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Application of Advanced Oxidation Processes
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Application of Advanced Oxidation Processes

A special issue of Processes (ISSN 2227-9717). This special issue belongs to the section "Environmental and Green Processes".

Deadline for manuscript submissions: closed (31 March 2020) | Viewed by 51674

Printed Edition Available!
A printed edition of this Special Issue is available here.

Special Issue Editors

Dr. Ciro Bustillo-Lecompte

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Guest Editor
Graduate Programs in Environmental Applied Science and Management, and School of Occupational and Public Health, Ryerson University, 350 Victoria Street, Toronto, ON M5B 2K3, Canada
Interests: advanced treatment of water and wastewater; waste minimization and water reuse; integration of advanced oxidation technologies and biological processes for industrial wastewater treatment; water, soil, and air quality; energy and resource recovery
Special Issues, Collections and Topics in MDPI journals
Dr. Jose Colina-Márquez

E-Mail Website
Guest Editor
Department of Chemical Engineering, Universidad de Cartagena, Sede Piedra de Bolívar, Avenida del Consulado 48-152, Cartagena, Colombia
Interests: heterogeneous catalysis; thin films and nanotechnology; chemical reaction engineering; adsorption; industrial wastewater treatment by solar photocatalysis; novel material synthesis for advanced oxidation processes applications
Special Issues, Collections and Topics in MDPI journals
Dr. Lars Rehmann

E-Mail Website
Guest Editor
Department of Chemical and Biochemical Engineering, Thompson Engineering Building, Western University, London, ON N6A 5B9, Canada
Interests: application of advanced oxidation processes; biomass pretreatment; bioassay development for emerging contaminants; quantification of genotoxicity and estrogenicity of micro-pollutants
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The increasingly stricter standards for effluent discharge and the decreasing availability of freshwater resources worldwide have made the development of advanced wastewater treatment technologies necessary. Advanced oxidation processes (AOPs) are becoming an attractive alternative and a complementary treatment option to conventional methods. AOPs are used to improve the biodegradability of wastewaters containing non-biodegradable organics. Besides, AOPs may inactivate pathogenic microorganisms without adding additional chemicals to the water during disinfection, avoiding the formation of hazardous by-products. This Special Issue of Processes aims at covering recent progress and novel trends in the field of AOPs, including UV/H2O2, O3, sulphate-radical oxidation, nanotechnology in AOPs, heterogeneous photocatalysis, sonolysis, Fenton, photo-Fenton, electrochemical oxidation, and related oxidation processes. Topics to be addressed in this Special Issue of Processes may also include the application of AOPs at various scales (laboratory, pilot, or industrial scale), the degradation of emerging contaminants in water and wastewater and pollutants in the gas phase, the quantification of toxicicy in residuals, the development of novel catalytic material and of hybrid processes, including the combination of AOPs with other technologies, process intensification, and the use of photo-electrochemical processes for energy production. Authors with expertise in these topics are invited to submit their original manuscripts and review articles to Processes.

Dr. Ciro Bustillo-Lecompte
Dr. Jose Colina-Márquez
Dr. Lars Rehmann
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Processes is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Advanced oxidation processes (AOPs)
  • Water and wastewater treatment
  • Hybrid processes
  • Process intensification
  • Heterogeneous photocatalysis
  • Fenton
  • Sulphate-radical oxidation
  • Advanced electrochemical oxidation
  • Sonolysis
  • Energy production

Published Papers (12 papers)

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Editorial

Jump to: Research, Review

3 pages, 167 KiB  
Editorial
Special Issue: Application of Advanced Oxidation Processes
by Ciro Bustillo-Lecompte, Jose Colina-Marquez and Lars Rehmann
Processes 2020, 8(7), 867; https://doi.org/10.3390/pr8070867 - 18 Jul 2020
Cited by 1 | Viewed by 2536
Abstract
Advanced oxidation processes (AOPs) are nowadays not only considered as a complementary treatment option but as an attractive alternative to conventional methods [...] Full article
(This article belongs to the Special Issue Application of Advanced Oxidation Processes)

