CASE STUDY
6 TANKS VAT LEACHING
- Consider a 6 vat gold VAT leaching plant processing 5,000 tonnes of ore.
❖ Data
Assumptions:
- Ore to process - 5,000 tonnes
- Gold grade - 3.0 g/t
- Recovery efficiency - 85 %
- Retention (leach time) - 72 hours
- Ore bulk density - 2.5 t/m³
- Shrinkage (compaction) - 10%
- Freeboard solution height - 0.10 m
- pH of leach solution - 10.5
- Cyanide dosage - 1.0 kg NaCN / tonne ore
- Operating days per year - 300 days
- Gold price - USD 60 / gram
❖ Volume & Tank Design
- Determine ore volume per vat
Each vat processes: 5,000 t / 6 ≈ 833.33 t
Let’s size per vat for a single batch capacity of 1,000 t/vat as a design capacity
Using density 2.5 t/m³:
Ore volume = 1,000 t/2.5 t/m^3 = 400 m^3
Including shrinkage 10% → required volume = 400 × 1.10 = 440 m³
- Vat geometry
Cylindrical vat design:
- Let depth (ore layer) = 3.0 m
- Cross-sectional area needed = 440 / 3.0 = 146.67 m²
- Radius = √(146.67/π) = ~6.84 m → diameter ≈ 13.7 m
- Add freeboard 0.1 m → total height = ~3.1 m
So each vat would be ~ 13.7 m diameter × 3.1 m height
NOTE
• This is a large vat you may prefer smaller batch sizes (e.g. 500 t per vat) for practicality.
- Throughput & Scheduling
With retention 72 hours, the cycle per vat = 3 days. With 6 vats, you can schedule:
- One vat loaded each day (in steady state)
- Daily throughput = 1 batch / 3 days × total design capacity
If design capacity = 6 × 1,000 t per vat = 6,000 t per cycle → average throughput = 6,000 / 3 =
2,000 t/day
But if your plant capacity is 5,000 t total, a more realistic:
- Design each vat for 833 t,
- Total per cycle = 5,000 t, cycle 3 days → throughput = ~1,667 t/day
(You must match vat capacity design with actual ore supply and economics.)
- Gold Recovery & Revenue
Using grade 3.0 g/t, recovery 85%:
- Gold in feed = 5,000 t × 3.0 g/t = 15,000 g
Recovered = 15,000 × 0.85 = 12,750 g (12.75 kg)
Revenue (USD 60/g): 12,750 × 60 = USD 765,000
(If operating 300 days a year (with multiple cycles), revenue scales accordingly.)
- Reagent & Operating Costs
• Cyanide cost
- 1 kg NaCN / t × 5,000 t = *5,000 kg* NaCN
- If NaCN cost = USD 5/kg → cost = 5,000 × 5 = USD 25,000
• Other costs (estimates)
- Lime, water, electricity, labor, maintenance, overhead, smelting, assays, tailings handling. Let’s
estimate:
- Lime, water, utilities - 10,000
- Labor & supervision - 20,000
- Maintenance & spare parts - 5,000
- Smelting & refining, assays - 5,000
- Tailings management / environment - 3,000
- Miscellaneous - 2,000
- Total OPEX - USD 45,000
Total all-in operating costs = 25,000 + 45,000 = USD 70,000
Profit before capex = 765,000 – 70,000 = USD 695,000
- Capital Cost (CAPEX)
Major cost items:
- Construction of 6 vats with liner, civil works
- Pumps, piping, solution tanks
- Crushing and ore handling infrastructure
- Gold recovery system (carbon or zinc precipitation)
- Smelting furnace
- Laboratory, building, site works
- Safety & environmental controls
: Let’s estimate CAPEX = USD 300,000 (this is a rough estimate — could be higher or lower
depending on location, materials, labor costs).
- Return, Breakeven, ROI
Gross profit = USD 695,000
- Payback period = 300,000 / 695,000 = 0.43 year (≈ 5.2 months)
- ROI = (Profit / CAPEX) × 100 = (695,000 / 300,000) × 100 ≈ 231%
(Assuming full operation, no downtime, perfect recovery, perfect costs. In reality, margin will be
lower.)
- Plant Optimization Calculations & Method
To optimize plant performance, you’d apply methods like Response Surface Methodology
(RSM) to find optimal:
- Cyanide concentration
- pH
- Particle size
For example, a Tanzanian small-scale vat leach study used 950 ppm cyanide, pH 10.5, and particle
size ~240 µm to reach ~83% recovery.
You’d run pilot experiments varying these parameters, fit a model, then choose the optimal
combination for max recovery at acceptable reagent cost.
Also monitor:Oxygen supply (aeration), Leach solution flow rate Drainage efficiency, Channeling
in vats
- Risk & Sensitivity
Perform sensitivity analysis
- If recovery drops to 80% → revenue falls proportionally
- If gold price drops to USD 50/g → revenue lower
- If operating cost increases 20% → margin squeezes
- Downtime, maintenance, ore variability
Prepare mitigation: buffer capacity, reserve capital, flexibility in vat use.
Business Plan Summary
- Ore processed - 5,000 t
- Gold grade - 3.0 g/t
- Recovery - 85%
- Recovered gold - 12,750 g
- Revenue (USD 60/g) - USD 765,000
- Operating cost - ~ USD 70,000
- CAPEX ~ USD 300,000
- Profit margin - USD 695,000
- Payback period - ~5.2 months
- ROI - ~231%
NOTE
This is to illustrate how all sections (design, throughput, recovery, costs, optimization) tie together.
To make this real, you must:
• Get lab & pilot testing for the specific ore
• Cost local materials, labor, equipment
• Adjust design accordingly
• Build a detailed cashflow and risk model.
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