JPH0331766B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for removing mercury from burned ore roasted in a roasting furnace by re-roasting it in a shell-and-tube kiln. Most of the ores of non-ferrous metals, including zinc ore, nickel ore, copper ore, lead ore, etc., are sulfide ores, which are usually roasted into oxides to obtain metals as raw materials. Roasting furnace gas containing SO ₂ gas generated during roasting is used to produce sulfuric acid. As the roasting furnace, a rotary kiln or a fluidized fluidized roasting furnace is used. After roasting, the burnt ore is processed according to the respective metal smelting process. In addition, various roasting processes are carried out to convert the ore into a form convenient for further processing. Burnt ore after roasting contains various impurities depending on the raw ore, but it is convenient to separate and remove some of the impurities early in the process in order to simplify the subsequent treatment process. One such impurity is mercury. Mercury, which cannot be removed in a roasting furnace, is traditionally
It was often removed during the sintering process, which is generally carried out as one of the post-processing processes for burnt ore, but it was removed in order to simplify the work in the sintering process or to improve the smelting process. Since the binding process itself has become omitted, it is desirable to remove mercury early in the process. In order to remove mercury from burnt ore, re-roasting, which involves roasting the burnt ore once again, may be considered, but burnt ore generally tends to generate scum, making it difficult to carry out the re-roasting process smoothly. In particular, when roasting is carried out in a fluidized roasting furnace, the lead ore contains both an overflow taken out from the top of the fluidized bed and a carryover that flows out from the top of the furnace together with the exhaust gas and is collected by a cyclone or the like. It is also collected from the roasting furnace,
Mercury is particularly likely to concentrate in the carry over, and when this carry over is re-roasted in the kiln, scum immediately adheres to the inside of the kiln, making continuous operation difficult. As a representative example, explain zinc sintered ore.
Zinc sulfide ore undergoes oxidative torrefaction in a fluidized torrefaction furnace with air blown in from the bottom. Overflow is extracted from the upper end of the fluidized bed through an extraction pipe. Carryover is released from the top of the furnace together with exhaust gas containing SO ₂ . The carryover is collected and recovered using a cyclone, Kottorel dust collector, etc., and the SO ₂ gas is sent to the sulfuric acid production process. Both overflow and carryover are collected as burnt ore. The sintered ore thus obtained was converted into a sintered mass in a sintering furnace and then reduced in an electric distillation furnace, from which metallic zinc was recovered, according to a typical conventional process. Sulfur contained in burnt ore in a sintering furnace,
Impurities such as mercury were removed. In order to simplify the impurity removal operation in the sinter furnace, it is better to remove mercury at a previous stage, which will reduce the burden on the entire process. And most importantly, in recent years, there has been a trend towards eliminating many of the disadvantages associated with the sintering process by omitting the sintering process and charging the sintered ore into granules or briquettes directly into the electric furnace. Proposals are promising to improve the zinc smelting process, which would make it impossible to remove mercury during the sintering process. From this point of view as well, it is desirable to remove mercury at an early stage. Under these circumstances, we investigated the method of removing mercury by re-roasting the burnt ore from the roasting furnace, and found that mercury could be removed efficiently by using a multi-tube kiln as the re-roasting furnace. I found it. Furthermore, it has been found that when S is also removed, mercury can be efficiently removed while minimizing the occurrence of slag. Thus, the present invention provides a process for removing mercury from ores by roasting the mercury-containing ore in a roasting furnace and re-roasting the obtained burned ore in a multi-tubular kiln. Provides a method for removing mercury. When a fluidized torrefaction furnace is used as the torrefaction furnace, the overflow stays at high temperature in the furnace for a relatively long time. Therefore, taking the zinc sintered ore as an example, the sulfur content is at a level of 0.5 to 0.7%. Mercury has also been removed to a level of less than 0.1 ppm, and it accounts for 50-60% of the total burned ore. On the other hand, carryover has a short residence time, so it contains 4-7% sulfur and 0.4-7% sulfur.
It contains 0.8ppm mercury and is also finer than the overflow. For this reason, carry-over tends to cause sagging during re-roasting. The fact that carryovers containing a large amount of mercury are more likely to produce beko is a major obstacle in re-roasting to remove mercury. In order to overcome this,
It has been found that it is good to mix about 5 to 40% of the overflow with the carryover based on the total amount. Therefore, the present invention roasts mercury-containing ore in a fluidized roasting furnace, and converts the obtained overflow burned ore into a carry-over burnt ore with a mercury content of 5 to 40% based on the total amount of burned ore.
To provide a method for removing mercury from ore, characterized in that mercury is removed by mixing 20% of ore and re-roasting the mixed burnt ore in a multi-tubular kiln. The present invention will be specifically explained below. It is well known that various ores are roasted in a roasting furnace such as a roasting kiln, a multistage roasting furnace, a fluidized roasting furnace, etc. in order to convert various ores into a form suitable for the next process after preliminary treatment. Roasted ore contains mercury as an impurity to varying degrees depending on the type of ore.
