If you’ve spent any time around a gold plant, you’ve heard the debate: ZADRA or AARL — which system gives better results?
It’s a question that comes up in almost every mine review or plant design meeting. Both systems work on the same principle, stripping gold from loaded carbon using heat, caustic solution, and cyanide, but how they get there differs.
In Zimbabwe, where water quality, energy stability, and batch volumes vary from site to site, the right choice can make a huge difference. Let’s break it down in simple, practical terms.
A Quick Refresher: What Happens During Elution
Before comparing the two systems, it helps to understand the basic process.
During elution, a hot caustic cyanide solution passes through loaded carbon, releasing the gold into liquid form. That gold-rich solution (known as “pregnant liquor”) is then sent to electrowinning, where electricity plates out the gold.
How the Elution Process Works: From Loaded Carbon to Pure Gold.
The ZADRA Elution System
The ZADRA system is one of the most commonly used methods in small to medium-scale gold operations across Africa.
It’s simple, continuous, and easier to maintain, ideal for plants that need reliability without high infrastructure costs.
How It Works:
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Uses a continuous flow of hot caustic cyanide solution through the carbon column.
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Operates at low to moderate pressure (1–2 bar) and around 110–120°C.
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Gold is stripped gradually over 8–14 hours, depending on system design and carbon quality.
Advantages:
✅ Simpler design, fewer valves and control systems
✅ Lower installation cost
✅ Easier maintenance
✅ Ideal for smaller operations or limited budgets
Limitations:
⚠️ Slower stripping time
⚠️ Slightly higher chemical consumption
⚠️ Requires stable heat source for consistency
In Bulawayo and Gwanda, many small-scale plants prefer ZADRA because of its balance between simplicity and reliability. When done properly, it delivers excellent recovery rates with minimal downtime.
The AARL Elution System
Developed by the Anglo American Research Laboratories, the AARL system is a more advanced batch process, often used in larger operations aiming for maximum efficiency and shorter cycle times.
How It Works:
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Begins with acid washing to clean the carbon.
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Then a pre-treatment stage flushes with cold cyanide and caustic solution.
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The actual stripping phase uses hot water at 130–140°C under higher pressure (3–5 bar).
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The process typically takes 5–6 hours, much faster than ZADRA.
Advantages:
✅ Faster stripping cycle
✅ Lower chemical consumption
✅ Higher gold recovery efficiency
✅ More consistent results for large batches
Limitations:
⚠️ Higher setup cost and more complex plumbing
⚠️ Requires precise temperature and pressure control
⚠️ Needs skilled operators
AARL systems perform beautifully when properly maintained, but downtime or poor calibration can hurt recovery quickly. They’re ideal for established operations with trained technicians and stable power supply.
ZADRA vs AARL: Side-by-Side Comparison
| Feature | ZADRA System | AARL System |
|---|---|---|
| Process Type | Continuous | Batch |
| Pressure | 1–2 bar | 3–5 bar |
| Temperature | 110–120°C | 130–140°C |
| Time per Cycle | 8–14 hours | 5–6 hours |
| Chemical Use | Moderate to high | Low |
| Setup Cost | Lower | Higher |
| Maintenance | Easier | More complex |
| Best For | Small–medium plants | Large operations |
Which System Works Best in Zimbabwean Conditions?
In Zimbabwe, conditions vary widely between mines. Factors like power reliability, water chemistry, and batch volume influence which system performs best.
Here’s what experience shows:
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For small to mid-scale producers, ZADRA is often more practical. It’s forgiving, easy to maintain, and ideal when infrastructure or budgets are limited.
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For larger, high-throughput plants, AARL delivers better efficiency and faster turnaround, provided that heat and pressure are consistently managed.
At Bulawayo Elutions, we’ve designed and optimized both systems. Our team understands that no two mines are alike, which is why we customize parameters for temperature, pressure, and chemical balance to match your operation’s specific needs.
Why Water Quality Affects Gold Elution Efficiency” once it’s live.
Final Say
There’s no universal winner between ZADRA and AARL, only what’s right for your setup.
If you’re running smaller batches and want simplicity and reliability, ZADRA gives excellent results with minimal fuss.
If you need fast cycles and high throughput, and can manage the maintenance, AARL is the way to go.
At the end of the day, experience matters more than the system. A well-run ZADRA will outperform a poorly managed AARL any day, and that’s why having the right elution partner is crucial.
“What Is Gold Elution and Why It’s the Heart of Gold Recovery.”
