Method for treating smelting acid high-concentration iron-containing sewage

Abstract

The present application relates to a kind of smelting acid high concentration iron-containing sewage treatment method, to solve the technical problem of the color of reuse water yellow greenish.The technical scheme is as follows: the acid high concentration iron-containing sewage and lime emulsion tank overflow lime emulsion are discharged into primary reaction tank, stirring, adjust to PH>7, in preparation tank, add trisodium phosphate solid, configure trisodium phosphate solution, transport to oxidation tank, while compressed air is introduced into oxidation tank, the liquid overflow in oxidation tank is discharged into secondary reaction tank, the PH of solution in secondary reaction tank is controlled at 7.8-8.5;The liquid in secondary reaction tank is overflowed to sewage thickener and settled, the underflow is filtered by filter press to produce reuse water, and trisodium phosphate and calcium ion in sewage form calcium phosphate precipitate.The acid high concentration iron-containing sewage treatment process has the advantages of preventing the color of reuse water yellow greenish, reducing the hardness of reuse water, improving the utilization rate of reuse water and the like.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating to a method for treating acidic, high-concentration iron-containing wastewater from smelting. Background Technology

[0002] In the smelting and production of rare and precious metals, the copper precipitation step increases the iron content in the resulting acidic wastewater. Conventional wastewater treatment uses the ferric salt lime method, employing lime slurry to adjust the wastewater pH and ferric salts to flocculate and remove trace amounts of arsenic. However, in actual production, when the ferrous ion content is high, not all precipitates can be formed and oxidized, causing the overall wastewater system to turn green and the reclaimed water to easily revert from clear to yellow. High ferric ion content also easily forms ferric hydroxide colloids under alkaline conditions. These colloid particles are smaller than 0.1 micrometers and cannot be filtered by a filter press, resulting in a dark yellow, gelatinous color in the reclaimed water. This yellowing or greening of the reclaimed water can easily lead to environmental accidents. Furthermore, the addition of large amounts of lime slurry in wastewater treatment increases the hardness of the reclaimed water, reducing its utilization rate. Summary of the Invention

[0003] The purpose of this invention is to solve the above-mentioned technical problems and provide a method for treating acidic, high-concentration iron-containing wastewater from smelting.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0005] A method for treating acidic, high-concentration iron-containing wastewater from smelting includes the following steps:

[0006] Step 1) The acidic, high-concentration iron-containing wastewater and the lime slurry overflowing from the lime slurry tank are discharged together into the primary reaction tank. The neutralization reaction occurs fully through stirring, and the pH value of the wastewater is adjusted to between 7 and 8. After the reaction, the liquid in the primary reaction tank overflows into the oxidation tank.

[0007] Step 2) Add solid trisodium phosphate to the preparation tank to prepare a 10% trisodium phosphate solution. The trisodium phosphate solution is pumped to the oxidation tank to precipitate the ferrous ions enriched in the oxidation tank.

[0008] Step 3) During the process of step 2), compressed air is simultaneously introduced into the oxidation tank to improve the aeration effect. Through aeration oxidation, ferrous hydroxide precipitate is transformed into ferric hydroxide precipitate and some ferric hydroxide colloid.

[0009] Step 4) The liquid in the oxidation tank overflows into the secondary reaction tank. Through stirring, the trisodium phosphate and the residual ferric hydroxide colloid are fully adsorbed, making the ferric hydroxide colloid particles larger, and the pH of the solution in the secondary reaction tank is controlled between 8 and 9.

[0010] Step 5) The liquid in the secondary reaction tank overflows into the sewage thickening tank for sedimentation. The underflow is filtered by a filter press to produce recycled water. Depending on the color of the recycled water, trisodium phosphate solution can be selectively added to the sewage thickening tank to remove colloidal impurities.

[0011] Step 6) Trisodium phosphate reacts with calcium ions in wastewater to form calcium phosphate precipitate, thereby reducing the hardness of the reclaimed water. The reclaimed water is then recycled for the preparation of lime slurry again.

[0012] Furthermore, the stirring time in both steps 1) and 4) is greater than 30 minutes.

[0013] Furthermore, in step 2), the amount of trisodium phosphate added is 1.1-1.3 times the molar amount of iron ions.

[0014] Furthermore, in step 4), the particle size of the colloidal suspension is increased from below 0.1 μm to above 45 μm.

[0015] Furthermore, the specific steps for selectively adding trisodium phosphate solution in step 5) are as follows:

[0016] If the liquid after passing through the filter press is not transparent and appears light yellow, add the prepared trisodium phosphate solution to the thickening tank at a volume ratio of 100:1 for iron-containing wastewater and trisodium phosphate solution, stir for 1 hour, and then filter again.

