JP2019063781A - Treatment method of waste acid generated in copper smelting - Google Patents

Abstract

To provide a method of treating waste acid capable of reducing the amount of cadmium repeated in the smelting process and reducing the amount of water carried in to reduce the drying cost.SOLUTION: The method of treating waste acid includes: a first sulfurization step of carrying out solid-liquid separation into the first sulfurized sediment and the first clear liquid after adding a sulfurizing agent to a waste acid containing a heavy metal and a sulfuric acid component, and then sulfidizing the heavy metal; a gypsum production step of carrying out solid-liquid separation into gypsum and gypsum final solution after adding a calcium-based neutralizing agent to the first clear liquid and then producing gypsum from the sulfuric acid; and a second sulfurization step of carrying out solid-liquid separation into a second sulfurized precipitate containing cadmium and a second clear liquid after adding a sulfurizing agent to the gypsum final solution and sulfidizing remaining heavy metal. When the cadmium grade of the second sulfurized precipitate is less than 40 mass%, the addition amount of the sulfurizing agent is increased in the second sulfurization step, and when the cadmium grade of the second sulfidation precipitate exceeds 50 mass%, the amount of the sulfurizing agent is decreased in the second sulfurization step.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for treating waste acid generated in copper smelting, and in particular, it is possible to adjust cadmium grade and moisture of precipitates generated when removing heavy metals from waste acid generated by water washing treatment of copper smelting waste gas It relates to a method of treating waste acid.

Since copper smelting waste gas generated in the copper smelting process contains sulfur dioxide gas (SO ₂ ), it has been conventionally sent to a sulfuric acid plant as a raw material for sulfuric acid, where sulfuric acid is produced by conversion and absorption steps. . This copper smelting exhaust gas contains smoke ash and fume of heavy metals such as copper (metal elements heavier than iron) in addition to sulfur dioxide gas, and for the removal thereof, washing water is used in the gas purification step prior to the conversion step. After washing with water, drying is performed.

The washing water used in the gas purification step is discharged continuously or periodically as washing waste containing heavy metals. The cleaning wastewater contains a sulfuric acid component derived from SO ₃ which is contained together with SO _{2 in the} copper smelting exhaust gas. For this reason, in the treatment of the washing waste water containing such a sulfuric acid (hereinafter referred to as waste acid), it is necessary to treat the sulfuric acid and the heavy metal. As a processing method of the above-mentioned waste acid, after adding calcium carbonate to waste acid and removing sulfuric acid as gypsum in patent documents 1 technology which adds sodium hydrosulfide and removes heavy metal as sulfide deposit Is disclosed. Further, Patent Document 2 discloses a technique of adding sodium hydrosulfide to waste acid in two steps to remove heavy metals as sulfide precipitates.

JP 2004-275895 A Unexamined-Japanese-Patent No. 2015-020103

  BACKGROUND ART In recent years, copper smelters have increasingly treated various raw materials containing many impurities. Along with this, the proportion of heavy metals other than copper such as arsenic, cadmium and zinc tends to increase in the above-mentioned sulfide deposits. Since sulfide precipitates are generally treated repeatedly in the copper smelting process, the circulation amount in the system will increase for certain heavy metals, and there is concern that the processing capacity of the present waste acid processing equipment will be exceeded. There is. Furthermore, when the process is repeated in the copper smelting process, water is carried along with the sulfide deposits, which may increase the cost required for the drying.

  The present invention has been made in view of the problems encountered in the above-described conventional waste acid treatment method, and the cadmium contained in the waste acid is separated and recovered from the heavy metals contained in the waste acid to repeat cadmium in the smelting process. It is an object of the present invention to provide a method for treating waste acid capable of reducing the amount of cadmium circulating in the system and reducing the amount of water brought in at the time of the above repetition to reduce the drying cost.

  As a result of investigations to achieve the above object, the present inventors separately generate the first and second sulfide deposits by adding the sulfiding agent in two times to the waste acid. It has been found that the cadmium grade and water content of the second sulfurized precipitate can be adjusted by adjusting the sulfurization reaction conditions in the sulfurization reaction step for producing the second sulfurized precipitate, and the present invention has been completed.

