Many scholars have proposed that the heap leaching rate is unbalanced according to the characteristics of the leaching curve in the heap leaching and the existence of two chemical reaction zones in the heap leaching. The initial heap leaching rate is proportional to the surface area of ​​the immersed ore, but in the later stage. It is proportional to the pore volume in the ore. Therefore, the dynamic process of heap leaching is a one-dimensional multiple equation. The empirical formula for the heap leaching rate is: η = a + a 1 t + a 2 t 2 + a 3 t 3 . The coefficients in the equation can be determined by processing the experimental data using the least squares method in mathematical statistics. The heap leaching rate is the first derivative of the above empirical formula.
The procedure for obtaining the heap leaching rate by this method is as follows: (1) performing column immersion test on different ore grades; (2) arranging the leaching rate versus time data, and making a curve, as shown in Fig. 1; The least squares method is used to find the corresponding coefficient, and the empirical formula is listed; (4) the first derivative of the empirical formula is obtained. The information of И.К. Lucenenko and others is used as an example. In this case, uranium ore is heap leached with dilute sulfuric acid. Table 1 is the experimental ore properties. Column immersion test conditions: column height 1.2m, diameter 0.3m, leached with dilute sulfuric acid solution, control residual acidity of 5g / L, spray 7h per day, spray intensity is 6L / (h · m 2 ), divided into four different The fractions are packed separately for column leaching.
Figure 3-7 Relationship between uranium leaching rate of granite -porphyry and ore grain size and time
1-the particle size is less than 25 mm; 2-the particle size is greater than 25 mm and less than 50 mm;
3-particle size greater than 50mm less than l00mm; 4-grain size greater than l00mm less than 200mm
Table 1 Test ore properties
Ore-bearing rock | Ore structure | Uranium mineral | grade(%) | Porosity(%) | Ore size (mm) | |
Total porosity | Effective porosity | |||||
Granite porphyry | Dip-dyed, fine vein | Asphalt uranium mine, uranium black | 0.041 | 1.5 | 1.1 | -200 |
Mud slate | Dip-dyed, fine vein | Asphalt uranium mine, uranium black | 0.042 | 1.1 | 0.72 | -200 |
The daily leaching rate obtained by the test is related to time, as shown in Fig. 1. (The curve of the granite-porphyry is only shown in the figure). The test data was processed by the least squares method to determine the coefficients in the empirical formula. Table 2 lists the asymptotic equations for the leaching rates of the two uranium ores in the first 62 days.
Table 2 Asymptotic equation for leaching rate of two uranium ore leached for 62 days
Granite-porphyry | -25mm | η=3.934+7.748t-0.391t 2 +0.667×10 -2 t 3 |
-50～+25 | η=2.867+2.069t-0.63×10 -1 t 2 +0.667×10 -2 t 3 | |
-1000～+50 | η=0.57+1.319t-0.49×10 -1 t 2 +0.63×10 -3 t 3 | |
-2000～+100 | η=0.042+0.436t-0.967×10 -2 t 2 +0.538×10 -4 t 3 | |
Mud slate | -25mm | =1=19.7+1.85t-0.15×10 -1 t 2 +0.406×10 -4 t 3 |
-50～+25 | =1=15.9+1.46t-0.119×10 -1 t 2 +0.341×10 -4 t 3 | |
-1000～+50 | =1=11.33+1.31t-0.104×10 -1 t 2 +0.298×10 -4 t 3 | |
-2000～+100 | η=6.95+1.26t-0.984×10 -1 t 2 +0.266×10 -4 t 3 |
It can be seen from Table 2: (1) The same ore, the larger the blockiness, the smaller the empirical coefficient. It indicates that the greater the porosity in the ore, the larger the mass transfer coefficient. (2) As the leaching time is extended, the coefficient becomes small. Explain that the heap leaching rate is not balanced. Therefore, when talking about the heap leaching rate equation, it is better to divide the order enthalpy according to the leaching process, and then obtain the empirical formula, and then obtain the first derivative of the empirical formula to obtain the heap leaching rate expression of each stage.
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