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Reselection test
I. Overview
   Compared with other beneficiation methods, the re-election process has lower cost and less environmental pollution. Therefore, in the optional study, the re-election test should be considered first for any ore that may be selected by re-election method.
Due to the relatively coarse grain size of the materials selected for re-election, the particle size range is relatively wide. Different materials require different equipment. Even materials that can be selected by the same type of equipment are often graded, and in order to avoid over-grinding. The adverse effects on re-election often use the stage selection process, resulting in a complex combination of re-election processes, and correspondingly large sample sizes. Conversely, reselection factors are relatively simple operation, various devices reselection, as long as the density of its composition and particle size substantially the same as the composition of the material selected, the sorting conditions will be substantially the same.
The main factors affecting the selectivity of ore re-election are density and particle size (in some cases, such as flaky minerals such as mica , the shape is also greatly affected). The difficulty of sorting minerals of different densities can be estimated by the following data:
Where δ 1 δ 2 and Δ—the density of light minerals, heavy minerals and medium, g/cm 3 ;
e - difficulty criteria. The larger the E, the lower the lower limit of the grain size that can be selected (1).
Table 1 Reselection selectability and corresponding optional lower limit of granularity
e value
Re-election difficulty
Optional lower limit of particle size, mm
>5
5~2.5
Extremely easy to choose
Easy selection
0.01~0.005
0.019
e value
2.5~1.75
Re-election difficulty
Easier to choose
Optional lower limit of particle size, mm
0.075~0.038
1.75~1.5
1.5~1.25
<1.25
Harder to choose
Difficult to choose
Not optional
0.5
Several millimeters or more
Since the confounding phenomenon in the re-election process is mainly caused by the part of the ore particles whose density is close to the separation density δ P , it is difficult to re-select the content of the components with a density of δ P ± 0.1 in the entrainment process. Ease of use, and judge the applicability of various re-election equipment based on this (Table 2). If the content of the intermediate component is small, all the re-election methods are applicable, so that a device with high productivity and easy operation can be selected; on the contrary, a method with high sorting efficiency must be selected, and at the same time, the amount of processing and operation should be controlled.
Table 2 The difficulty of re-election and the applicability of various re-election methods
δ±0.1 component content, %
Re-election difficulty
Re-election methods, equipment and operational requirements
Typical application
Reselection method
Method and apparatus
Processing capacity
Operation and control
0~7
7~10
10~15
15~20
20~25
>25
easy
Easier
Harder
difficult
Hard
Hard to limit
all
High sorting efficiency
High sorting efficiency
High sorting efficiency
High sorting efficiency
Sorting efficiency is very high
Big
Big
Moderate
Moderate
Moderate
small
general
general
Good operation
Skilled in operation
Skillful and tight control
Extremely tight operation control
Ordinary chute, jig
Cone concentrator 1
Shaker 1 , spiral concentrator heavy medium dressing
Heavy medium dressing
Heavy medium dressing
Automatic instrument with tight control of specific gravity
1 does not exclude the use of jigs to handle coarse particles
In practice, the various table placer mostly a first and second class; tungsten, tin and noble metals belonging to the third category plurality ore vein; pre-lost after several categories of waste rock and useful operations are generally mineral density is not high genus .
Second, re-election test process
In the reselection selectivity study, the main task is to select and determine the process flow and the corresponding equipment.
The test procedure is usually determined according to the nature of the ore and with reference to the production practice of the same ore, but it should be more flexible than the production process, because many specific problems such as the selected particle size, the tailing particle size and the medium-mine processing method can be determined through trial and comparison. The raw materials required for the test process are mainly: [next]
(1) The degree of muddyness and fragmentation of the ore, according to which the necessity of washing and “sludge separation†is determined.
(2) The depletion rate of ore, according to which it is judged whether it is necessary to use pre-selection by means of heavy medium beneficiation, photoelectric selection or hand selection, and discard waste rock.
(3) The grain size composition of the ore and the distribution rate of the metal in each grain size, which is especially important for sand deposits, because in most sand mines, useful minerals are often concentrated in the level of each intermediate grain size.
(4) The embedding characteristics of the ore, which determines the selection of the beneficiation method and the process structure, including a series of basic problems such as the selected particle size, the tailing particle size, the number of selected sections, the medium-mine processing method and equipment combination.
(5) The nature and content of symbiotic heavy minerals in ore and its mosaic relationship with the main useful minerals, which involves the trend of these symbiotic heavy minerals in the re-election process, as well as the processing of re-election of coarse concentrates and medium-minerals. method.
Figure 1 and Figure 2 show an example of a tungsten-tin primary vein re-election test procedure with certain typicality. According to the material composition research data, it is preliminarily determined that the selected particle size is 12 mm, and the final crushing particle size is 0.5 mm. Considering the high value of tungsten and tin minerals, the brittleness is easy to be pulverized, and the three-stage grinding and sorting process is prepared.
