Aachen Oxidation Technology
The enabling technology of Maelgwyn Mineral Services’ Aachen™ reactor, achieves efficient high level oxygen mass transfer along with shear exposure. Slurry is pumped from the process tank through the reactor where the oxygen is introduced under pressure at high shear / high velocity in a specially engineered aerator system. This slurry is returned to the process tank. If the flow through the reactor is a multiple of the slurry flow rate at plant level, a system of multiple pass rates is established, usually leading to increased benefits.
The additional gold recovery and / or reagent savings must outperform the operating costs of the Aachen™ reactor (power, oxygen and lease charges). Proving to be a viable solution, the technology is used at the following sites:
- Loulo and Morila (Mali, Randgold Resources);
- Tongon (Côte d’Ivoire, Randgold Resources);
- Kibali (Democratic Republic of the Congo, Randgold Resources);
- Barberton Mines (South Africa, Pan African Resources); and
- New Liberty (Liberia, Avesoro Resources).
In most cases, the achievable benefits place the technology below bio-leaching or POX (Pressure Oxidation), but at much reduced CAPEX expenditure and OPEX cost. For many projects with restricted life span or rapidly changing mineralogy (oxide through transitional to sulphide ores), the CAPEX associated with the other technologies tends to be prohibitive and Leachox™ may offer the best solution, especially when combined with UFG (Ultra Fine Grinding) to around 10 µm.
Aachen Based Oxidation Concept and Pass Definition
These units, fabricated in several sizes to suit the site-specific flow rate requirements, enable efficient oxygen dispersion under high shear (velocities of up to 10 m/s within the unit) and pressure (~4 bar). Furthermore, the shear exposure reduces boundary layer resistance which influences most solid / liquid reaction rates, enhancing the reaction kinetics. Some basic elements are described below.
Refer to Figure 1: Reactor Installation for dimensions and physical shape.
The required degree of oxidation is determined through testwork in a laboratory unit. Slurry from the tank is pumped through the Aachen unit(s) and returned to the tank. The concept of cross-flow leads to the term “pass or passes”, a term used from testwork to define the required level of Aachen unit deployment. As mentioned before, one pass is obtained if the slurry pump rate through the Aachen™ unit(s) equals the volumetric flow of the plant. By way of example, if the plant processes 500 m3/h and the Aachen unit(s) receive the same from the slurry pump, 1 pass is obtained. Should the slurry stream through the Aachens reach 2500 m3/h, 5 passes would be reached.
Potential applications are:
- Presence of coarse gold (where no gravity recovery system is installed);
- Recovery restrictions of more than 5% where finer grind in isolation will not significantly increase the leach recovery;
- Presence of gold along labile sulphide mineral boundary layers; and
- Presence of gold within sulphide minerals but not as solid solution.
MMSA will, based on the envisaged degree of technology deployment and related input requirements, assess the OPEX cost versus expected revenues. The parameters considered include power cost, oxygen cost and MMSA lease fees. CAPEX issues are not usually considered (the Aachen™ technology is normally supplied on a lease contract, including maintenance).