Research

Jump to: Editorial, Review

14 pages, 2408 KiB  
Article
Simultaneous Electrochemical Generation of Ferrate and Oxygen Radicals to Blue BR Dye Degradation
by Mauricio Chiliquinga, Patricio J. Espinoza-Montero, Oscar Rodríguez, Alain Picos, Erick R. Bandala, S. Gutiérrez-Granados and Juan M. Peralta-Hernández
Processes 2020, 8(7), 753; https://doi.org/10.3390/pr8070753 - 28 Jun 2020
Cited by 8 | Viewed by 3139
Abstract
In this study, electro-oxidation (EOx) and in situ generation of ferrate ions [Fe(VI)] were tested to treat water contaminated with Blue BR dye (BBR) using a boron-doped diamond (BDD) anode. Two electrolytic media (0.1 M HClO4 and 0.05 M Na2SO [...] Read more.
In this study, electro-oxidation (EOx) and in situ generation of ferrate ions [Fe(VI)] were tested to treat water contaminated with Blue BR dye (BBR) using a boron-doped diamond (BDD) anode. Two electrolytic media (0.1 M HClO4 and 0.05 M Na2SO4) were evaluated for the BDD, which simultaneously produced oxygen radicals (•OH) and [Fe(VI)]. The generation of [Fe(VI)] was characterized by cyclic voltammetry (CV) and the effect of different current intensity values (e.g., 7 mA cm−2, 15 mA cm−2, and 30 mA cm−2) was assessed during BBR degradation tests. The discoloration of BBR was followed by UV-Vis spectrophotometry. When the EOx process was used alone, only 78% BBR discoloration was achieved. The best electrochemical discoloration conditions were found using 0.05 M Na2SO4 and 30 mA cm−2. Using these conditions, overall BBR discoloration values up to 98%, 95%, and 87% with 12 mM, 6 mM, and 1 mM of FeSO4, respectively, were achieved. In the case of chemical oxygen demand (COD) reduction, the EOx process showed only a 37% COD reduction, whereas combining [Fe(VI)] generation using 12 mM of FeSO4 achieved an up to 61% COD reduction after 90 min. The evolution of reaction byproducts (oxalic acid) was performed using liquid chromatography analysis. Full article
(This article belongs to the Special Issue Application of Advanced Oxidation Processes)
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15 pages, 1687 KiB  
Article
Investigations on Ozone-Based and UV/US-Assisted Synergistic Digestion Methods for the Determination of Total Dissolved Nitrogen in Waters
by Xiaofang Sun, Huixuan Chen, Zhengyu Liu, Mengfei Zhou, Yijun Cai, Haitian Pan and Luyue Xia
Processes 2020, 8(4), 490; https://doi.org/10.3390/pr8040490 - 23 Apr 2020
Cited by 6 | Viewed by 2944
Abstract
Over the past two decades, the alkaline persulfate oxidation (PO) with thermal and/or ultraviolet (UV) assisted digestion method has been widely used for digestion of nitrogen containing compounds (N-compounds) in water quality routine analysis in laboratory or on-line analysis, due to its simple [...] Read more.
Over the past two decades, the alkaline persulfate oxidation (PO) with thermal and/or ultraviolet (UV) assisted digestion method has been widely used for digestion of nitrogen containing compounds (N-compounds) in water quality routine analysis in laboratory or on-line analysis, due to its simple principle, high conversion rate, high percent recovery, low-cost. However, this digestion method still has some inevitable problems such as complex operations, high contamination potential, batch N blanks, higher reaction temperature (120–124 °C) and time-consuming (30–60 min). In this study, ozone (O3) was selected as the oxidant for digestion of N-compounds through analysis and comparison firstly. Secondly, we proposed and compared the UV and/or ultrasound (US) combined with ozone (UV/O3, US/O3 and UV/US/O3) synergistic digestion methods based on O3 with sole O3 oxidation method on digestion efficiency (digestion time and conversion rate) of standard N-compounds. Simultaneously, the influence of reaction temperature, pH of water sample, concentration of O3 and mass flow rate, UV intensity, US frequency and power on digestion efficiency were investigated, and then the optimum parameters for digestion system were obtained. Experimental results indicated that UV radiation can effectively induce and promote the decomposition and photolysis of O3 in water to generate hydroxyl radicals (•OH), while US can promote the diffusion and dissolution of O3 in water and intensify the gas-liquid mass transfer process for the reaction system. Meanwhile, results showed that the UV/US/O3 synergistic digestion method had the best digestion efficiency under the optimum conditions: water sample volume, 10 mL; pH of water sample, 11; O3 mass flow rate, 3200 mg/h; reaction temperature, 30 °C; digestion time, 25 min; UV lamp power, 18 W; distance between UV lamp and reactor, 2 cm; US frequency, 20 kHz; US power, 75 W. The conversion rate (CR) of synthetic wastewater samples varied from 99.6% to 101.4% for total dissolved nitrogen (TDN) in the range of 1.0~4.0 mg/L. The UV/US/O3 synergistic digestion method would be an effective and potential alternative for digestion of N-compounds in water quality routine analysis in laboratory or on-line analysis. Full article
(This article belongs to the Special Issue Application of Advanced Oxidation Processes)
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31 pages, 9363 KiB  
Article
Mesoporous Mn-Doped Fe Nanoparticle-Modified Reduced Graphene Oxide for Ethyl Violet Elimination: Modeling and Optimization Using Artificial Intelligence
by Yu Hou, Jimei Qi, Jiwei Hu, Yiqiu Xiang, Ling Xin and Xionghui Wei
Processes 2020, 8(4), 488; https://doi.org/10.3390/pr8040488 - 22 Apr 2020
Cited by 11 | Viewed by 2922
Abstract
Mesoporous Mn-doped Fe nanoparticle-modified reduced graphene oxide (Mn-doped Fe/rGO) was prepared through a one-step co-precipitation method, which was then used to eliminate ethyl violet (EV) in wastewater. The prepared Mn-doped Fe/rGO was characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, high-resolution transmission [...] Read more.
Mesoporous Mn-doped Fe nanoparticle-modified reduced graphene oxide (Mn-doped Fe/rGO) was prepared through a one-step co-precipitation method, which was then used to eliminate ethyl violet (EV) in wastewater. The prepared Mn-doped Fe/rGO was characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, high-resolution transmission electron microscopy, scanning electron microscopy, energy dispersive spectroscopy, N2-sorption, small angle X-ray diffraction and superconducting quantum interference device. The Brunauer–Emmett–Teller specific surface area of Mn-doped Fe/rGO composites was 104.088 m2/g. The EV elimination by Mn-doped Fe/rGO was modeled and optimized by artificial intelligence (AI) models (i.e., radial basis function network, random forest, artificial neural network genetic algorithm (ANN-GA) and particle swarm optimization). Among these AI models, ANN-GA is considered as the best model for predicting the removal efficiency of EV by Mn-doped Fe/rGO. The evaluation of variables shows that dosage gives the maximum importance to Mn-doped Fe/rGO removal of EV. The experimental data were fitted to kinetics and adsorption isotherm models. The results indicated that the process of EV removal by Mn-doped Fe/rGO obeyed the pseudo-second-order kinetics model and Langmuir isotherm, and the maximum adsorption capacity was 1000.00 mg/g. This study provides a possibility for synthesis of Mn-doped Fe/rGO by co-precipitation as an excellent material for EV removal from the aqueous phase. Full article
(This article belongs to the Special Issue Application of Advanced Oxidation Processes)
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15 pages, 3715 KiB  
Article
Effect of Initial Salt Composition on Physicochemical and Structural Characteristics of Zero-Valent Iron Nanopowders Obtained by Borohydride Reduction
by Denis Leybo, Marat Tagirov, Dmitry Arkhipov, Elizaveta Permyakova, Evgeny Kolesnikov and Denis Kuznetsov
Processes 2019, 7(10), 769; https://doi.org/10.3390/pr7100769 - 21 Oct 2019
Cited by 3 | Viewed by 3218
Abstract
The effect of initial salt composition on characteristics of zero-valent iron nanopowders produced via borohydride reduction was studied. The samples were characterized by X-ray diffraction, scanning and transmission electron microscopy, and low-temperature nitrogen adsorption. The efficiency of Pb2+ ions removal from aqueous [...] Read more.
