr) Electrode: FepH = 5/9 60 Cr > 99% – Kim et al. (2020)
Tab.3  The synergistic effects of photocatalysis and electrocoagulation for Cr removal in wastewater
Fig.5  (A) Characterization of •OH production by FMI. Copyright 2017, Elsevier (Zhang et al., 2017b). (B) Formation of fluorescing molecules by the reaction of coumarin and CCA with •OH radicals in different states. Copyright 2023, Elsevier (Miao et al., 2023).
Cr intermediates Detection method Experimental conditions Ref.
Cr(V) EPR direct detection EPR spectrometer: central field 3480 G; microwave power 20 mW; modulation frequency: 100 kHz; modulation amplitude 0.968 G; receiver gain: 2 × 104; conversion time: 5.12 ms; time constant: 1.28 ms; number of scans: 20; data acquisition time: 140 s; temperature: 293 K. Zhang & Lay (1998)
Cr(V) EPR equipped with an Oxford ESr910 liquid helium cryostat EPR spectrometer settings: microwave frequency: 9.393 GHz; microwave power: 1 mW; modulation frequency: 100 kHz; time constant: 20.48 ms; conversion time: 40.96 ms. Dong et al. (2020b)
Cr(V) UV-visible spectrophotometer Cr(V)-EHBA and Cr(IV)-EHBA complexes have characteristic absorbance bands at 510 nm. Bokare & Choi (2010)
Cr(V) EPR X-band EPR spectra were recorded on a JEOL JES-PE ESR spectrometer operating at about 9.4 GHz, and Q-band spectra were recorded on a Varian V-4052 spectrometer operating at about 35 GHz. Barr-David et al. (1995)
Cr(V) ESR All ESR measurements were performed using a Varian E4 or E9 ESR spectrometer and flat-panel cell assembler. Shi et al. (1994)
Cr(IV) HPLC Mobile phase: H3PO4/H2PO4− buffer (50 mmol/L; flow rate: 1 mL/min; sampling volume: 10 μL. Chromatograms were recorded at 267 nm 3 min after sample injection and 13 min after mixing. Bose et al. (1992)
Cr(IV)/Cr(V) X-ray photoelectron spectroscopy A monochromatic Al kα X-ray source (1487 eV) was used in the analysis chamber with a reference pressure of 1 × 10−9 Torr. Banerjee & Nesbitt (1999)
Cr(IV) XAFS Transmission (CrO2) and fluorescence yield (photocatalyst) spectra were obtained using a twin-crystalline silicon (1 1 1) monochromator, ion chamber, and 19-element germanium solid-state detector (SSD) equipped with a vanadium filter. Irie et al. (2010)
Cr(V) EPR A large number of Cr(V) EPR signals are generated by the reaction of K2Cr2O7 with reducing agents such as catecholamines. Pattison et al. (2000)
Tab.4  Detection methods of Cr intermediates
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