SAG milling & grinding pilot plants

Pilot grinding services

Every pilot plant project will have different requirements insofar as sample characteristics, throughput, and feed and product PSDs, which results in a different grinding circuit almost every time. Thus, achieving the correct pilot grinding solution requires a large equipment inventory together with a flexible approach and requisite expertise to build and operate the plant. The main factors involved are outlined below:

Grinding mills: There is no one size fits all when it comes to grinding and many different mills are required to achieve a range of applications. Broadly, ALS holds the following pilot mill types and sizes in inventory:

• AG/SAG mill: One of the few remaining Hardinge 6’ x 2’ high aspect pilot 18 kW SAG mills in the world is fully operational at the ALS Metallurgy, Balcatta campus in Western Australia. Installed with a shell hatch to facilitate easy charge removal, the mill is installed on load cells connected to a SCADA system to collect mill weight, mill power, motor current, drive chain sprocket torque, and mill rotational speed (variable drive from 0% to 75 N c ). The mill is steel lined with a nominal 10 mm grate size with conventional hockey stick pulp lifters. Outer discharge grate panels can be installed to facilitate two or four x 75 mm ports pebble ports.

Integrated with a classification tower and feed/discharge conveyor system, the mill can be set-up to facilitate open circuit, single stage closed circuit, AG/SAG and ball mill circuit (SAB), and AG/SAG and ball mill circuit with recycle pebble crushing (SABC).

The 450 mm feed chute takes full size ROM ore or feed stock can be artificially created from the appropriately sized drill core intervals. Throughputs are commensurate with ore competencies but typically range from 1 tph to 4 tph. Depending on ore competencies, stable-equilibrium operation durations can be usually achieved in 3 to 10 hours. Sample requirements thus range between 10t to 60t depending on the number of variables and circuits to be trialed.


• Rod mills: Although rarely used in industrial practice, ALS has 2 x 2.3 kW rod mills for small (<50 kg/h) throughputs where preferential coarse grinding is advantageous for the downstream processing.


• Ball mills: Ball mills are the stalwart unit of the majority of pilot grinding circuits. ALS has a range of rubber lined overflow ball mills including: 2.3kW, 4.4 kW high aspect (900 mm Dia x 400 mm EGL), 3 x units of 5.5 kW and 7.5 kW (900 mm Dia x 790 mm), 1 x 15 kW 900 mm Dia x 1800 mm EGL, 1 x 30 kW 1240 mm Dia x 1440 mm EGL). All of the above units can be operated in either primary or regrind grinding applications depending on the pilot design criteria. The larger units can also be matched with the SAG mill in SAB/SABC configuration.


• Stirred mills (Regrinding). Finer regrinding or ultra-fine grinding is a frequent requirement in pilot plants and ALS has a range of units that can run continuously in pilot applications. The following mills are located at Balcatta: ISAMill tm , Deswik, and Metprotech as well as some non-branded stirred mills. The IOTC in Wangara also houses the pilot Outotec HIG (High Intensity Grinding) Mill and two Nippon-Eirich Stirred Tower Mills (a large continuous mill and a batch unit). All of the above can be operated independently, and all but one seamlessly integrated into a continuous pilot plant circuit.

Feed arrangements & slurry handling: No mill can operate without the appropriate before and after materials handling arrangements. ALS has a range of different sized feed hoppers and belt/screw feeders to match the mill size. Similarly, a range of slurry pumps in various sizes is available to handle mill slurry product including: Open bowl Sala and Metso pumps, Warman AH Slurry pumps, Bredle peristaltic hose pumps and Sandpiper peristaltic diaphragm pumps. In combination, the above equipment can meet most grinding solutions.

Classification systems: Closed circuit classification to emulate industrial scale practice is imperative for pilot scale operations. Typically, this falls into two main categories:

• Vibrating screens: Despite producing a truncated PSD, vibrating screens are quite adequate mill product classifiers in most-small scale pilot circuits. The go to unit for ALS is the circular Kason screen, which is available in multiple diameters and can run either a single or multi-deck configuration with interchangeable screen aperture sizes. Gravity is an important factor in pilot plant set-up and ALS has a range of stands and infrastructure available to position the screens in close proximity to the mill to take advantage of gravitational flow.


• Hydro-cyclone circuits: Unfortunately, hydro-cyclones are not scalable for lower throughput (i.e. a small diameter hydro-cyclone cannot be matched to a small flowrate unless the PSD is very fine). The cyclone size is entirely predicated on the product PSD and cut size. This often results in an entirely mismatched mill feed rate versus cyclone feed rate (e.g. a P 80 150 µm COF product requires a 100 mm hydro-cyclone that needs ~1 tph or ~4 m 3 /h, which is completely mismatched to a 250 kg/h mill feed). This is why vibrating screens are often the most practical solution for pilot grinding circuits. However, there are circumstances where a hydro-cyclone can be employed whereby it is run in a closed loop at the appropriate flowrate and pressure, with auto-controlled slurry splitters set-up to cut the appropriate volume from the overflow and underflow streams.

Need more information or want to devise a specific grinding circuit?

ALS can meet your needs and can also leverage off vendors for specific or non-conventional equipment items.

Please contact us for further details.

Associated testwork services

Related testwork

Grinding always precedes other processes, both at bench scale and pilot scale that may include:

• Head Analysis
• Comminution
• Mineralogy
• Grinding
• Beneficiation
• Flotation
• Hydrometallurgy

Click on the above links or contact us for further information. We can integrate a full program for you if required.