Improvement of heap leaching process (2)

6 reverse belt granulator. Figure 6 shows a steeply inclined conveyor belt granulator that feeds ore at the upper end. The speed of the conveyor belt attempts to send the ore to the top of the conveyor belt, but the steep slope of the belt causes the ore to slide.

The granulation treatment has a short leaching period and a high leaching rate. The use of granulation process to treat those ore and tailings with high mud content and poor permeability can achieve better recovery and economic benefits.
2. Wetting effect
The basic principle of increasing the heap leaching of precious metals with a wetting agent is a recovery is being greatly valued. In theory, the addition of a special surfactant, a wetting agent, to the leachate reduces their surface tension and allows the ore and immersion agent to be more completely in contact. Thereby increasing permeability and recovery. Increased permeability can reduce leaching time, reduce cyanide and pumping costs, reduce dry areas in the heap leaching field, and enhance penetration of individual ore particles. Finally, the purpose of improving metal recovery rate is achieved. The wetting agent is a material that enhances leaching. It not only increases the leaching speed and final recovery rate, but also ensures that the wetting agent does not adversely affect the adsorption and desorption of precious metals.
1) Type of Wetting Agent A general chemical agent used in heap leaching that has the ability to increase the wetting efficiency of the leaching agent is called a surfactant. These agents may have a variety of chemical derivatives, charge characteristics and relative molecular mass. The classification of surfactants is listed in Table 1. [next]

2) Liquid surface characteristics Water cohesion is the key to the surfactant process. Since the water molecules are dipolar, Figure 7 depicts the water molecules in a triangular form. The oxygen atoms occupy one corner and the hydrogen atoms occupy the other two corners. Although the molecule is electrically neutral, the negative charge field surrounds the oxygen atom and the positive charge field surrounds the hydrogen atom. These areas of water molecules are far apart to affect the nature of the water. The dipole polarity of water and the negative charge at the highest point attract the positive charge zone at the bottom, indicating the tendency of the water itself to bond. This trend of each water molecule produces a surface tension of water to molecules near it. [next]

(a) in Fig. 8 indicates that the molecule is in the liquid, and (b) indicates that the molecule is at the liquid-air interface, and the source of the force acting on one molecule in the water should be considered. In the liquid, the adhesion is uniformly attracted in all aspects. molecular. For molecules on the surface, the attraction is directed downward into the liquid so that the surface acts like compression.

This phenomenon reduces the wettability of the water and reduces the contact surface of the leachate uniformly with the ore. The reduction in surface tension results in more complete wetting of all solid surfaces. A good surfactant reduces the surface tension of water from 0.72 N/m to 0.3 N/m at its relatively low concentration (100 μg/g or less). An example of a typical surfactant is shown in Figure 9.

[next]

In terms of the ability to reduce the surface tension of the surfactant, to a large extent, one feature is the presence of hydrophilic groups and hydrophobic groups on the same molecule. These parts of the wetting agent have different properties when they are dissolved in water. The hydrophilic end of the surfactant has an affinity to attract itself to the water and is readily soluble in water. The hydrophobic end of the surfactant has no affinity for water and is itself oriented on the surface of the water.
If low concentrations of surfactant are added to the water, they tend to accumulate on the water surface. The hydrophobic ends of the molecules are extruded and arranged in a row on the surface of the water, as shown in FIG. As more molecules accumulate on the surface, the surface tension is reduced until the surface is completely covered. The concentration at which the surface tension is no longer further reduced is called the critical colloidal ion concentration. When the concentration of the surfactant is not additionally increased on the surface, excess activator is necessarily left in the solution.