[0017] If the liquid after passing through the filter press is initially clear, but turns light yellow and becomes less transparent after a while, add the prepared trisodium phosphate solution to the thickening tank at a volume ratio of 100:3 for iron-containing wastewater and trisodium phosphate solution, stir for 1 hour, and then filter again.

[0018] If the liquid after passing through the filter press is initially clear, but turns dark yellow and loses its transparency after a while, add the prepared trisodium phosphate solution to the thickening tank at a volume ratio of 100:5 for iron-containing wastewater and trisodium phosphate solution. Stir for 2 hours and then filter again.

[0019] Furthermore, the hardness of the recycled water in step 6) is ≤50mg / L.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] 1. This invention promotes the formation of ferrous hydroxide precipitate from the ferrous ions enriched in the oxidation tank by adding saturated trisodium phosphate solution, and then oxidizes it into ferric hydroxide in the air, thus avoiding the green color of the wastewater caused by excessive ferrous ions.

[0022] 2. In this invention, iron ions readily generate ferric hydroxide colloids under alkaline conditions, which cannot be filtered by a filter press. Phosphate ions can adsorb the ferric hydroxide colloids, thereby causing them to settle and preventing the wastewater from turning yellow and reverting to its original color.

[0023] 3. The trisodium phosphate of this invention can react with calcium and magnesium ions in wastewater to produce precipitation, which reduces the hardness of the recycled water. The recycled water is then used to prepare lime slurry, which improves the utilization rate of the recycled water.

[0024] 4. The acidic high-concentration iron-containing wastewater treatment process of the present invention has the advantages of preventing the reclaimed water from turning yellow or green, reducing the hardness of the reclaimed water, and improving the utilization rate of the reclaimed water. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the process flow of the present invention;

[0026] Figure 2 The image shows the experimental results obtained from treating iron-containing wastewater according to the example. Detailed Implementation

[0027] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0028] like Figure 1 As shown, a method for treating acidic, high-concentration iron-containing wastewater from smelting includes the following steps:

[0029] Step 1) Discharge the acidic, high-concentration iron-containing wastewater and the lime slurry overflowing from the lime slurry tank into the primary reaction tank. Stir for 1 hour to fully neutralize the wastewater and adjust the pH value of the wastewater to 7.5. After the primary reaction tank has reacted, the liquid overflows into the oxidation tank.

[0030] Step 2) Add solid trisodium phosphate to the preparation tank. The amount of trisodium phosphate added is 1.2 times the molar amount of iron ions. Prepare a 10% trisodium phosphate solution. The trisodium phosphate solution is pumped to the oxidation tank. Trisodium phosphate is a strong base salt and can undergo a double hydrolysis reaction to promote the formation of ferrous hydroxide precipitate from ferrous ions, so that the ferrous ions enriched in the oxidation tank are precipitated.

[0031] Step 3) During the process of step 2), compressed air is simultaneously introduced into the oxidation tank to improve the aeration effect. Sufficient aeration can fully oxidize ferrous hydroxide into ferric hydroxide, reducing the color return of recycled water. Through aeration oxidation, ferrous hydroxide precipitate is transformed into ferric hydroxide precipitate and some ferric hydroxide colloid.

[0032] Step 4) The liquid in the oxidation tank overflows into the secondary reaction tank. During this process, the negatively charged phosphate ions in the trisodium phosphate solution are attracted to the positively charged ions of the ferric hydroxide colloid, which disrupts the stability of the ferric hydroxide colloid and causes the colloidal particles to precipitate. After stirring for 1 hour, the residual phosphate ions in the trisodium phosphate solution promote the precipitation of ferrous iron in the oxidation tank. In the secondary reaction tank, the colloids rapidly aggregate (>45μm) through charge neutralization and bridging. This effect is significantly better than single-stage treatment in the segmented process. The pH of the solution in the secondary reaction tank is controlled at 8.5.

[0033] Step 5) The liquid overflowing from the secondary reaction tank is transferred to the wastewater thickening tank for sedimentation. The underflow is filtered by a filter press to produce recycled water. Depending on the color of the recycled water, trisodium phosphate solution can be selectively added to the wastewater thickening tank to remove colloidal impurities, as detailed below:

[0034] If the liquid after passing through the filter press is not transparent and appears light yellow, add the prepared trisodium phosphate solution to the thickening tank at a volume ratio of 100:1 for iron-containing wastewater and trisodium phosphate solution, stir for 1 hour, and then filter again.

[0035] If the liquid after passing through the filter press is initially clear, but turns light yellow and becomes less transparent after a while, add the prepared trisodium phosphate solution to the thickening tank at a volume ratio of 100:3 for iron-containing wastewater and trisodium phosphate solution, stir for 1 hour, and then filter again.

