Method for removing arsenic in low-concentration mine wastewater by hydrated ferric sulfate

Abstract

The invention discloses a method for removing arsenic in low-concentration mine wastewater by hydrated ferric sulfate. The method comprises the following steps: continuously dropwise adding a solution prepared from hydrated ferric sulfate into the mine wastewater, adjusting the pH value of the solution by using a calcium hydroxide suspension, stirring and reacting at room temperature to stabilize the pH value, then dropwise adding an acid-modified kaolin flocculant, continuously reacting, flocculating and settling, and carrying out solid-liquid separation to obtain filtrate and filter residues. The arsenic concentration in the filtrate is lower than 50 micrograms per liter and reaches the class III standard of the basic project standard limit value of Environmental Quality Standard for Surface Water GB3838-2002, and the filter residue is identified as a class of general industrial solid waste through a toxicity leaching test and is beneficial to stockpiling together with ore dressing tailings. The treatment time is greatly shortened, and the cost is greatly reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of heavy metal pollution control, and specifically relates to a method for removing arsenic from low-concentration mine wastewater by using hydrated ferric sulfate. Background Art

[0003] Arsenic pollutants in mine wastewater mainly exist in the form of As(III) or As(V) oxygen-containing anions. During the mining and beneficiation of gold mines, due to multiple factors such as the continuous improvement of wastewater recycling efficiency and the continuous increase in the amount of beneficiation wastewater, arsenic elements in water bodies such as underground water, beneficiation wastewater, and circulating water in tailings ponds are continuously enriched and their concentrations are significantly increased. The continuous increase in arsenic concentration in circulating water may also have a certain negative impact on beneficiation indicators. Summary of the invention

[0004] The purpose of the present invention is to provide a method for removing arsenic from low-concentration mine wastewater by using hydrated ferric sulfate, which utilizes the characteristics of hydrolysis precipitation, direct adsorption of arsenic ions, and precipitation of ferric arsenate of hydrated ferric sulfate, combined with the strong flocculation characteristics of kaolin modified with sulfuric acid, to achieve efficient removal of low-concentration arsenic from mine wastewater.

[0005] The present invention provides a method for removing arsenic from low-concentration mine wastewater by using hydrated ferric sulfate, comprising the following steps:

[0006] S1. Prepare ferric sulfate solution and acid-modified kaolin flocculant;

[0007] S2. adding the iron sulfate solution obtained in step S1 to the arsenic-containing wastewater, stirring continuously, and then adding a calcium hydroxide suspension to adjust the pH, reacting at room temperature for a preset time to obtain a reaction intermediate solution;

[0008] S3. Add the acid-modified kaolin flocculant obtained in step S1 to the reaction intermediate solution obtained in step S2, continue stirring the reaction, then let it stand for sedimentation, filter, and obtain a precipitate and a solution after arsenic removal.

[0009] Furthermore, in step S1, the concentration of the ferric sulfate solution is 100 g / L.

[0010] The configuration method of the acid-modified kaolin flocculant is:

[0011] The kaolin and 25% sulfuric acid solution are mixed evenly, stirred fully until the mixture becomes a gel, sealed and allowed to stand for 4 to 8 hours, and then placed in a drying oven at 90 to 120° C. for 12 to 24 hours, cooled and crushed to obtain an acid-modified kaolin flocculant.

[0012] Specifically, the usage ratio of 25% sulfuric acid solution to kaolin is 3-5 mL / g.

[0013] Furthermore, in step S2, the arsenic concentration in the arsenic-containing wastewater is 50-200 μg / L.

[0014] The process conditions of the reaction in step S2 are: room temperature, pH 8 to 8.5, reaction time 15 to 25 min, and stirring rate 400 to 800 rpm.

[0015] Furthermore, in step S3, the amount of the acid-modified kaolin flocculant added is 3 to 5 g / m 3 , based on the volume of the reaction system;

[0016] The process conditions of the reaction in step S3 are: room temperature, reaction time of 5 to 10 min, and stirring rate of 400 to 800 rpm.

[0017] The static sedimentation time is 30 to 60 minutes.