  That is, according to the first waste acid treatment method of the present invention, after a sulfiding agent is added to the waste acid containing heavy metal and sulfuric acid component discharged during the water-washing treatment of copper smelting exhaust gas to sulfide the heavy metal A first sulfiding step of solid-liquid separating the obtained slurry into a first sulfide precipitate and a first clear liquid, and adding a calcium-based neutralizing agent to the first clear liquid to form gypsum from the sulfuric acid component And a gypsum production step of solid-liquid separating the slurry containing gypsum into gypsum and gypsum final solution, and adding a sulfiding agent to the gypsum final solution to sulfidize the remaining heavy metal, the obtained slurry is then cadmium And a second sulfurizing step of solid-liquid separation into a second sulfurous residue and a second clear liquid, and the cadmium content of the second sulfurization residue is less than 40% by mass in the second sulfurizing step. Cadmium grade of the second sulfide deposit is 5 by increasing the addition amount of the sulfiding agent If greater than percent by weight is characterized by reducing the amount of the sulfurizing agent in a second sulfurization step.

  Further, in the second waste acid treatment method according to the present invention, after a sulfurizing agent is added to a waste acid containing heavy metal and a sulfuric acid component discharged during water washing treatment of copper smelting exhaust gas to sulfide the heavy metal A first sulfiding step of solid-liquid separating the obtained slurry into a first sulfide precipitate and a first clear liquid, and adding a calcium-based neutralizing agent to the first clear liquid to form gypsum from the sulfuric acid component And a gypsum production step of solid-liquid separating the slurry containing gypsum into gypsum and gypsum final solution, and adding a sulfiding agent to the gypsum final solution to sulfidize the remaining heavy metal, the obtained slurry is then cadmium And a second sulfurizing step for solid-liquid separation into a second sulfurous residue and a second clear liquid, wherein the water content of the second sulfurized residue is determined by the addition amount of the sulfurizing agent in the second sulfurizing step. It is characterized by adjusting.

  According to the present invention, since the cadmium contained in the waste acid can be discharged out of the system as a second sulfide deposit, the amount of cadmium repeated in the copper smelting process can be reduced.

It is a block flow figure showing an example of a disposal method of waste acid concerning the present invention.

  Hereinafter, one specific example of the method of treating waste acid of the present invention will be described. As shown in FIG. 1, in the copper smelting process 1 in which copper concentrate is processed to produce copper in a copper smelting plant, copper smelting waste gas containing sulfur dioxide gas, which is a source of sulfuric acid, is generated. In step 2, after the sulfurous acid gas is washed by washing with water in which washing water is brought into contact with the copper smelting smelting exhaust gas, it is sent to a sulfuric acid production step 3 to produce sulfuric acid.

  First, a sulfurizing agent is added to the waste acid containing heavy metal and sulfuric acid component discharged in the water-washing treatment of the copper smelting waste gas in the first sulfurizing step 4 to form sulfide deposits from heavy metals, The sulfide precipitate is removed by liquid separation. Next, a calcium-based neutralizing agent is added to the treatment liquid after removal of sulfide deposits in the first sulfurization step 4 in the gypsum production step 5 to recover sulfuric acid as gypsum.

  Next, after adding a sulfiding agent again in the second sulfiding step 6 to the treatment liquid after the gypsum is recovered in the above-mentioned gypsum production step 5 to form sulphide from heavy metals remaining, solid-liquid separation The sulfide precipitate is recovered by The sulfide precipitate recovered in the second sulfurization step 6 is treated in the valuable metal recovery step 7 to recover cadmium and zinc as valuable metals, and the treatment liquid separated from the sulfide precipitate in the second sulfurization step 6 is Treat in the wastewater treatment process 8

The steps after the first sulfurizing step 4 will be specifically described below. In the first sulfurization step 4, the oxidation / reduction potential (ORP) on the basis of the silver-silver chloride electrode becomes about 80 mV or more and 160 mV or less by adding and mixing the sulfurizing agent to the waste acid in the first sulfurization reaction step 41 first. Conduct the sulfidation reaction under the conditions. Thus, copper and arsenic contained in the waste acid can be selectively converted into sulfide. As the above-mentioned sulfurizing agent, general sulfurizing agents such as sodium hydrosulfide (sodium hydrogen sulfide) NaHS, hydrogen sulfide H ₂ S, sodium sulfide Na ₂ S and the like can be used. Among these sulfurizing agents, sodium hydrosulfide and hydrogen sulfide are particularly preferable in terms of cost and in that a gypsum start solution having a sulfuric acid concentration suitable for gypsum production can be obtained.

