Sampling of heap leaching ore has been the subject of many researchers to date. At this stage, most sampling methods have deficiencies, so the applicability of sampling methods can only be relative. Ore sampling should generally be based on the nature of the ore, especially the mineral size of the component to be tested in the ore, its uniformity in the ore, and the specific conditions at the time and local to develop the sampling process. Uranium ore can be used for its radioactive characteristics and is sampled by radiation. Gold ore is often grooved or drilled into core or cuttings. The ore sampling of foreign heap leaching fields is generally sampled at the stope, while the pile leaching field in China is mostly for sampling the ore before the pile. No matter which sampling method is used, the essential problem is that the lithology and composition of the sample to be taken must truly represent or reflect a lump represented by it, a pile of ore, a mining tool (car, train) The whole (mother) material in the human trolley, mining truck). It is not easy to do this completely. In some cases, such as low grade ore containing coarse gold, sampling is mostly impossible at a reasonable cost. Strictly speaking, most sampling methods at this stage have deficiencies.
First, the main factors affecting the sampling of heap leaching ore
The sampling method, the number of samples, the weight of each sample, the sampling method, and the sample preparation (processing) process are the main influencing factors for ore sampling.
(1) Sampling method
Refers to the method of collecting samples. There are currently many different methods. For example, the foreign heap leaching field collects core samples, rock fragments, or mud samples. The rigs used are also different, including impact drills , rotary drills, reverse circulation drills, and the like. In China's heap leaching field, it is often used in the ore mining tool, or fixed or timed sampling on the transport belt, and randomly picking samples on the ore heap.
(2) Number of samples
Undoubtedly, the more the number of samples, the more representative the final result of the sample, and the more the number of samples, the more valuable the statistical processing of the analytical data of the sample. However, as the number of samples increases, the cost of consumption increases. Because the number of samples and the accuracy of the final result are in a square root relationship, that is, in order to increase the accuracy of the final result by a factor of two, the number of samples must be increased by a factor of four. Therefore, the number of samples must be weighed between needs and possibilities, especially economical problems, and then the appropriate number of samples.
(3) Sample volume
This refers to the amount of sample sent to the sample before processing, ie the amount of sample taken directly from the stop, or the amount of sample taken into the heap at the heap immersion field. It does not refer to the shrinkage during sample processing and the final amount of analytical sample. It is generally required that the amount of sample at this time satisfies both the processing needs of the sample and the ore grade and lithology within the sampling range represented. Therefore, the amount of sample should be determined based on the nature of the ore. When sampling low-grade gold ore containing coarse gold, it is necessary to increase the amount of sampling. Because gold is different from other metal minerals, it is mostly found in natural or gold in the ore.
Sampling of gold ore has published many articles in recent years. GY. Mckinstry, Metz, Clifton et al. have conducted a more detailed study of the sampling of ore containing coarse gold. Clifton believes that "the amount of gold particles in a sample is the only factor that controls the precision of chemical analysis." He assumed that the gold particles were irregularly distributed in the ore, and statistical methods were used to determine the relationship between the sample quality and the gold particle size and gold grain quality in the sample, as shown in Fig. 1. Modern research indicates that the amount of gold in a sample obtained by chemical analysis or instrumental analysis at 95% probability, with at least 20 gold particles in each sample, is ±50% of the gold content. Within.
Figure 1 shows the relationship between sample quality and gold particle size and overall grade with the desired 20 gold particles.
(assuming all gold particles are the same size and are irregularly distributed in the ore)
(4) Sampling method
The sampling method can be regular or irregular, but generally adopts regular sampling. For example, sampling in the stope is basically arranged at equal intervals; when dividing, the splitter or splitting method is often used; on the transport belt When sampling, the interval is the same, and the length of the scraped sample is equal. The so-called irregular sampling, when sampling in the stope, according to the mineralization properties, the sampling length can be different on the same section, such as 1.0m, 0.5m, 0.3m and so on.
