Removal of Heavy Metals from Industrial Effluent using Electrogravimetric Technique

Heavy metals, a byproduct of industrial activities, have become a pervasive environmental pollutant, posing severe risks to Human Health [1], Ecosystems [2], and the Economy [3]. Industrial effluents contaminated with toxic heavy metals such as lead, cadmium, chromium, copper, nickel, zinc, and mercury, are released into water bodies, soil, and air, causing irreversible damage [4]. The consequences of heavy metal pollution are far-reaching and multifaceted. Human health is compromised through increased risk of Cancer [5], neurological damage [6], Kidney Dysfunction [7], and reproductive issues [8]. Environmental degradation occurs as heavy metals accumulate in ecosystems, harming aquatic life, contaminating food chains, and altering ecosystem dynamics [9]. Furthermore, heavy metal pollution has significant economic impacts, affecting agriculture, fisheries, and tourism [10]. Traditional treatment methods, including chemical precipitation, adsorption, and membrane filtration, often struggle to effectively remove heavy metals from industrial effluents due to limitations in efficiency, high operational costs, generation of secondary pollutants, and inability to target specific heavy metals [11]. In response, electrogravimetric technique, or electrochemical precipitation, has emerged as a promising solution [12]. This innovative approach leverages electrical energy to precipitate heavy metals, offering numerous advantages, including high removal efficiency, selectivity for specific heavy metals, energy efficiency, compact design, and costeffectiveness [13]. This review provides a comprehensive evaluation of electrogravimetric technique for heavy metal removal from industrial effluents. The discussion encompasses the principles, advantages, and parameters influencing its performance, as well as applications in various industrial settings, to assess its effectiveness and potential for widespread adoption (Figure 1).

Figure 1:Schematic aim of proposed work.

Electrogravimetric technique, also known as electrochemical precipitation, is a process that utilizes electrical energy to remove heavy metals from industrial effluents. The principle involves the application of an electric potential between two electrodes immersed in the effluent, inducing electrochemical reactions that precipitate heavy metals.

Electrochemical reactions

Cathodic reaction: At the cathode (negatively charged electrode), heavy metal ions (Mn+ ) in the effluent are reduced to their elemental form (M) through electron transfer..

Anodic reaction: At the anode (positively charged electrode), water is oxidized, releasing oxygen gas and hydrogen ions.

Understanding the principle of electrogravimetric technique is crucial for optimizing its performance, scaling up applications, and exploring new electrode materials and configurations [14-20] (Table 1).

Table 1:Heavy metals removed, removal efficiencies and effluent sources.

Electromigration

Heavy metal ions in the effluent migrate towards the cathode under the influence of the electric field.

Electrochemical reduction

At the cathode, heavy metal ions are reduced to their elemental form, precipitating out of solution.

Nucleation and growth

Precipitated heavy metals form nuclei, which grow into larger particles, facilitating easy separation.

a. Electrode Material: Cathode material affects removal efficiency, with materials like graphite [21], Stainless Steel [22], and Titanium [23] showing promise.
b. Electrode Potential: Optimal potential range for heavy metal precipitation.
c. Current Density: Influences precipitation rate and efficiency.
d. pH: Affects heavy metal speciation and precipitation [24].
e. Temperature: Impacts reaction kinetics and efficiency [25].

Advantages

a. High removal efficiency [26]
b. Selectivity for specific heavy metals [27]
c. Energy efficiency [28]
d. Compact design [29]
e. Cost-effective [30]

Electrogravimetric technique varisations

a. Direct Current (DC) electrogravimetry: Traditional method using constant DC.
b. Pulsed Current electrogravimetry: Uses pulsed current to enhance removal efficiency.
c. Alternating Current (AC) electrogravimetry: Utilizes AC to reduce electrode corrosion.

Electrogravimetric technique has achieved impressive removal efficiencies for heavy metals (Figure 2):

Figure 2:Factor Influencing removal efficiency.

Factors influencing removal efficiency

a. Electrode material
b. Electrode potential
c. Current density
d. pH
e. Temperature
f. Heavy metal concentration

Industrial applications

Electro gravimetric technique has been applied in various industries:
a. Electroplating [31]
b. Textile manufacturing [32]
c. Tannery [33]
d. Mining [34]
e. Chemical processing [35]
f. Battery manufacturing [36]
g. Printed circuit board manufacturing [37]

By effectively removing heavy metals, electrogravimetric technique helps mitigate environmental pollution, protects human health, and ensures compliance with regulatory standards (Figure 3).

