JP7031207B2 - Treatment method of waste acid generated in copper smelting - Google Patents

Description

The present invention relates to a method for treating waste acid generated in copper smelting, and in particular, it is possible to adjust the cadmium grade and water content of a starch generated when heavy metals are removed from the waste acid generated by washing the copper smelting exhaust gas with water. Regarding the treatment method of waste acid.

Since the copper smelting exhaust gas generated in the copper smelting process contains sulfurous acid gas (SO ₂ ), it has been conventionally sent to a sulfuric acid factory as a raw material for sulfuric acid, where sulfuric acid is produced by a conversion step and an absorption step. .. In addition to sulfite gas, this copper smelting exhaust gas contains smoke ash and fume of heavy metals such as copper (metal elements heavier than iron), and in order to remove them, wash water was used in the gas refining step before the conversion step. After being washed with water, it is dried.

The washing water used in the gas refining step is continuously or periodically discharged as washing wastewater containing heavy metals. This washing wastewater contains sulfuric acid derived from SO ₃ contained in the copper smelting exhaust gas together with SO ₂ . Therefore, in the treatment of the washing wastewater containing such sulfuric acid (hereinafter referred to as waste acid), it is necessary to treat these sulfuric acids and heavy metals. As a method for treating waste acid as described above, Patent Document 1 describes a technique in which calcium carbonate is added to waste acid to remove sulfuric acid as gypsum, and then sodium hydrosulfide is added to remove heavy metals as sulfide starch. 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 starch.

Japanese Unexamined Patent Publication No. 2004-275895 Japanese Unexamined Patent Publication No. 2015-02103

In recent years, copper smelting factories often process various raw materials containing a large amount of 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 starch. Since sulfide starch is generally treated repeatedly in the copper smelting process, the amount of circulation in the system increases for specific heavy metals, and there is concern that it will exceed the treatment capacity of the current waste acid treatment equipment. There is. Further, when the copper smelting process is repeated, water is brought in along with the sulfide starch, so that the cost required for drying the copper smelting step may increase.

The present invention has been made in view of the problems of the above-mentioned conventional waste acid treatment method, and cadmium is repeatedly produced in the smelting process by separating and recovering cadmium from the heavy metals contained in the waste acid. It is an object of the present invention to provide a waste acid treatment method capable of reducing the amount of cadmium circulating in the system and reducing the amount of water brought in during the above repetition to reduce the drying cost.

As a result of repeated studies to achieve the above object, the present inventors produced first and second sulfurized starches by adding a sulfurizing agent to waste acid in two portions, respectively. It has been found that the cadmium grade and water content of the second sulfurized starch can be adjusted by adjusting the sulfurization reaction conditions in the sulfurization reaction step of producing the second sulfurized starch, and the present invention has been completed.

That is, the first waste acid treatment method according to the present invention comprises waste acids containing copper, arsenic, cadmium, zinc and sulfuric acid as heavy metals discharged during the washing treatment of exhaust gas generated in the copper smelting process. After adding a sulfurizing agent and selectively sulfurizing copper and arsenic among the heavy metals under the condition of redox potential of 80 mV or more and 160 mV or less (based on silver-silver chloride electrode), the first clarified solution is obtained from the obtained slurry. After the first sulfurization step in which the first sulfurized starch obtained by solid-liquid separation is repeated in the copper smelting step, and a calcium-based neutralizing agent is added to the first clarified solution to generate gypsum from the sulfuric acid content. , A gypsum manufacturing process in which the slurry containing this gypsum is solid-liquid separated into gypsum and gypsum final solution, and the redox potential of -10 mV or more + 10 mV or less (silver-silver chloride ) by adding a sulfurizing agent to the gypsum final solution. It has a second sulfurization step of recovering cadmium as a second sulfurized starch by solid-liquid separation of the second clear liquid from the obtained slurry after sulfurization under the conditions of the electrode standard) . When the cadmium grade of the disulfide starch is less than 40% by mass, the amount of the sulfurizing agent added is increased in the second sulfurization step, and when the cadmium grade of the second sulfurized starch is more than 50% by mass, the second sulfurization is performed. It is characterized in that the amount of the sulfurizing agent added is reduced in the process.

