Leachox Technology

Leachox™ Technology

Deployment

Processing of current gold mining projects are generally more difficult than their historical counterparts, mainly because of mineralogy. Processing difficulties could include:

  • Excessive cyanide consumption due to severe side reactions from sulphide mineral dissolution, often inadequately suppressed through inefficient pre-oxidation regimes;
  • Slow leach kinetics as a function of inadequate oxygen supply during the leach (thus leaving an imbalance between available cyanide and oxygen for the gold dissolution to proceed); and
  • Partial or complete lock-up of the gold within specific sulphide host minerals such as pyrite, arsenopyrite or pyrrhotite.

The scope of objectives could range from:

  • Oxidising solution species (Fe2+ to Fe3+) to save reagents;
  • Passivation of sulphide solids to prevent further dissolution (saving reagent);
  • Purposefully oxidising sulphide matrices to liberate locked-up gold; and
  • Boosting of dissolved oxygen (DO) levels during the leach to values promoting fast oxidation reactions (either gold dissolution or sulphide phases).

Whilst oxygen needs for a solution species oxidation often only requires modest oxygen input masses, oxidising solid sulphide phases requires fairly high levels of oxygen addition.  The oxygen required is often much higher than the stoichimetric oxygen requirement for gold dissolution only.

Furthermore, the reaction kinetics are often a function of film diffusion layers and their relative thickness. Decreasing this film thickness through the application of elevated shear levels can double or triple the reaction rate.

Key Basic Design Criteria

  • The centrifugal slurry pump must be able to deliver against a water head of 50 m; and
  • The oxygen delivery system to the Aachen™ reactors must operate with a delivery pressure of 2 bar higher than the Aachen back-pressure, which is approximately 4 bar i.e. 6 bar requirement.

Oxygen Feed

The feed system of each reactor should be equipped with:

  • Needle valves for flow regulation;
  • A pressure regulator; and
  • An oxygen flowmeter.

Safety Systems Requirements

Each reactor should be equipped with:

  • Pressure trip switch;
  • Flow trip switch; and
  • Both interlocked with the relevant pumps.

Pumping of slurry without supporting gas flow must be avoided.

MMSA will ensure satisfactory commissioning of the units.

Defining Criteria (Example)

 

Typical hyper-oxygenation level tank example using Aachen REA 450 unit (s)
Tank volume (process dependent) 1000 m3
Minimum residence time during hyper-oxygenation To be defined hours
REA 450 Feed Pump requirement, nominal flow (per unit) 600-700 m3/h
REA 450 Feed Pump requirement, head pressure 50 m water head
REA 450 Feed Pump installed power 200 kW (per unit)
Oxygen delivery, capacity range (per unit) 30 – 150 kg/h
Aachen unit pressure drop 4 bar
Oxygen delivery excess head pressure 2 bar
Interlocks (oxygen pressure and flow) to stop slurry pump DP to be defined bar
Interlocks (DP slurry to O2 P) >0.5 bar
Piping diameter (inlet and exit) DN250

 

Typical pre-oxidation suction arrangement (2 x REA 450 units fed by one KREBS 350 pump)

Typical pre-oxidation suction arrangement (2 x REA 450 units fed by one KREBS 350 pump).

 

Typical pre-oxidation delivery arrangement (2 x REA 450 units feeding separately back to tank)

Typical pre-oxidation delivery arrangement (2 x REA 450 units feeding separately back to tank).

 

Different slurry delivery arrangement; directly submerged into slurry (extending with pipe to near bottom of tank)

Different slurry delivery arrangement; directly submerged into slurry (extending with pipe to near bottom of tank).

 

2 x Aachen 450 type units; Aerators at mentis grating level (and oxygen feed-lines)

2 x Aachen 450 type units; Aerators at mentis grating level (and oxygen feed-lines).

 

Typical pre-oxidation Aachen feed arrangement

Typical pre-oxidation Aachen feed arrangement (2 x REA 450 units fed by one KREBS 350 pump). Note the elephant hoses to allow for flexible maintenance.

 

CIL space for 6 Aachen units Type 450 (2 installed, 4 awaiting)

CIL space for 6 Aachen units Type 450 (2 installed, 4 awaiting).

 

Oxygen management system

Oxygen management system (L to R): Oxygen feed line, isolation valve, static pressure gauge, Coriolis type flow meter, mass controller, NRV, P-transducer, feed to Aachen inlet.