The effect of initial salt composition on characteristics of zero-valent iron nanopowders produced via borohydride reduction was studied. The samples were characterized by X-ray diffraction, scanning and transmission electron microscopy, and low-temperature nitrogen adsorption. The efficiency of Pb2+ ions removal from aqueous media was evaluated. The use of ferric salts led to enhanced reduction kinetics and, consequently, to a smaller size of iron particles in comparison with ferrous salts. A decrease in the ionic strength of the synthesis solutions resulted in a decrease in iron particles. The formation of small highly-reactive iron particles during synthesis led to their oxidation during washing and drying steps with the formation of a ferrihydrite phase. The lead ions removal efficiency was improved by simultaneous action of zero-valent iron and ferrihydrite phases of the sample produced from iron sulphate. Full article
(This article belongs to the Special Issue Application of Advanced Oxidation Processes)
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12 pages, 1809 KiB  
Communication
Reusing Cow Manure for the Production of Activated Carbon Using Potassium Hydroxide (KOH) Activation Process and Its Liquid-Phase Adsorption Performance
by Wen-Tien Tsai, Po-Cheng Huang and Yu-Quan Lin
Processes 2019, 7(10), 737; https://doi.org/10.3390/pr7100737 - 14 Oct 2019
Cited by 24 | Viewed by 3430
Abstract
In this work, cow manure (CM) was reused as a potential precursor in the production of activated carbon (AC) using a potassium hydroxide activation process at different temperatures (i.e., 500, 600 and 700 °C). The optimal activated carbon from cow manure (CM-AC) with [...] Read more.
In this work, cow manure (CM) was reused as a potential precursor in the production of activated carbon (AC) using a potassium hydroxide activation process at different temperatures (i.e., 500, 600 and 700 °C). The optimal activated carbon from cow manure (CM-AC) with high specific surface area (ca. 950 m2/g) was further investigated for its adsorption performance in the removal of a model compound (i.e., methylene blue) from aqueous solution with various initial concentrations and adsorbent dosages at 25 °C. It was found that the resulting AC could be an effective adsorbent for removal of cationic dye from aqueous solution in comparison with a commercial coal-based AC. Based on the observations of the energy dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy (FTIR), the CM-AC adsorbent has a stronger interaction with the cationic compound due to its more oxygen-containing complex on the surface. Furthermore, the adsorption kinetic parameters fitted using the pseudo-second order model with high correlations were in accordance with their pore properties. Full article
(This article belongs to the Special Issue Application of Advanced Oxidation Processes)
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10 pages, 4463 KiB  
Article
Effect of Heating Oxidation on the Surface/Interface Properties and Floatability of Anthracite Coal
by Guoqiang Rong, Mengdi Xu, Dongyue Wang, Xiahui Gui and Yaowen Xing
Processes 2019, 7(6), 345; https://doi.org/10.3390/pr7060345 - 06 Jun 2019
Cited by 5 | Viewed by 2706
Abstract
Oxidation processes of coal surfaces are both fundamental and interesting from academic and engineering points of view. In this work, we comprehensively analyzed the mechanism of heating oxidation at 200 °C on the surface/interface characters and the floatability of anthracite coal. The variations [...] Read more.
Oxidation processes of coal surfaces are both fundamental and interesting from academic and engineering points of view. In this work, we comprehensively analyzed the mechanism of heating oxidation at 200 °C on the surface/interface characters and the floatability of anthracite coal. The variations of surface/interface characters were studied using SEM (scanning electron microscopy), FTIR (Fourier transform infrared spectroscopy), and XPS (X-ray photoelectron spectroscopy). The floatability was further identified using Induction Time and Bubble-Particle Wrap Angle. It was found that, after heating oxidation at 200 °C, both surface ravines and oxygen-containing groups were increased. The degradation of hydroxyl on anthracite could be neglected during the heating, while the oxidation of hydrocarbon chains dominated the balance of hydrophobicity and hydrophilicity on coal surface. The induction time significantly increased from 200 ms to 1200 ms and 2000 ms after 10 h and 20 h of heating oxidation at 200 °C, respectively. Additionally, raw coal exhibited the fastest kinetics of bubble-particle attachment and the largest wrap angle, directly proving that the floatability decreased after oxidation. Full article