Figure 3:Industrial applications.

Case study 1

i. Removal of Pb and Cd from Textile Industry Wastewater [38] ii. Location: Textile mill in Gujarat, India
iii. Effluent characteristics: pH 6.5-7.5, Pb 50-70mg/L, Cd 30- 50mg/L
iv. Electrogravimetric technique: DC electrogravimetry with graphite cathode and stainless steel anode
v. Operating conditions: Current density 20mA/cm², electrolysis time 2 hours
vi. Results: Pb removal 95%, Cd removal 92%
vii. Conclusion: Electrogravimetric technique effectively removed Pb and Cd from textile industry wastewater.

Case study 2

i. Electrogravimetric Treatment of Electroplating Industry Effluent [39]
ii. Location: Electroplating unit in Tamil Nadu, India iii. Effluent characteristics: pH 4.5-5.5, Cu 100-150mg/L, Ni 50- 70mg/L
iv. Electrogravimetric technique: Pulsed current electrogravimetry with titanium cathode and stainless-steel anode
v. Operating conditions: Current density 30mA/cm², pulse frequency 100Hz, electrolysis time 3 hours
vi. Results: Cu removal 98%, Ni removal 95%
vii. Conclusion: Electrogravimetric technique efficiently removed Cu and Ni from electroplating industry effluent.

Case study 3

i. Heavy Metal Removal from Mining Industry Wastewater [40] ii. Location: Mining site in Australia
iii. Effluent characteristics: pH 3.5-4.5, Zn 500-700mg/L, Pb 200- 300mg/L
iv. Electrogravimetric technique: AC electrogravimetry with graphite cathode and stainless steel anode
v. Operating conditions: Current density 40mA/cm², frequency 50Hz, electrolysis time 4 hours
vi. Results: Zn removal 90%, Pb removal 92%
vii. Conclusion: Electrogravimetric technique successfully removed Zn and Pb from mining industry wastewater.

Case study 4

i. Removal of Cr from Tannery Effluent [41]
ii. Location: Tannery unit in Italy
iii. Effluent characteristics: pH 4.5-5.5, Cr 150-200mg/L iv. Electrogravimetric technique: DC electrogravimetry with stainless steel cathode and titanium anode
v. Operating conditions: Current density 25mA/cm², electrolysis time 2.5 hours
vi. Results: Cr removal 95%
vii. Conclusion: Electrogravimetric technique effectively removed Cr from tannery effluent.

Case study 5

i. Treatment of Battery Manufacturing Wastewater [42]
ii. Location: Battery manufacturing unit in China
iii. Effluent characteristics: pH 6.5-7.5, Pb 100-150mg/L, Cd 50- 70mg/L
iv. Electrogravimetric technique: Pulsed current electrogravimetry with graphite cathode and stainless-steel anode
v. Operating conditions: Current density 30mA/cm², pulse frequency 100Hz, electrolysis time 3 hours
vi. Results: Pb removal 98%, Cd removal 95%
vii. Conclusion: Electrogravimetric technique efficiently removed Pb and Cd from battery manufacturing wastewater.
viii. These case studies demonstrate the effectiveness of electrogravimetric technique in removing heavy metals from various industrial effluents, showcasing its potential as a reliable and efficient treatment technology.

Despite its effectiveness, the electrogravimetric technique faces several challenges that must be addressed to fully harness its potential. One of the primary challenges is scaling up, transitioning from laboratory-scale to industrial-scale operations, which requires significant design and operational adjustments [43]. Additionally, electrode corrosion remains a concern [44], reducing efficiency and increasing maintenance costs. The presence of competing ions in complex effluents also interferes with the technique’s performance, necessitating strategies to mitigate their impact. Furthermore, optimizing energy consumption is crucial to enhance the technique’s energy efficiency and reduce operational costs. The capital and operating costs associated with electrogravimetric technique must also be minimized to make it a viable solution for industries. Ensuring stability and reliability is another critical aspect, as consistent performance is essential for industrial applications. Lastly, navigating varying regulatory frameworks poses a challenge, requiring compliance with diverse standards and guidelines. Addressing these challenges will be essential to overcome the limitations of electrogravimetric technique and unlock its full potential for heavy metal removal from industrial effluents. By tackling these hurdles, researchers and industries can work together to develop more efficient, cost-effective, and sustainable solutions.

