Method for continuous and simultaneous collection and deposition of mercury from its containing gases
(57) Abstract:The invention can be used for separation of mercury from gases, in particular for the continuous and simultaneous collection and deposition of mercury from mercury-containing gases. The method comprises passing a gas containing mercury through a wash column in which Inuktitut hydrogen sulfide is continuously or periodically in time, coinciding with a rinse solution containing stable in the acidic environment of the complex of mercury (II), for example, [I4Hg]2-or [(SCN)4Hg]2-that does not require the use of additional oxidant. The collection and deposition of mercury, as well as the regeneration solution containing the complex of mercury (II) are performed simultaneously and only in one stage. Achieved simplification of the process, reduced operational costs. 6 C.p. f-crystals, 1 Il. The invention relates to a method of excretion of mercury from gases containing it, and in particular to a method for continuous and simultaneous collection and deposition of mercury contained in these gases, at one stage.There are many processes of extraction, mercury-containing gases, not only on the companies that produce mercury, but also processes such as obtaining chlorine with alkali, about the different minerals with getting SO2and H2SO4or when removing such metals as lead, copper, zinc, etc.Gases with a high content of mercury clean as dry method (using decantation, electrostatically precipitators, and so on), and wet: a flushing and cooling, the use of wet electrostatic precipitators, and so on, but despite these measures, due to the high vapor pressure of mercury gas may contain significant amounts of mercury. For example, the gas is cooled to 30oC may contain up to 30 mg/nm3.As on environmental grounds, if the gases are released into the atmosphere, and prevent contamination of foods produced using these gases, it is necessary to ensure proper cleaning in order to reduce the mercury content to 0.05 mg/nm3.There are several ways to clean these gases.So, in the literature  described the way in which use the filters on solid materials such as coal.In the literature  used the method with washing in certain solutions, which used a process consisting of two stages, one of which is in the collection of mercury by washing in the scrubber (wash number and the oxidation and precipitation of part of the mercury.In the literature [3-5] described a method of purification of the gas generated during firing, in which the oxidation of mercury is carried out with the use of SO2contained in the same gas.Further, in the literature  asserts that the specified process is carried out in two stages using two separated wet electrostatic precipitator wash columns with aqueous solution of thiocyanate and active coal.Known methods described in the literature [3,4,5], applicable only to gases containing SO2.In the present invention, a method of gathering and extraction of mercury contained in flue gases, the gases generated in furnaces sulfate, other gases containing mercury in the gas phase, through direct deposition of mercury in the form of a sulfide of mercury.In accordance with the invention the method, which is carried out only in one stage and in one and the same washing column, includes passing a gas containing mercury through a wash column in which Inuktitut hydrogen sulfide (gas) continuously or periodically in those moments of time that are leaching solution containing a complex of mercury (11), stable in the acidic environment, such as [I4Hd]2-or [(SCN)4Hd]2-and does not require hetenyi the method of separation of Hg from its containing gases, comprising contacting these gases in a single washing column with a solution containing a complex of mercury (11), stable in the acidic environment may contain suspended active carbon, characterized in that the collection and deposition of Hg in the form of mercury sulfide and the regeneration of the complex of mercury (11) being carried out simultaneously by the injection of gaseous H2S specified in the wash column.To achieve good results the temperature of the gas at the entrance of the wash column should not be above the 50oC.In accordance with the invention, the collection and deposition of mercury occurs as a result of several reactions, giving mercury compounds (1), which immediately oxidize and precipitate as sulfide mercury (11).These reactions can be summarized as follows:
Hg0+ [I4Hg]H2--->I2Hg2+ 2HI; (1)
I2Hg2+ 2HI + H2S ---> [I4Hg]H2+ HgS + H2; (2)
Hg0+ [I4Hg]H2+ H2S ---> [I4Hg]H2+ HgS + H2(3)
In the case of thiocyanate as a complexing anion reaction will be the same, but with the replacement of the I-on SCN-.As can be seen from the above reactions, the concentration is necessary to extract the liquid from the wash column for regeneration, as this is required by the known methods.The addition of hydrogen sulfide easy to control, since it is enough to analyze the amount of Hg(II) in solution and to keep it at the original fixed level of concentration.If the complexing agent is used, the anion iodide, the concentration of Hg(II) to be maintained within the range between 0.3 and 1.0 g/l, and if the complexing agent is used, the anion thiocyanate concentration should be from 3 to 10 g/L. it is Possible to work with large concentrations of Hg(II), but this is undesirable, both from a financial point of view, because then you will require a large concentration of complexing anions, and from a practical point of view, as the cleaned gas may be contaminated when removing the wash solution with a high content of mercury.The concentration of complexing anions must be greater than stoichiometric amount, to the formation of the complex of mercury (II) to avoid the conditions under which become stable intermediate compounds of mercury (1).The washing solution should be slightly acidic, and because of its acidity does not change during the course the acid (H2SO4.Despite this, the use of higher acid concentration does not reduce the efficiency of the system.In some cases, when the concentration of mercury in the gas is high, the rearrangement reaction