(This article belongs to the Special Issue Application of Advanced Oxidation Processes)
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9 pages, 1372 KiB  
Article
Photocatalytic Treatment of Paracetamol Using TiO2 Nanotubes: Effect of pH
by S. Alejandro Lozano-Morales, Graciela Morales, Miguel Ángel López Zavala, Augusto Arce-Sarria and Fiderman Machuca-Martínez
Processes 2019, 7(6), 319; https://doi.org/10.3390/pr7060319 - 29 May 2019
Cited by 27 | Viewed by 5621
Abstract
Pharmaceuticals are considered among the group of emerging contaminants. Paracetamol is a moderate painkiller, which has been detected in ground and surface water. Photodegradation of paracetamol at a wavelength of radiation of 254 nm with TiO2 nanotubes was studied by UV-spectroscopy, HPLC [...] Read more.
Pharmaceuticals are considered among the group of emerging contaminants. Paracetamol is a moderate painkiller, which has been detected in ground and surface water. Photodegradation of paracetamol at a wavelength of radiation of 254 nm with TiO2 nanotubes was studied by UV-spectroscopy, HPLC and measurement of the potential zeta in dependence of the solution pH. The efficiency of the photodegradation of paracetamol (20 mg L−1) was 99% after 100 min exposure. Application of the Langmuir-Hinshelwood equation allowed the evaluation of the rate constant. Non-organic by-products were detected under the conditions of the chromatographic analysis. The photoreaction was faster at pH 6.5, a value at which adsorption was favored, leading to higher efficiency. Full article
(This article belongs to the Special Issue Application of Advanced Oxidation Processes)
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16 pages, 6409 KiB  
Article
Degradation of Aqueous Polycyclic Musk Tonalide by Ultraviolet-Activated Free Chlorine
by Lili Wang and Xiaowei Liu
Processes 2019, 7(2), 95; https://doi.org/10.3390/pr7020095 - 14 Feb 2019
Cited by 13 | Viewed by 4362
Abstract
Chlorine-incorporating ultraviolet (UV) provides a multiple barrier for drinking water disinfection. Meanwhile, post-UV employment can promote the degradation of micropollutants by radical production from chlorine residual photolysis. This work studied the degradation of one such chemical, tonalide (AHTN), by low-pressure UV-activated free chlorine [...] Read more.
Chlorine-incorporating ultraviolet (UV) provides a multiple barrier for drinking water disinfection. Meanwhile, post-UV employment can promote the degradation of micropollutants by radical production from chlorine residual photolysis. This work studied the degradation of one such chemical, tonalide (AHTN), by low-pressure UV-activated free chlorine (FC) under typical UV disinfection dosage of <200 mJ·cm−2 and water matrix of filtered tank effluent. AHTN was rapidly degraded by UV/FC in accordance with pseudo-first-order kinetics. The reaction rate constants of AHTN with reactive chlorine species and hydroxyl radical (HO•) were estimated. Mechanistic exploration evidenced that under UV/FC, AHTN degradation was attributable to direct photolysis, ClO•, and HO•. The carbonyl side chain of AHTN served as an important attack site for radicals. Water matrices, such as natural organic matter (NOM), HCO 3 − , Cu 2 + , PO 4 3 − , and Fe 2 + , showed noticeable influence on the UV/FC process with an order of NOM > HCO 3 − > Cu 2 + > PO 4 3 − > Fe 2 + . Reaction product analysis showed ignorable formation of chlorinated intermediates and disinfection byproducts. Full article
(This article belongs to the Special Issue Application of Advanced Oxidation Processes)
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Review