To overcome the challenges and enhance the electrogravimetric technique, several future directions can be pursued. One key area of focus is the development of novel electrode materials with improved corrosion resistance [45], which would significantly enhance the technique’s efficiency and longevity. Additionally, optimizing operating conditions by investigating the effects of pH, temperature, and current density can lead to improved performance [46]. Another promising approach is the integration of electrogravimetry with other technologies to create hybrid treatment approaches, leveraging the strengths of multiple methods [47]. Modular design is also essential, enabling the development of compact, scalable, and flexible systems suitable for various industrial settings. Furthermore, implementing advanced monitoring and control systems through automation and control will ensure seamless operation and maximize efficiency [48]. Conducting thorough economic analyses is also crucial to understand the cost-benefit dynamics of electrogravimetric technique and identify areas for improvement. Finally, establishing industry-wide standards through standardization and certification will facilitate widespread adoption and ensure consistency across applications. By exploring these future directions, researchers and industries can work together to advance electrogravimetric technique and create a more effective, efficient, and sustainable solution for heavy metal removal from industrial effluents.

Research Opportunities abound in the field of electrogravimetric technique, offering avenues for advancement and innovation. Fundamental studies are needed to investigate the underlying electrochemical mechanisms, shedding light on the technique’s intricacies. Material science research can focus on developing new electrode materials with enhanced properties, while process modelling can simulate and optimize electrogravimetric processes to improve efficiency. Pilot-scale testing is crucial to validate laboratory results and demonstrate scalability. Industrial collaborations are also vital, enabling partnerships with industries to apply electrogravimetric technique in real-world settings. By bridging the gap between research and practice, these collaborations can inform the development of practical solutions.

Emerging trends are poised to shape the future of electrogravimetric technique. Integrating sustainable technologies with renewable energy can minimize environmental footprint. Adopting circular economy principles enables the recovery of valuable metals and reuse of treated effluent. Water reuse strategies can treat effluent for reuse in industries, conserving resources. Furthermore, combining electrogravimetry with advanced oxidation processes can unlock synergies and enhance treatment efficacy. By embracing these trends, researchers and industries can unlock new possibilities and propel electrogravimetric technique toward widespread adoption.

In conclusion, the electrogravimetric technique has demonstrated significant potential in effectively removing heavy metals from industrial effluents, offering a promising solution to a pressing environmental concern. By addressing the existing challenges, such as scaling up, electrode corrosion, and competing ions, and exploring future directions, including novel electrode materials, optimization of operating conditions, and hybrid treatment approaches, the efficiency, scalability, and costeffectiveness of this technique can be substantially enhanced. Ongoing research and development are crucial to ensure the continued relevance and improvement of electrogravimetric technique in industrial wastewater treatment. As the technology advances, its integration with emerging trends, such as sustainable technologies, circular economy, and water reuse, will further solidify its position as a leading solution for heavy metal removal. The successful implementation of electrogravimetric technique has far-reaching implications, including improved environmental protection, enhanced human health, and reduced economic burdens associated with heavy metal pollution. Ultimately, this innovative technology has the potential to transform industrial wastewater treatment, providing a cleaner, safer, and more sustainable future for generations to come.

To fully harness the potential of electrogravimetric technique for heavy metal removal from industrial effluents, several key recommendations must be implemented. Firstly, conducting thorough economic analyses is crucial to understand the costbenefit dynamics and identify areas for improvement. Additionally, developing novel electrode materials with enhanced properties can significantly boost efficiency and longevity. Optimizing operating conditions, such as pH, temperature, and current density, is also vital to maximize performance. Furthermore, exploring hybrid treatment approaches that combine electrogravimetry with other technologies can unlock synergies and enhance treatment efficacy. Finally, establishing industry-wide standards through standardization and certification will facilitate widespread adoption and ensure consistency across applications. By addressing the challenges and capitalizing on emerging trends, electrogravimetric technique can overcome its limitations and become a leading technology for heavy metal removal from industrial effluents, driving innovation and sustainability in environmental remediation. Effective implementation of these recommendations will pave the way for electrogravimetric technique to make a significant impact in mitigating heavy metal pollution.

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