Reduction Of Hexavalent Chromium Research Articles

Ultrasonic controllable synthesis of sulfur-functionalized metal–organic frameworks (S-MOFs) and their application in piezo-photocatalytic rapid reduction of hexavalent chromium (Cr)

The United Nations’ Sustainable Development Goals (SDGs) are significant in guiding modern scientific research. In recent years, scholars have paid much attention to MOFs materials as green materials. However, piezo catalysis of MOFs materials has not been widely studied. Piezoelectric materials can convert mechanical energy into electrical energy, while MOFs are effective photocatalysts for removing pollutants. Therefore, it is crucial to design MOFs with piezoelectric properties and photosensitivity. In this study, sulfur-functionalized metal–organic frameworks (S-MOFs) were prepared using organic sulfur-functionalized ligand (H2TDC) ultrasonic synthesis to enhance their piezoelectric properties and visible light absorption. The study demonstrated that the S-MOFs significantly enhanced the reduction of a 10 mg/L solution of hexavalent chromium to 99.4 % within 10 min, using only 15 mg of catalyst. The orbital energy level differences of the elements were analyzed using piezo response force microscopy (PFM) and X-ray photoelectron spectroscopy (XPS). The results showed that MOFs functionalized with sulfur atom ligands have a built-in electric field that facilitates charge separation and migration. This study presents a new approach to enhance the piezoelectric properties of MOFs, which broadens their potential applications in piezo catalysis and piezo-photocatalysis. Additionally, it provides a sustainable method for reducing hexavalent chromium, contributing to the achievement of sustainable development goals, specifically SDG-6, SDG-7, SDG-9, and SDG-12.

Simulation of hexavalent chromium removal by electrocoagulation using iron anode in flow-through reactor

An electrocoagulation (EC) model is developed for hexavalent chromium reduction and precipitation, using iron electrodes. Parallel removal mechanisms such as adsorption of chromium on ferrihydrite and direct reduction at the cathode is assumed negligible due to low concentration of Cr(VI). The reaction model presented for batch system represents species complexation, precipitation/dissolution, acid/base, and oxidation-reduction reactions. Batch reactor simulation is verified using experimental data obtained by Sarahney et al. (2012), where the effect of initial chromium concentration, pH, volumetric current density, and ionic strength is considered (Sarahney et al., 2012). The model couples multicomponent ionic transport in MATLAB with chemical reaction model in PHREEQC, as a widely used computational programming tool and a geochemical reaction simulator with comprehensive geochemistry databases. The suggested current density is 0.05−0.3mA/cm2 and the surface to volume ratio in batch reactor is considered 0.017 1/cm. Design parameters are presented for operation of a flow-through hexavalent chromium removal using electrocoagulation by iron electrode to treat Cr(VI) in range of 10–50 mg/L. The operational parameters for a flow-through EC reactor for Cr(VI) removal is suggested to follow 0.05mA/cm2≤3nFeQcCrVIinlet≤0.3mA/cm2.

Fate of hexavalent chromium reduction by using Halomonas maridiana EA1

The present study is focused on the reduction of hexavalent chromium by using the isolated bacterium Halomonas maridiana EA1. H. maridiana EA1 has shown a > 90 % reduction of 100 ppm hexavalent chromium on day 1 and a > 70 % reduction of 1200 ppm hexavalent chromium on day 4. ICP-OES analysis revealed that H. maridiana EA1 has efficiently reduced hexavalent chromium into trivalent chromium. The occurrence of the chrA gene in H. maridiana EA1, which regulates the ChrA (reductase) enzyme, may be associated with the reduction of hexavalent chromium into trivalent chromium. TEM images depicted the alteration in the morphology of H. maridiana EA1 under hexavalent chromium stress conditions. The LCMS result illustrates the role of metabolites in hexavalent chromium reduction by regulating two main pathways: cell wall strengthening and biofilm formation, which help to maintain the cell integrity. Hence, applications of such dynamic bacteria H. maridiana EA1 can be useful to minimize the burden of hexavalent chromium in the soil for the sustainability of the ecosystem.