[0036] If the liquid after passing through the filter press is initially clear, but turns dark yellow and loses its transparency after a while, add the prepared trisodium phosphate solution to the thickening tank at a volume ratio of 100:5 for iron-containing wastewater and trisodium phosphate solution. Stir for 2 hours and then filter again.

[0037] Step 6) Trisodium phosphate reacts with calcium ions in wastewater to form calcium phosphate precipitate, thereby reducing the hardness of the reclaimed water to ≤50mg / L. The reclaimed water is then recycled for the preparation of lime slurry again.

[0038] This method is applicable to acidic wastewater with an iron ion concentration ≥1000 mg / L.

[0039] The stirring time in steps 1) and 4) can also be any value greater than 30 minutes.

[0040] In step 2), the amount of trisodium phosphate added can be any value between 1.1 and 1.3 times the molar amount of iron ions.

[0041] The hardness of the recycled water in step 6) can also be any value ≤50mg / L.

[0042] Regularly test the iron content in wastewater and the hardness of recycled water, and rationally adjust the amount of trisodium phosphate added.

[0043] Table 1. Experimental results of this embodiment

[0044]

[0045] like Figure 2 As shown, after iron-containing wastewater is treated by the method of this embodiment, the resulting water is clear and transparent, and can be reused as recycled water.

Claims

1. A method for treating acidic, high-concentration iron-containing wastewater from smelting, characterized in that, Includes the following steps: Step 1) The acidic, high-concentration iron-containing wastewater and the lime slurry overflowing from the lime slurry tank are discharged together into the primary reaction tank. The neutralization reaction occurs fully through stirring, and the pH value of the wastewater is adjusted to between 7 and 8. After the reaction, the liquid in the primary reaction tank overflows into the oxidation tank. Step 2) Add solid trisodium phosphate to the preparation tank to prepare a 10% trisodium phosphate solution. The trisodium phosphate solution is pumped to the oxidation tank to precipitate the ferrous ions enriched in the oxidation tank. Step 3) During the process of step 2), compressed air is simultaneously introduced into the oxidation tank to improve the aeration effect. Through aeration oxidation, ferrous hydroxide precipitate is transformed into ferric hydroxide precipitate and some ferric hydroxide colloid. Step 4) The liquid in the oxidation tank overflows into the secondary reaction tank. Through stirring, the trisodium phosphate and the residual ferric hydroxide colloid are fully adsorbed, making the ferric hydroxide colloid particles larger, and controlling the pH of the solution in the secondary reaction tank between 8 and 9. Step 5) The liquid overflowing from the secondary reaction tank is transferred to the wastewater thickening tank for sedimentation. The underflow is filtered by a filter press to produce recycled water. Depending on the color of the recycled water, trisodium phosphate solution can be selectively added to the wastewater thickening tank to remove colloidal impurities. The specific steps are as follows: If the liquid after passing through the filter press is not transparent and appears light yellow, add the prepared trisodium phosphate solution to the thickening tank at a volume ratio of 100:1 for iron-containing wastewater and trisodium phosphate solution, stir for 1 hour, and then filter again. If the liquid after passing through the filter press is initially clear, but turns light yellow and becomes less transparent after a while, add the prepared trisodium phosphate solution to the thickening tank at a volume ratio of 100:3 for iron-containing wastewater and trisodium phosphate solution, stir for 1 hour, and then filter again. If the liquid after passing through the filter press is initially clear, but turns dark yellow and loses its transparency after a while, add the prepared trisodium phosphate solution to the thickening tank at a volume ratio of 100:5 for iron-containing wastewater and trisodium phosphate solution, stir for 2 hours, and then filter again. Step 6) Trisodium phosphate reacts with calcium ions in wastewater to form calcium phosphate precipitate, thereby reducing the hardness of the reclaimed water. The reclaimed water is then recycled for the preparation of lime slurry again.

2. The method for treating high-concentration, acidic iron-containing wastewater from smelting according to claim 1, characterized in that, The stirring time for both steps 1) and 4) is greater than 30 minutes.

3. The method for treating high-concentration, acidic iron-containing wastewater from smelting according to claim 1, characterized in that, In step 2), the amount of trisodium phosphate added is 1.1-1.3 times the molar amount of iron ions.

4. The method for treating high-concentration, acidic iron-containing wastewater from smelting according to claim 1, characterized in that, In step 4), the particle size of the colloidal suspension is increased from below 0.1 μm to above 45 μm.

5. The method for treating high-concentration, acidic iron-containing wastewater from smelting according to claim 1, characterized in that, The hardness of the recycled water in step 6) is ≤50mg / L.

6. The method for treating high-concentration, acidic iron-containing wastewater from smelting according to claim 1, characterized in that, The method is applicable to acidic wastewater with an iron ion concentration ≥1000 mg / L.

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