Abstract
Current efficiency and anode‑scrap rate are two core economic‑technical indicators for copper electrolytic refining. Especially for traditional electrolytic processes using titanium‑base starting sheets as cathodes, continuous process optimization is essential to raise current efficiency and cut anode‑scrap loss. This article analyzes major influencing factors from practical production experience and summarizes actionable countermeasures for electrolytic copper plants.
1. Current Efficiency: Definition, Influencing Factors & Practical Solutions
Current efficiency refers to the percentage ratio between actual copper output and theoretical copper output calculated by Faraday’s law.
Current Efficiency η = (Actual copper production / Theoretical copper production) ×100%
Actual copper output equals the weighed cathode copper mass minus the weight of starting sheets. Theoretical copper production is calculated based on applied current, electrolysis duration and the number of electrolytic cells. Short‑circuits, improper additive dosing, poor electrical contact and inaccurate current metering are primary causes of low current efficiency.
1.1 Short‑Circuits Between Anodes and Cathodes
Short‑circuits inside electrolytic cells consume electric power without contributing to copper deposition and directly pull down current efficiency. Common triggers and remedies are listed below:
- Anode burrs and flash edges: Unremoved flash and burrs on cast copper anodes may physically touch starting‑sheet cathodes after loading into cells.
- Remedies: Straighten and calibrate anodes before tank loading. Large‑scale plants adopt automatic anode straightening units. Small‑capacity facilities (e.g., 50 kt‑per‑year lines) perform manual calibration for anode lugs. Trim all surface burrs and flash edges; reject badly deformed anodes to avoid cell feeding.
- Non‑uniform electrode spacing: Without positioning fixtures for conductive bus‑bars, manual adjustment may create uneven inter‑electrode gaps and cause contact between electrodes.
- Remedies: Use acid‑resistant tension ropes to align all anodes within and across electrolytic cells to guarantee consistent electrode spacing.
- Insufficient anode pickling: Oxide scales and copper powder remaining on anode surfaces after pickling can adhere to cathode sheets and trigger short‑circuits.
- Remedies: Maintain sufficient acidity and moderate temperature in pickling tanks to fully dissolve surface oxides. Thoroughly rinse anodes with clean water post‑pickling to prevent copper powder from entering electrolyte and generating cathode particles.
- Tilted anodes from deformed or damaged lugs: Bent or broken anode lugs make plates tilt inside cells and create unintended electrode contact.
- Remedies: Pry tilted anodes toward vertical position; hammer the contact side of anode lugs; insert thin copper shims under lugs to keep anodes upright.
1.2 Mis‑dosing of Electrolytic Additives
Typical additives include glue (bone glue), thiourea, casein, hydrochloric acid and Avitone‑A. Correct additive proportions produce smooth, compact cathode copper with fine striations. Once glue feeding stops for more than 12 hours, cathodes turn dark‑red, develop massive surface nodules and become brittle; nodules readily bridge electrodes and create short‑circuits.
- Practical guidance: Adjust additive dosage according to anode composition. Normally, thiourea dosage accounts for 50 ~ 70 % of glue dosage. Casein and Avitone‑A can be omitted depending on cathode deposition quality.
1.3 Poor Electrical Contact Between Electrodes and Conductive Bus‑Bars
Bad contact between anode lugs / cathode conducting bars and copper bus‑bars results in anode re‑dissolution or cathode burning, lowering current efficiency.
- Remedies: Routinely flush conductive bus‑bars to remove copper sulfate crystalline deposits which increase contact resistance. Regularly inspect and replace insulating rubber sheets to maintain proper height matching; prevent anode re‑dissolution and cathode burning caused by loose contact.
1.4 Deviation Between Rectifier Output Current and Real Cell Current
Silicon‑controlled rectifier displayed current may deviate from actual working current. When inconsistency occurs, inspect current transformers and measure current on individual conducting bars at cell level to identify whether output reading is higher or lower than real operational current.
2. Anode‑Scrap Rate: Concept, Key Factors & Reduction Measures
Anode‑scrap rate reflects copper loss of consumed anodes after electrolysis. Monthly statistical calculation is commonly adopted even though the normal anode service cycle runs 18‑21 days (often crossing calendar months). Simplified definition: the weight percentage of washed anode scrap (after removing surface anode slime) relative to the original weight of the corresponding fresh anode plate. Major loss drivers include anode re‑dissolution, limited effective immersed area and anode passivation.
2.1 Eliminate Anode Re‑dissolution
Anode re‑dissolution happens when anodes lose good electric contact with bus‑bars: plates turn copper‑red without normal electrochemical dissolution, generating heavy anode scraps.
- Remedies: Bend anode lugs during calibration for improved surface contact against conductive bus‑bars. Perform regular tank‑side inspection; once re‑dissolving anodes are spotted, pry and hammer lugs to restore tight contact. Notice that obviously elevated single‑cell voltage may also indicate poor lug‑bus‑bar contact even without visible re‑dissolution; poor conduction leads to incomplete anode dissolution and heavier scrap output.
2.2 Maximize Anode Effective Working Area
Effective anode area means the plate surface immersed in electrolyte for electrochemical dissolution.
- Reduce lug weight under mechanical load limits of anode lugs.
- Raise electrolyte liquid level appropriately to enlarge immersed anode area, but never let liquid reach the bottom of lugs to avoid scrap dropping into cells.
- The upper zone of anodes dissolves faster because upper electrolyte features higher acidity and lower copper concentration. Modify casting moulds by deepening the upper section by approx. 2 mm. This improves mechanical strength of anode upper portions and prevents premature plate fracture in late electrolysis phase which would raise scrap rate.
2.3 Mitigate Anode Passivation
Excessive lead, nickel and other impurities in anode copper will form hard, slime‑like barrier layers covering anode surfaces, causing passivation. Passivation raises cell voltage sharply and leaves heavy residual anode scrapPAS Journa….
- Remedies: Strictly control impurity content in cast anodes; lead and nickel content are preferably kept below 0.2 %. For individual passivated cells, vibrate anodes with hammer tools to loosen surface anode‑slime layers. Severe passivation requires tank draining and flushing for anode cleaning, though this brings heavy workload.
3. Conclusion
Current efficiency and anode‑scrap rate are tightly connected to operational management, anode quality, additive control and electrical contact conditions in copper electrolytic refining. By eliminating cell short‑circuits, stabilizing additive feeding, guaranteeing reliable electric contact, optimizing anode casting design and suppressing anode passivation, operators can achieve higher current efficiency and lower anode‑scrap loss, effectively cutting comprehensive production costs for electrolytic copper refining plants.