[0018] Principle of the present invention:

[0019] The present invention uses hydrated ferric sulfate to adsorb and remove arsenic from wastewater, and uses acid-modified kaolin for flocculation. The Fe(OH)2 and Fe(OH)3 produced by the hydrolysis of ferric sulfate in aqueous solution can react with arsenic compounds and adsorb arsenic in the solution. The main reaction equation is as follows:

[0020] AsO3 3- +Fe 3+ =FeAsO3

[0021] AsO4 3- +Fe 3+ =FeAsO4

[0022] As2O3+2Fe(OH)2=Fe2As2O5+2H2O

[0023] As2O3+2Fe(OH)3=2Fe(AsO2)3+3H2O

[0024] AsO3 3- +Fe(OH)3=FeAsO3+3OH -

[0025] AsO4 3- +Fe(OH)3=FeAsO4+3OH -

[0026] After acid modification, the surface properties of kaolinite change. With the dissolution of effective ions, the internal element phase changes to form particulate matter and soluble matter. Metal ions dissolve and the strength of surface metal oxides weakens. Therefore, acid-modified kaolinite has a good flocculation effect.

[0027] Beneficial effects of the present invention:

[0028] (1) The hydrated ferric sulfate used in the present invention is low in cost and easy to purchase, the entire arsenic removal process is simple, the reaction rate is fast, and the wastewater arsenic removal efficiency is high;

[0029] (2) The acid-modified kaolin flocculant used in the present invention has the advantages of no biological toxicity, strong flocculation effect, low price and wide source;

[0030] (3) The arsenic concentration in the treated aqueous solution is less than 50 μg / L, meeting the Class III standard limit value of the Surface Water Environmental Quality Standard GB3838-2002;

[0031] (4) Arsenic precipitation waste residue is a general industrial solid waste and can be stored in a tailings pond together with mineral processing tailings. DETAILED DESCRIPTION

[0032] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described below in conjunction with various embodiments. The implementation of the present invention includes but is not limited to the following embodiments.

[0033] Example 1

[0034] The composition of the wastewater used in this example is shown in Table 1. The wastewater comes from the underground water tank of the No. 1 mining area of ​​a gold mining enterprise in Jiangxi Province. Except for arsenic, all other indicators meet the standard limit value Class III standard of the "Surface Water Environmental Quality Standard" GB3838-2002.

[0035] Table 11# Composition of underground water tank wastewater in the mining area (μg / L)

[0036] As pH COD Ammonia nitrogen Sulfide Hg Cd 124 8.0 9.0 0.94 Not Detected Not Detected Not Detected

[0037] The method for removing arsenic from wastewater by using hydrated ferric sulfate described in this embodiment comprises the following specific steps:

[0038] (1) preparing an ferric sulfate solution with a mass concentration of 100 g / L using analytically pure hydrated ferric sulfate;

[0039] (2) Mix kaolin and 25% sulfuric acid solution uniformly, wherein the amount ratio of 25% sulfuric acid solution to kaolin is 3 mL / g; stir thoroughly at room temperature until the mixture becomes a gel, seal and let stand for 6 hours, then put into a 100° C. high-temperature drying oven for drying for 24 hours, take out, cool and crush to obtain an acid-modified kaolin flocculant. The composition of the flocculant is shown in Table 2. The main elements are Al, Si, K and S, and these elements mainly exist in the form of their oxides;

[0040] (3) adding the ferric sulfate solution in (1) to the arsenic-containing wastewater solution by continuous dropwise addition, the amount added being 0.6% of the volume of the wastewater (i.e., the amount of hydrated ferric sulfate added being 600 mg / L), and continuously stirring the solution to ensure uniform mixing;

[0041] (4) preparing a 10% suspension of calcium hydroxide and adding it to the mixed solution in (3), and adjusting the pH of the solution to 8-8.5 by controlling the amount of calcium hydroxide added;

[0042] (5) stirring the solution (4) at room temperature for 15 minutes;

[0043] (6) Add 5 g / m 3 Add acid-modified kaolin flocculant in an amount of , and continue stirring and reacting for 5 minutes.

[0044] (7) Filter the solution (6) to separate the precipitate and the arsenic-free solution. The precipitate is sent for leaching toxicity testing, and the arsenic-free solution is analyzed by ICP-MS for residual arsenic concentration (see Table 3).

[0045] Table 2 Main element composition of kaolin flocculant after sulfuric acid modification

[0046] element Al Si K S content(%) 11.2 16.2 1.6 7.2

[0047] It can be seen from Table 3 that the arsenic concentration decreased from 124 μg / L (initial concentration) to 12.1 μg / L, and the arsenic removal rate reached 90.2%.

[0048] Table 3 Arsenic concentration in the filtrate

[0049] Element As Content(μg / L) 12.1

[0050] The toxicity leaching test of the filter residue after arsenic precipitation was carried out according to the sulfuric acid and nitric acid method (HJ / T299) and the horizontal oscillation method (HJ557-2010). The toxicity test results are shown in Table 4.