In addition, the second waste acid treatment method according to the present invention comprises waste acids containing copper, arsenic, cadmium, zinc and sulfuric acid as heavy metals discharged during the washing treatment of exhaust gas generated in the copper smelting process. After adding a sulfurizing agent and selectively sulfurizing copper and arsenic among the heavy metals under the condition of redox potential of 80 mV or more and 160 mV or less (based on silver-silver chloride electrode), the first clarified solution is obtained from the obtained slurry. After the first sulfurization step in which the first sulfurized starch obtained by solid-liquid separation is repeated in the copper smelting step, and a calcium-based neutralizing agent is added to the first clarified solution to generate gypsum from the sulfuric acid content. , A gypsum manufacturing process in which the slurry containing this gypsum is solid-liquid separated into gypsum and gypsum final solution, and the redox potential of -10 mV or more + 10 mV or less (silver-silver chloride ) by adding a sulfurizing agent to the gypsum final solution. It has a second sulfurization step of recovering cadmium as a second sulfurized starch by solid-liquid separation of the second clear liquid from the obtained slurry after sulfurization under the conditions of the electrode standard) . 2. It is characterized in that the water content of the second sulfurized starch is adjusted by the amount of the sulfurizing agent added in the disulfide step.

According to the present invention, cadmium contained in waste acid can be discharged to the outside of the system as a second sulfide starch, so that the amount of cadmium repeated in the copper smelting process can be reduced.

It is a block flow figure which shows a specific example of the waste acid treatment method which concerns on this invention.

Hereinafter, a specific example of the method for 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 factory, copper smelting exhaust gas containing sulfite gas, which is a raw material for sulfuric acid, is generated, so that gas purification is performed. In step 2, the sulfite gas is washed by a water washing treatment in which the washing water is brought into contact with the copper smelting exhaust gas, and then sent to the sulfuric acid manufacturing step 3 to produce sulfuric acid.

A sulfurizing agent is first added to the waste acid containing heavy metals and sulfuric acid discharged during the washing treatment of the copper smelting exhaust gas to generate sulfurized starch from the heavy metals in the first sulfurization step 4, and then solidified. The sulfide starch is removed by liquid separation. Next, a calcium-based neutralizing agent is added to the treatment liquid after the sulfurized starch is removed in the first sulfurization step 4 in the gypsum production step 5, and the sulfuric acid content is recovered as gypsum.

Next, a sulfurizing agent is added again in the second sulfurization step 6 to the treatment liquid after the gypsum is recovered in the gypsum manufacturing step 5 to generate sulfurized starch from the remaining heavy metals, and then solid-liquid separation is performed. The sulfide starch is recovered by. The sulfide starch recovered in the second sulfurization step 6 is treated in the valuable metal recovery step 7 to recover the valuable metals cadmium and zinc, and the treatment liquid separated from the sulfide starch in the second sulfurization step 6 is It is treated in the wastewater treatment step 8.

Each step after the first sulfurization step 4 described above will be specifically described below. In the first sulfurization step 4, the redox potential (ORP) in the silver-silver chloride electrode standard is about 80 mV or more and 160 mV or less by first adding a sulfurizing agent to the waste acid and mixing it in the first sulfurization reaction step 41. Perform sulfurization reaction under the conditions. This makes it possible to selectively convert copper and arsenic contained in waste acid into sulfide starch. As the sulfide agent, a general sulfide agent such as sodium hydrosulfide (sodium hydrogen sulfide) NaHS, hydrogen sulfide H _{2S, 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 starting 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 sulfurized starch produced in the first sulfurization reaction step 41 is improved. As a result, the cadmium grade of the sulfide starch produced in the second sulfurization reaction step described later is lowered. On the contrary, 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 manufacturing step 5 of the subsequent step increases.

Next, in the first solid-liquid separation step 42, the sulfurized starch is separated into the first slurry containing the sulfurized starch obtained in the first sulfurization reaction step 41 by a solid-liquid separation means such as a thickener. A rich first concentrate and a first clarified solution are obtained. Since the first concentrate containing the sulfide starch obtained in the first solid-liquid separation step 42 contains copper, the copper smelting step as the first sulfide starch after reducing the water content in the first dehydration step 43. Repeat to 1. In the first dehydration step 43 described above, good dehydration can be achieved by using a general dehydrator such as a filter press, a vacuum filter, a belt press, and a centrifuge.

On the other hand, the first clarified liquid obtained in the first solid-liquid separation step 43 is treated as a gypsum starting liquid in the gypsum manufacturing step 5. In the gypsum manufacturing step 5, for example, a 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 contained in the gypsum starting solution can be precipitated as gypsum. .. The gypsum can be recovered by solid-liquid separating the slurry containing the gypsum with a solid-liquid separating means such as a filter press or a centrifuge. As the above-mentioned calcium-based neutralizing agent, it is preferable to use pulverized calcium carbonate (limestone), calcium hydroxide, calcium oxide or the like from the viewpoint of cost.

