Introduction：Preparation of cyanide leaching for gold ore Before entering cyanide leaching, gold bearing ores need a series of necessary preparation and pretreatment: Raw material for leaching needsuitable fineness;Flotation reagentin flotation gold con

Preparation of cyanide leaching for gold ore
Before entering cyanide leaching, gold bearing ores need a series of necessary preparation and pretreatment: Raw material for leaching need suitable fineness;Flotation reagent in flotation gold concentrate shuould be reduced. These chemicals often have a negative effect on the dissolution of gold to a large extent; We shuold reduce the amount of harmful impurities in cyanide ore or inhibit the influence of these harmful impurities. Thus, the best cyanide leaching effect can be obtained with lower consumption.
1.ore grinding
Gold in ore is usually encapsulated or contiguous with gangue minerals, while cyanide leaching requires gold particles to be dissociated or fully exposed to cyanide and oxygen in solution, so that leaching reaction can proceed smoothly. The size of gold in ore is usually very fine, to meet the requirements of cyanide leaching, must have a high grinding fineness. Generally speaking, the fineness of the row ore leaching should reach -200 mesh content 85 ~ 95%, and the fineness of flotation concentrate cyanide should be -320 mesh content 90% ~ 95%.
During the grinding process, as the ore particles continue to grind, some of the gold particles become smaller, and the shape of the gold also changes from granular, columnar to flake, increasing the specific surface area of gold, thus increasing the chances of contact between gold with cyanide and oxygen. It is beneficial to increase the leaching rate of gold. In addition, in the process of continuously deforming and thinning, the fresh surface of gold particles is exposed, and the film that is unfavorable to cyanide leaching is removed, which also helps to improve the leaching rate of gold.
The addition of alkali in the grinding system can cause alkali leaching of some minerals, which is helpful to eliminate the adverse effects of harmful impurities in slurry on leaching. Because the surface of gold particles in contact with cyanide and oxygen is mostly fresh, the leaching rate of gold is often very high. The leaching rate in grinding system is generally more than 50%.
The suitable grinding fineness should be determined by test. If the grinding fineness is too low, the gold particles in the ore can not be fully dissociated or exposed, which affects the leaching of gold. If the grinding fineness is too high, it will not only increase the cost of grinding, but also increase the viscosity of slurry, and reduce the diffusion rate of Au(CN)₂^- CN^-and O₂ in leaching solution, thus reducing the leaching rate, and will also give subsequent pre-leaching concentration Carbon adsorption and other operations to bring adverse effects. Therefore, grinding fineness must be strictly controlled.
2.Detoxification and pre-leaching concentration
The cyanidation of flotation concentrate is unfavorable to gold leaching because it contains a lot of flotation reagents. It has been proved that the more the flotation reagent content in gold concentrate, the more obvious the hindrance to gold leaching. Therefore, the flotation reagents contained in gold concentrate must be removed as thoroughly as possible before leaching. Demineralization equipment is usually used by thickener or chamber filter press. Because of the need of economy, process and operation management, thickener is used in production.
The pulp concentration of the raw ore is generally very low before the leaching operation, so it is necessary to concentrate the pulp, which is called pre-leaching concentration. On the one hand, the concentration of concentrated pulp should meet the requirements of leaching process, on the other hand, the requirement of activated carbon adsorption on pulp concentration must be considered. In order to improve the concentration efficiency, the flocculant is usually added to increase the settling rate of solid. It should be noted that the dosage of flocculant should not be too large, otherwise it will increase the viscosity of pulp and adversely affect the leaching and adsorption operation.
3.alkaline leaching
    For some refractory ores, the method of alkali leaching before leaching can eliminate the adverse effects of some impurities on the leaching. The so-called alkaline leaching is under alkaline conditions to fill the ore slurry with oxygen and make strong agitation to precipitate or dissolve some impurities by oxidation and eliminate its effect on leaching. For example, pyrrhotite and pyrite in ore, By alkali leaching it will be converted to Fe (OH)₃ precipitation, thereby reducing the consumption of cyanide and oxygen in the leaching process. For example, the gold ore containing arsenic and antimony is soaked through alkali, the realgar in the ore, the orpiment , stibium and so on, which will produce soluble Na₃AsO₃ and Na₃SbO₃, and then remove these impurities by dehydration.
In actual production, many factories and mines directly add lime to the ball mill, so that the grinding and alkali leaching process are carried out simultaneously.
In the process of alkali leaching, we should also pay attention to the control of alkalinity. Too low basicity can not achieve the purpose of alkali leaching, too high alkalinity will affect the leaching effect of gold. This effect is more obvious when lime is used for alkali leaching. As far as possible, pH automatic control system is used to control alkalinity in production, which can ensure the accuracy and stability of alkalinity in alkali leaching process.