CN105060431A - Treatment method for high arsenic contaminated acid wastewater - Google Patents

Abstract

The invention discloses a method for treating high-arsenic polluted acid wastewater. This method uses iron salt as a precipitant to control the formation of minerals in high-arsenic acid wastewater to achieve the purpose of directly removing trivalent arsenic without oxidation. The initial As(III) concentration in high-arsenic polluted acid wastewater is 1.5-7.5g/L, the molar ratio of iron and arsenic is controlled to be 1-2, the pH value is 2.8-4.5, the temperature is room temperature 15-30°C, and the stirring speed is 400- 500rpm, the reaction time is more than 10h, the obtained mineral crystal form is good, and the arsenic removal efficiency is more than 90%. The method has the advantages of simple operation, small amount of added medicine, low cost, no need of oxidation, small and relatively stable slag, and the like.

Description

A method for treating high-arsenic polluted acid wastewater

technical field

The invention belongs to the field of environmental engineering, and in particular relates to a method for treating high-arsenic polluted acid wastewater.

Background technique

A large amount of SO ₂ flue gas mixed with heavy metal fumes such as arsenic and mercury produced in the smelting process of non-ferrous metals is mainly used to prepare sulfuric acid. The high-concentration acidic heavy metal wastewater produced by washing and dust removal before flue gas acid production is non-ferrous heavy metal smelting flue gas washing wastewater (referred to as "polluted acid"), which has the characteristics of high acidity, high arsenic content, and complex components. The concentration of sulfuric acid in polluted acid is between 4-11%. It contains arsenic, lead, cadmium, zinc, copper, iron, mercury and other heavy metal ions, as well as high-concentration fluorine, chlorine, sulfate and other anions. The concentration of arsenic pollutants is As high as 0.72-9g/L, far higher than the 0.5ppm discharge standard of arsenic in industrial wastewater, which seriously threatens environmental safety and residents' health.

At present, the commonly used treatment methods for acidic arsenic-containing wastewater are mainly lime neutralization method, iron salt precipitation method and sulfide precipitation method, etc., but all of them have deficiencies. The lime neutralization method needs to add a large amount of calcium hydroxide to neutralize the acid in the wastewater and produce a large amount of neutralization slag. Due to the high solubility of calcium arsenite, the removal effect of trivalent arsenic is not satisfactory; the iron salt method The key to removing arsenic is to oxidize trivalent arsenic by exposing oxygen (air) or adding hydrogen peroxide, which increases the cost and also increases the difficulty of operation; although the sulfide precipitation method can effectively remove trivalent arsenic, the cost is high and in acidic conditions Hydrogen sulfide will be produced under the environment, and the working environment will be seriously affected; although the adsorption method, ion exchange method and membrane separation method developed rapidly in recent years have achieved good arsenic removal effects, these methods are only suitable for dealing with low concentrations and components. Single waste water containing arsenic, and the cost is relatively high.

The invention intends to control the formation of minerals in high-arsenic polluted acid wastewater, so as to realize the purpose of directly removing trivalent arsenic in wastewater without oxidation, and has a good application prospect.

Contents of the invention

Aiming at the characteristics of high arsenic concentration and sulfuric acid concentration in polluted acid wastewater, the present invention provides a method for treating high-arsenic polluted acid wastewater. The method has the advantages of simple operation, less drug dosage, low cost, no need for oxidation, small and relatively stable slag amount and other advantages.

The purpose of the present invention is achieved in the following manner:

A method for treating high-arsenic polluted acid wastewater: adding an iron reagent to the high-arsenic polluted acid wastewater, adjusting the pH value, stirring and reacting, and removing arsenic by solid-liquid separation.

The concentration of trivalent arsenic As(Ⅲ) in the high-arsenic polluted acid wastewater by the above method is 1.5-7.5g/L.

The iron reagent in the above method includes ferric sulfate, ferric chloride, ferric nitrate, preferably ferric sulfate.

The dosage of the iron reagent in the above method is controlled at a molar ratio of Fe(III) to As(III) of 0.8-2; preferably 1.5.

The pH value of the above method reaction system is adjusted to 2.8-4.5. Sulfuric acid or sodium hydroxide solution is used as a pH adjuster.

The magnetic stirring speed of the above method is 400-500rpm, and the continuous reaction time is longer than 10h.

The temperature in the reaction process of the above method is controlled at 15-30°C.

The smelting process of non-ferrous metals produces a large amount of SO ₂ flue gas mixed with heavy metal fume including arsenic and mercury, which is mainly used to prepare sulfuric acid; the high-concentration acidic heavy metal waste water produced by washing and dust removal before the flue gas acid production is polluted acid; The concentration of sulfuric acid in the acid is between 4-11%, containing arsenic, lead, cadmium, zinc, copper, iron, mercury heavy metal ions and high concentrations of fluorine, chlorine, and sulfate anions, and the concentration of arsenic pollutants is as high as 0.72-9g /L.

