Preparation of a new Fenton-like catalyst from red mud using molasses wastewater as partial acidifying agent

A review of metallurgical slags as catalysts in advanced oxidation processes for removal of refractory organic pollutants in wastewater

With the rapid growth of the metallurgical industry, there is a significant increase in the production of metallurgical slags. The waste slags pose significant challenges for their disposal because of complex compositions, low utilization rates, and environmental toxicity. One promising approach is to utilize metallurgical slags as catalysts for treatment of refractory organic pollutants in wastewater through advanced oxidation processes (AOPs), achieving the objective of "treating waste with waste". This work provides a literature review of the source, production, and chemical composition of metallurgical slags, including steel slag, copper slag, electrolytic manganese residue, and red mud. It emphasizes the modification methods of metallurgical slags as catalysts and the application in AOPs for degradation of refractory organic pollutants. The reaction conditions, catalytic performance, and degradation mechanisms of organic pollutants using metallurgical slags are summarized. Studies have proved the feasibility of using metallurgical slags as catalysts for removing various pollutants by AOPs. The catalytic performance was significantly influenced by slags-derived catalysts, catalyst modification, and process factors. Future research should focus on addressing the safety and stability of catalysts, developing green and efficient modification methods, enhancing degradation efficiency, and implementing large-scale treatment of real wastewater. This work offers insights into the resource utilization of metallurgical slags and pollutant degradation in wastewater.

Preparation of High-Performance Zn-Based Catalysts Using Printing and Dyeing Wastewater and Petroleum Coke as a Carrier in Acetylene Acetoxylation

In this study, novel Zn catalysts were prepared by the wet impregnation method using printing and dyeing wastewater (PDW)-modified petroleum coke (petcoke) as a carrier, and they were applied to the acetylene acetoxylation. The pretreated petroleum coke has a high specific surface area which provides sufficient space for the loading of Zn. Calcination further increases catalyst activity, but when calcination temperatures exceed 1000 °C, a significant loss of Zn occurs, resulting in a dramatic decrease in catalyst activity. This enables the conversion of acetic acid up to 85%. X-ray photoelectron spectroscopy confirmed that a large amount of N is introduced into PC from PDW, which changes the electron transfer around Zn. Temperature-programmed desorption (TPD) analysis revealed that the nitrogen-doped Zn(OAc)2 catalyst enhanced the catalytic activity by modulating the intensity of the catalyzed adsorption of acetic acid and acetylene. This study provides a new way to reuse petroleum coke and printing and dyeing wastewater to support the sustainable development of the vinyl acetate industry.

Preparation and application of a new Fenton-like catalyst from red mud for degradation of sulfamethoxazole

In this work, using molasses wastewater as a partial acidifying agent and bagasse pith as a pore-enlarging agent, a new low-cost Fenton-like catalyst (ACRM_bp) used for degradation of sulfamethoxazole was prepared through a simple process of acidification and calcination using red mud (RM) as the main material. The optimum preparation conditions of ACRM_bp were acquired, and the optimum preparation conditions of ACRM_bp were as follows: mass ratio of bagasse pith to RM (m_bp:m_RM) 0.033:1, particle size of bagasse pith 0.10-0.20 mm, calcination temperature 773 K, and calcination time 2 h. The ACRM_bp catalyst was characterized by XRD, SEM, EDS, and BET. According to the results of characterizations, it was found that the iron phase of ACRM_bp had completely transformed into α-Fe₂O₃ after the process of acidification and calcination, and the addition of bagasse pith significantly improved the surface area of the prepared ACRM_bp. Furthermore, under the reaction conditions of catalyst dosage of 2 g/L, initial pH 3 and reaction time 90 min, the ACRM_bp has showed the highest catalytic activity. ACRM_bp had significantly higher activity than red mud, and exhibited a remarkable settleability. Besides, ACRM_bp retained good recyclability and stability during use. Kinetic studies showed the degradation process could be described with the first-order model. Overall, the prepared ACRM_bp was an effective and excellent catalyst in the Fenton-like process.