[0051] Table 4 Toxicity leaching results of filter residue

[0052] Element As(HJ / T299) As(HJ557-2010) Content(mg / L) 0.002 0.00188

[0053] It can be seen from Table 4 that the leaching concentration of As in the waste residue of this embodiment is only about 0.002 mg / L, which is far lower than the maximum allowable emission concentration of 0.5 mg / L in GB8978 "Comprehensive Sewage Discharge Standard", so the waste residue belongs to a general industrial solid waste.

[0054] Example 2

[0055] The composition of the wastewater used in this example is shown in Table 5. The wastewater comes from the tailings pond wastewater in the mining area of ​​a gold mining enterprise in Jiangxi Province.

[0056] Table 5 Tailings pond wastewater composition (μg / L)

[0057] As pH COD Ammonia nitrogen Sulfide Hg Cd 95.7 8.3 6.0 0.70 Not Detected Not Detected Not Detected

[0058] The method for removing arsenic from wastewater by using hydrated ferric sulfate described in this embodiment comprises the following specific steps:

[0059] (1) Prepare an analytically pure hydrated ferric sulfate solution with a mass concentration of 100 g / L.

[0060] (2) Mix kaolin and 25% sulfuric acid solution evenly, wherein the dosage ratio of 25% sulfuric acid solution to kaolin is 4 mL / g; stir thoroughly at room temperature until the mixture becomes a gel, seal and let stand for 6 hours, then place in a 100° C. high-temperature drying oven and dry for 24 hours, take out, cool and crush to obtain an acid-modified kaolin flocculant.

[0061] (3) The ferric sulfate solution in (1) is added to the arsenic-containing wastewater solution by continuous dropwise addition, with the added amount being 0.6% of the wastewater volume (i.e., the added amount of hydrated ferric sulfate is 600 mg / L), and the solution is continuously stirred to ensure uniform mixing.

[0062] (4) Calcium hydroxide is prepared into a 10% suspension and added to the mixed solution in (3), and the pH value of the solution is adjusted to 8-8.5 by controlling the amount of calcium hydroxide added.

[0063] (5) Stir the solution (4) at room temperature for 20 minutes.

[0064] (6) Add 3 g / m 3 Add acid-modified kaolin flocculant in an amount of , and continue stirring and reacting for 5 minutes.

[0065] (7) Filter the solution (6) to separate the precipitate and the arsenic-free solution. The precipitate is sent for leaching toxicity testing, and the arsenic-free solution is analyzed by ICP-MS for residual arsenic concentration (see Table 6).

[0066] Table 6 Arsenic concentration in the filtrate

[0067] Element As Content(μg / L) 0.5

[0068] It can be seen from Table 6 that the arsenic concentration decreased from 95.7 μg / L (initial concentration) to 0.5 μg / L, and the arsenic removal rate reached 99.5%.

[0069] The toxicity leaching test of the filter residue after arsenic precipitation was carried out according to the sulfuric acid and nitric acid method (HJ / T299) and the horizontal oscillation method (HJ557-2010). The toxicity test results are shown in Table 7.

[0070] Table 7 Toxicity leaching results of filter residue

[0071] Element As(HJ / T299) As(HJ557-2010) Content(mg / L) 0.00043 0.00089

[0072] It can be seen from Table 7 that the leaching concentration of As in the filter residue of this embodiment is 0.00043-0.00089 mg / L, which is far lower than the maximum allowable discharge concentration of 0.5 mg / L in GB8978 "Comprehensive Sewage Discharge Standard", so the waste residue belongs to a general industrial solid waste.

[0073] Example 3

[0074] The composition of the wastewater used in this example is shown in Table 8. The wastewater comes from the underground water tank wastewater in the No. 2 mining area of ​​a gold mining enterprise in Jiangxi Province.

[0075] Table 82# Composition of underground water tank wastewater in the mining area (μg / L)

[0076] As pH COD Ammonia nitrogen Sulfide Hg Cd 183 8.8 6.0 1.02 Not Detected Not Detected Not Detected

[0077] The method for removing arsenic from wastewater by using hydrated ferric sulfate described in this embodiment comprises the following specific steps:

[0078] (1) Prepare an analytically pure hydrated ferric sulfate solution with a mass concentration of 100 g / L.

[0079] (2) Mix kaolin and 25% sulfuric acid solution evenly, wherein the amount ratio of 25% sulfuric acid solution to kaolin is 5 mL / g; stir thoroughly at room temperature until the mixture becomes a gel, seal and let stand for 6 hours, then put it in a 100°C high-temperature drying oven and dry it for 24 hours, take it out, cool it, and then crush it to obtain an acid-modified kaolin flocculant.

