SAMPLING , ANALYSIS AND LAB ASSAY
FLSmidth says it has installed automated mining laboratories across the globe within many different commodities
priorities and optimise sampler placement .
“ This is where FLSmidth has an advantage because we can design the whole process area , even the whole plant in some cases ,” Knudsen said . “ As a result , we can design in the right sampling locations to ensure they are located in the optimal place to take that specific sample at the right time .”
Site audits at brownfield operations can reveal plenty of opportunities to improve the sampling process , too . These visits will acknowledge the whole process – from preparing the sample , acquiring the sample and getting results – Knudsen added .
But , back to the potential ‘ quantum leap ’ in mineral sampling accuracy …
There is a general acceptance in the industry that there is a 10 % to > 100 % possible uncertainty associated with ‘ field sampling ’ and ‘ sample preparation and sub-sampling ’ compared with a 5-
20 % uncertainty associated with ‘ chemical preparation ’ and just 1-10 % uncertainty associated with the type of ‘ measurement ’ procedures that take place in the lab .
As these numbers would indicate , a lab environment is much easier to control from a sampling perspective . Knudsen acknowledges this : “ The smaller the particle size you get with crushing , grinding , etc in the lab , the lower the error is , all things being equal . There are more factors to handle when you are out on site . The material characteristics are not as well defined as they are in the lab .”
This uncertainty and increased number of factors for consideration can have a major financial impact , as an example from FLSmidth indicates .
The example involves a copper process plant where tailings were typically sold to a third party for treatment . At this site , the amount of tailings sent to this third party came to about 96,000 t / d of ore . Based on calculations , the plant assumed a tailings grade of 0.15 % Cu , working out at about 144 t / d of copper metal .
After many years of making this assumption , the plant installed a representative sampling station that revealed the actual tailings grade to be 0.2 % Cu . The plant worked out that this difference in the assumed versus actual grade of copper was costing them $ 105,600 / d with the previous arrangement , which , over a 20-year period , worked out at $ 38.5 million / y . And what was the cost to find this out ? It was around $ 500,000 for the sampling station , meaning it