Dealkalization and Leaching Behavior of Fe, Al, Ca, and Si of Red Mud by Waste Acid from Titanium White Production

Dealkalization is the necessary step for the multipurpose use of red mud (RM), and acid leaching is a productive method to realize the dealkalization of RM. Most researches focus on recovering metals from the highly alkaline waste by pure acid leaching or stabilization by dealkalization. In this study, according to the strong alkalinity of RM and strong acidity of the waste acid from titanium dioxide production, the waste acid was used for the dealkalization of RM. The effects of leaching temperature, reaction time, the concentration of waste acid, liquid-solid ratio (L/S), and stirring rate on the dealkalization of RM were investigated, and the main metal ions in the dealkalization solution were analyzed. The results show that the leaching ratio of sodium can reach 92.3591% when the leaching temperature is 30 °C, the reaction time is 10 min, the concentration of waste acid is 0.6238 mol/L, the L/S is 4:1, and the stirring rate is 300 rpm. The residual alkali content in the treated RM is 0.2674%, which is a reduction to less than 1%. The phase analysis results show that the sodalite and cancrinite in RM are dissolved, decomposed, and transformed after acid leaching. Therefore, RM meets the requirements of building materials after dealkalization, which provides further development as building material products.

The remediation of textile wastewater using solid Bauxite Residue waste as a potential Fenton catalyst in the fluidized bed Fenton process

The synergistic relationship between the reactor and the catalysts has gained immense popularity in the field of Chemical Engineering due to their wide application. Catalytic processes have evolved over the decades from expensive commercial catalysts to low-cost solid waste catalysts for the sustainable development and reduction of their impacts on the environment. This alternative use of solid waste can greatly decrease the cost of wastewater treatment and addresses solid wastes issues. Bauxite Residue (BR) is one such waste from alumina-based industries with excellent catalytic properties. The fluid dynamics of fluidized bed technology improves profoundly the hydrodynamics and mass transfer of the heterogeneous Fenton process. This paper presents the preparation of the catalyst with minimum processing effort. It was characterized and factors affecting the degradation efficiency of synthetic dye wastewater were investigated. The optimum conditions for the eosin yellow dye were observed at a pH of five, oxidant concentration of 30 mM, catalyst dosage of 4 g/L. The removal efficiency at these optimum conditions was observed to be 91%. The residence time distribution (RTD) study was aimed to determine the behavior of the reactor using the mean residence time, variance, and dispersion number for the fluidized bed reactor.

Degradation of trypan blue dye using neutralized red mud in circulating fluidized bed reactor and its kinetics study

Dye is a common pollutant present in many chemical industrial waste water. Advanced oxidation processes are widely used for dye degradation. In this study, the degradation of trypan blue dye was examined by Fenton process. Neutralized red mud catalyst was used as a source of ferrous ion for Fenton’s process. The dye degradation performance has been analyzed by using circulating fluidized-bed reactor. The influence of some key parameters such as pH, initial dye concentration, catalyst dosage and hydrogen peroxide concentration on the degradation of dye has been investigated. All the experiments were performed for 90 min. The initial dye concentration was taken as 1.56 × 10−5 and 2.60 × 10−5 mol L−1 and the amount of catalyst was varied from 0.5 to 0.7 gm/L. The hydrogen peroxide was taken in the ratio of 1:20 with the catalyst. The effect of pH was studied in the varying range from 3–5. It was found that the more the acidic pH, more will be the rate of degradation. The increase in pH results in the lower degradation rate. As the amount of catalyst was increased, the degradation rate got increased. The optimized results were obtained at pH 3, catalyst dosage of 0.7 gm/L and dye concentration of 1.56 × 10−5 mol L−1. Subsequently, the reaction kinetics of Fluidized-bed reactor was also studied.