[0080] (3) The ferric sulfate solution in (1) is added to the arsenic-containing wastewater solution by continuous dropwise addition, with the added amount being 0.6% of the wastewater volume (i.e., the added amount of hydrated ferric sulfate is 600 mg / L), and the solution is continuously stirred to ensure uniform mixing.

[0081] (4) Calcium hydroxide is prepared into a 10% suspension and added to the mixed solution in (3), and the pH value of the solution is adjusted to 8-8.5 by controlling the amount of calcium hydroxide added.

[0082] (5) Stir the solution (4) at room temperature for 25 minutes.

[0083] (6) Add 4 g / m 3 Add acid-modified kaolin flocculant in an amount of , and continue stirring and reacting for 5 minutes.

[0084] (7) Filter the solution (6) to separate the precipitate and the arsenic-free solution. The precipitate is sent for leaching toxicity testing, and the arsenic-free solution is analyzed by ICP-MS for residual arsenic concentration (see Table 9).

[0085] Table 9 Arsenic concentration in filtrate

[0086] Element As Content(μg / L) 1.88

[0087] It can be seen from Table 9 that the arsenic concentration decreased from 183 μg / L (initial concentration) to 1.88 μg / L, and the arsenic removal rate reached 99.0%.

[0088] The toxicity leaching test of the filter residue after arsenic precipitation was carried out according to the sulfuric acid and nitric acid method (HJ / T299) and the horizontal oscillation method (HJ557-2010). The toxicity test results are shown in Table 10.

[0089] Table 10 Toxicity leaching results of filter residue

[0090] Element As(HJ / T299) As(HJ557-2010) Content(mg / L) 0.0018 0.0020

[0091] It can be seen from Table 10 that the leaching concentration of As in this embodiment is only about 0.0018-0.0020 mg / L, which is far lower than the maximum allowable discharge concentration of 0.5 mg / L in GB8978 "Comprehensive Sewage Discharge Standard", so the waste residue belongs to a general industrial solid waste.

Claims

1. A method for removing arsenic from low-concentration mine wastewater by hydrated ferric sulfate, characterized in that: The following steps are involved: S1. Prepare ferric sulfate solution and acid-modified kaolin flocculant; S2. adding the iron sulfate solution obtained in step S1 to the arsenic-containing wastewater, stirring continuously, and then adding a calcium hydroxide suspension to adjust the pH, reacting at room temperature for a preset time to obtain a reaction intermediate solution; S3. Add the acid-modified kaolin flocculant obtained in step S1 to the reaction intermediate solution obtained in step S2, continue stirring the reaction, then let it stand for sedimentation, filter, and obtain a precipitate and a solution after arsenic removal.

2. The method for removing arsenic from low-concentration mine wastewater by hydrated ferric sulfate according to claim 1, characterized in that: In step S1, the concentration of the ferric sulfate solution is 100 g / L.

3. The method for removing arsenic from low-concentration mine wastewater by hydrated ferric sulfate according to claim 1, characterized in that: The configuration method of the acid-modified kaolin flocculant is: The kaolin and 25% sulfuric acid solution are mixed evenly, stirred fully until the mixture becomes a gel, sealed and allowed to stand for 4 to 8 hours, and then placed in a drying oven at 90 to 120° C. for 12 to 24 hours, cooled and crushed to obtain an acid-modified kaolin flocculant.

4. The method for removing arsenic from low-concentration mine wastewater by hydrated ferric sulfate according to claim 3, characterized in that: The dosage ratio of 25% sulfuric acid solution to kaolin is 3-5 mL / g.

5. The method for removing arsenic from low-concentration mine wastewater by hydrated ferric sulfate according to claim 1, characterized in that: In step S2, the arsenic concentration in the arsenic-containing wastewater is 50-200 μg / L.

6. The method for removing arsenic from low-concentration mine wastewater by hydrated ferric sulfate according to claim 1, characterized in that: The process conditions of the reaction in step S2 are: room temperature, pH 8 to 8.5, reaction time 15 to 25 min, and stirring rate 400 to 800 rpm.

7. The method for removing arsenic from low-concentration mine wastewater by hydrated ferric sulfate according to claim 1, characterized in that: In step S3, the amount of the acid-modified kaolin flocculant added is 3 to 5 g / m 3 , based on the volume of the reaction system.

8. The method for removing arsenic from low-concentration mine wastewater by hydrated ferric sulfate according to claim 1, characterized in that: The process conditions of the reaction in step S3 are: room temperature, reaction time of 5 to 10 min, and stirring rate of 400 to 800 rpm.

9. The method for removing arsenic from low-concentration mine wastewater by hydrated ferric sulfate according to claim 1, characterized in that: The static sedimentation time is 30 to 60 minutes.