Layered double hydroxide (LDH)-derived zinc oxide (ZnO) nanorod on exfoliated graphene oxide (GO) nanosheet for photocatalytic dye degradation and hexavalent chromium reduction

A new low-temperature facile chemical decomposition of layered double hydroxide (LDH) has been developed for the large-scale controlled synthesis of zinc oxide (ZnO) nanorod on exfoliated graphene oxide (GO) nanosheet. ZnAl-LDH/GO composite precursor was prepared via in situ growth of the LDH on the exfoliated GO nanosheets. Thermo-chemical decomposition of ZnAl-LDH/GO composite at 80 °C produced highly dispersed ZnO nanorods on GO nanosheets. Although, neat ZnAl-LDH produces ZnO nanoparticle aggregates in the absence of GO. The morphology and properties of ZnO nanorods/GO nanocomposite was studied by X-ray diffraction analysis (XRD), transmission electron microscopy (TEM), UV–vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). The band gap engineering of the nanocomposite was evaluated by varying GO content. The ZnO/GO nanocomposites materials exhibited excellent photo-catalytic activity towards the degradation of methylene blue (MB) and Cr(VI) reduction under the irradiation of direct sunlight at ambient condition. GO plays a crucial role in the directional growth of nanorods and enhances the photocatalytic activity of ZnO nanorods via the synergistic hole formation and electron transfer effect for the potential remediation of waste water.

Photoelectrocatalytic Reduction of Cr(VI) in Wastewater with a CuBi2O4 Thin Film Photocathode

Photoelectrocatalytic approaches show promise for contaminate removal in wastewater through redox reactions. However, the direct treatment of very low concentration heavy metals is a challenging task. Copper bismuth oxide is considered as a potential photocathode material due to its appropriate bandgap width and excellent light absorption properties. In this work, we utilize copper bismuth oxide photoelectrodes with micrometer-scale pores to achieve the efficient and complete reduction of micromolar-level hexavalent chromium(VI) in wastewater. In a continuous 180 min experiment, the reduction rate of 5 µM hexavalent chromium reached 97%, which is an order lower than the drinking standard. Such a process was facilitated by the unique hierarchical microstructure of the oxide thin film and the porous morphology. On the other hand, the structural evolution during the operation was analyzed. A surface passivation was observed, suggesting the possible long-term practical application of this material. This study serves as an important reference for the application of photoelectrocatalysis in addressing Cr(VI) pollution in wastewater, with implications for improving water quality and environmental protection.

Growth-dependent cr(VI) reduction by Alteromonas sp. ORB2 under haloalkaline conditions: toxicity, removal mechanism and effect of heavy metals.

Bacterial reduction of hexavalent chromium (VI) to chromium (III) is a sustainable bioremediation approach. However, the Cr(VI) containing wastewaters are often characterized with complex conditions such as high salt, alkaline pH and heavy metals which severely impact the growth and Cr(VI) reduction potential of microorganisms. This study investigated Cr(VI) reduction under complex haloalkaline conditions by an Alteromonas sp. ORB2 isolated from aerobic granular sludge cultivated from the seawater-microbiome. Optimum growth of Alteromonas sp. ORB2 was observed under haloalkaline conditions at 3.5-9.5% NaCl and pH 7-11. The bacterial growth in normal culture conditions (3.5% NaCl; pH 7.6) was not inhibited by 100mg/l Cr(VI)/ As(V)/ Pb(II), 50mg/l Cu(II) or 5mg/l Cd(II). Near complete reduction of 100mg/l Cr(VI) was achieved within 24h at 3.5-7.5% NaCl and pH 8-11. Cr(VI) reduction by Alteromonas sp. ORB2 was not inhibited by 100mg/L As(V), 100mg/L Pb(II), 50mg/L Cu(II) or 5mg/L Cd(II). The bacterial cells grew in the medium with 100mg/l Cr(VI) contained lower esterase activity and higher reactive oxygen species levels indicating toxicity and oxidative stress. In-spite of toxicity, the cells grew and reduced 100mg/l Cr(VI) completely within 24h. Cr(VI) removal from the medium was driven by bacterial reduction to Cr(III) which remained in the complex medium. Cr(VI) reduction was strongly linked to aerobic growth of Alteromonas sp. The Cr(VI) reductase activity of cytosolic protein fraction was pronounced by supplementing with NADPH in vitro assays. This study demonstrated a growth-dependent aerobic Cr(VI) reduction by Alteromonas sp. ORB2 under complex haloalkaline conditions akin to wastewaters.

