Cyanidation wastewater treatment - alkali chlorine process p
2020-10-13 10:25Introduction：Cyanidation wastewater treatment - alkali chlorine process practice In actual production, various plants and mines have evolved different process configurations and auxiliary facilities according to their own characteristics.For example, t
Cyanidation wastewater treatment - alkali chlorine process practice
In actual production, various plants and mines have evolved different process configurations and auxiliary facilities according to their own characteristics.For example, the original design production process of zhangjiakou Gold Mine is shown in figure 6.1-2.The production process after the transformation is shown in figure 6.1-3.The original design production process had problems of unstable operation, pollution of operating environment, corrosion equipment, high chlorine consumption and high cost.In view of these problems, the following technical improvements were made in the mine:
⑵Change the way to add chlorine and prepare calcium hypochlorite solution by adding chlorine from four points to slurry and one point to limestone.
⑶The cyanogen tailings are injected directly into the second reaction tank, and chlorine gas is added into the slurry in the form of calcium hypochlorite solution.
⑷Eliminate chlorine gas washing equipment, do not consume sodium hydroxide, reduce the cost of operation and maintenance;
⑸The control loop is reduced from 6 sets to 2 sets
After the above transformation, obvious economic benefits have been obtained.The annual sewage treatment cost was reduced to 640,000 yuan.At the same time, this successful transformation promoted the development of alkali chlorine process. In particular, chlorine gas was first absorbed in the lime milk to be prepared into calcium hypochlorite solution, and then the reaction of chlorine oxidation cyanide was conducted to avoid the emission of chlorine gas and hydrogen chloride. Zhangjiakou Gold Mine was the first gold mine in China to use this process.Later, this process was applied in HuaJian Gold Mine and good results were achieved.This process is worthy of comprehensive promotion.
For another example, Jinchangyu Gold Mine initially used bleaching powder to treat cyanide-containing wastewater. In 1972, it changed to alkali chloride process with liquid chlorine as the raw material, and the technological process is shown in figure 6.1-4.It has been proved that the following problems exist in the reform process:
⑴Due to open circuit process, incomplete reaction, low oxidation efficiency, workshop drainage is not up to standard;
⑵Use air blower to adjust the paddle, without mechanical stirring device, a large amount of lime deposition, the pH value is difficult to control and be stable, causing chlorine gas and hydrogen chloride to escape and pollute the operating environment.
⑶The negative pressure of chlorine adding machine is small and the amount of chlorine is insufficient, which affects the treatment effect
Aiming at these problems, since 1979 the sewage treatment process conducted two bold reform in the mine, form the incomplete oxidation under acid condition, under alkaline conditions completely the new technology of oxidation reaction, high removal rate of the reaction is raised, High cyanide removal rate , chlorine consumption of small, low cost, no pollution operating environment, etc.See figure 6.1-5 for the flow chart.
After alkali chlorine treatment, cyanide content can fully meet the industrial wastewater discharge standard (no more than 0.5mg/l), or even meet the standard of drinking water (no more than 0.05mg/l).However, the tailings treated with alkali-chloride process contain relatively high concentration of free chlorine, sometimes up to 50mg/l.When the standard of chlorine content in waste water is high, the tailings must be removed before discharge.Sodium thiohydride (NaHS) was commonly used for chlorine removal.The key technical condition of this process is to control REDOX potential.The chlorine content of treated wastewater can be lower than 0.3mg/l.
If the wastewater contains heavy metal ions and ferrocyanide (Fe(CN)64-) and other substances, activated carbon or resin can be used for adsorption after alkali chloride process.