Jump to: Editorial, Research

19 pages, 863 KiB  
Review
Applications of Electrolyzed Water as a Sanitizer in the Food and Animal-By Products Industry
by Juan C. Ramírez Orejel and José A. Cano-Buendía
Processes 2020, 8(5), 534; https://doi.org/10.3390/pr8050534 - 02 May 2020
Cited by 23 | Viewed by 7728
Abstract
Food demand is increasing every year and, usually animal-derived products are generated far from consumer-places. New technologies are being developed to preserve quality characteristics during processing and transportation. One of them is electrolyzed water (EW) that helps to avoid or decrease the development [...] Read more.
Food demand is increasing every year and, usually animal-derived products are generated far from consumer-places. New technologies are being developed to preserve quality characteristics during processing and transportation. One of them is electrolyzed water (EW) that helps to avoid or decrease the development of foodborne pathogens, or losses by related bacteria. Initially, EW was used in ready-to-eat foods such as spinach, lettuce, strawberries, among others; however, its application in other products is under study. Every product has unique characteristics that require an optimized application of EW. Different sanitizers have been developed; unfortunately, they could have undesirable effects like deterioration of quality or alterations in sensory properties. Therefore, EW is gaining popularity in the food industry due to its characteristics: easy application and storage, no corrosion of work surfaces, absence of mucosal membrane irritation in workers handling food, and it is considered environmentally friendly. This review highlights the advantages of using EW in animal products like chicken, pork, beef, eggs and fish to preserve their safety and quality. Full article
(This article belongs to the Special Issue Application of Advanced Oxidation Processes)
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23 pages, 1072 KiB  
Review
Characteristics and Treatment of Wastewater from the Mercaptan Oxidation Process: A Comprehensive Review
by Ernesto Pino-Cortés, Silvio Montalvo, César Huiliñir, Francisco Cubillos and Juan Gacitúa
Processes 2020, 8(4), 425; https://doi.org/10.3390/pr8040425 - 03 Apr 2020
Cited by 13 | Viewed by 6415
Abstract
Sulfur compounds are removed from petroleum by the addition of sodium hydroxide at a very high concentration. As a result, a residue called spent soda or spent caustic is generated, being extremely aggressive to the environment. In this work, the chemical properties of [...] Read more.
Sulfur compounds are removed from petroleum by the addition of sodium hydroxide at a very high concentration. As a result, a residue called spent soda or spent caustic is generated, being extremely aggressive to the environment. In this work, the chemical properties of this residue are described in detail. The sodium hydroxide remains that have not reacted, sulfur compounds, and organic matter are the primary pollutants reported. Additionally, the main characteristics of the methods of treatment used to reduce them are described. This review comes from comprehensive and updated research and bibliographic analysis about the investigation on the topic. The advantages and disadvantages of the different treatment methods are highlighted. We established some criteria to set out when assessing the application of each one of these treatments is considered. Full article
(This article belongs to the Special Issue Application of Advanced Oxidation Processes)
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24 pages, 1401 KiB  
Review
Recent Developments in the Photocatalytic Treatment of Cyanide Wastewater: An Approach to Remediation and Recovery of Metals
by Luis Andrés Betancourt-Buitrago, Aracely Hernandez-Ramirez, Jose Angel Colina-Marquez, Ciro Fernando Bustillo-Lecompte, Lars Rehmann and Fiderman Machuca-Martinez
Processes 2019, 7(4), 225; https://doi.org/10.3390/pr7040225 - 20 Apr 2019
Cited by 29 | Viewed by 5822
Abstract
For gold extraction, the most used extraction technique is the Merrill-Crow process, which uses lixiviants as sodium or potassium cyanide for gold leaching at alkaline conditions. The cyanide ion has an affinity not only for gold and silver, but for other metals in [...] Read more.
For gold extraction, the most used extraction technique is the Merrill-Crow process, which uses lixiviants as sodium or potassium cyanide for gold leaching at alkaline conditions. The cyanide ion has an affinity not only for gold and silver, but for other metals in the ores, such as Al, Fe, Cu, Ni, Zn, and other toxic metals like Hg, As, Cr, Co, Pb, Sn, and Mn. After the extraction stage, the resulting wastewater is concentrated at alkaline conditions with concentrations up to 1000 ppm of metals. Photocatalysis is an advanced oxidation process (AOP) able to generate a photoreaction in the solid surface of a semiconductor activated by light. Although it is well known that photocatalytic processes can remove metals in solution, there are no compilations about the researches on photocatalytic removal of metals in wastewater with cyanide. Hence, this review comprises the existing applications of photocatalytic processes to remove metal and in some cases recover cyanide from recalcitrant wastewater from gold extraction. The use of this process, in general, requires the addition of several scavengers in order to force the mechanism to a pathway where the electrons can be transferred to the metal-cyanide matrices, or elsewhere the entire metallic cyanocomplex can be degraded by an oxidative pathway. Full article
(This article belongs to the Special Issue Application of Advanced Oxidation Processes)
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