(5) Sample processing (preparation) process
Processing equipment during sample processing should be free from contamination, and the loss of processed ore should be minimized and should not exceed 5%. Sample shrinkage is undoubtedly an important step in this process. The split is generally a two-pointer, and the split-shovel method can also be used. The number of slots in the two-divider must be an even number, and not less than 10. The more the number of slots, the higher the accuracy. The minimum reliable mass of the sample at the time of shrinking Q is calculated according to the Jochet formula:
Q=kd 2
Where, the minimum reliable mass of the Q-sample, kg;
D-the largest particle diameter in the sample, mm;
K - the coefficient of shrinkage associated with the nature of the ore.
The k value is related to the type of ore, the change of the main metal grade in the ore, the uniformity of distribution, and the size of the mineral. It is experimentally determined: as long as the k value is reliable, the application of the Jochet formula is feasible for sample processing of physical and chemical analysis of general ore. However, some special steps are taken for the gold ore to be considered as the size of the gold particles. There are three types of gold size:
1, fine grain type
The particle size of the gold in the sample is less than 0.007 mm, which can be reduced according to the Jochet formula. The k value is 0.4, and the sample amount is 10-20 g.
2, medium grain type
In the case of gold, the particle size of 20% is 0.07-0.3mm, and 80% is less than 0.07mm. During the processing, the roller machine should not be used. After coarse crushing, it is ground with a disc crusher until the sample size is less than 0.84mm. Then shrink. The sample after shrinking shall not be less than 500g, and the quality of the analytical sample is 20-30g.
3, coarse and giant
For the processing of these samples, the particle size of the first shrinkage should be determined experimentally.
CIMM conducted the following comparative experimental study: a batch of -10mm gold ore was divided into two groups of 30kg each. One group is directly reduced from -10 mm to 1 kg, and the other group is 30 kg sample first from -10 mm to 28 mesh, and then reduced to 1 kg. The two were then processed to -150 mesh using the same procedure using the same analytical method. The results and precision are shown in the table below.
Table of effects of gold ore shrinkage process on measurement precision
Measure the average grade of gold in the ore (g∕t) | Precision (±2δ*)(g∕t) | |
30kg-10mm ore directly reduced to -10mm 1kg | 30kg-10mm ore broken to -28 mesh and then reduced to 1kg | |
4.1 | ±1.5 | ±0.21 |
3.2 | ±1.0 | ±0.15 |
* δ- represents the deviation.
As can be seen from the above table, the amount of sample in the shrinkage depends on the size of the ore block. In general, the finer the ore is, the better the representativeness of the sample. The experience of China's uranium hydrometallurgical plant also shows that the representativeness of the ball milling sampling is better than the belt sampling, and the representativeness of the belt sampling is better than the sampling of the briquettes in the train wagon.
2. Sampling of ore into the ore
Some of the major domestic dumping sites are basically sampling before the ore is piled up. Develop specific sampling procedures based on the tools that carry the ore into the heap.
(1) Car transport ore
Including mine cars, rear dump trucks, front-end loaders, human trolleys, etc., generally in the ore carrying vehicles, fixed point, quantitatively shovel sample, through a certain number of cars (such as 100 cars) of mineral samples, integrated into a collection Sample, the aggregate sample is first broken to a certain particle size, mixed, divided into the required amount with a two-pointer, and then sent to the laboratory for sample processing and analysis.
(2) Belt transport ore
It is generally used to scrape the same length of the ore sample on the belt (such as 5min). After a certain period of time (such as 24h), the ore sample is mixed, and the two parts are used to reduce the amount to the required amount, and then the laboratory is processed and analyzed.
3. Sampling of stope for heap leaching ore
The ore sampling of most heap leaching sites in the United States is carried out at the stop. The specific method is: drilling at the current point before mining, the drilling density is 5 × 5m, the hole depth is 6 ~ 8m (for the height of the operating platform), the debris samples of each hole are collected, and the laboratory is ground. Sample, analysis. The analysis results of each borehole sample are input into a computer processing, and the geological personnel delineate the block segments of different grades and divide them into different groups. The miners are divided into assembled drugs and blasted separately. On each pile formed by the blast, flags of different colors are inserted to guide the shipment. They believe that this method can guarantee the quality of mining and control the quality of the ore into the pile. It also greatly simplifies the sampling workload and combines mining and in-situ ore grade monitoring without duplication of effort.
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