During the cyanidation operation, oxygen is supplied by aeration into the slurry. The solubility of oxygen in the cyanide solution is one of the main factors determining the effect of cyanide gold extraction. First, the concentration of oxygen in the solution The solubility of oxygen in an aqueous cyanide solution varies with temperature and pressure on the liquid surface. In a special equipment, the solubility of oxygen in the solution depends mainly on the local atmospheric pressure on the liquid surface of the equipment and the salt concentration of the solution during operation. Generally, the highest solubility of oxygen in water is in the range of 5 to 10 mg ∕L (5 to 10) × 10 - 4 %). Under normal conditions, the cyanidation operation does not require control of high solution temperatures (except for the necessary conditions to prevent slurry freezing), nor does it require an increase in oxygen pressure (eg, using high pressure air or supplying oxygen in a closed vessel). Instead, the oxygen in the slurry is saturated by the aeration of the mixer impeller or by the supply of compressed air. If the Pachuca air agitation leaching tank is used, the exhaust gas is blown into a concentrated slurry tank containing 12 to 16 m depth by a blower, and a high concentration of oxygen is supplied into the slurry. Second, the determination of oxygen concentration The concentration of oxygen in the cyanide solution can be determined in a number of ways. The commonly used methods are: (a) White's colorimetric method. The alkaline pyrogallol solution was added to the cyanide solution, and the presence of oxygen was confirmed when the solution turned brown, and then the colorimetric determination of the oxygen content was carried out. (2) Weinig's fast capacity method. The indigo disulfonate was used as an indicator and titrated with dithionite. (3) Solid-state electrode polarography and Bechman oxygen electrode direct insertion. This is two methods for measuring oxygen concentration in modern times. As long as the electrode is slightly inserted into the slurry, the oxygen content corresponding to the sample of the clear solution can be obtained. In view of the difficulty in determining the absolute concentration of oxygen in a solution, a rapid method is generally employed to determine the percentage of oxygen saturation in the solution. This readily available value allows for a more efficient comparison of the actual changes in oxygen concentration of the solution between the various devices due to different aerations. The oxygen content in the cyanide solution can be determined from a sample of a solution of a particularly saturated oxygen through which air bubbles pass through the apparatus, using standard methods. Third, the consumption of oxygen At the cyanide plant, the amount of oxygen that the ore needs to consume is not known. The main loss of oxygen in the total consumption is during the grinding and classification process. In addition, although the total amount of oxygen supplied by the agitation is known (the same air is supplied), these oxygens are generally not always available. This is because the supplied air is dispersed in an approximate small bubble distributed throughout the slurry, but most of it may later escape to the atmosphere. Therefore, the amount of oxygen actually used is greatly different from the amount of oxygen supplied to the air. The standard consumption of oxygen may be only 4 to 5 kg 矿t ore. The rate at which oxygen is transported from the gas phase to the liquid phase is reduced by the thickness of the slurry. The transfer rate in viscous pulp is much slower than in water. Therefore, some plants use dilute slurry as much as possible to increase the solubility of oxygen. The main oxygen-consuming substances in the ore are gold, iron , and sulfide. (1) Gold. The oxygen consumed by gold during the dissolution process is only a small fraction of the total oxygen consumption. If the gold content per ton of ore is 8g, the amount of oxygen required to dissolve the gold can be determined by the Elsner reaction: 4Au+8NaCN+O 2 +2H 2 O Calculate: 4Au+8CN - +O 2 +2H 2 O O 2 ∕g·t - 1 = 8× Therefore, the amount of oxygen consumed when gold is dissolved is only one ten thousandth of the actual supply. (2) Metal iron. The metal iron in the ore is mainly derived from the mechanical wear of the grinding equipment lining and the iron ball (about 0.5 to 2.5 kg per ton), which also consumes a certain amount of cyanide and oxygen. In closed-circuit operation, the oxidation of metallic iron may first form an iron oxide film on the surface of the gold particles to prevent or prevent further dissolution. However, the oxidation of metallic iron can inhibit itself and only oxidize the surface. (3) Sulphide. Sulfide in the slurry is the main consumer of oxygen. Pyrite is almost always present in gold ore, and its oxidation rate is controlled by chemical action at room temperature. Pyrite and pyrrhotite often consume significantly more than stoichiometric amounts of active oxygen. In order to obtain a satisfactory cyanidation effect, the ore should be calcined before cyanidation. Alternatively, most of the sulfides are removed by enrichment by appropriate aeration, and are often one of the important measures to increase the cyanidation effect. After extensive research on the mechanism of oxidation activity of sulfide minerals in aqueous solution, JT Woodcock pointed out that the reaction of pyrite in aqueous solution can be expressed by the following formula: 4FeS 2 +16OH - +15O 2 The final product shown by the reaction formula is sulfate ion and iron hydroxide, but the intermediate product includes ferrous ion and thiosulfate, and thiocyanate and ferricyanide complex formed in the presence of cyanide. The reaction process is controlled by chemical action, which tends to inhibit itself, producing iron hydroxide precipitate only on the surface of the mineral, and a small amount of pyrite can actually act as an oxidant. (4) Control of oxygen concentration. Since the distribution of air in the mixer is observable, many plants use either manual air conditioning valve adjustments. EK Penrose et al. measured data for six Delphus mixers. Each mixer has a diameter of 10m and a depth of 5.4m. The air supply of each mixer is 14m 3 ∕min, 85kPa, and the oxygen saturation rate of the solution stirred by each mixer (see table below): The oxygen saturation rate of the solution stirred by each mixer Mixer number l 2 3 4 5 6 Oxygen saturation rate /% 35 45 45 55 90 100 A. Gold (King) cited Pachuca air stirring leaching tank and mechanical mixer stirring solution oxygen concentration changes as shown in Figure 1. Figure 1. Relationship between changes in oxygen concentration and gold dissolution in Pachuca air mixers and mechanical mixers (Woodcock, 1949) Rectangle Carbide Insert ,Carbide Milling Inserts,Carbide Tool Inserts,Sharpening Carbide Inserts SICHUAN TELOS NEW MATERIAL TECHNOLOGY CO., LTD , https://www.sichuankenlarcutters.com
4NaAu(CN) 2 +4NaOH 4Au(CN) 2 - +4OH - =0.32 8SO 4 2 - +4Fe(OH) 3 +2H 2 O
May 11, 2024