Cyanide Dosing in Mining Explained

During cyanidation, cyanide reacts with exposed gold in the presence of oxygen and water to form a soluble gold-cyanide complex. This transfers gold from the solid ore into the liquid phase so it can be recovered later.

The process may be applied in agitated leach tanks, carbon-in-leach and carbon-in-pulp circuits, or heap-leach operations. The best route depends on factors such as ore mineralogy, gold liberation, particle size, permeability, and the presence of minerals that react with cyanide.

Cyanide is therefore only one part of the leaching environment. Gold dissolution also depends on oxygen availability, pH, residence time, slurry density, mixing, temperature, and the accessibility of the gold particles. A dosing system cannot correct unsuitable ore preparation or poor leach conditions by adding more cyanide alone.

Cyanide demand is not constant across all ores or operating periods. Some minerals consume cyanide without contributing to gold recovery. Copper minerals are a common example, but other reactive ore components can also increase chemical consumption. Changes in ore blend can therefore alter the cyanide requirement even when plant throughput remains steady.

Process water also matters. Recycled water may carry dissolved species that influence cyanide chemistry and demand. Changes in solids concentration, oxygen availability, feed rate, or upstream grinding can further affect the amount of cyanide required to maintain the intended leaching conditions.

This is why a fixed dosing rate has limitations. The process may run acceptably while the ore remains stable, then drift when mineralogy or feed conditions change. Controlled cyanide dosing needs to respond to actual process demand rather than assuming that one setting will remain appropriate throughout every shift.

Cyanide leaching is maintained under alkaline conditions. At lower pH, a greater proportion of cyanide can convert to hydrogen cyanide, a highly hazardous and volatile compound. Lime or caustic soda is therefore commonly used to establish and maintain the required alkaline environment.

This makes cyanide and alkali dosing closely connected. More cyanide cannot compensate for inadequate pH control, and an alkaline setpoint alone cannot correct inconsistent cyanide delivery. Both reagent systems need to support the same leach conditions.

The interaction also affects process interpretation. If gold dissolution changes, the cause may be cyanide availability, pH, oxygen, mineralogy, residence time, or a combination of these factors. Stable reagent delivery removes one source of uncertainty and makes the remaining process signals easier to understand.

A dosing system may report the correct hourly flow while delivering the reagent unevenly within that hour. Pulsating pumps create alternating peaks and troughs in instantaneous flow. The totalized volume may still match the target, but the chemical enters the process in repeated surges rather than as a continuous stream.

The significance depends on the application, injection arrangement, mixing conditions, and residence time. A large, thoroughly mixed vessel may dampen some variation. A smaller line, local injection point, or faster-reacting process may be more sensitive to short-term changes.

This is why dosing repeatability should not be assessed by total flow alone. The shape of the delivery matters, particularly when the process relies on a stable relationship between reagent addition and measured response.

Controlled dosing requires reliable information from the process. Cyanide concentration, pH, oxygen availability, solution chemistry, feed rate, and metallurgical response may all contribute to dosing decisions. The exact control arrangement depends on the plant and should be based on test work, process design, applicable regulations, and site-specific operating procedures.

The dosing pump still plays a fundamental role. The control system may issue the correct command, but that command only has value when the pump delivers a predictable flow. Pressure variation, equipment wear, leakage, blockage, crystallization, or poor calibration can create a difference between the requested dose and the dose that reaches the process.

Repeatable chemical delivery provides a more stable foundation for process control. It allows operators to distinguish changes in ore behavior from variation created by the dosing equipment itself.

Sodium cyanide solutions require carefully selected wetted materials. Pump components, seals, piping, valves, gaskets, and instrumentation must be compatible with the chemical concentration, process temperature, and surrounding operating conditions.

Compatibility cannot be judged from the chemical name alone. Concentration and temperature can change how a material performs, while impurities or cleaning chemicals may introduce additional requirements. Every component in the dosing path needs to be reviewed as part of the complete duty.

A broad choice of construction materials is therefore important. It allows the dosing equipment to be configured around the specific chemical environment rather than forcing one material selection across very different mining reagents.

Cyanide is highly hazardous and requires formal controls throughout production, transport, storage, use, recycling, treatment, and eventual decommissioning. The dosing system sits within this wider management framework and must follow applicable laws, site procedures, risk assessments, and recognized industry practices.

Relevant design priorities include preventing unintended releases, minimizing potential exposure, maintaining suitable containment, monitoring system condition, and ensuring equipment can be inspected and serviced safely. Emergency planning, worker training, and documented operating procedures also remain essential.

A reliable pump does not replace these controls. It supports them by reducing avoidable variation, leakage risk, and unplanned intervention within the dosing process. Cyanide facilities should always be designed and operated by qualified personnel under the site’s approved safety and environmental requirements.

Residual cyanide in process water or tailings may require treatment before reuse, discharge, or further processing. The selected detoxification method depends on the process stream, cyanide species, treatment objective, and site requirements.

Excess cyanide added during leaching does not disappear from the wider process. It can increase the load on downstream treatment and raise chemical consumption beyond the leach circuit itself. This creates a broader cost than the cyanide purchase price alone.

Controlled dosing helps reduce this burden by matching reagent addition more closely to the actual leaching requirement. The goal is not to minimize cyanide regardless of recovery. It is to use enough reagent to support the intended extraction while avoiding unnecessary excess.

A suitable dosing pump needs to provide accurate and repeatable delivery across the required operating range. Constant metering at operating pressure is particularly important because the process should receive the requested dose even when discharge conditions change.

SEEPEX progressive cavity pumps convey fluid through fixed-shape cavities. This creates controlled volumetric delivery with pulse-free flow. Pump output can be adjusted through speed, helping maintain a predictable relationship between the dosing command and the actual reagent flow.

For lower-flow duties, SEEPEX MD metering pumps provide capacities up to 1,000 l/h and pressures up to 24 bar. The product range supports precise chemical dosing where repeatability and pulse-free delivery are central to the application. A large choice of construction materials allows the pump configuration to be matched to the chemical duty.

This is only a brief technical bridge. The wider question of pump sizing, material selection, controls, containment, and maintenance belongs within the complete dosing-system design.

Cyanide dosing should give the leaching circuit a consistent chemical input. When delivery varies unexpectedly, it becomes harder to determine whether a change in gold recovery comes from the ore, oxygen availability, pH, residence time, or the dosing equipment. When delivery is repeatable, process data becomes easier to interpret and corrective action becomes better targeted.

That is the larger value of controlled cyanide dosing. It reduces avoidable variation in a process already influenced by complex mineralogy and changing operating conditions. It also helps control chemical use and the burden placed on downstream detoxification.

Reliable cyanide dosing does not replace metallurgical testing, process monitoring, containment, or responsible cyanide management. It gives all of those elements a more predictable chemical delivery system to work with.