Development of Mn doped ZnAl2O4 via hydrothermal method as photocatalyst for Cr(VI) reduction under visible light

A hydrothermal method was employed to synthesise zinc aluminate oxides doped with manganese, with the aim of enhancing the photocatalytic reduction of hexavalent chromium to trivalent chromium. The optical, textural, microscopic, and structural features of the materials were assessed by a range of analytical techniques. These results revealed that incorporation of Mn dopant into the ZnAl2O4 (ZAO) reduced to band gap of ZAO and MD-ZAO are 3.56 and 2.79 eV, respectively. The best photoreduction efficiency was found with manganese-doped ZnAl2O4 (MD-ZAO) is 86.39 % than ZAO (69.38 %) after 120 min. The surface area study displays the 21.43 and 38.65 m2 g−1 for ZAO and MD-ZAO, respectively. When surface area of a nanomaterial is increased, a greater percentage of the material in contact with Cr ion, which increases the photocatalytic activity. A large interfacial area and pore volume aids in development of photoinduced electrons (e−) as well as hole pairs. The impedance study indicates the lower Rct value of ZAO and MD-ZAO are 0.45 Ω and 0.7 Ω, respectively. The finding indicates that Mn doped ZnAl2O4 work as excellent photocatalyst for photoreduction of hexavalent of Cr. The doped material can also act as potential catalyst in different future electrochemical and photocatalytic study.

Microbial communities outperform extracellular polymeric substances in the reduction of hexavalent chromium by anaerobic granular sludge

The reduction of hexavalent chromium [Cr(VI)] by microbiota agents is a potential method for ecological remediation in heavily contaminated soil. This study investigated the contribution of microbial community and extracellular polymeric substances (EPS) to reduce Cr(VI) using lab-cultured anaerobic granular sludge (AGS). The AGS demonstrated an impressive reduction efficiency of 99.3% for Cr(VI) in soil, operating within an initial Cr(VI) concentration range of 500–3000 mg/kg. The distribution of typical electron acceptors, e.g., SO42-, NO3-, and Fe3+, had a negligible influence on microbial Cr(VI) reduction. The contribution of EPS on Cr(VI) reduction accounted for only 2.1% of the total Cr(VI) reduction, implying that Cr(VI) reduction driven by AGS was primarily caused by the direct effect of microbiota. High-throughput sequencing analysis confirmed that an increasing trend in the relative abundance of Cr reduction bacteria (Sphingopyxis: 0.40–5.54%, Thermonas: 0.41–5.70%, Edaphobaculum: 0.35–6.64%, etc.), and the stability (0.716–4.114) of microbial co-occurrence networks was significantly promoted by the end of the experiment. Materials characterization indicated that successful reduction of Cr(VI) to trivalent chromium [Cr(III)] and formed in Cr(OH)3, and functional groups, O-H, N-H, -CH, and -CH2, of AGS likely played a vital role in Cr(VI) reduction. Overall, these findings offer insights into the remediation technique of microbial Cr(VI) reduction in highly-contaminated soil based on the interaction network stability of the microbial community in AGS.

A carbon-promoted galvanic replacement method to synthesize efficient PdNi nanoalloy catalyst

PdNi nanoalloy catalysts were prepared by a carbon-promoted galvanic replacement method. Characterizations and control experiments show the increased replacement rate of metal Ni with Pd2+ ion can be attributed to the higher electrode potential and smaller crystalline sizes caused by carbon doping. Introduction of carbon (C) into Ni particles not only accelerates the formation process of PdNi nanoalloys, but also enables C atoms to successfully enter the lattice interstices of PdNi nanoalloys. C regulates the surface electronic properties of PdNi nanoalloys by the electron transfer between different elements and improves their activity. The PdNi@C-650 exhibits extraordinary activity and long-term stability for hydrogenation reduction of hexavalent chromium (Cr (VI)) and hydrodechlorination of chlorophenols in comparison with PdNi/CNTs (carbon nanotubes) and commercial Pd/C. Density functional theory calculations together with investigations of mechanism reveal that the high electron-deficient PdNi nanoalloys from the redistribution of electron between Ni, Pd and C of the PdNi@C-650 promote the surface adsorption of substrate molecules and H2, which accordingly enhances the hydrogenation activity. This study brings a new method for the design and preparation of high active noble metal nanoalloy.

Hexavalent Chromium Reduction Mediated by Interfacial Electron Transfer over the Co@NC Nanosheet-Assembled Microflowers.