  When the redox potential of the first sulfurization reaction step 41 becomes less than 80 mV, the sulfurization reaction of cadmium in the waste acid proceeds, and the cadmium grade of the sulfide precipitate formed in the above first sulfurization reaction step 41 increases, As a result, the cadmium grade of the sulfide precipitate formed in the second sulfurization reaction step described later is lowered. On the other hand, when the redox potential exceeds 160 mV, the amount of arsenic remaining in the waste acid becomes too large, and the arsenic grade of the gypsum produced in the gypsum production process 5 of the post process increases.

  Next, in the first solid-liquid separation step 42, solid-liquid separation is performed on the first slurry containing the sulfide precipitate obtained in the first sulfurization reaction step 41 by solid-liquid separation means such as thickener, or the like. A rich first concentrate and a first clear solution are obtained. Since the first concentrate containing sulfide residue obtained in the first solid-liquid separation step 42 contains copper, the water content is reduced in the first dehydration step 43, and then the copper smelting step is carried out as the first sulfide residue. Repeat to 1. In the first dewatering step 43 described above, dewatering can be satisfactorily performed by using a general dewatering device such as a filter press, a vacuum type filter, a belt press, a centrifuge or the like.

  On the other hand, the first clarified solution obtained in the first solid-liquid separation step 43 is treated in the gypsum production step 5 as a gypsum initial solution. In the gypsum production step 5, for example, the neutralization reaction is carried out by adding a calcium-based neutralizing agent to the gypsum starting solution received in the neutralization tank, whereby the sulfuric acid component contained in the gypsum starting solution can be precipitated as gypsum. . The gypsum can be recovered by solid-liquid separation of the slurry containing gypsum by solid-liquid separation means such as a filter press or a centrifuge. It is preferable from a cost viewpoint to use what grind | pulverized calcium carbonate (limestone), calcium hydroxide, calcium oxide etc. as said calcium type | system | group neutralizing agent.

  The gypsum final solution from which the sulfuric acid content has been removed by the solid-liquid separation in the above-mentioned gypsum production process 5 is then treated in the second sulfurization process 6. In the second sulfurization step 6, the gypsum final solution is treated in the order of the second sulfurization reaction step 61, the second solid-liquid separation step 62, and the second dehydration step 63. Specifically, in the second sulfurization reaction step 61, sodium hydrosulfide or hydrogen sulfide as a sulfurizing agent is added to the gypsum final solution and mixed, and the redox potential at the silver-silver chloride electrode basis is about -10 mV or more + 10 mV The sulfidation reaction is performed under the following conditions, more preferably under the conditions of 0 mV to 10 mV, to obtain a second slurry containing sulfide precipitate.

  If the above redox potential is less than -10 mV, the zinc grade in the sulfide deposit produced in the second sulfurization reaction step 61 may increase, and as a result, the cadmium grade in the sulfide deposit becomes Unfavorably because it decreases. In particular, if the above-mentioned redox potential is less than 0 mV, the amount of the sulfiding agent to be added increases and the cost increases. Conversely, if this redox potential exceeds +10 mV, the cadmium in the gypsum final solution becomes difficult to be sulfided, and as a result, some of the cadmium is not removed but is contained in the second clear liquid, and the waste water treatment process of the post process This is not preferable because the processing load of 8 is increased. That is, the cadmium grade of the sulfide precipitate can be adjusted by the addition amount of the sulfiding agent. In the present invention, in adjusting the cadmium grade, if the cadmium grade of the second sulfide deposit to be described later is less than 40% by mass, the addition amount of the sulfiding agent is increased in the second sulfiding step 6, and conversely, the second sulfide deposit is When the cadmium grade of the material exceeds 50% by mass, the amount of the sulfiding agent added is reduced in the second sulfiding step 6. In addition, the cadmium grade and the zinc grade in the present invention are dry matter-based masses, with the mass in the dry state being 100%.

