Gold Recovery Problems in CIP/CIL Plants: Why Activated Carbon Iodine Value and Pore Structure Matter More Than Most Operators Realize

In many gold cyanide leaching plants, operators focus heavily on leaching efficiency, reagent consumption, and equipment performance. However, one factor that is often underestimated is the quality of the activated carbon used in the CIP and CIL circuits.

Over the years, we have seen many operations struggle with low gold loading, excessive carbon consumption, and disappointing recovery rates. In a large number of cases, the root cause was not the leaching process itself but an activated carbon that was not properly matched to the operating conditions.

Two properties deserve particular attention: iodine value and pore structure.

Higher Iodine Value Does Not Automatically Mean Better Gold Recovery

Many buyers assume that the higher the iodine value, the better the activated carbon. While iodine value is an important indicator, the reality is more complicated.

The iodine value generally reflects the amount of microporous surface area available inside the carbon. Since gold cyanide complexes are primarily adsorbed within these micropores, a reasonable iodine value is essential for achieving high gold loading.

For most CIP and CIL applications, coconut shell activated carbon with an iodine value between 1150 and 1300 mg/g typically provides reliable performance.

When iodine value falls below approximately 1000 mg/g, the available adsorption space becomes limited. Carbon reaches saturation faster, gold loading decreases, and more dissolved gold may remain in solution or report to tailings.

However, pursuing the highest possible iodine value is not always the best strategy. Extremely high iodine values are often associated with a very high proportion of ultra-fine micropores. While these pores may contribute to laboratory test results, they do not always improve practical plant performance and may sometimes make desorption and regeneration less efficient.

The goal should not be the highest iodine value available on the market. The goal should be the iodine value that matches your process conditions.

Why Pore Structure Is Equally Important

In actual plant operation, adsorption capacity is only part of the equation. Adsorption speed can be just as important.

This is where pore structure becomes critical.

A well-designed activated carbon contains a balanced combination of micropores and mesopores.

Micropores provide the primary sites where gold cyanide complexes are ultimately retained. They determine the carbon's loading capacity.

Mesopores act as transport channels. They allow gold-bearing solution to move efficiently into the interior of the carbon particle and reach the adsorption sites.

Think of mesopores as highways and micropores as storage warehouses. Even if you build a large warehouse, material cannot arrive efficiently if there are not enough roads leading to it.

We occasionally encounter carbons with impressive laboratory specifications but poor adsorption kinetics in operating plants. In many cases, the issue is an insufficient mesopore network that restricts mass transfer and slows the movement of gold ions into the carbon structure.

As a result, gold loading may appear acceptable in extended laboratory tests but underperform in high-throughput industrial circuits where contact time is limited.

Common Carbon Selection Mistakes in Gold Plants

One of the most common mistakes is purchasing carbon based solely on price.

Low-cost activated carbon may initially reduce procurement expenses, but the savings often disappear when operators experience:

• Lower gold loading per tonne of carbon

• Increased carbon replacement frequency

• Higher carbon losses in the circuit

• Reduced overall recovery efficiency

• Greater gold losses to tailings

Another common mistake is relying exclusively on iodine value when evaluating suppliers.

Two carbons can have similar iodine values while delivering significantly different adsorption performance due to differences in pore distribution, hardness, abrasion resistance, and raw material quality.

For this reason, plant-scale testing remains one of the most reliable methods for evaluating activated carbon performance.

Recommended Carbon Specifications for Typical CIP/CIL Operations

While every operation is unique, the following guidelines are commonly effective:

Standard CIP/CIL Gold Recovery Plants

• Coconut shell activated carbon

• Iodine value: 1150–1300 mg/g

• Particle size: 6×12 mesh or 8×16 mesh

• High hardness and low abrasion loss

• Balanced micro- and mesopore structure

Low Gold Concentration Solutions

Where dissolved gold concentrations are relatively low, carbon with slightly higher micropore volume may improve gold capture efficiency.

Recommended iodine value:

• 1250–1350 mg/g

High Throughput Circuits

Where adsorption tanks operate with shorter residence times, adsorption kinetics become increasingly important.

Recommended focus:

• Enhanced mesopore development

• Rapid mass transfer characteristics

• Consistent particle size distribution

The Real Objective: Maximizing Overall Recovery, Not Chasing a Single Specification

In practice, no single specification determines activated carbon performance.

Iodine value indicates the potential adsorption capacity available inside the carbon. Pore structure determines how effectively gold-bearing solution can access that capacity.

The most successful gold recovery operations typically focus on overall carbon performance rather than chasing the highest laboratory numbers.

When selecting activated carbon for a CIP or CIL circuit, evaluating adsorption capacity, adsorption rate, hardness, abrasion resistance, and regeneration performance together will usually produce the best long-term economic results.

If you are experiencing low gold loading, excessive carbon consumption, or declining recovery rates, it may be worthwhile to review whether your current activated carbon is properly matched to your operating conditions.

Our technical team supplies coconut shell activated carbon specifically developed for gold recovery applications and can provide free samples for plant trials. By testing carbon performance under actual operating conditions, you can determine which product delivers the highest loading efficiency and the lowest overall recovery cost.