Cyanide (often refers to sodium and potassium cyanide) are chemical products, mainly used in gold production and electroplating industries, so that these industries generate a large amount of toxic wastewater containing cyanide; at the same time, most of the gold ores are associated there are many valuable elements such as sulfur, zinc-lead-silver-copper, however, many companies tend to focus only on gold recovery of gold and associated elements of recovery is generally low, resulting in a waste of resources. In addition, cyanide is widely used in metallurgy, electroplating, printing and dyeing, household chemicals and agriculture. Cyanide is widely found in various organisms, including photosynthetic bacteria, algae plants and animals. More cyanide comes from human production activities, such as electroplating smelting printing and dyeing wastewater, landfill leachate, cyano-containing chemicals, etc. From the perspective of environmental engineering and bio-safety, we should attach great importance to the detoxification treatment of cyanide-containing wastewater. The consumption of cyanide in production is mainly in the following aspects: (1) Mechanical consumption, such as running, running, etc. (2) When the pH value in the slurry is too low, HCN is generated. (3) Formation of thiosulfate, when a large amount of S 2- is present in the slurry, CNS - is easily formed. (4) Formation of a metal complex, such as a complex with Cu 2 S , ZnS, FeS, etc. in the mineral. Each gram of copper, zinc and iron consumes 2. 7, 3. 0, 5. 26g of sodium cyanide. (5) Adsorption of cyanide by silicate colloid or silica in the slurry. 1 Cyanide hazards It refers to a molecule cyanide compound containing cyano - substance (CN). The cyanide is classified into two major classes, organic cyanide and inorganic cyanide, depending on whether the element or group attached to the cyano group is organic or inorganic. Inorganic cyanide has a wide range of applications and sources, and it is divided into two types according to its nature and composition, namely simple cyanide and complex cyanide. See Table 1 for details. As we all know, most inorganic cyanide is highly toxic, highly toxic, and a very small amount of cyanide will cause humans and animals to die in a short period of time, and will also reduce crop yields. Examples of cyanide-contaminated water bodies causing acute poisoning of fish, livestock and humans have been reported both at home and abroad. 1.1 The impact of cyanide on people Cyanide is more harmful to warm-blooded animals and humans. It is characterized by high toxicity and quick action. CN - Hydrogen cyanide is formed when it enters the human body. Its action is extremely rapid. In the air containing very low concentration (0.005 mg/L) hydrogen cyanide, it will cause headache, discomfort, palpitations and other symptoms in a short time; In high concentrations (> 0.1 mg / L) of hydrogen cyanide in the air can cause people to die in a very short time. The US Environmental Protection Agency (USEPA) proposes that the highest concentrations of cyanide in drinking water and ecological waters are 0.05 mg/L and 0.20 mg/L, respectively. The highest concentration of cyanide in domestic drinking water and industrial discharge wastewater is 0.05mg/L and 0.50mg/L - respectively . 1.2 Cyanide poisoning aquatic organisms Cyanide is very toxic to aquatic organisms. When the cyanide ion concentration is 0.02 to 1. 0 mg / L (within 24 h), the fish will die. At a concentration of 3.4 mg / L, 48 h of water mites were lethal; the maximum allowable concentration of cyanide in plankton and crustaceans was 0.01 mg / L. Microorganisms in water can destroy low concentrations ( < 2 mg / L) of cyanide, making it a simple, non-toxic substance, but it consumes dissolved oxygen in the water, reducing biochemical oxygen demand, reducing digestion, and producing a series of Water quality problem. 1.3 The effect of cyanide on plants When the concentration of cyanide in irrigation water is below 1 mg/L, the growth of wheat and rice is normal. When the concentration is 10 mg/L, the rice begins to suffer. The yield is 78% of the control group, and the damage of wheat is not obvious. The concentration is 50 mg. At / L, both rice and wheat were significantly affected, but the damage to rice was more serious. The yield was only 34.7 % of the control group and 63% of the control group. When the cyanide content was 1 mg/L in hydroponic culture, the growth and development of rice began to be affected. When the concentration was 10 mg/L, the growth of rice was obviously inhibited, and the yield was 50% lower than that of the control group. At 50 mg/L, it was large. Part of the victim was killed, and a few remaining plants could not be fruited. In the land with serious pollution of cyanide-containing wastewater, the yield of fruit trees is reduced and the fruit is reduced. In addition, when rice, wheat and fruit trees are irrigated with cyanide-containing wastewater, the fruit will contain a certain amount of cyanide. 