Metalcess provides complete EPC solutions for zinc oxide dust recycling plants, specializing in the recovery of zinc and other valuable metals from steel mill dust, EAF dust, secondary zinc oxide and other zinc-bearing residues.
Our solutions combine Waelz kiln roasting, hydrometallurgical zinc recovery, zinc electrowinning, zinc melting and casting, wastewater treatment and plant automation into one integrated engineering package.
For customers planning a zinc production capacity of more than approximately 10,000 tonnes of metallic zinc per year, Metalcess generally recommends a sulfuric acid-based zinc recovery and electrowinning process, particularly where a high level of automation and stable long-term operation is required.
1. Waelz Kiln – Converting Zinc Dust into Secondary Zinc Oxide
For zinc-bearing dust containing approximately 12–22% Zn, Metalcess can provide a Waelz kiln reduction-volatilization process.
The zinc-bearing material is mixed with a carbonaceous reducing agent and processed at high temperature in the rotary kiln.
The basic process mechanism is: Zinc Oxide → Reduction → Metallic Zinc → Vaporization → Re-oxidation → Secondary Zinc Oxide
Zinc is reduced and volatilized inside the kiln. Zinc vapor is subsequently oxidized and collected together with the kiln off-gas in the dust collection system.
The collected secondary zinc oxide typically contains approximately:60–80% ZnO product.
Depending on the feed material, the secondary zinc oxide may also contain approximately: 3–10% chloride, as well as smaller quantities of: Lead, Iron, Silicon, Calcium, Other oxides and impurities. The secondary zinc oxide then becomes the feedstock for the next stage of zinc recovery.
3. Sulfuric Acid Based Zinc Hydrometallurgical Recovery
Sulfuric acid based zinc hydrometallurgical recovery process is mostly suitable for projects with annual metallic zinc production exceeding approximately 10,000 t/y, particularly when the project requires a high degree of automation and stable continuous operation.
The process consists of the following major steps: Secondary Zinc Oxide àAlkaline Dechlorination / DefluorinationàSulfuric Acid LeachingàLeach Solution PurificationàZinc ElectrowinningàCathode ZincàZinc Melting & CastingàZinc Ingots
This route can be integrated with lead recovery from the leaching residue.
4. Automated Zinc Electrowinning Workshop
Metalcess has accumulated extensive engineering experience in the automation of sulfuric acid zinc electrowinning and zinc melting/casting workshops.
For large-capacity projects, the automation system can integrate the major production equipment into a centralized SCADA platform.
The system can monitor:
Ø Rectifier voltage
Ø Rectifier current
Ø Individual cell electrical conditions
Ø Electrolyte temperature
Ø Electrolyte flow
Ø Rich electrolyte flow
Ø Cooling water flow
Ø Cathode operating conditions
Ø Short-circuit signals
Ø Production status
Ø Zinc harvesting status
Ø Equipment operating status
The purpose of automation is not simply to replace operators.
The more important objective is to transform the plant from a collection of individual machines into an integrated intelligent production system.
5. SCADA-Based Monitoring of Zinc Electrowinning
The SCADA system can continuously collect and analyze the operating data of the electrowinning system.
Changes in voltage and current provide valuable information about the condition of the electrolytic cells.
Together with the short-circuit monitoring system, these signals can be used for analysis and prediction of abnormal operating conditions.
Ø Electrolyte Condition Analysis: Changes in electrical parameters can be correlated with electrolyte operating conditions and process fluctuations.This helps operators identify abnormal conditions at an early stage.
Ø Cathode Contact Analysis: Abnormal electrical behavior may indicate poor electrical contact, abnormal plate positioning or other cathode-related problems.
Ø Short-Circuit Prediction: Continuous monitoring of electrical behavior, combined with short-circuit detection, can help identify developing short-circuit conditions before they become serious production problems.
Ø Zinc Production Prediction: The SCADA system can use electrical operating data together with production parameters to estimate zinc production performance.
Ø Zinc Harvesting Planning: Production information can be used to optimize cathode harvesting schedules and coordinate the downstream zinc melting and casting section.
6. Dynamic Control of Electrolyte Flow and Cooling
The automation system can also connect the electrical operating condition with the hydrometallurgical process control system.
For example, according to the actual current condition and operating requirements, the control system can dynamically adjust:
Ø Rich electrolyte feed
Ø Electrolyte circulation
Ø Electrolyte cooling capacity
Ø Related process parameters
This provides a more stable operating environment for zinc electrowinning.
The objective is to maintain the electrowinning system within its designed operating range while minimizing unnecessary energy and cooling consumption.
This approach is particularly valuable for large zinc production plants where even small process deviations can accumulate into significant production losses.
7. Chloride Removal and Wastewater Treatment
Chloride is one of the key factors affecting the selection of a zinc oxide processing route.
When secondary zinc oxide contains significant quantities of chloride, Metalcess can provide an alkaline washing process before sulfuric acid leaching.
The objective is to remove chloride and fluoride from the zinc oxide while preparing the material for the subsequent sulfate-based hydrometallurgical process.
The chloride-containing wastewater can then be treated through an integrated separation and concentration system.
It can reduce wastewater discharge and improve the overall environmental performance of the plant.
8. Build a Zinc Recycling Plant with Metalcess
If your steel plant generates zinc-bearing dust, or you are considering a secondary zinc recycling project, you may have the question:
“Which process and plant configuration provides the best economic and operational solution for our specific raw material and production scale?”
Metalcess can evaluate the feed material, compare process routes and develop a complete engineering solution.
Whether your project requires:
Ø Waelz kiln zinc recovery
Ø Secondary zinc oxide production
Ø Chloride removal
Ø Sulfuric acid leaching
Ø Ammonium chloride leaching
Ø Solution purification
Ø Zinc electrowinning
Ø Cathode zinc handling
Ø Zinc melting
Ø Automatic zinc casting
Ø Lead recovery
Ø Wastewater treatment
Ø SCADA automation
Ø Complete EPC execution
Metalcess can provide an integrated engineering solution.
