Tailored sample preparation processes using our individual sample preparation methods
All samples are always dried at 70°C or 105°C no matter what the earlier sample preparation history was (Methods 10 or 12). Exceptionally wet and large samples e.g. RC-, chip samples, blast hole samples etc. require longer drying in elevated temperature (Method 14).
The standard scheme consists of direct one–stage fine crushing using a special type jaw crushers (Method 31; nominal particle size > 70 % < 2 mm), precision riffle splitting (Method 35) for pulverising the split sample (Methods 40 and 50). This is a suitable method if crushed reject is needed for future work. However if more than 4 splittings are required the representativity of the split subsample cannot be assured. Ultra fine crushing to >90% < 2mm particle size using a Boyd crusher is also possible (Method 33).
For samples containing visible gold and/or for unusually big or heterogeneous samples i.e.max.3.5 kg, we recommend standard crushing to 5-10mm (Method 30) followed by pulverising the entire test sample (Methods 50) using Essa LM5 mills.
If crushed reject is required for future work the crushed material can be split to two e.g. 1-2 kg subsamples by riffle splitting (Method 35) – one for storage and the other for pulverising. Also if the weight of the sample is bigger than 3.5 kg, an additional splitting is required to obtain a adequite sample for pulverzing with method 50.
In most cases the sample size must be reduced before proceeding pulverisation. This is routinely done by riffle splitting (Method 35), where the sample can be split into two equal subsamples. Depending on original sample size and proceeding pulverising method, this will be repeated until the required sample size is obtained. The splitting can also be done by mat-rolling (Method 36) on hard paper and subsampling from the mat.
The state-of-the-art splitting method is rotary splitting (Method 37). This is a routine method in our robotic sample preparation and for subsampling of concentrates, and can be used also for other sample preparation processes.
Pulverising will always cause unavoidable contamination of wear metals at trace level from the grinding surfaces. This contamination may vary depending on material of the bowl, hardness of the sample material, pulverising time etc. The pulverising method must be selected to best serve the requirements of the client.
Some examples of bowl materials used at Labtium and expected contamination:
- Carbon steel < 0.2 % Fe, no base metals
- Hardened steel < 0.2 % Fe, low Mn, Ni, Cu, Cr, Co
- Low chrome steel up to 200 ppm Cr, < 0.2 % Fe, traces Mn, Cu, Co
- Tungsten carbide (WC) W, Co
To minimise cross-contamination during pulverisation, cleaning of pulverising bowls between samples by pulverising with barren quartzite is always performed. This is included in the price in all Labtium pulverising methods.
The client is obliged to inform Labtium for any observed components in the samples causing potential occupational health e.g. asbestos, radioactivity or environmental risk beyond the normal geolaboratory operation. Labtium is entitled to cease the processing of the samples if any of these risks are observed until the process is duly modified to eliminate the risks.