The gypsum final liquid from which the sulfuric acid content has been removed by the solid-liquid separation in the gypsum manufacturing step 5 is then treated in the second sulfurization step 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 hydroxide or hydrogen sulfide is added and mixed as a sulfurizing agent with the final solution of gypsum, and the redox potential based on the silver-silver chloride electrode is about -10 mV or more + 10 mV. The sulfurization reaction is carried out under the following conditions, more preferably 0 mV or more and +10 mV or less to obtain a second slurry containing a sulfurized starch.

When the redox potential is less than -10 mV, the zinc grade in the sulfurized starch produced in the second sulfurization reaction step 61 may be increased, and as a result, the cadmium grade in the sulfurized starch may be increased. It is not preferable because it decreases. In particular, when the redox potential is less than 0 mV, the amount of the sulfurizing agent added is large, which increases the cost. On the contrary, when this redox potential exceeds +10 mV, the cadmium in the final gypsum solution is less likely to be sulfided, and as a result, some of the cadmium is not removed and is contained in the second clarified solution, and the wastewater treatment step in the subsequent step. It is not preferable because the processing load of 8 increases. That is, the cadmium grade of the sulfurized starch can be adjusted by the amount of the sulfurizing agent added. In the present invention, in the adjustment of the cadmium grade, when the cadmium grade of the second sulfurized starch, which will be described later, is less than 40% by mass, the amount of the sulfurizing agent added is increased in the second sulfurizing step 6, and conversely, the second sulfurized starch is added. When the cadmium grade of the product exceeds 50% by mass, the amount of the sulfurizing agent added is reduced in the second sulfurizing step 6. The cadmium grade and zinc grade referred to in the present invention are masses based on dry matter, with the mass in a dry state being 100%.

The above-mentioned second slurry is then solid-liquid separated in the second solid-liquid separation step 62 to obtain a second concentrate and a second clarified liquid rich in sulfide starch. This second concentrate is recovered as a second sulfide starch after reducing the water content in the second dehydration step 63. On the other hand, the second clarified liquid obtained in the second solid-liquid separation step 62 is treated by a general water treatment method such as activated sludge in the wastewater treatment step 8. In the second solid-liquid separation step 62 and the second dehydration step 63, the same solid-liquid separation means as those in the first solid-liquid separation step 42 and the first dehydration step 43 described above can be used, respectively.

Since the second sulfide starch obtained in the second dehydration step 63 above contains cadmium, which is a valuable metal, cadmium can be recovered by using a known purification method in the valuable metal recovery step 7. In this valuable metal recovery step 7, the higher the cadmium grade and the lower the water content of the second sulfide starch, the lower the purification cost can be. Therefore, in the waste acid treatment method of one specific example of the present invention, the redox potential is adjusted in the second sulfurization reaction step 62 of the second sulfurization step 6 as described above. That is, since the gypsum final solution, which is the initial solution of the second sulfurization step 6, contains almost no copper, arsenic, and sulfuric acid, and cadmium and zinc remain, the second sulfurization reaction step 62. Then, the cadmium grade of the second sulfurized starch can be adjusted by appropriately adjusting the redox potential among the sulfurization reaction conditions.

At that time, the second sulfide starch has a correlation that the higher the cadmium grade, the lower the water content of the second sulfide starch. This correlation is believed to be due to the higher dehydration of cadmium in the second sulfide starch than in other sulfides. By utilizing this correlation, the cadmium grade of the second sulfide starch can be adjusted to be higher, and as a result, the water content of the second sulfide starch can be adjusted to be lower. This means that the water content of the second sulfurized starch is adjusted by the amount of the sulfurizing agent added. Specifically, as described above, in the second sulfurization step 6, the cadmium grade of the second sulfurized starch is adjusted to a relatively high grade of about 40 to 50% by mass (dry matter standard) by adjusting the addition amount of the sulfurizing agent. Therefore, the water content of the second sulfide starch 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 (wetting standard).

Waste acid of pH 0 containing heavy metals and sulfuric acid discharged from the copper smelting plant was treated according to the flow shown in FIG. Specifically, the waste acid is supplied to the reaction vessel at a flow rate of 300 L / min, and sodium sulfide having a concentration of 25% by mass is added thereto so that the redox potential is 150 mV (based on the silver-silver chloride electrode). The first slurry containing the first sulfurized starch was obtained (first sulfurization reaction step 41). This first slurry was introduced into a thickener for solid-liquid separation, and the first concentrate that had been settled and concentrated while overflowing the first clear liquid was extracted from the bottom (first solid-liquid separation step 42). The first sulfide starch was recovered by solid-liquid separation of the first concentrate with a filter press (first dehydration step 43). Calcium carbonate was added to the above-mentioned first clarification solution to adjust the pH to 2.3, and gypsum was precipitated (gypsum manufacturing step 5). The slurry containing this gypsum was solid-liquid separated into gypsum and gypsum final solution.