These mercury must be removed at some stage in the smelting process. Typical examples of ores containing mercury include zinc ore, lead ore, nickel ore, and copper ore. According to the invention, the burnt ore is removed at an early stage of the smelting process by subsequent re-roasting, and a shell-and-tube kiln is used as the re-roasting furnace. A multi-tube kiln is a type of kiln in which a plurality of tubes are arranged circumferentially inside one elongated cylindrical body, and the material to be processed is fed into each tube from one end. The cylindrical body is placed horizontally with a slight incline and rotated during operation. Combustion gas is flowed into the space outside the tube inside the cylindrical main body, and heats the object to be processed inside the tube. The material to be treated is fed into the tubes each time each tube is sequentially rotated and indexed to a fixed supply position. As the cylindrical main body rotates, the material to be treated is fed from one end of the tube, rolls within the tube, receives heating from the surroundings, advances within the tube, and is finally discharged from the end of the tube. A multi-tube kiln has a small amount of exhaust gas in each tube, has excellent uniform heating properties, and is also good in terms of thermal efficiency. The reroasting temperature when only mercury is removed is
The temperature is 400 to 700°C, and the reroasting temperature when S is also removed is 900 to 1000°C. Burnt ore contains many impurities, and if S is also removed at the same time, the low melting point compounds will melt during reroasting and adhere to the reroast furnace wall, which will be the starting point for deposits to accumulate and eventually produces a ring-shaped deposit inside the furnace. Therefore, when burnt ore is reroasted in a normal cylindrical roasting kiln, scum is immediately generated inside the kiln, making continuous operation difficult. Since beko is sticky, a great deal of effort is required to remove it. When burned ore was re-roasted using the multi-tubular kiln, it was surprisingly discovered that the occurrence of scorch was significantly reduced. This seems to be because the multi-tubular roasting furnace has very good uniform heating properties, so that the object to be processed is heated uniformly. Re-roasting is completed in about 5 minutes of transit time through each tube. During re-roasting, the mercury in the burnt ore is removed from the furnace by a carrier gas. Roasting of sulfide ores, typified by zinc ores, is carried out by using a fluidized roasting furnace and forming a fluidized bed with air blown in from the bottom of the furnace, as described above. The roasting temperature is
The temperature is 880 to 1100°C, and after a residence time of about 1.5 hours, the produced sintered ore is extracted from the upper part of the fluidized bed through an extraction pipe as an overflow. At the same time, fine particles of carry over are discharged together with the exhaust gas. The carryover is separated and recovered from the exhaust gas in a cyclone and Kottorell dust collector. Traditionally, overflow and carry over were collected together and sent to the next process.
According to the invention, re-roasting is carried out as described above in order to remove the mercury therefrom. Because the overflow has already been exposed to high temperatures for a relatively long period of time, its mercury content has fallen to less than 0.1 ppm, and there is no need to carry out mercury removal, which is below the permissible level. On the other hand, carryover contains mercury above the permissible level of 0.4 to 0.8 ppm. Therefore, if only the carry-over is re-roasted, the amount of mercury in the entire burnt ore can be reduced to below the allowable limit, but due to the unique properties of the carry-over, even if it is Even if you use a furnace, it is easy to cause rashes. Overflow has relatively coarse particles and impurities have been sufficiently removed, so by mixing overflow with carry overflow,
It has been found that the generation of beko can be avoided during re-roasting in a shell-and-tube kiln. The overflow is mixed at 5-40% of the total overflow+carry over. If it is less than 5%, it is insufficient to prevent the occurrence of curling, and if it exceeds 40%, the carryover processing efficiency will decrease. In particular, when there is a large amount of Kottorel dust, it is desirable to increase the overflow blending ratio. The re-roasted burnt ore is thus mixed with the untreated overflow and sent to the next step. Regarding zinc sinter, the sinter is converted into pellets or briquettes in a molding machine and then charged into an electric distillation furnace together with grain coke. Since mercury and other impurities are removed in the re-roasting process, the reduction process in the electric distillation furnace can be carried out without any problems. Therefore, the present invention makes it possible to simplify the zinc refining process by eliminating the sintering step. Example 1 Burnt ore obtained by oxidative roasting of zinc ore in a rotary kiln was re-roasted in a multi-tube roasting furnace.
Although a small amount of dust adhered to the inside of the pipe, continuous operation was possible by light hammering. Example 2 Zinc sulfide ore was oxidized and roasted in a fluidized roasting furnace. The overflow exited the torrefaction furnace with an average residence time of 1.5 hours and the carry over with an average residence time of 10 seconds. These were made into a mixture of 10 to 30% overflow and 70 to 90% carry over based on the total amount of burnt ore, and were re-roasted in a multi-tubular kiln. There was almost no buildup, and the small amount of deposits could be easily removed by hammering the tube. The carrier gas was flowed in countercurrent and cocurrent. The test results are shown in the table below.

【table】

[Table] When overflow and carry over were mixed, there was almost no occurrence of sagging.
In the case of a single carry-over, a problem occurred immediately. Example 3 When only mercury in zinc sulfide ore is removed, the temperature is 300℃.
With a residence time of 15 minutes, a removal rate of 98% was achieved without the formation of sludge.

Claims (1)

[Claims] 1. Mercury from ore, characterized in that mercury is removed by roasting the mercury-containing ore in a roasting furnace and re-roasting the obtained burnt ore in a multi-tubular kiln. How to remove. 2 Roasting ore containing mercury in a fluidized roasting furnace,
It is characterized by removing mercury by mixing the obtained overflow sintered ore with a carry-over sintered ore in an amount of 5 to 40% based on the total amount of sintered ore, and then re-roasting the mixed sintered ore in a multi-tubular kiln. How to remove mercury from ore.