Fig.1 Exploratory test procedure for unequal-grained embedded tungsten-tin ore (1)
Fig. 2 Exploratory test procedure for coarse-grained inlaid tungsten-tin ore (2)
Figure 2 shows the first part of the test procedure, the coarse-grained fraction. The main purpose of the test is to examine whether the selected inclusion particle size is reasonable and at what granularity it is possible to start tailing. If the coarse fraction is neither capable of obtaining concentrate nor tailings, all samples should be re-crushed to a smaller particle size and the test should be restarted. If the coarse-grained grade can get the concentrate, but the tailings cannot be lost, the middle mine and the tailings should be combined as the “jigging tailings†and sent to the next section. If the tailings can be thrown at the same time, only the middle can be thrown. The mine sent the next section to sort. If the jigging can only lose tailings, it will only be pre-selected, that is, the initial frequency enrichment.
The second part of the process shown in Figure 2 is the fine particle sorting section. The main equipment is the shaker. The main tasks of the test are: (1) If the +2 mm level fails to throw out the tailings that can be discarded, it needs to continue. Exploring the starting particle size of the tailing; (2) determining the final grinding grain size; (3) selecting the equipment, especially the sorting equipment of the middle grain part. For example, the -2+0.5 mm class can also be changed to a shaker; for example, if the role of the medium jigging in the process is pre-selected, the possibility of switching to a conical concentrator should also be considered. [next]
The -75 micron slime sorting process is not shown in the figure. At present, the most commonly used processes in China are: first sorting with a cyclone; coarse mud larger than 38 microns is sent to the bed shaker for sorting; fine mud smaller than 38 microns is coarsely selected by centrifugal chute, and the belt chute is selected. When the metal in the slime is mainly distributed in the coarser grade, it can also be directly selected by automatic chute or ordinary chute, and the belt chute is selected, and it is not necessary to classify in advance.
After the exploratory test is completed, a larger number of samples must be taken again, and a formal process test is performed according to the selected process in order to obtain a process index that can be used as a design basis.
Third, re-selection test equipment
In order to predict the future production process under laboratory conditions, it is possible to correctly judge and predict the corresponding parameters and indicators of industrial equipment according to the size, processing volume, operating parameters and selection indicators of the test equipment, and must follow the similar theory correctly. Based on the production equipment, the test equipment is designed and manufactured according to a certain scale. Through the study of the similarity principle of the model test of some equipments, the scale of the prototype and the model can not be too large, that is, the size of the test equipment should not be too small, and the actual condition can not be satisfied when the scale is too large. For example, in theory, the model is preferably normal, that is, its length, width, height, etc. should preferably be reduced by the same scale. In fact, in many cases, the scale can not be achieved. A very important reason is that the size of the ore particles is not allowed to scale down. Therefore, for the re-election process test that provides the basis for the design of the concentrator, it is generally preferred to semi-industrial test equipment.
(1) Ultra-small-scale test equipment process Before the test, some exploratory tests can be carried out with some equipment with very small processing capacity. We call it an ultra-small scale test. The purpose of the test is to observe the dissociation status of minerals and the method of re-election. The possibility of processing. The earliest such equipment was an artificial sanding disc. As long as it contained a sufficient amount of heavy minerals, a few grams of the sample could be tested. Obviously, the separation is closely related to the skill of the operator, and it can be used skillfully. Not many people. Today's attention is paid to vibrating sanding discs, such as the Mozley sanding pan. This is actually an oblique vibration chute with two disk faces, a 10 to 100 micron sample suitable for a flat disk surface, and a 100 to 2000 micron sample suitable for a U-shaped disk with an angle of 165°. , driven by a crank mechanism similar to a shaker. Each time the material is 50~100g, it is pre-wetted and then it is close to the working end of the disk. The ore particles are layered under the action of vibration. The flushing water is fed from the upper part, and the upper layer of light mineral is flushed to the tail to discharge. The mechanical movement makes it The heavy minerals at the bottom move up, and the middle mines are distributed at the tail of the disk. The selection lasts for about 3 to 5 minutes. After the shutdown, the heavy products and intermediate products are washed out by washing water, respectively, and collected, weighed and tested.
(2) Heavy medium beneficiation test equipment Heavy medium beneficiation test, usually starting from density component analysis (mainly heavy liquid and resuspension separation test). In order to provide a formal design basis, formal testing must be further carried out in a continuity test device simulating the structure and form of the production equipment.
(3) In jig metal ore dressing, the jig is mainly used to process coarse particles of 20~0.5 mm. At present, the most widely used domestic laboratory jigs are diaphragms of 150 × 100 and 300 × 200 mm, but each unit also retains some equipment that has been produced in the past or purchased abroad, such as a 50 × 50 mm diaphragm. Jig, 150 x 150 and 300 x 200 mm piston jigs, as well as larger 300 x 300 mm lower cone diaphragm jigs and 450 x 300 mm upper diaphragm jigs. Also trial-produced is a ladder type jig with a production scale of 2. All smaller equipment is suitable for laboratory small and selective testing; larger equipment is used for laboratory process testing or intermediate testing.