The invention uses iron salt as a precipitating agent to regulate the formation of minerals in high-arsenic polluted acid wastewater to achieve the purpose of directly removing trivalent arsenic without oxidation. The method has the advantages of simple operation, small amount of added medicine, low cost, no need of oxidation, small and relatively stable slag, and the like.

Description of drawings

Figure 1: Effect diagram of arsenic removal under different pH conditions;

Figure 2: XRD patterns of arsenic slag under different pH conditions;

Figure 3: Effect diagram of removal of trivalent arsenic at different concentrations in wastewater;

Figure 4: XRD pattern of arsenic slag obtained from treating different concentrations of trivalent arsenic in wastewater;

Figure 5: Effect diagram of arsenic removal under different reaction time conditions;

Figure 6: XRD patterns of arsenic slag under different reaction time conditions;

Figure 7: XRD pattern of arsenic slag obtained from copper polluted acid treatment.

Detailed ways

The following examples are intended to further illustrate the present invention, but not limit the present invention.

Example 1

Prepare a sulfuric acid solution with a pH value of 1.8 with concentrated sulfuric acid, use the sulfuric acid solution to prepare respectively the acidic arsenic-containing wastewater with an As(III) concentration of 0.2mol/L and the precipitant storage solution with a Fe(III) concentration of 0.4mol/L, At the same time, a small amount of Cu(II) and Zn(II) were added to the prepared arsenic-containing wastewater, with concentrations of 0.01mol/L and 0.005mol/L, respectively. Take 10 cups of 50mL prepared acidic arsenic-containing wastewater, add an appropriate amount and equal volume of precipitant storage solution to it, mix well and use sodium hydroxide to adjust the pH to 1.8, 2.05, 2.3, 2.55, 2.8, 3.05, 3.3, 3.55 , 4.0, 4.5, stir the reaction at room temperature (25±1°C) with a magnetic stirring speed of 480rpm. After the reaction is completed, centrifuge at a speed of 5000rpm to obtain the supernatant and arsenic residue, and vacuum dry the arsenic residue at 60°C.

Figure 1 shows the arsenic removal effect under different pH conditions. It can be seen from Figure 1 that as the pH value increases, the removal efficiency of arsenic is significantly improved. When the pH is 1.8, the arsenic removal efficiency is only 33%, and the arsenic removal rate is higher than 95% when the pH is between 2.8 and 4.5. When the pH is 4, the arsenic removal rate has reached 99%, and at the same time, 95% above iron.

Fig. 2 is the XRD pattern of the obtained arsenic slag when the pH value is 1.8-4.5. It can be seen from Figure 2 that under different pH values, although the intensities of the XRD peaks are slightly different, the positions of the main diffraction peaks are basically the same, indicating that minerals with better crystal forms are formed in this pH value range.

Example 2

Prepare a sulfuric acid solution with a pH value of 1.8 with concentrated sulfuric acid, and use the sulfuric acid solution to prepare acidic arsenic-containing wastewater with an As(III) concentration of 6, 4.5, 3, 1.5, and 0.5 g/L (simultaneously prepared arsenic-containing wastewater also contains A small amount of Cu(II) and Zn(II) were added, the concentrations were 0.01mol/L and 0.005mol/L respectively), and 50ml of prepared acidic arsenic-containing wastewater was taken respectively, and an equal volume of ferric sulfate precipitant was added to each of them for storage solution, adjust the molar ratio of iron and arsenic to 2, adjust the pH value to 4 with sodium hydroxide after fully mixing, stir the reaction at room temperature (25±1°C) at a speed of 480rpm, and centrifuge at a speed of 5000rpm after the reaction is completed to obtain The supernatant and arsenic residue were vacuum-dried at 60°C.

Figure 3 shows the arsenic removal effect under different trivalent arsenic concentrations. It can be seen from Figure 3 that as the initial concentration of trivalent arsenic increases, the removal efficiency of arsenic increases significantly. When the initial trivalent arsenic concentration is 1.5g/L and above, the removal efficiency of arsenic can reach more than 90%, and almost all of the iron is also removed at the same time.

Fig. 4 is the XRD pattern of the arsenic slag obtained under different concentrations of trivalent arsenic. It can be seen from Figure 4 that at different initial concentrations of trivalent arsenic, although the intensities of the XRD peaks are slightly different, the positions of the main diffraction peaks are basically the same, indicating that the initial concentration of trivalent arsenic is in the range of 1.5-7.5g/L Minerals with good crystalline forms were formed.

Example 3

Use concentrated sulfuric acid to mix sulfuric acid solution with a pH value of 1.8, and use the sulfuric acid solution to prepare high-arsenic wastewater with an As(III) concentration of 0.2mol/L (simultaneously, a small amount of Cu(II), Zn (II) ion, concentration is respectively 0.01mol/L and 0.005mol/L) and Fe(III) concentration is the precipitant stock solution of 0.4mol/L. Take 10 cups of 50mL prepared high-arsenic wastewater, add an equal volume of precipitant stock solution to each of them, mix well, adjust the pH to 4.0 with sodium hydroxide, and keep stirring at room temperature (25±1°C) at a speed of 480rpm , and samples were taken at different reaction times, and the supernatant and arsenic slag were obtained by centrifugal separation at a speed of 5000 rpm, and the arsenic slag was vacuum-dried at 60°C.