Mechanical properties and permeability of red mud-blast furnace slag-based geopolymer concrete

Red mud, a by-product of alumina production, has a great impact on the environment due to its high alkalinity. In this paper, two-part geopolymer mortar was synthesized by combining red mud and blast furnace slag (BFS) to obtain optimized compressive strength and flexural strength for construction materials. Geopolymer concrete was prepared with the cementitious material in the concrete replaced by geopolymer mortar. Mechanical properties, permeability and microscopic properties of geopolymer concrete were measured. The results showed that the compressive strength grade of concrete prepared with geopolymer concrete can reach 54.43 MPa indicating that the geopolymer concrete can be used as materials for load-bearing members in structures. Due to lower total porosity and better pore structure, the permeability resistance of geopolymer concrete was significantly better than ordinary concrete. Microscopic analysis indicated that a large amount of aluminosilicate reaction products was generated in a geopolymer by the reaction of OH− with the aluminosilicate components in red mud and BFS in a strongly alkaline environment. The surface [SiO4]4− and [AlO4]4− tetrahedrons form chemical bonds through dehydroxylation, which is the direct reason for their high strength and determines their excellent physical and chemical properties.

A way out of the alkaline bauxite residue: Synthesizing micro-electrolysis composite material towards the synergistic fenton degradation of high-concentration organic wastewater

Over 150 million tons of high-alkaline bauxite residue was produced during the Bayer process of Bauxite smelting in the world annually, causing massive encroachment and irreversible pollution of soil. In this work, we proposed a new way out of bauxite residue, synthesizing a micro-electrolysis composite material (MECM) by carbothermal reduction of the bauxite residue towards the degradation of high-concentration organic wastewater. Batch experiments of organic compounds degradation were conducted to evaluate the performance of MECM with or without synergistic Fenton process. XRD and SEM-EDS analysis results indicated that a proper calcination temperature (1000℃) could facilitate the generation and growth of zero-valent iron (ZVI), thereby forming a large number of galvanic cells with carbon, which could efficiently break the azo bonds. Additionally, the micro-electrolysis reaction of MECM could provide lots of Fe(Ⅱ), which constituted the Fenton system with the additional H₂O₂. In Fenton system, the aromatic rings and alkyl chains were further degraded and mineralized, which reduced the chemical oxygen demand (COD) of methyl orange (MO) from 450 to 54 mg/L. Therefore, the combination of the micro-electrolysis and Fenton process provides a clean and efficient method for the treatment of organic wastewater, which is a promising way out for bauxite residue.

Mechanochemical synthesis of Fe2O3/Zn-Al layered double hydroxide based on red mud

In this work, using industrial waste red mud (RM) as main starting material, a simple method of mechanochemical synthesis (MCS) was introduced as a green approach to synthesize heterogeneous Fe₂O₃/Zn-Al layered double hydroxide (F/ZA-LDH), which could be used as a new low-cost catalyst for photo-Fenton reaction. The optimum preparation conditions of F/ZA-LDH were as follows: mass ratio of Zn(NO₃)₂·6H₂O to RM (m_Zn:m_RM) 2:1, dry milling time 6 h, H₂O dosage 2 mL, ball-to-powder mass ratio 50:1, and milling speed 250 rpm. The effects of the synthesis conditions on the crystal structure and catalytic activity of F/ZA-LDH were analyzed. The F/ZA-LDH was characterized by XRD, TG, XPS, SEM, (HR)TEM. The characterization results showed the composite had a crystallized hydrotalcite-like structure, and the crystalline phases in the optimum F/ZA-LDH were Fe₂O₃ and Zn-Al LDH. A hetero-interfaces between Fe₂O₃ and Zn-Al LDH existed in the synthesized Fe₂O₃/Zn-Al LDH composite. Furthermore, the possible mechanism for F/ZA-LDH formation in the MCS process was proposed. Overall, our results provide a systematic understanding of the preparation of LDH composite through MCS using RM as main material, and our findings help to develop green technology for reusing RM.

Insight into the enhanced catalytic activity of a red mud based Fe2O3/Zn–Al layered double hydroxide in the photo-Fenton reaction

In this work, the enhanced catalytic activity of red mud based Fe₂O₃/Zn–Al layered double hydroxide in the photo-Fenton reaction has been studied in detail.