The above gypsum final solution was received in a reaction tank, and sodium hydrosulfide was added thereto to obtain a second slurry containing a second sulfurized starch (second sulfurized reaction step 61). The redox potential of the second slurry was +20 to +30 mV (based on the silver-silver chloride electrode). This second slurry was introduced into a thickener for solid-liquid separation, and the second concentrate that had been settled and concentrated while overflowing the second clear liquid was extracted from the bottom (second solid-liquid separation step 62). The second sulfide starch of Sample 1 was recovered by solid-liquid separation of this second concentrate with a filter press (second dehydration step 63).

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

Subsequently, the sample was the same as in the case of sample 4 except that the addition of sodium hydrosulfide was less than that of sample 4 and the redox potential of the second slurry was stabilized at 0 mV (based on the silver-silver chloride electrode). The second sulfide starch of No. 5 was recovered. The cadmium grade and water content of the second sulfide starch of these samples 1 to 5 were measured based on ICP emission spectroscopy and dry weight loss method, 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 amount of the sulfurizing agent added to lower the redox potential, the cadmium grade can be improved and the water content can be lowered, and conversely, the sulfurizing agent can be used. By reducing the amount added and increasing the redox potential, the cadmium grade can be lowered and the water content can be increased. That is, it can be seen that the cadmium grade and water content of the second sulfurized starch can be indirectly adjusted within a desired range by adjusting the amount of the sulfurizing agent added in the second sulfurization reaction step. Further, it can be seen that the water content can be suppressed to about 30 to 40% by mass by setting the cadmium grade of the second sulfide starch to about 40 to 50% by mass.

1 Copper smelting process 2 Gas refining process 3 Sulfuric acid production process 4 1st sulphurization process 5 Gypsum production process 6 2nd sulphurization process 7 Valuable metal recovery process 8 Wastewater treatment process 41 1st sulphurization reaction process 42 1st solid-liquid separation process 43rd 1 Dewatering step 61 Second sulfide reaction step 62 Second solid-liquid separation step 63 Second dewatering step

Claims (3)

Redox potential 80 mV or more and 160 mV or less ( silver- The first sulfurized starch obtained by selectively sulfurizing copper and arsenic among the heavy metals under the conditions of silver chloride electrode standard) and then solid-liquid separating the first clarification solution from the obtained slurry is made of the copper. After the first sulfurization step repeated in the smelting step and the calcium-based neutralizing agent being added to the first clarification solution to generate gypsum from the sulfuric acid, the slurry containing the gypsum is solid-liquid separated into gypsum and gypsum final solution. From the slurry obtained after sulfurizing the remaining heavy metals by adding a sulfurizing agent to the gypsum final solution under the conditions of redox potential of -10 mV or more and +10 mV or less (based on silver-silver chloride electrode). It has a second sulfurization step of recovering cadmium as a second sulfurized starch by solid-liquid separation of the second clear liquid .
When the cadmium grade of the second sulfurized starch is less than 40% by mass, the amount of the sulfurizing agent added is increased in the second sulfurizing step, and when the cadmium grade of the second sulfurized starch exceeds 50% by mass, the second sulfurizing agent is added. 2. A method for treating waste acid, which comprises reducing the amount of the sulfurizing agent added in the sulfurization step. Redox potential 80 mV or more and 160 mV or less ( silver- The first sulfurized starch obtained by selectively sulfurizing copper and arsenic among the heavy metals under the conditions of silver chloride electrode standard) and then solid-liquid separating the first clarification solution from the obtained slurry is made of the copper. After the first sulfurization step repeated in the smelting step and the calcium-based neutralizing agent being added to the first clarification solution to generate gypsum from the sulfuric acid, the slurry containing the gypsum is solid-liquid separated into gypsum and gypsum final solution. From the slurry obtained after sulfurizing the remaining heavy metals by adding a sulfurizing agent to the gypsum final solution under the conditions of redox potential of -10 mV or more and +10 mV or less (based on silver-silver chloride electrode). It has a second sulfurization step of recovering cadmium as a second sulfurized starch by solid-liquid separation of the second clear liquid .
A method for treating waste acid, which comprises adjusting the water content of the second sulfurized starch according to the amount of the sulfurizing agent added in the second sulfurizing step. The method for treating waste acid according to claim 1 or 2 , wherein the second sulfide starch has a cadmium grade of 40 to 50% by mass and a water content of 30 to 40% by mass.

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