  The second slurry is then subjected to solid-liquid separation in a second solid-liquid separation step 62 to obtain a sulfide-rich second concentrate and a second clear liquid. The second concentrate is recovered as a second sulfurized sediment after the water content is reduced in the second dehydration step 63. On the other hand, the second clarified solution obtained in the second solid-liquid separation step 62 described above is treated by a general water treatment method such as activated sludge in the waste water treatment step 8. In the second solid-liquid separation step 62 and the second dehydration step 63, the same solid-liquid separation means as the first solid-liquid separation step 42 and the first dehydration step 43 can be used, respectively.

  Since the second sulfurized sulfide obtained in the second dehydration step 63 contains cadmium which is a valuable metal, cadmium can be recovered using a known purification method in the valuable metal recovery step 7. In this valuable metal recovery step 7, the purification cost can be suppressed as the cadmium grade of the second sulfurized precipitate is higher and the water content is lower. For this reason, in the method for treating waste acid according to one specific example of the present invention, as described above, the redox potential is adjusted in the second sulfurization reaction step 62 of the second sulfurization step 6 described above. That is, since the gypsum final solution corresponding to the start of the second sulfurizing step 6 contains almost no copper, arsenic, and sulfuric acid, and cadmium and zinc remain, the second sulfurizing reaction step 62 is performed. The cadmium grade of the second sulfide precipitate can be adjusted by appropriately adjusting the oxidation-reduction potential of the sulfurization reaction conditions.

  At this time, there is a correlation that the higher the cadmium grade, the lower the proportion of the water content of the second sulfide sulfide. It is believed that this correlation is due to the higher dewaterability of cadmium in the second sulfide precipitate than in the other sulfides. By using this correlation to adjust the cadmium grade of the second sulfide deposit higher, it is possible to adjust the water content of the second sulfide deposit lower as a result. This means that the moisture content of the second sulfide precipitate is adjusted by the addition amount of the sulfiding agent. Specifically, as described above, by adjusting the addition amount of the sulfiding agent in the second sulfiding step 6, the cadmium grade of the second sulphide sulfide is made relatively high grade of about 40 to 50 mass% (dry matter basis) The water content of the second sulfide residue obtained by solid-liquid separation by a pressing method such as a filter press can be indirectly adjusted to a relatively low value of about 30 to 40% by mass (wet basis).

  A pH 0 waste acid containing heavy metals and sulfuric acid discharged from a copper smelting plant was treated along the flow shown in FIG. Specifically, the waste acid is supplied to the reaction tank at a flow rate of 300 L / min, and sodium hydrogen sulfide having a concentration of 25% by mass is added thereto so that the redox potential becomes 150 mV (based on silver-silver chloride electrode) As a result, a first slurry containing the first sulfurized precipitate was obtained (first sulfurization reaction step 41). The first slurry was introduced into a thickener and subjected to solid-liquid separation, and the first concentrate precipitated and concentrated while overflowing the first clear liquid from the top was withdrawn from the bottom (first solid-liquid separation step 42). The first sulfide was separated by solid-liquid separation of the first concentrate with a filter press (first dehydration step 43). Calcium carbonate was added to the above first clarified solution to adjust to pH 2.3, and gypsum was precipitated (gypsum production process 5). The slurry containing this gypsum was solid-liquid separated into gypsum and gypsum final solution.

  The gypsum final solution described above was received in a reaction tank, and sodium hydrogen sulfide was added thereto to obtain a second slurry containing a second sulfide deposit (a second sulfide reaction step 61). The redox potential of the second slurry was +20 to +30 mV (based on silver-silver chloride electrode). The second slurry was introduced into a thickener and subjected to solid-liquid separation, and the second concentrate, which was sediment-concentrated while overflowing the second clear liquid from the top, was withdrawn from the bottom (second solid-liquid separation step 62). The second sulfurized precipitate of sample 1 was recovered by solid-liquid separation of the second concentrate with a filter press (second dehydration step 63).

  Furthermore, secondary sulfide precipitates of Samples 2 to 4 were recovered in the same manner as in the case of Sample 1 except that the reduction potential of the second sulfurization reaction step 61 was decreased by increasing the amount of sodium hydrogen sulfide. As the amount of sodium hydrogen sulfide increased, the redox potentials of Samples 2, 3 and 4 gradually decreased. Sample 2 was obtained when the oxidation reduction potential of the second slurry was stabilized at +10 mV (based on a silver-silver chloride electrode).

