Real-Time Monitoring of Key Parameters in Selenium Recovery Using Biosensors

Abstract

Biosensors enable real-time monitoring of redox potential (ORP), selenium (Se) concentration, and toxic by-products during selenium recovery processes. Typical applications include: (1) microbial fuel cell sensors based on sulfate-reducing bacteria (SRB), which dynamically reflect Se(IV) concentration via current changes with a sensitivity of 0.2 μA/mg Se and a detection limit of 0.05 mg/L; (2) DNA aptamer fluorescence sensors specifically recognizing Se(VI) with response times under 3 minutes; (3) enzyme electrodes (glutathione peroxidase) for H₂Se gas detection with accuracy of ±0.1 ppm. Integrated with IoT platforms, data refresh rates reach 1 Hz, enabling coordinated control of pH and reductant dosing, improving recovery efficiency to 95% while suppressing excessive Se⁰ formation (<5%).

1. Monitoring Requirements in Selenium Recovery and Advantages of Biosensors

1.1 Key Control Parameters

• Redox potential (ORP): Selenium speciation transformations (Se(VI) → Se(IV) → Se⁰) depend on ORP ranging from –200 mV to +400 mV, directly influencing recovery yield and product purity.
• Selenium concentration gradients: The ratio of Se(IV)/Se(VI) in leachate determines reductant (e.g., Fe²⁺) dosing; fluctuations exceeding 10% risk over-reduction producing excess Se⁰ (>20%).
• Toxic by-products: Real-time monitoring of H₂Se gas (threshold limit 0.05 ppm) and SeS₂ precipitates is critical to prevent leaks.

1.2 Biosensor Technical Features

• High specificity: Microbial, enzymatic, and nucleic acid aptamer sensors differentiate Se(IV), Se(VI), and organic selenium species (e.g., selenomethionine) with cross-reactivity under 5%.
• Rapid response: Compared to offline ICP-MS requiring over 2 hours, biosensors provide second-level feedback suitable for process control.

2. Biosensor Design and Integration

2.1 Microbial Electrochemical Sensor

• SRB anode: Desulfovibrio desulfuricans’ membrane cytochrome c3 mediates Se(IV) reduction; current output correlates linearly with Se(IV) concentration (R² = 0.998).
• Signal conversion: Nanoampere signals amplified 10⁶-fold to 4–20 mA standard output; detection range 0.1–100 mg/L.
• Case data: Pilot testing at a Jiangxi smelter optimized NaHS dosing guided by sensor feedback, increasing Se⁰ purity from 88% to 96% and reducing reductant consumption by 30%.

2.2 DNA Aptamer Fluorescence Sensor

• Se(VI) specificity: Aptamer sequence 5′-ATCCAGAGTGACGCAGCATGGCGGGTGG-3′ folds into G-quadruplex; binding Se(VI) enhances fluorescence intensity 50-fold.
• Microfluidic detection cell: Integrated 470 nm LED excitation and photodiode detection; online detection limit 0.01 mg/L; resistant to Cu²⁺/Zn²⁺ interference up to 100 mg/L.

2.3 Enzyme Electrode Gas Sensor

• H₂Se detection principle: Immobilized glutathione peroxidase (GPx) catalyzes H₂Se + 2GSH → GSSG + H₂O; oxygen consumption quantified by Clark electrode within 0.01–1 ppm linear range.
• Sulfide interference mitigation: Dual-layer membrane (PTFE + silicone rubber) blocks >99.9% H₂S permeation ensuring selectivity.

3. Multi-Sensor Data Integration and Process Optimization

3.1 IoT Platform Architecture

• Edge computing: STM32 microcontrollers process sensor data at 10 Hz sampling rate, uploading via Modbus RTU to PLC.
• Feedback control logic: Automatic FeSO₄ dosing pump activation with PID flow control (±2% precision) triggered when Se(IV) >50 mg/L and ORP >+150 mV.

3.2 Dynamic Process Control Cases

• Selenium precipitation control: Sensor network detects Se⁰ nanoparticle size >200 nm via enhanced light scattering, activating ultrasonic fragmentation (20 kHz, 200 W) to maintain particle size <100 nm, improving purity.
• Toxic gas emergency response: H₂Se concentration >0.03 ppm triggers alkaline spray (pH >10), achieving neutralization efficiency >99%.

4. Techno-Economic and Environmental Benefits

4.1 Cost Analysis

• Capital investment: Biosensor system including installation costs approximately USD 50,000, 67% lower than traditional online spectrometers (>USD 150,000).
• Operating costs: Monthly microbial sensor culture media expense about USD 200; enzyme electrodes require replacement every six months or longer.

4.2 Environmental Risk Management

• Leak warning: Real-time monitoring reduces H₂Se exposure incidents by 90%, complying with OSHA 1910.1000 standards.
• Sludge reduction: Precise Se⁰ generation control reduces overdosing of precipitants (e.g., FeCl₃), lowering sludge volume by 25%.

5. Challenges and Innovation Directions

5.1 Stability Enhancement

• Biocomponent immobilization: Sodium alginate–silica composite gel encapsulation of SRB maintains activity over 180 days versus 30 days for free cells.
• Anti-fouling design: Sensor surfaces coated with polyethylene glycol (PEG) layer inhibit sensitivity decay from Se⁰ deposition (<5% loss per month).

5.2 Intelligent Upgrades

• Machine learning prediction: LSTM neural networks forecast Se concentration trends with errors under ±5%, enabling proactive process adjustments.
• Digital twin system: ANSYS simulation platform optimizes sensor placement and fluid dynamics, reducing dead zones by 70%.

5.3 Novel Sensor Development

• Full selenium speciation chip: Microarray integrates Se(IV), Se(VI), and Se⁰ recognition units, completing full-spectrum analysis within 5 minutes.
• Live cell sensors: Engineered yeast expressing GFP reporter gene shows luminescence proportional to Se(VI) concentration, suitable for complex matrices.

Conclusion

Biosensors utilizing microbial, nucleic acid aptamer, and enzymatic specificity achieve real-time monitoring of ORP, selenium speciation, and toxic gases during selenium recovery. Multi-sensor data integration combined with IoT control can enhance recovery efficiency beyond 95% while mitigating environmental risks. Future advancements should focus on long-term biocomponent stability and comprehensive parameter integration to propel selenium resource recovery toward intelligent and precise operation.