The reductive transformation of Cr(VI) into Cr(III) mediated by formic acid with efficient, stable, and cost-effective catalysts is a promising strategy for remediating Cr(VI) contamination. Herein, we report the facile construction of uniform Co@NC nanosheet-assembled microflowers for the reduction of Cr(VI). Both experimental results and density functional theory (DFT) calculations reveal the vital role of the intensive interfacial electronic interaction between Co nanoparticles and the N-doped carbon layer in facilitating the anchoring and dispersion of Co nanoparticles within the carbon framework. The interfacial electron transfer from Co to NC contributes to the interaction with Cr2O72- ions, promoting the subsequent H-transfer reaction. A Langmuir-Hinshelwood kinetic model has been established for the Cr(VI) reduction catalyzed by the CNCF2 (pyrolyzed at 700 °C), which shows a superior reaction performance. This study provides a facile strategy to delicately design well-assembled heterostructures with rich interfaces and strong interfacial interactions for a series of applications in environmental/thermal catalysis.

One-step synthesis of ferrous disulfide and iron nitride modified hydrochar for enhanced adsorption and reduction of hexavalent chromium in Bacillus LD513 by promoting electron transfer and microbial metabolism

Microbial immobilization technology is effective in improving bioremediation efficiency and heavy metal pollution. Herein, Bacillus LD513 with hexavalent chromium (Cr(VI)) tolerance was isolated and immobilized on a novel ferrous disulfide (FeS2)/iron nitride (FeN) modified hydrochar (Fe3-SNHC) prepared from waste straws. The prepared Fe3-SNHC-based LD513 (FeLD) significantly improves Cr(VI) adsorption and reduction by 31.4 % and 15.7 %, respectively, compared to LD513 alone. Furthermore, the FeLD composite system demonstrates efficient Cr(VI) removal efficiency and good environmental adaptability under different culture conditions. Microbial metabolism and electrochemical analysis indicate that Fe3-SNHC is an ideal carrier for protecting LD513 activity, promoting extracellular polymer secretion, and reducing oxidative stress. Additionally, the carrier serves as an electron shuttle that accelerates electron transfer and promotes Cr(VI) reduction. Overall, FeLD is an environmentally friendly biocomposite that shows good promise for reducing Cr(VI) contamination in wastewater treatment.

Hydrothermal preparation of Nb5+-doped α-Fe2O3 nanorods for efficient visible light-driven photocatalytic reduction of hexavalent chromium

Nb5+ doped α-Fe2O3 (Nb-Fe2O3) nanorods with different Nb5+ contents were prepared using a low-temperature, short-time, one-pot hydrothermal method. All the prepared Nb-Fe2O3 products showed better photocatalytic activities than α-Fe2O3 nanorods in the reduction of aqueous Cr(VI) under visible light (wavelength > 420 nm). 4% Nb-Fe2O3 had the maximum photocatalytic activity, which was 2.24 times that of α-Fe2O3 nanorods and surpassed those of many newly reported visible light photocatalysts. Moreover, the photocatalytic efficiency of 4% Nb-Fe2O3 can be further improved by proper increasing its dosage, decreasing the initial pH and Cr(VI) concentration of K2Cr2O7 solution. Furthermore, 4% Nb-Fe2O3 showed rather good photocatalytic stability and reusability. Besides, 4% Nb-Fe2O3 was efficient in visible light-driven photocatalytic reduction of Cr(VI) in diluted black chrome plating solution. Nb5+-doping can efficaciously enhance the abilities of α-Fe2O3 in absorbing visible light and transferring and separating photogenerated carriers, thereby contributing to the elevated photocatalytic activity of Nb-Fe2O3.

Efficient reduction of hexavalent chromium by Fe-Mn bimetallic nanoparticles: Performance and role of manganese

Modification of zero-valent iron by manganese doping is a potential way to improve the properties of zero-valent iron, but the role of manganese in Fe/Mn bimetallic nanoparticles during the reduction process of hexavalent chromium is not yet fully recognised. Nano-Fe/Mn bimetals (NFMB) was synthesized through one-step chemical reduction method and characterized by Transmission Electron Microscope (TEM), Scanning Electron Microscope-Energy Dispersive Spectrometer (SEM-EDS) and X-ray Photoelectron Spectroscopy (XPS). The results showed that dispersed particles owned a rough surface and six functional groups, namely, C-O, C=O, O-H, and -COOH, Fe-O, Mn-O. XPS analysis results showed that four elements in NFMB: Fe, Mn, C, and O, along with Fe0, Mn0, Fe2O3, and FeOOH were confirmed. The composition analysis indicated an approximate content of Fe (16.74 %) and Mn (12.59 %), with the detection of Cr (1.51 %) after the reaction. The batch experiments revealed a significant enhancement of reduction efficiency of Cr (VI) at a lower pH level and higher temperature, with a consistent removal rate of around 99.9 % within the pH range of 3-9, showcasing the adaptability of NFMB across a wide pH range. The maximum removal capacity of Cr (VI) by NFMB was determined to be 35.54 mg·g−1. The removal process involved the adsorption of Cr (VI) to the surface of NFMB, followed by a series of chemical reduction and precipitation processes, and the final removal from the aqueous solution. Therefore, the Fe/Mn bimetallic nanocomposites was proved to be promising for the removal of Cr (VI) from aqueous environments.