  Subsequently, a sample was prepared in the same manner as in the case of the above sample 4 except that the addition of sodium hydrogen sulfide was restrained more than the sample 4 and the redox potential of the second slurry was stabilized at 0 mV (silver-silver chloride electrode reference). The second sulfurized sediment of 5 was recovered. The cadmium grade and water content of the second sulfurized precipitates of these samples 1 to 5 were measured based on ICP emission spectroscopy and loss on drying, respectively. The results are shown in Table 1 below.

  As can be seen from Table 1 above, in the second sulfurization reaction step, by increasing the addition amount of the sulfurizing agent and decreasing the redox potential, it is possible to increase the cadmium grade and to lower the water content, By reducing the amount added and raising the redox potential, it is possible to lower the grade of cadmium and to increase the water content. That is, it is understood that by adjusting the addition amount of the sulfiding agent in the second sulfidation reaction step, it is possible to indirectly adjust the cadmium grade and the water content of the second sulphide sulfide within a desired range. Moreover, it turns out that the moisture content can be restrained to about 30-40 mass% by making the cadmium grade | grade of a 2nd sulfide deposit about 40-50 mass%.

1 Copper Smelting Step 2 Gas Purification Step 3 Sulfuric Acid Production Step 4 First Sulfurization Step 5 Gypsum Production Step 6 Second Sulfurization Step 7 Valuable Metal Recovery Step 8 Waste Water Treatment Step 41 First Sulfurization Reaction Step 42 First Solid-Liquid Separation Step 43 First Step 1Dehydration process 61 Second sulfurization reaction process 62 Second solid-liquid separation process 63 Second dehydration process

Claims (4)

After the sulfiding agent is added to the waste acid containing heavy metal and sulfuric acid component discharged in the water-washing treatment of copper smelting exhaust gas to sulfide the heavy metal, the obtained slurry is subjected to the first sulfide precipitate and the first clear liquid A first sulfurizing step of solid-liquid separation into a solid solution, and adding a calcium-based neutralizing agent to the first clear liquid to form gypsum from the sulfuric acid, and then making a slurry containing this gypsum into gypsum and gypsum final solution The gypsum production process for liquid separation, and a sulfurizing agent is added to the gypsum final solution to sulfide the remaining heavy metals, and then the obtained slurry is solid-liquid with a second sulfide precipitate containing cadmium and a second clear liquid. And a second sulfurizing step to separate,
When the cadmium grade of the second sulfide deposit is less than 40% by mass, the addition amount of the sulfiding agent is increased in the second sulfiding step, and when the cadmium grade of the second sulfide deposit is more than 50% by mass, A method for treating waste acid, comprising reducing the amount of the sulfurizing agent added in a sulfurizing step. After the sulfiding agent is added to the waste acid containing heavy metal and sulfuric acid component discharged in the water-washing treatment of copper smelting exhaust gas to sulfide the heavy metal, the obtained slurry is subjected to the first sulfide precipitate and the first clear liquid A first sulfurizing step of solid-liquid separation into a solid solution, and adding a calcium-based neutralizing agent to the first clear liquid to form gypsum from the sulfuric acid, and then making a slurry containing this gypsum into gypsum and gypsum final solution The gypsum production process for liquid separation, and a sulfurizing agent is added to the gypsum final solution to sulfide the remaining heavy metals, and then the obtained slurry is solid-liquid with a second sulfide precipitate containing cadmium and a second clear liquid. And a second sulfurizing step to separate,
A method of treating waste acid, comprising adjusting the water content of the second sulfide deposit by the addition amount of the sulfurizing agent in the second sulfurizing step.   The method for treating waste acid according to claim 1 or 2, wherein the redox potential is adjusted to -10 mV or more and +10 mV or less on the basis of a silver-silver chloride electrode.   The waste according to any one of claims 1 to 3, wherein the second sulfide precipitate has a cadmium grade of 40 to 50% by mass and a water content of 30 to 40% by mass. Acid treatment method.

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