Laboratory and Pilot Plant

Overview

Maelgwyn Mineral Services Africa (MMSA) provides specialised mineral processing technology in the form of proprietary equipment and processes.

The key elements of Maelgwyn equipment are their unique flotation cells (Imhoflot G-Cells™) and their high-shear gas diffusion reactors (Aachen Reactor™). The major processes are represented by Leachox™ (to make refractory ores amenable to leaching) and the MMSA CN-D™ (cyanide destruction process).

The company established a metallurgical laboratory in 2009, excelling in project work, covering a wide range of the beneficiation chain from ore assessment, comminution, up-grading and extraction, to residue detoxification. Scope of work undertaken ranges from ad hoc testwork to full bankable feasibility study level and consulting. The laboratory and the MMSA offices are located in Johannesburg in the Maraisburg area (Stormill Ext 2).

Core Laboratory Capabilities

Comminution

The comminution section consists of various types and sizes of crushers and mills for crushing and milling samples ranging from 75 mm in size down to a few microns. Where dry comminution is involved, dust extraction systems are in place for safe and dust free operations.

Available crushers:

5″ jaw crusher: size reduction from 75 mm to 20 mm.

3″ jaw crusher: size reduction from 40 mm to 10 mm.

Cone crusher: size reduction from 10 mm to 3 mm.

Available mills:

200 litre batch dry ball mill for milling samples of up to 50 kg from 3 mm to 38 μm.

10 litre dry or wet batch ball mill for milling 1 kg samples from 3 mm to 25 μm.

300 litre continuous wet ball mill for operation in either open circuit or closed circuit with a classification screen or hydrocyclone. The feed size to the mill is normally 3 mm for milling down to d80 25 μm.

10 litre batch ultrafine grind mill for milling 2 kg to 20 kg at a time, from a top size of d80 150 μm to a product of d80 5 μm.

Size Classification

Size classification is done by screening batches or in continuous mode. A sieve shaker is used for batch screening, which is loaded with screens of various aperture sizes as required. For continuous screening, a Sweco screen is used.

A Mozley cyclone rig comprising of different cyclones, vortex finders and spigots is also available for either batch or continuous size classification. A minimum of 30 litres slurry is required for a batch Mozley cyclone test.

Gravity recovery tests

The testwork is primarily done by centrifugal gravity concentrators, in batch mode.

Gravity separation equipment is rented from distribution agents, as and when required. Two units are available, the Falcon L40, specifically designed for laboratory testwork and the Falcon iCON unit, primarily used for open circuit operation up to 1 ton.

The Falcon L40 is used for gravity recovery of small ore samples or concentrate cleaning; and can be used for testing of both semi batch and continuous applications. The following operating parameters apply:

  • Feed Capacity: 0-300 kg/h solids (depending on material)
  • Maximum Feed Density: 75% solids by weight, 55% recommended
  • Particle Size – Minus 1.7 mm
  • Typical Fluidization Water Requirement: 4 – 20 litres per minute – depending on material
  • Concentrate Volume: 65 ml
  • Concentrate Weight: 0.07 – 0.15 kg

Flotation

The flotation section consists of the laboratory flotation testwork area and the pilot flotation testwork area.

Laboratory Flotation

For the laboratory flotation tests, Denver D12 flotation machines are used. Three machines are available with 10 litre, 4 litre, 2 litre and 1 litre stainless steel cells. The following types of batch flotation tests can be carried out:

Rougher flotation determining the best feed particle size distribution and optimizing rougher flotation chemicals and conditions.

Different stages of cleaning with or without re-grinding of the rougher concentrate to determine the number of cleaning stages and conditions required to achieve the required concentrate grades.

Rougher and cleaning stages flotation to determine the sample’s flotation kinetics and the best flotation times for rougher and cleaner flotation.

Pilot Plant Flotation

Two types of flotation testwork can be conducted in the pilot plant; batch or continuous mode.

Pilot Plant Flotation

Batch Flotation Testwork

The 200 litre Wemco cell is used for large scale rate flotation to determine the flotation kinetics of a sample and to produce concentrate for subsequent metallurgical testwork.

Continuous Flotation Testwork

Testwork in the laboratory includes but are not limited to complete milling, conditioning and flotation circuits.

Milling Circuit

The circuit comprises of:

  • A variable speed belt feeder;
  • A 300 litre capacity ball mill with overflow discharge;
  • A Sweco vibrating screen with varying aperture size screens for classification; and
  • Vertical spindle pumps for pumping the oversize back to the mill and the undersize to the flotation section.

Continuous Flotation Circuit

The circuit comprises of:

  • Reagent conditioning tanks;
  • Pneumatic Imhoflot G-cells; and
  • V-cells.

Depending on the circuit configuration, the throughput of the cells varies from 200 – 400 kg/h. If the sample available is not adequate to operate the flotation circuit continuously; the plant can be operated in a batch mode with the flotation tails being recycled back to the feed tank. Concentrate samples are taken at time periods to represent passes through the cells. This is similar to kinetic flotation in the laboratory.

For continuous rougher and cleaner modes, configurations of 50 litre, 100 litre and 200 litre Wemco tank cells are available.

Leaching Tests

MMSA’s core technology is based on the Aachen Reactor™ high-shear reactor (HSR) technology; used for relatively straightforward pre-oxidation, boosting of leach kinetics, or the more demanding partial sulphide dissolution, often in conjunction with ultra-fine grinding (UFG). The industrial scale Aachen reactors are represented by laboratory units which are utilised to apply the desired degree of oxidation to a pre-leach slurry. The benefits achieved would be measured through reagent consumption savings, enhanced kinetics or additional gold dissolution. This is determined on the basis of in-house leach test results.

Leaching Tests

The laboratory is equipped to perform monitored bottle roll leach tests, as well as stirred reactor leaches, tracking pH, Eh and DO. The largest leach test feasible would be sized around 200 litres. All leach work conducted can be validated by full metal balances including solid, liquid and carbon for metal content.

Cyanide Destruction Testwork

The Aachen Reactor™ HSR technology forms the basis of MMSA’s CN-D™ cyanide destruction process.

This proprietary process relies on correct combinations of oxygenation, shear and catalytic oxidation of cyanide based on activated carbon. MMSA can perform scouting or pilot testwork to evaluate the technical feasibility for a specific application. The results are used for a techno-commercial assessment of the process application including comparison to competing processes. The test size limitations are 200 litres. Both batch and continuous testing can be performed.

MMSA can conduct testwork on reagent consumptions; standard detox procedures based on peroxide, SMBS/air, ferrous sulphate or other reagents. The resulting reagent consumptions are used in the techno-commercial evaluation.

Process Development and Sustainability Issue Consultation

MMSA is well known for its areas of expertise, namely flotation, gold leach, cyanide speciation, cyanide and arsenic management.

Key staff have considerable expertise in these fields and this experience is available for process development and / or consultation purposes:

  • Flotation; associated design and process issues;
  • Gold processing (gravity, pre-oxidation steps, leach technology);
  • Cyanide management (MMSA has an ICMI Technical Expert Auditor); and
  • Arsenic management, general environmental compliance issues.

Quality Control and Outsourcing

All assays are outsourced to accredited laboratories (ISO 17025). CN-D related analysis is performed by MINTEK’s accredited Cyanide Centre.