The Maelgwyn CN-D™ process depends on catalytical activity (where no consumption of the reagent (granular activated carbon) takes place) rather than reagent addition in its standard layout. Oxygen supplied as compressed gas in moderate excess is the main oxidant, therefore no chemical reagent consumption other than carbon losses associated with normal attrition losses during in-pulp use and elution/regeneration can be associated with the process. As the process is not directly reliant on reagent additions linked to relatively minor cyanide level fluctuations (±30% from average), such changes will as a rule not influence the operational cost.
Site specific circumstances can influence the potential contributors to reagent consumption and hence OPEX:
Cyanide on-line analysis instruments.
This process is extremely well suited for the treatment of slurries. Solutions would require a modified approach of the operation. All ICMI criteria based testwork indicated that the process will be compliant with the use of a 2 – 4 tank system.
In applications where thiocyanate as well as CN WAD must be reduced, the CN-D™ process offers advantages. Testing of post BIOX® leach residues (where residual cyanide levels are much higher than that of ordinary leach tails) and other refractory ore environments indicated considerably reduced thiocyanate levels.
In cases with temporarily or permanent high gold levels, which offers the prospects of additional gold recoveries; the potential benefits of using the CN-D™ process should be evaluated from a gold recovery perspective, rather than savings in OPEX.
The Maelgwyn CN-D™ process can be applied in a wide variety of residue environments with comparably little change to the main cost contributing factors. Since the process is not linked to a metered reagent dosage, fluctuations within reasonable levels can be accommodated without changes to the system. To improve the chemical performance in more challenging environments; dosing of copper could be added. Detoxification costs can be off-set against additional gold loadings onto the activated carbon used in the process. The system units are standard CIL application technology (e.g. carbon, carbon screens, oxygen, measuring instrumentation etc.), with the only new technology being the Aachen™ high-shear reactors used for the gas mass-transfer, although the units have been in trouble free operation at numerous mines for years.
The hyper-oxygenation is achieved through the use of the Aachen™ high-shear reactors. Refer to Figure One: Reactor Installation for dimensions and physical shape. The units are available in different sizes to accommodate the optimal oxygen/shear requirements for each specific application. The definition of technology deployment is based on the concept of passes.
For a typical layout and installation option for an Aachen™ reactor receiving slurry from a carbon containing tank, refer to Figure 2: Installation Layout. If a carbon free oxygenation is required, no separate carbon screening will be necessary. Slurry feed will be from the lower part of the tank (1.5 m – 2 m) above the bottom, avoiding oversize material intake.
For wide ranged engineering specifications – refer to Table 1: Typical Example of Installation Criteria.
Simultaneous deployment of Aachen™ based hyper-oxygenation in combination with activated carbon based catalysis in several stages, the slurry transfer between stages will have to be through inter-stage screening and the Aachen™ inlet itself would require carbon screening.
Typical hyper-oxygenation level tank example using Aachen REA 450 unit (s)
Tank volume (process dependent)
Minimum residence time during hyper-oxygenation
Acid (HCl) dosing capacity, ratio controlled maximum addition
REA 450 Feed Pump requirement, flow (per unit)
REA 450 Feed Pump requirement, head pressure
m water head
Oxygen delivery, capacity range (per unit)
Oxygen flow, nominal operational (per unit)
Aachen unit pressure drop
Oxygen delivery excess head pressure
Interlocks (oxygen pressure and flow) to stop slurry pump