Correct sampling and measurement—the foundation of accurate metallurgical accounting

Mining companies devote considerable effort to reconciliation of production tonnages and metallurgical accounting in processing plants. However, in many cases the sampling, weighing and analysis methods used to obtain the raw data for metal balancing are still not given the attention they deserve. There is little point in using the latest metallurgical accounting package to improve metal balancing if the data used are unreliable in the first place. The basic rule for correct sampling is that all parts of the ore, concentrate, slurry or other material being sampled must have an equal probability of being collected and becoming part of the final sample for analysis. Unfortunately, this rule is not respected in many processing plant environments, resulting in both bias and poor precision of the analyses. Of these, bias is the more serious, because no amount of replicate sampling and analysis will reduce bias once it is present. isture content and wet mass of the material being sampled are of equal importance in determining the mass of metal. However, the accurate determination of moisture content is particularly difficult, because the moisture content of samples can change rapidly after the sample is taken, e.g., due to moisture evaporation in hot climates. Hence, moisture samples must be taken quickly, placed in sealed bags or containers that are impervious to moisture, and the moisture content determined without delay, preferably by preparing and weighing moisture samples immediately. To determine wet mass, a range of weighing methods is used in industry, including weighbins, weighbridges, conveyor weightometers and platform scales. However, the precision and accuracy of these methods vary considerably, so it is important to select a method with the appropriate precision and ensure that the weighing system is well maintained and regularly calibrated.