Arsenic-containing multi-metal co-contaminated soil remediation agent and its preparation method and application

Abstract

The invention discloses a method for preparing a soil remediation agent containing arsenic and multiple metals co-contaminated, comprising the following steps: dissolving ferrous sulfate in water to obtain Fe 2+ A ferrous sulfate solution with a concentration of 20 to 30 g / L; adding hydrogen peroxide to the ferrous sulfate solution, and maintaining the pH value at 2 to 4 during the addition process, wherein the hydrogen peroxide and the Fe 2+ The molar concentration ratio is 1:(0.8-1.5); the pH value of the mixed solution obtained in the mineralization step is adjusted to 6-8, and the mixture is evenly stirred and then filtered by plate and frame; the filter cake obtained in the adjustment step is dried to obtain Schmidt mineral, and the Schmidt mineral is evenly mixed with calcium carbonate in a mass ratio of 1:(0.5-2) to obtain an arsenic-containing multi-metal co-contaminated soil remediation agent. The present invention also discloses an arsenic-containing multi-metal co-contaminated soil remediation agent prepared by the above preparation method and its application in remediating arsenic-containing multi-metal co-contaminated soil. The soil remediation agent of the present invention effectively adsorbs and fixes arsenate ions and metal cations such as cadmium in the soil, which is beneficial to the recovery of the soil ecosystem.

Description

Technical Field

[0001] The present invention belongs to the technical field of soil remediation and environmental functional materials, and more specifically, relates to an arsenic-containing multi-metal co-contaminated soil remediation agent and a preparation method and application thereof. Background Art

[0002] Arsenic (As) is a non-essential metal element that is harmful to the human body. It is widely distributed in the soil and has a strong migration ability. Large-scale mining and smelting activities are the main sources of increased soil arsenic pollution. It is worth noting that arsenic and metal elements such as cadmium (Cd) often coexist in metal or non-metallic ores. Therefore, industrial activities such as mining, mineral processing and smelting often cause the soil in the surrounding areas to suffer from arsenic-containing multi-metal complex pollution. Given the significant differences in the existence forms and chemical properties of metal elements such as As and Cd in the soil, the remediation of As-containing multi-metal co-contaminated soil is more complex and challenging than the remediation of single As-contaminated soil.

[0003] In-situ chemical passivation technology for heavy metals in soil has attracted wide attention due to its simple operation, short remediation time, relatively low cost and good field applicability. The prior art with Chinese patent document publication number CN115920825A discloses a modification method of Schroeder mineral and its application, which can simultaneously passivate As and Cd.

[0004] Although the modified Schmidt mineral in the prior art has a certain adsorption capacity and stability for Cd and As, its maximum adsorption capacity and stability are still relatively limited, especially the adsorption ratio for Cd is very limited, and this ability is significantly affected by the soil pH value. In daily applications, in order to completely passivate Cd, a large amount of modified Schmidt mineral is often required, which causes a huge waste of resources for the passivation of As and increases the cost of soil remediation. It is more noteworthy that the arsenic and heavy metals after stabilization treatment are still retained in the soil, and under certain conditions, they will be reactivated and enter the soil again, causing secondary pollution. Flooding conditions, as one of the natural environmental factors, have a significant impact on the migration, transformation and bioavailability of heavy metals in the soil. Under flooding reduction conditions, the soil Eh and pH fluctuate greatly, resulting in the reduction dissolution and phase change of oxides in the soil, and the adsorbed and fixed As(V) and Cd will be released into the soil solution again as the oxides dissolve. In particular, As(V) may also be reduced to the more toxic As(III), further improving the mobility and bioavailability of As in the soil. Moreover, when Fe(II) and weakly crystalline iron minerals coexist, Fe(II) can catalyze the transformation of minerals with poor crystallinity and thermodynamic instability to generate other crystalline iron oxides. This process will also cause the originally adsorbed heavy metal elements to be re-released and distributed as the minerals are transformed. Therefore, although modified Schroeder minerals show certain potential in the passivation of soil heavy metals, there are still problems such as high soil remediation costs, limited remediation effects, insufficient long-term stability, and limited application scenarios. Summary of the invention

[0005] 1. Problem to be solved

[0006] In view of the problems of high soil remediation cost, limited remediation effect, insufficient long-term stability and limited application scenarios when modified Schreiberite is used to treat heavy metals such as As and Cd, the present invention provides an arsenic-containing multi-metal co-contaminated soil remediation agent and a preparation method and application thereof. On the basis of being able to simultaneously passivate As and Cd in the soil, the passivation ratio of Cd is increased and the adsorption capacity of As and Cd per unit soil remediation agent is further increased, the long-term stability of As and Cd complexation and adsorption is greatly improved, and the application scenarios of the soil remediation agent are expanded, so that it can be applied to soil under flooded conditions, such as rice fields.

