Gold Leaching Explained: From Ore to Pure Gold

What Is GOLD LEACHING and Why It Still Dominates Gold Recovery

If you visit a 5,000 TPD gold mine in West Africa or Central Asia, you will rarely see traditional smelting as the main recovery method. Instead, you will see tanks, pipelines, heap pads, and cyanide solution flowing quietly. That is GOLD LEACHING in action.

In simple words, the GOLD LEACHING PROCESS dissolves gold from crushed ore using a chemical solution, most commonly sodium cyanide. The dissolved gold is then recovered later by adsorption or precipitation.

Why is it so popular? Because even low-grade ore — say 0.8–1.2 g/t — can still make money. Thirty years ago, such ore might be waste rock.

Step-by-Step View of the GOLD LEACHING PROCESS

1. Crushing and Grinding

Ore is crushed down to 10–15 mm for HEAP LEACHING, or even to 75 microns for tank leaching (CIL/CIP). Finer particles mean better contact with cyanide, but also higher power cost. Engineers always balance these two.

2. Cyanide Dissolution

Gold reacts with cyanide and oxygen under alkaline conditions:

• Optimal pH: 10.5–11

• Cyanide concentration: 200–500 ppm

• Dissolution time: 24–60 days (heap), 24–36 hours (CIL)

A small pH mistake (below 10) can increase cyanide loss sharply. I've seen projects lose 15% more reagent just because lime dosing was unstable. It sounds minor, but it's expensive.

3. Adsorption and Recovery

In CIL plants, activated carbon adsorbs dissolved gold. In HEAP LEACHING, pregnant solution flows to adsorption columns. Later, gold is stripped and sent to electrowinning.

HEAP LEACHING vs Tank Leaching

The choice depends on ore grade, climate, and capital budget.

See the first chart above: recovery difference between HEAP LEACHING and CIL can exceed 15%.

But here is the real story: HEAP LEACHING wins in low-grade, large-tonnage mines because capital cost per ton can be 40–60% lower.

How Recovery Changes Over Time in HEAP LEACHING

The second chart above shows a typical recovery curve over 60 days. Notice how gold recovery rises fast in the first 20 days, then slows down.

This tells engineers something important:

• Most easy-to-leach gold dissolves early.

• Remaining gold is locked in sulfides or coarse particles.

Extending leach time from 45 to 60 days may only add 1–2% recovery. Mines must calculate whether that extra time is worth tying up working capital.

Common Problems in the GOLD LEACHING PROCESS

High Cyanide Consumption

If copper content is high, cyanide consumption can double. In one 3,000 TPD mine, cyanide use increased from 0.6 kg/t to 1.1 kg/t because of reactive copper. Pre-treatment solved it.

Poor Heap Permeability

If ore contains too much clay, solution flow slows down. Channels form, and some areas never get enough contact. Agglomeration with cement (2–5 kg/t) usually helps.

Carbon Fouling

Organic matter can block adsorption sites. Regular carbon acid washing improves performance.

Environmental Control in GOLD LEACHING

Modern plants use detox systems to reduce cyanide in tailings to below 50 ppm, often even below 10 ppm.

Water recycling rates now exceed 70% in arid regions. Compared to 1990s operations, overall cyanide discharge risk has been reduced significantly.

FAQs About GOLD LEACHING

1. What is the typical recovery rate in the GOLD LEACHING PROCESS?

CIL: 88–93%. HEAP LEACHING: 65–75%, depending on ore type.

2. Is HEAP LEACHING suitable for high-grade ore?

Usually no. High-grade ore justifies higher recovery via tank leaching.

3. How long does HEAP LEACHING take?

Normally 30–90 days.

4. What affects cyanide consumption most?

Copper minerals, pH control, and oxygen level.