2 Process mineralogy of cyanide tailings The cyanide tailings are tailings obtained by pressure filtration of flotation gold concentrate by cyanidation. Due to the nature of the ore and the gold extraction process, the content of valuable metals and minerals in the tailings is also different. . The main metal minerals in cyanide tailings are sulfides: mainly pyrite, followed by chalcopyrite, a small amount of galena, sphalerite, etc.; gangue minerals are mainly quartz , a small amount of chlorite, mica , long Stone , kaolin stone, etc. The relative content of minerals is shown in Table 2. It can be seen from Table 2 that the main copper mineral in the cyanide tailings is chalcopyrite, so copper can be recovered by conventional flotation. Since the content of sphalerite and galena is small and the content of pyrite is the largest, it is considered to recover copper and sulfur. Some cyanide tailings main common features: very small mineral grain size, clay serious; more complex mineral composition; containing a certain amount of CN - and part of the drug residue, the influence due to the above factors, a portion of mineral cyanide tailings The floatability is greatly reduced, and it is difficult to recover valuable elements. The recovery of metals from cyanide tailings is different from the recovery of metals from ore. 1) After the gold concentrate is re-grinded and agitated for a long time, the mineral particle size is very fine (-0.045mm particle size reaches 95%, even finer, larger than the surface area, showing a colloidal dispersion system, resulting in floating It is difficult to choose separation. 2) Metallic minerals are severely over-grinded, and some metal minerals are strongly inhibited by excessive oxidation during cyanidation and are difficult to activate. 3) A large amount of shale silicate minerals and cyanide in the pulp will deteriorate the flotation process and affect the grade and recovery rate of the concentrate. 3 cyanide treatment There are many methods for treating cyanide-containing wastewater, including alkali chloride method, acid recovery method, sulfur dioxide-air oxidation method, electrochemical method, activated carbon adsorption catalytic oxidation method, peroxide oxidation method, ferrous sulfide method, biochemical method, ion Exchange method, natural purification method, ozone oxidation method, emulsion membrane method, and pressurized hydrolysis method. The following is a summary of the main treatment methods for cyanide and cyanide tailings. 3.1 Chemical treatment 3.1.1 alkaline chlorination The alkali chlorination process treats high concentrations of cyanide, the treatment effect is very remarkable, and the processing equipment is simple and easy to operate. Good results can be achieved in both small batch processing and large scale processing. This method has achieved very good results in the application of waste cyanide for enterprises and institutions. The reaction principle is as follows: Under alkaline conditions, the bleaching powder [mainly composed of calcium hypochlorite Ca(ClO) 2 ] is used to oxidize CN- in the solution to extremely weak CNO - , CNO - which is further oxidized to non-toxic Carbon dioxide and nitrogen. Its reaction formula is: ClO - + CN - + H 2 O → ClCN + 2OH - ClCN + 2OH → NCO - + Cl - + H 2 O 2NCO - + 3ClO - + H 2 O → 3Cl - + N 2 ↑ + 2CO 2 ↑ + 2OH - First, add sodium hydroxide to a container filled with water, adjust the pH of the aqueous solution to 11 to 12, then add the waste cyanide to the pH-adjusted aqueous solution, and gently stir to completely dissolve. Add the industrial bleaching powder and continue to stir gently to facilitate the reaction. During the reaction, cyanide is first oxidized to cyanate, and the toxicity of cyanate is only 1 毒性 of the toxicity of cyanide. The cyanate continues to oxidize and eventually oxidizes completely to carbon dioxide and nitrogen. 3.1.2 3.2 Biological treatment Microbial degradation of cyanide biochemical process has four main kinds of ways: hydrolysis, oxidation, reduction and substitution -. Among them, hydrolysis and oxidation are dominant. 3.3 Comprehensive recovery Solomo nson LP. 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