[0007] 2. Technical solution

[0008] Based on the above purpose, the present invention provides a soil remediation agent for arsenic-containing multi-metal co-contaminated soil, which is mainly composed of Schroeder mineral and calcium carbonate mixed in a certain mass ratio. The combined use of Schroeder mineral and calcium carbonate can produce a synergistic effect and improve the overall remediation effect of the soil remediation agent. Specifically, the purpose of the present invention is achieved through the following technical solutions:

[0009] [A method for preparing a soil remediation agent containing arsenic and multiple metals co-contaminated]

[0010] The first aspect of the present invention provides a method for preparing an arsenic-containing multi-metal co-contaminated soil remediation agent, comprising the following steps:

[0011] Dissolution step: ferrous sulfate is dissolved in water to obtain Fe 2+ Ferrous sulfate solution with a concentration of 20-30 g / L;

[0012] Mineralization step: adding hydrogen peroxide to the ferrous sulfate solution and maintaining the pH value at 2-4 during the addition process. 2+ The molar concentration ratio is 1:(0.8-1.5);

[0013] Adjustment step: adjusting the pH value of the mixed solution obtained in the mineralization step to 6-8, stirring evenly and then performing plate and frame filter pressing;

[0014] Compounding step: drying the filter cake obtained in the adjustment step to obtain Schroeder mineral, and uniformly mixing the Schroeder mineral with calcium carbonate in a mass ratio of 1:(0.5-2) to obtain an arsenic-containing multi-metal co-contaminated soil remediation agent.

[0015] Preferably, in the compounding step, the particle size of the schreberite and calcium carbonate is less than or equal to 0.3 mm;

[0016] In the compounding step, the schreberite and calcium carbonate are uniformly mixed in a mass ratio of 1:(0.8-1.2), and the most preferred ratio is 1:1.

[0017] Preferably, the Schreiber mineral further contains iron oxyhydroxide mineral, and the iron oxyhydroxide mineral accounts for 1 / 9 to 1 / 7 of the total mass of the Schreiber mineral.

[0018] Preferably, in the mineralization step, the flow rate of adding hydrogen peroxide is 20 to 30 L / h;

[0019] In the mineralization step, the pH value is maintained at 2 to 3 during the addition process, and is most preferably 2.5;

[0020] In the mineralization step, hydrogen peroxide and the Fe 2+ The molar ratio is 1:(1.1-1.4), and the most preferred ratio is 1:1.2;

[0021] A stirring step is performed in the mineralization step, wherein the stirring speed in the stirring step is 80 to 100 rpm and the stirring time is not less than 24 hours.

[0022] Preferably, in the adjustment step, the pH value of the mixed solution is adjusted to 6.5 to 7.5, most preferably 7.

[0023] [A remediation agent for soil contaminated with arsenic and multiple metals]

[0024] The second aspect of the present invention provides an arsenic-containing multi-metal co-contaminated soil remediation agent prepared by the preparation method of an arsenic-containing multi-metal co-contaminated soil remediation agent according to any embodiment of the first aspect of the present invention.

[0025] As a preferred arsenic-containing multi-metal co-contaminated soil remediation agent of the second aspect of the present invention, the arsenic-containing multi-metal co-contaminated soil remediation agent has an adsorption capacity of 100 mg / g to 180 mg / g for arsenic, and an adsorption capacity of cadmium of 30 mg / g to 70 mg / g; the arsenic-containing multi-metal co-contaminated soil remediation agent has a stabilization efficiency of greater than or equal to 50% for arsenic, and a stabilization efficiency of greater than or equal to 75% for cadmium.

[0026] As used herein, the "stabilization efficiency" refers to the heavy metal stabilization efficiency (W), which is specifically calculated by the following method:

[0027]

[0028] Among them, C0 and C i They refer to the leaching concentrations of heavy metals in soils without passivators and with passivators, respectively, calculated based on the water extraction horizontal vibration method.

[0029] [Application of an arsenic-containing multi-metal co-contaminated soil remediation agent in remediating arsenic-containing multi-metal co-contaminated soil]

[0030] The third aspect of the present invention provides the use of the arsenic-containing multi-metal co-contaminated soil remediation agent according to any embodiment of the second aspect of the present invention in remediating arsenic-containing multi-metal co-contaminated soil.

[0031] As a preferred application of the arsenic-containing multi-metal co-contaminated soil remediation agent of the third aspect of the present invention in remediating arsenic-containing multi-metal co-contaminated soil, the arsenic content in the arsenic-containing multi-metal co-contaminated soil is 10 to 1800 mg / kg, and the cadmium content is 1 to 40 mg / kg.

[0032] Further preferably, the moisture content of the arsenic-polymetallic co-contaminated soil is 25% to 35%, most preferably 30%;

[0033] The particle size of the arsenic-containing and multi-metal co-contaminated soil is less than 1 mm;

[0034] The pH value of the arsenic-containing and multi-metal co-contaminated soil is 2 to 8;

[0035] The amount of the arsenic-containing multi-metal co-contaminated soil remediation agent added is 2.25 kg / m 2 ~11.25kg / m 2 , more preferably 6.75kg / m 2 ~11.25kg / m2 , the most preferred is 11.25kg / m 2 ;

[0036] Further preferably, the arsenic-containing and multi-metal co-contaminated soil is riverbed mud;

[0037] The water content of the riverbed mud is 25% to 35%;

[0038] The riverbed mud contains quartz sand of different particle sizes;

[0039] The amount of the arsenic-containing multi-metal co-contaminated soil remediation agent added is 18kg / m 2 ~27kg / m 2 .