< / BR>can go faster than the oxidation reaction and deposition (2). In this case, to prevent the departure Hg0you can use activated carbon, which adsorbs Hg0and facilitates its oxidation and precipitation.The method in accordance with the invention is characterized by simplicity and allows you to carry out the whole process in one stage, using only the wash of the column.In order to illustrate the invention in more detail, please refer to the drawing, which shows a diagram of the steps of the method in accordance with the invention.As shown in the drawing, wash the column has an inlet 1 for mercury-containing gas, the injector 2 hydrogen sulfide (H2S (gas) tank 3 containing leaching solution and is supplied to the outlet opening 4 for output of solid substances containing mercury, as well as an inlet opening 5, through which the injected reagents. The wash liquid is served by the pump 6 through the pipe 7, fitted with a valve 8 for oomine column, passes drip separator 11 and it is already free from mercury through the pipeline 12.In comparison with known methods proposed in this invention has the following advantages:
the process occurs in one stage and requires only a single washing of the column, whereas in the known method  assumes the use of two washing columns and wet electrostatic precipitator between the two columns;
gases intended for cleaning, do not necessarily have to contain SO2for oxidation of elemental mercury, as required in the methods described in the literature [3-5] because the present invention is applicable not only to gases, obtained by roasting of sulfide minerals, but also to other types of gases containing mercury;
requires no second stage for regeneration of the solution or the use of additional oxidant, as is necessary in the method .Injection H2S (gas) wash the column itself is the key to the method in accordance with the present invention, since the injection
- does not change the volume of wash liquid because of the added substance is in the gaseous state;
), and supplied hydrogen replenish substances released as a result of oxidation of elemental mercury, and therefore the acidity really remains constant;
- does not change the concentration of the complex of mercury (1), as can be seen from reaction (3).Consequently, there is no need to extract the liquid from the wash column for its regeneration, as required in the literature . You only need to remove the solids content of the precipitated mercury, and to compensate for mechanical losses of reagents. Hydrogen sulfide (H2S (gas) is the only product that is consumed in the reaction, and in very small quantities: 0,17 kg H2S for every 1 kg of purified mercury.The method in accordance with the invention will be described below using examples, which should only be considered as illustrative in respect of the whole of the invention as a whole, and under no circumstances can not be interpreted as limiting in any way the present invention.Example 1. A stream of nitrogen (N2saturated mercury Hg0at a temperature of 20oC (15 mg/Hg01 nm3) with a flow rate of 30 l/h, together with the other stream of nitrogen (N2with the 7 speed is g (II), 3 g/l 1-b 5 g/l H2SO4. These conditions were maintained for 120 h, the exit gas was analyzed, the concentration of mercury was below 0.05 mg/nm3.Example 2. In the wash column, similar to those shown in the drawing, were processed 50000 nm3/h of gas leaving the kiln blende containing 7% SO2and 25 mg/m3Hg0. The gas in the wash column at a temperature of 30oC. Injection of hydrogen sulfide (H2S was 140 nl/h of the Leaching solution contained 8 g/l Hd (II). This gas was used for the production of sulfuric acid, the content of mercury in the acid was below 0.5 ppm. 1. The method of collection and deposition of mercury from its containing gases, including the interaction of these gases in the washing column with a solution containing stable in the acidic environment of the complex of mercury (II), which can be suspended active carbon, characterized in that takes place simultaneously and at one stage the collection and deposition of mercury in the form of mercury sulfide and the regeneration of the complex of mercury (II) only by injection into the wash column of gaseous hydrogen sulfide.2. The method according to p. 1, characterized in that the quantity of hydrogen sulphide injectate, present in the gas.3. The method according to p. 1, characterized in that the quantity of the injected hydrogen sulfide regulate on the basis of the analysis of mercury (II) in aqueous solution.4. The method according to p. 1, characterized in that as anions, forming a complex with mercury, preferably using the thiocyanate anions for the formation of the complex [(SCN)4Hg] 2-or iodine anions for the formation of the complex [I4Hg]2-.5. The method according to p. 1, characterized in that, when a chelating agent for mercury using the thiocyanate anion, the amount of mercury in the solution is chosen at least equal to 3 g/L.6. The method according to p. 1, characterized in that, when a chelating agent for mercury using the iodine anion, the amount of mercury in the solution is chosen at least equal to 0.3 g/L.7. The method according to p. 1, characterized in that one chooses the concentration of anions, forming a complex with Hg (II), which exceeds the stoichiometric quantity necessary for the formation of this complex.
FIELD: production of aluminum in cells with self-fired anodes, possibly processes for cleaning anode gases.
SUBSTANCE: method comprises steps of accumulating anode gases, preliminarily combusting them together with air in burner devices mounted in cells; supplying gas-air mixture after preliminary combustion of anode gases along gas duct to stage of dust and gas trapping and blowing out to atmosphere. Before supplying gas-air mixture from burner devices to stage of dust and gas trapping, it is fed to process for oxidizing roasting; heated up to temperature 800-1100°C and then it is cooled until 230-290°C and heat is used for production needs.
EFFECT: lowered content of carbon, resin and CO in exhaust gases.