This reduction in surface tension also helps to increase the metal recovery during the leaching process because more or more liquid must be brought into close contact with many irregular surfaces of the ore to achieve a gold dissolution effect.
3) The role of the wetting agent The wetting agent actually acts as a desirable surfactant in the heap leaching. The effect of wetting agents on improving the recovery rate of gold leaching is still in the experimental research stage. In 1984, SRJosph and HNJames proposed a plan to improve the permeability and recovery of the heap using a wetting agent, which was tested separately at the laboratory column leaching and production heap leaching of the Ortiz mine in New Mexico. The test was done to identify the following questions:
1 Does the addition of surfactant increase recovery and permeability? 2 What is the mechanism if the recovery rate increases? 3 How much do you need to use to achieve the above requirements? 4 Can the addition of surfactants yield enough to compensate for the cost of the chemical? 5 What is the best way to apply chemicals? 3 Should the chemical be added at the beginning of the leaching or during the entire spraying process?
As can be seen from the experimental results (Table 2), the results of the two experiments are promising. The recovery rates of the two yards (both E-22 and G-22) increased by 7.7% and 9.5%, respectively, compared to the two pile immersion fields adjacent to each other. Drew739 and Nalco 2DA-375 were used, respectively. Later, the 2DA-375 was changed to 85DA-059, and two experiments were conducted. 85DA-059 is a mixture of fatty acids and alkoxides. There was no future for this second round of trials. The recovery rate was 1.0% with Nalco 85DA-059 and 2.3% with Drew739. At the end of the year, the last two trials were carried out, this time using Nalco 85DA-059. The recovery rate increased by 4.7% and 5.0% respectively. The total recovery of these 6 trials increased by an average of 4.3%. The amount of administration in each of the six tests was maintained at 16 μg/g. [next]

The Ortiz mine has an average annual production of 50,000 ounces of gold. For mines of this size, the recovery rate is increased by 4.3%, which will increase the annual gold production by more than 2,750 ounces ($1.3 million for the price of $480/oz). The cost of surfactants per ton of ore is less than 2 cents, and the Ortiz mine processes 900,000 tons of ore. The annual cost of mines of this size increases by less than $20,000, so the profit margin of investment is quite attractive.
As with most pharmaceutical agents, wetting agents react differently with different ores. At the Ortiz mine, using one of three surfactants, the recovery was significantly improved by 4.3%. However, in other mining areas, such as the Mesquite mine, there is no significant improvement, which indicates that there is still much work to be done on the mechanism of the improvement of the wetting agent. In summary, tests at the Ortiz mine have shown that the profit from the use of wetting agents for ores that are beneficial to the reaction is enormous.
3. Oxygen leaching
According to CMKenney (1987), the results of the atmospheric column immersion test performed by Hamzen for Kamyr showed that oxygen has a good influence on the heap leaching of low-grade gold mines in California (1.3g/t), and the particle size is 25.4mm. The ore pellets were subjected to 6 column immersion tests in a column of 14 cm in diameter and 1.8 m in height. Oxygen was sprayed into 4 columns, 2 of which were capped; the remaining 2 columns were uncapped and did not spray oxygen. The cyanide solution was passed through a leaching column 34d, followed by washing with water for 2 d. The results of the column immersion test are summarized in Table 3. [next]

In order to determine the impact on other ores and the economics of adding oxygen to special heap leaching, although trials and further studies are needed, the trends demonstrated in the current study are encouraging.
The above description shows that the rate of gold leaching with oxygen-enriched air is much higher than that of air. In the roller bottle test, the test was carried out for 24 hours with oxygen and air, and the leaching test was carried out with oxygen-enriched air, and the gold leaching rate was 93.3%. Therefore, oxygen increases the rate at which gold dissolves, but does not affect the final recovery.
In the column immersion test in a 14 m column, the gold leaching rate was also increased with oxygen. After leaching for 36 days, the leaching rate of the four columns with oxygen was between 89.4% and 92.3%, with an average of 91.1%, while the gold leaching rate for the two ordinary column immersion tests with air was only between 78.2% and 85.4%. After leaching for 15 days, the gold leaching rate in the oxygen-filled immersion column averaged 86%, while the average leaching rate of the ordinary column using air was only 76%. The sodium cyanide consumption of all tests was less than 0.23 kg/t, and the sodium cyanide consumption of the oxygenation column was slightly lower than that of the ordinary column.

Stainless Steel Casting

Ningbo City Yinzhou Ruican Machinery Co.,Ltd , https://www.kstcasting.com