Mechanically pulverized covalent organic framework as a metal-free photocatalyst for fenton-like degradation of organic pollutants and hexavalent chromium reduction

Visible light active, metal-free heterogeneous photocatalysts are required to achieve sustainable and green chemical processes. Development of such a catalyst is reported here. Mechanical pulverization of a covalent organic framework (COF) resulted in enhanced visible light photocatalytic activity for environmental remediation. The pulverized COF have achieved the apparent quantum yield (AQY) up to 41% for photo-Fenton-like degradation of organic dyes. Photocatalytic activity of the pulverized COF is one of the highest amongst the metal-free catalysts reported so far. The photocatalyst can operate under a broad range of pH, unlike metal-based photocatalysts. The catalyst does not lose its activities on recycling over several cycles. The exceptional performance of the pulverized COF is due to the high dispersibility, efficient visible light absorption, and excellent charge mobility. Moreover, the photocatalyst have also been used in continuous flow photo-Fenton-like degradation. The photocatalytic space time yield (PSTY) in continuous flow was boosted by twenty-eight times than the conventional batch photocatalysis. Moreover, the pulverized COF showed an outstanding photocatalytic reduction of toxic hexavalent chromium (Cr6+) to non-toxic trivalent (Cr3+).

Cellulose/GO monolith covered with Pd–Pt bimetallic nanocrystals for continuous-flow catalytic reduction of hexavalent chromium

Cellulose monolith materials have interconnected open porous structures with very high porosity, making them attractive structures for use as support materials in heterogeneous catalysis applications. In this study, we developed a highly efficient and reusable continuous-flow reactor for Cr(VI) remediation by combining the advantageous features of cellulose monoliths with suitable reinforcement techniques. We fabricated a porous monolithic cellulose/graphene oxide (GO) composite with a continuous three-dimensional skeletal framework using the thermally induced phase separation technique. Pd nanocrystals were synthesized in situ on the surface of the composite monolith, and then converted to porous Pd–Pt bimetallic nanocrystals through a galvanic replacement reaction. This approach eliminated the need for additional reductants and stabilizers, making the process simpler and more environmentally friendly. Under carefully optimized conditions, the cellulose/GO/Pd–Pt nanocomposite monolith exhibited outstanding performance in continuous-flow reactions for Cr(VI) reduction, achieving a maximum conversion rate of 98 %. Moreover, the nanocomposite monolith-based heterogeneous catalyst exhibited remarkable long-term stability, maintaining its catalytic activity even after extended periods of storage in the dried state. These findings highlight the potential of cellulose-based composite monoliths as versatile and robust support materials for heterogeneous catalysis.

Three-Dimensional Multihierarchical Hexagonal/Cubic ZnIn2S4 S-Scheme Heterophase Junction for Superior Photocatalysis.

It is an important strategy to design composite materials with a special microstructure and a tunable electronic structure through structural compatibility. In this work, a novel hexagonal/cubic ZnIn2S4 polymorphic heterophase junction with a three-dimensional multihierarchical structure is successfully constructed by in situ growth of hexagonal ZnIn2S4 nanosheets on the surface of cubic ZnIn2S4 flower-like microspheres prepared by topological chemical synthesis. On the one hand, the multihierarchical architecture provides large specific surface area, abundant active sites, and excellent light trapping capability. On the other hand, the construction of a direct S-scheme heterophase junction enables the formation of a special charge-transfer channel under the force of a built-in electric field, which not only improves the separation efficiency of carriers but also ensures the stronger reaction activity of charges. The prepared ZnIn2S4 heterophase junction composite photocatalyst exhibits greatly boosted photocatalytic efficiency in rhodamine B degradation, hexavalent chromium reduction, and water splitting for hydrogen production, which are 12.3, 6.5, and 3.1 times higher than that of pure hexagonal ZnIn2S4 and 8.1, 5.1, and 2.3 times higher than that of pure cubic ZnIn2S4, respectively, demonstrating its significant potential for applications in energy and environmental fields.

