However, cyanide waste water will become the main pollution source of water bodies, and the discharge of waste gas will cause direct harm to people and biological groups, and the dumping of waste residues will also cause deterioration of the ecological environment.
Alkaline chlorination refers to using chlorine gas or liquid chlorine and bleaching powder to oxidize cyanide in wastewater into non-toxic substances such as carbon dioxide and nitrogen. It is a commonly used method for treating cyanide-containing wastewater.
According to the different chlorine-based oxidants added, the alkaline chlorination method can be divided into bleaching powder method, liquid chlorine method, electrolytic salt method, etc. The advantages and disadvantages are shown in Table 1.
However, it also has some disadvantages, for example, HCN gas is dangerous, must be carefully sealed; the amount of sulfuric acid used for desorption is large; the resin bed may be blocked by metal precipitates; and the investment cost is relatively high.
Activated carbon adsorption catalytic oxidation method to treat cyanide-containing wastewater is a new method occurred in recent years. The use of activated carbon adsorption method to treat wastewater has low cost, and it can comprehensively recover valuable metals such as gold while removing cyanide in wastewater. The effect is very significant, which opens up a new way for the transformation from pure consumption sewage treatment to profitable sewage treatment.
The content of impurities such as copper, lead, zinc and chlorine in the treated wastewater is relatively small, and the drainage outside the tailings dam can be fully recycled, achieving a good effect of zero discharge. It can not only exempt the sewage discharge fee, but also save the cost of using fresh water, which solves the problem of water shortage.
There are many methods for cyanide removal in cyanide tailings of gold mines, but most of them require higher investment or advanced technology, and need to increase the investment in the gold cyanidation plant.
But there is a more convenient method that can save the process of cyanide removal, which is choosing eco-friendly agents for gold extraction. CNLITE gold dressing agent is such a eco-friendly agent. It can completely replace the role of cyanide in the gold cyanidation plant, and is low-toxic. It does not require harmless treatment of tailings, and can save big expenses for your gold cyanidation plant.
Cyanide gold leaching is a process of extracting gold with cyanide as the leaching reagent, which is the most important gold extraction method because of its mature process, high recovery rate, low cost, etc. However, there are still some aspects to be improved, such as improving the cyanide gold extraction process, shortening the cyanide leaching time, decreasing the cyanide consumption. Therefore the intensified cyanide leaching is particularly important in improving the cyanide leaching effect.
Intensified cyanidation is mainly use physical methods to improve the physical and chemical conditions of cyanide leaching and increase the leaching speed so as to increase the recovery rate of gold ore. The main methods of intensive cyanidation are:
Research and production practice has proved that peroxygen reagents such as H2O2, Na2O2, CaO2, BaO2, and persulfate have obvious effects on strengthening gold leaching. This is because they can not only increase the content of dissolved oxygen in the slurry, also have the advantages of high utilization of active oxygen.
Lead salt, mercury salt, and bismuth salt can all be used as cyanidation accelerants. These heavy metal salt accelerators accelerate the speed of gold leaching. The principle is to form a local galvanic cell between gold and heavy metals such as lead or mercury. The addition of lead salts and other accelerators to the cyanide slurry has been applied in many plants at home and abroad. For example, in some cyanide plants in Canada, by addingPb(NO3)2 and maintaining a good concentration of dissolved oxygen in the cyanide circuit, thus overcoming the adverse effects of sulfide minerals on the cyanidation process. However, it should be pointed out that all cyanidation plants should control the amount of accelerators within a certain range according to the specific conditions of gold ore.
The oxygen-enrich intensified gold leaching process is also known as the CIG oxygenation process, that is, pure oxygen is filled into the leaching tank to replace the traditional process of filling compressed air. This process can increase the dissolved oxygen content in the slurry and therefore accelerate the leaching speed, improve the leaching rate of gold and the processing capacity. Oxygen is fed into the leaching tank from below the agitator and dissolved in the slurry. The concentration of oxygen in the slurry can be maintained at about 2010-6.
When[CN]/[O2]>6, the dissolution reaction of gold is controlled by the diffusion of oxygen, and when[CN]/[O2]<6, the dissolution reaction of gold is controlled by the diffusion of CN-. Most cyanide plants operate under the condition of [CN]/[O2]>6, so that the dissolution of gold mainly depends on the concentration of dissolved oxygen. The relationship between gold dissolution rate and oxygen concentration is shown in Table 1. The rate of gold leaching with oxygen is 5 times faster than that with air. If the leaching capacity is the same, the volume of the leaching tank can be greatly reduced.