(4) Shaker The effective size of the shaker is 2~0.038 mm. The specifications of the experimental shaker are roughly divided into three categories: 1) a small test shaker of length × width of about 1 × 0.5 m; 2) a semi-industrial shaker of length × width of about 2 × 1 m; 3) length × width 4.5 × 1.8 m industrial shaker. The second most common application is the second category. If it is not a special equipment test, it is ok regardless of which bed is used. The form of the bed is similar to that of industrial equipment. The coarse grain is used to bring the double bed surface, and the fine grain is used to groove the bed surface.
(5) The effective separation size of the spiral concentrator of the spiral concentrator is 2~0.075 mm. The laboratory uses small-sized industrial equipment with a diameter of about 0.6 meters.
(6) Shrink chutes (fan-shaped chutes and conical concentrators) The shrinkable chute can handle a range of material sizes that are 3 to 0.038 mm wider than a spiral concentrator. Regardless of whether the production equipment is a fan-shaped chute or a conical concentrator in the future, laboratory tests can only use fan-shaped chutes because the conical concentrator is too large. The commonly used test chute size is: 600 × 1000 mm long, the width of the ore end is 150 × 300 mm, and the ratio of the pinch (the ratio of the width of the ore end to the end of the ore) is about 20, and the inclination is 15~19°.
(7) Centrifugal concentrator and belt chute centrifugal concentrator is a well-recognized roughing equipment for slime. The best choice is 38~19 microns. The most common equipment size in the laboratory is Ф400 × 300 mm. Belt chutes are usually used in conjunction with centrifugal concentrators for selection. The size of the industrial equipment is width × length = 1 × 3 m, and the test equipment is only reduced in width and the length is generally not changed.
(8) The most effective particle size of the cross-flow belt chute cross-flow belt chute is 40~20 microns. It is said that the recovery rate of the operation can reach more than 70%, and the recovery rate of 5~10 micron can also reach 50%. Enrichment ratio is more than 20%. The test chutes currently produced in China are available in sizes of 700 × 1200 and 1200 × 2750 mm. [next]
Fourth, the re-election process factors
The process factors that need to be examined and adjusted in the re-election test are as follows:
(1) Load: It is the factors related to the ore supply, including the ore supply or volume load, the ore concentration and the ore pressure (when the ore is the pressure flow).
(2) Water volume: including under-supplement water for equipment such as feed water, classifier and jig, and flushing water during film processing.
(3) Medium and bed: such as the rheological properties of the suspension, the bed composition of the jig and the thickness of the bed.
(4) Equipment structural parameters: The structural parameters of the jig are generally determined by the manufacturer. Generally, the ore dressing process test is no longer adjusted. The structural factors to be adjusted by the film casting equipment are generally only the slope; the structural parameters of the hydrocyclone are Almost all are adjustable.
(5) Equipment motion characteristics parameters, such as the stroke and stroke of most reciprocating mechanisms are the main operational factors that need to be adjusted. The equipment for the rotary motion needs to examine the effect of the speed.
(6) Working time.
V. Evaluation of re-election test results
In addition to general process criteria such as grade and recovery, (1) fractional recovery and (2) distribution curves are often used to assess the efficiency of the reselection process.
The fractional recovery rate refers to the recovery rate (ie, the distribution ratio) of the useful components (such as metals) of each of the fractions calculated at the fractional level in each product. With the fractional recovery rate, the sorting efficiency of different equipments for different fractions can be judged.
The distribution curve is a graphical representation of the partition ratios for different grades (for graded operations) or for different density components (for re-election operations) in coarse and fine or heavy and light products. The distribution rate ε can be calculated as follows:
(1)
Where γ is the yield of the product;
α and β — the content of a component in the ore and product.
Since the concepts of distribution rate and recovery rate are inherently consistent, their calculation methods are also consistent. Only when calculating the recovery rate, the content index (α and β) refers to the content of metal or other useful components (according to the test results); when calculating the particle size distribution curve, $ and # refer to the content of a specific size in the ore and product. The density distribution curve is the content of a specific density component in the ore and product.
Figure 3 shows the distribution curve of a diamond heavy medium beneficiation. The points on the curve represent the distribution ratio of various density ore in the concentrate. The distribution rate curve in the tailings is not shown on the graph. It should be the reflection of the concentrate distribution curve. In the ideal case, the distribution of the ore with a density greater than the separation density δ P = δ 50 in the concentrate should be 100%, and the distribution of the ore with a density less than the separation density in the concentrate should be zero, only the density is just right. The distribution ratio of the ore particles equal to δ P should be 50%. In the actual sorting process, the separation density is fluctuating, and the density corresponding to the distribution ratio of 50% represents only the average value of the separation density. The greater the fluctuation range, the wider the intermediate density of light and heavy ore particles, which means that the sorting efficiency is lower. Therefore, the “offset distance†E p (separation density average offset distance) is commonly used to measure the sorting efficiency:
(2)
Where δ 75 and δ 25 - the partition ratio is the specific gravity value at 75% and 25%.
The offset is also often referred to as the Tromp indicator.
Figure 3 distribution curve