LED-enhanced photocatalytic reduction of hexavalent chromium by Cu-doped ZnO nanorods: kinetic modeling, cost analysis, and toxicity assessment

ABSTRACT This study unveils the synthesis and application of Cu-doped ZnO nanorods (NRS) as an efficient catalyst for the photocatalytic reduction of hazardous hexavalent chromium (Cr6+) in water. Synthesized via a simplified co-precipitation method, the NRS demonstrated enhanced performance, achieving an 89.35% Cr6+ reduction efficiency under optimal conditions. The catalyst’s performance was significantly augmented in the presence of hydrogen peroxide (H2O2) and revealed a first-order kinetic model. Radical trapping experiments highlighted the pivotal role of hydroxyl radicals in the photocatalytic process. A comparative analysis of the NRS with LED/ZnO and undoped ZnO underscores the superior efficiency of the Cu-doped variant. Moreover, the applicability of this system was validated in real water and wastewater matrices containing Cr6+, indicating its promising potential for industrial and environmental applications. An in vivo bioassay using Daphnia magna further confirmed the reduced toxicity post-treatment, underscoring the environmental friendliness of this innovative approach. The findings present Cu-doped ZnO nanorods as a promising, effective, and eco-friendly catalyst for the remediation of Cr6+ contaminated water, marking a significant stride towards sustainable and efficient water treatment solutions.

Synergistic effect of adsorption-photocatalytic reduction of Cr(VI) in wastewater with biochar/TiO2 composite under simulated sunlight illumination.

Photocatalysis, which is an alternative technology to conventional methods, utilizes solar energy as the driving force to address environmental concerns and has attracted widespread attention from chemists worldwide. In this study, a series of photocatalytic materials composed of agricultural waste and titanium dioxide (TiO2) nanomaterial was prepared for the synergistic adsorption-photocatalytic reduction of hexavalent chromium in wastewater under mild conditions. The results showed that the TiO2 nanomaterial exhibited a higher photogenerated carrier separation efficiency and performance for the adsorption-photocatalytic reduction of Cr(VI) after loading straw biochar (BC). When the loading amount of BC was 0.025 g (i.e., TBC-3), the removal efficiency of Cr(VI) was as high as 99.9% under sunlight irradiation for 25 min, which was 2.9 and 3.5 times higher than that of pure TiO2 and BC samples, respectively. Additionally, after four cycles of experiments, the removal efficiency of Cr(VI) by TBC-3 remained at about 93.0%, proving its good chemical ability in our reaction system. Its excellent adsorption-photocatalytic performance is mainly attributed to the synergistic effect of the strong adsorption of BC and the outstanding photocatalytic performance of TiO2. Finally, the possible mechanism for the synergistic adsorption-photocatalytic reduction on BC/TiO2 to remove the highly toxic Cr(VI) in wastewater was proposed.

Investigation of Hexavalent Chromium Reduction in Strong Saline and Acidic Nitro-Phosphate Solutions

Investigation of Hexavalent Chromium Reduction in Strong Saline and Acidic Nitro-Phosphate Solutions

Methods for Electrolyte Treatment and Hexavalent Chromium Reduction in Industrial Electrochemical Machining (ECM)

Electrochemical Machining (ECM) is a metal removal process that operates on the principle of anodic dissolution. ECM has the ability to produce complex shapes in difficult-to-machine alloys with precision and excellent surface finish. However, since most of these alloys contain chromium, one of the major challenges to ECM’s wider utilisation in industry is how to eliminate the resulting hexavalent chromium (Cr+6) from the spent electrolyte. This paper presents methods for controlling the Cr+6 level to within the permitted guidelines for an industry application of ECM, and reducing it to trivalent chromium (Cr+3), to then precipitating it from the electrolyte solution,The workpiece material – Triboloy (Co; Mo; Cr alloy) has hitherto not been machined by ECM and hence no literature exists on how to treat the by-products generated. This research involves experimental analysis of various Cr+6 to Cr+3 chemical reduction methods for ECM of Tribaloy in sodium nitrate electrolyte, using spent electrolyte samples. The reduction in Cr+6 is assessed over time. It was observed that the concentration of Cr+6 decreased within a span of two minutes. Subsequently, the solution pH level was increased by the addition of an alkali to precipitate the Cr+3 ions, which then can be filtered out from the solution. The optimum solution for hexavalent chromium is thus implemented in the industrial electrolyte system for successfully machining the Tribaloy component.