Pressure cyanide leaching is a process in which the cyanidation process is realized in a pressure vessel, and the reaction pressure is increased to strengthen the cyanidation process. The initial research focused on the extraction of gold from refractory gold ore. When the air pressure is 2105Pa, the dissolution rate of gold is 10-20 times that under normal pressure, realizing the so-called flash cyanidation. This means that the efficiency of cyanide leaching is improved.
Ultrasonic intensified leaching method (PUL) refers to the introduction of ultrasonic during the leaching process. Ultrasonic can play an enhanced leaching effect, mainly due to the formation of cavitation zone in the liquid phase under the action of specific acoustic waves, so that the pressure reaches 101.3 MPa, temperature and time change rate of 109 k / s, and accompanied by a strong impact. The local erosion, destruction or removal of the solid surface affects the leaching of the film and the passivation film generated in the chemical reaction.
The above are several methods on how to intensify the cyanide leaching effect of gold ore. Intensified gold cyanide leaching technology can effectively increase the cyano-gold reaction rate, increase the gold recovery rate and reduce the amount of sodium cyanide. For gold cyanidation, the methods used vary from one gold ore type to another. It is recommended to conduct beneficiation tests first, understand the nature and characteristics of the ore, and select the appropriate process flow with comprehensive consideration of the investment budget, in order to obtain the ideal separation index and economic benefits.
Gold, precious forever but especially lately, is a tricky metal. Bound up in consumer electronics, jewelry and the ores that it comes from, gold is difficult to extract, and most modern processes do it with a highly toxic combination of cyanide salts. The cyanide leaches the gold out, but the cyanide can seep into the ground, causing environmental problems and posing threats to human health.
Researchers at Northwestern University recently stumbled upon a solution that uses cornstarch instead. It involves some complex chemistry, but its cheap, biologically friendly and nasty-ingredient-free.
Led by Sir Fraser Stoddart, a chemistry professor at Northwestern, the team discovered this method by accident when looking for something else. A postdoc named Zhichang Liu was trying to make three-dimensional cubes out of gold and starch, aiming to use them as storage containers for gases and small molecules. But a liquid mixture of dissolved gold-bromide salts and a starch-derived sugar didnt form cubes, it formed needles. This was strange, so the team decided to try to replicate it and tested different forms of sugars.
Alpha-cyclodextrin, a cyclic starch fragment with six glucose molecules, is the best way to isolate gold, they found. Zhichang stumbled on a piece of magic for isolating gold from anything in a green way, Stoddart says in a statement. The spontaneous bundle of needles is made of thousands of nanowires, each 1.3 nanometers in diameter, which contain a charged gold atom inside four bromine atoms.
The interaction between the starch fragment and the gold allows the precious metal to be selectively recovered from other materials, including platinum, palladium and others. The researchers already developed a process to isolate gold from scraps, and they hope this will lead to an environmentally friendly, cheap way to recover gold from anything. The research is published in Nature Communications.
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The effect of pyrite, pyrrhotite, chalcopyrite, realgar and arsenopyrite on gold dissolution in cyanide media was investigated. The cyanidation of synthetic gold ores in the presence of various concentrations of sulfides was studied under constant experimental conditions. A mineralogical analysis of the minerals was performed. The leaching kinetics were determined. The negative effect of sulfides on the gold dissolution rate varies with the sulfide mineral and decreases according to the following order: realgar > pyrrhotite > chalcopyrite > pyrite > arsenopyrite. The chemical characterization of gold and sulfide minerals surfaces using X-ray photoelectron spectroscopy (XPS) was undertaken to identify the mechanisms involved. XPS analysis showed that a passivation layer of sulfides, arsenic or iron compounds might form on the gold surface as a result of the dissolution of the sulfide minerals.
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Deschnes, G., Lastra, R. and Fulton, M., 2001, Effect of the mineralogy of sulphide-bearing gold ores on the performance of cyanidation and its control variables, Proc. 33rd Ann. Mtg. Can. Min. Processors, pp. 325338.
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Research scientist, Research scientist, Research scientist, laboratory technician, Mining and Mineral Sciences Laboratories, CANMET, Natural Resources Canada, Ottawa, Ontario, Canada
Deschnes, G., Pratt, A., Riveros, P. et al. Reactions of gold and sulfide minerals in cyanide media. Mining, Metallurgy & Exploration 19, 169177 (2002). https://doi.org/10.1007/BF03403265