Figure 5 shows the arsenic removal effect at different reaction times. It can be seen from Figure 5 that the removal efficiency of arsenic gradually increases with the prolongation of time, and the removal rate of arsenic reaches as high as 99% after 24 hours of reaction.

Figure 6 is the XRD pattern of arsenic slag obtained at different reaction times. It can be seen from Figure 6 that characteristic diffraction peaks appeared in the arsenic slag reacted for 10 hours. And as time continues to prolong, the intensity of this characteristic peak increases gradually. It is shown in conjunction with Fig. 5 that the mineral is formed after the reaction is carried out for 10 hours, and the longer the time, the better the crystal form, the arsenic removal rate can reach more than 90%, and almost all the iron is removed at the same time.

Example 4

The concentration of trivalent arsenic in the sewage acid wastewater produced by a copper smelter is 7.66g/L, and it also contains sulfate, sodium, silicon, copper, zinc, iron, etc. as shown in Table 1. Take 100mL of the polluted acid wastewater into a 200mL beaker, add 4.8g of ferric sulfate solid, add sodium hydroxide to adjust the pH value to 4, use a magnetic stirrer with a rotation speed of 480rpm to stir at room temperature, and centrifuge after the reaction to obtain the supernatant liquid and arsenic slag. The supernatant adopts inductively coupled plasma spectrometer (ICP) to detect the residual arsenic concentration therein, and the removal efficiency of total arsenic is calculated to be 90.3%; the concentration of iron before and after the reaction is measured simultaneously, and the removal rate of iron is calculated to be 98%; the arsenic residue It was dried under vacuum at 60°C, and the mineralization was analyzed by X-ray diffraction (XRD).

Table 1 Composition of sewage acid wastewater from a copper smelter (g/L)

substance As As(III) S Na Si Ca Zn Bi Cu Fe Mg pH concentration 9.01 7.66 26.4 7.04 0.67 0.54 0.37 0.26 0.18 0.12 0.11 1.21

Figure 7 is the XRD pattern of the arsenic slag obtained from the treatment of polluted acid wastewater. It can be seen from the figure that there are indeed characteristic diffraction peaks of minerals, but compared with the above examples, the peak positions are slightly shifted, and Fe ₄ (AsO ₄ ) ₃ (SO ₄ )OH·15H ₂ O characteristic peak, because the initial wastewater contains about 1/3 of pentavalent arsenic. In addition, since the raw acid contains a large amount of sulfate and sodium ions, there is also an obvious diffraction peak of sodium sulfate in the arsenic slag. A small amount of Cu ²⁺ and S ^2- in the solution formed Cu ₉ S ₅ precipitate, and its characteristic peak appeared. The above analysis shows that this method can also form minerals with better crystal form and achieve a better preliminary arsenic removal effect in the actual sewage acid wastewater treatment. The arsenic removal rate can reach more than 90%, and at the same time remove 98% of iron and a small amount of copper.

Claims (10)

1. A method for processing high-arsenic polluted acid wastewater, characterized in that: add iron reagent to high-arsenic polluted acid wastewater, adjust pH value, and after stirring reaction, solid-liquid separation removes arsenic. 2. The method according to claim 1, characterized in that the concentration of trivalent arsenic As(III) in the high-arsenic polluted acid wastewater is 1.5-7.5g/L. 3. The method according to claim 1, wherein the ferric reagent comprises ferric sulfate, ferric chloride, ferric nitrate, preferably ferric sulfate. 4. according to the described method of claim 1 or 2 or 3, it is characterized in that, the dosage of iron reagent is controlled at Fe(III) and As(III) molar ratio is 0.8-2. 5. The method according to claim 4, characterized in that the iron reagent dosage is controlled at Fe(III) and As(III) molar ratio of 1.5. 6. The method according to claim 1, characterized in that the pH value of the reaction system is adjusted to 2.8-4.5. 7. method according to claim 6 is characterized in that, adopts sulfuric acid and sodium hydroxide solution as pH value adjusting agent. 8. The method according to claim 1, characterized in that, the magnetic stirring speed is 400-500rpm, and the continuous reaction time is greater than 10h. 9. The method according to claim 1 or 6 or 7 or 8, characterized in that the temperature of the reaction process is controlled at 15-30°C. 10. The method according to claim 1, characterized in that, a large amount of inclusions including arsenic and mercury heavy metal fumes produced by the smelting process of nonferrous metals The flue gas is mainly used for the preparation of sulfuric _acid ; the flue gas is washed before making acid The high-concentration acidic heavy metal wastewater produced by dust removal is sewage acid; the concentration of sulfuric acid in sewage acid is between 4-11%, containing arsenic, lead, cadmium, zinc, copper, iron, mercury heavy metal ions and high concentrations of fluorine and chlorine , Sulfate anion, in which the concentration of arsenic pollutants is as high as 0.72-9g/L.