[0040] Further preferably, the surface layer of the arsenic-containing and multi-metal co-contaminated soil has a water layer of at least 2 cm;

[0041] The amount of the arsenic-containing multi-metal co-contaminated soil remediation agent added is 2.25 kg / m 2 ~11.25kg / m 2 , more preferably 6.75kg / m 2 ~11.25kg / m 2 , the most preferred is 11.25kg / m 2 ;

[0042] The continuous action time of the arsenic-containing multi-metal co-contaminated soil remediation agent is 3 to 12 minutes.

[0043] It should be noted that when the soil surface contains a water layer, the soil adsorbent is usually easy to redissolve. Therefore, the soil remediation agent that can be used for metal adsorption under normal conditions is not necessarily applicable to the soil environment with a water layer on the surface. However, it is found in the present invention that the arsenic-containing multi-metal co-contaminated soil remediation agent prepared by the method of the first aspect of the present invention can be used in arsenic-containing multi-metal co-contaminated soil with at least 2 cm of water layer on the surface, and is used to adsorb arsenic and cadmium. It not only has an increased adsorption amount, but also can continue to adsorb for 3 to 12 months without redissolution, indicating that the soil remediation agent has a high adsorption stability efficiency for arsenic and cadmium.

[0044] 3. Beneficial effects

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] (1) Arsenic-containing multi-metal co-contaminated soil remediation agent (SC) mainly repairs the combined pollution of As and Cd through ion exchange, surface complexation and precipitation. Schroederite (S) coordinates with As through the surface hydroxyl groups and SO4 in the Schroederite structure. 2-Exchange with As to fix As in the Schreiberite, producing a passivation effect. Adding sodium hydroxide during the preparation of the arsenic-containing multi-metal co-contaminated soil remediation agent can remove sulfate on the outer surface of the Schreiberite, retain sulfate in the internal tunnel structure, and improve the long-term stability of the Schreiberite adsorption of As. In addition, the hydroxyl groups on the surface of the Schreiberite can combine with metal ions such as Cd, reduce the bioavailability of metal ions such as Cd, and improve the adsorption capacity of the Schreiberite for metal ions such as Cd. Adding sodium hydroxide can also promote the formation of oxyhydroxide iron minerals in the Schreiberite, which can passivate metal ions such as Cd in the soil, further improving the adsorption capacity of the Schreiberite for metal ions such as Cd. On the other hand, calcium carbonate (C) adjusts the soil pH value while adsorbing metal ions such as Cd, promotes the precipitation of heavy metals, reduces their mobility, and makes the arsenic-containing multi-metal co-contaminated soil remediation agent negatively charged, further improving the adsorption capacity of the arsenic-containing multi-metal co-contaminated soil remediation agent for metal ions such as Cd. Therefore, the combined use of Schroeder mineral and calcium carbonate has a synergistic effect, which is not only reflected in the improvement of As adsorption capacity, but also in the improvement of Cd adsorption capacity. The value of this synergistic effect in practical applications is that it can reduce the amount of soil remediation agent used, and there is no need to use excessive amounts of soil remediation agent to completely passivate Cd; in addition, cheap and readily available calcium carbonate can also reduce the manufacturing cost of soil remediation agents, further reducing the cost of soil remediation.

[0047] (2) The remediation effect of arsenic-containing multi-metal co-contaminated soil remediation agent (SC) is long-term and stable, effectively reducing the reactivation of arsenic and cadmium and preventing them from entering the soil again and causing pollution. Whether under normal conditions or under acidic conditions, the remediation effect can last for at least 60 days; even when remediating river sludge rich in quartz sand, the remediation effect can last for at least 30 days.

[0048] (3) Even under the extreme conditions of flooding reduction, the remediation effect of arsenic-containing multi-metal co-contaminated soil remediator (SC) on As and Cd still has long-term stability and can be applied to a wider range of pollution remediation scenarios.

[0049] (4) In general, the arsenic-containing multi-metal co-contaminated soil remediation agent (SC) of the present invention has a simple preparation method, low preparation cost, a wide range of applications, and will not introduce new pollutants. It is a green and sustainable remediation method with high market value. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 This is the XRD diagram of the synthesis of Schroeder mineral from ferrous sulfate mineralization in Preparation Example 1 of the present invention.

[0051] Figure 2 This is a schematic diagram of the arsenic-containing multi-metal co-contaminated soil remediation agent (SC) sample in Preparation Example 1 of the present invention.

[0052] Figure 3 The adsorption capacity of As and Cd by the arsenic-containing multi-metal co-contaminated soil remediation agent (SC) prepared in Example 1 of the present invention is compared with that of schrenkinerite (S) and calcium carbonate (C).

[0053] Figure 4 The results show the change of As in water-extractable state (a) and Cd in water-extractable state (b) in soil after stabilization and remediation for 60 days with different addition amounts of arsenic-containing multi-metal co-contaminated soil remediation agent (SC) in Example 2 of the present invention.

[0054] Figure 5 The results show the change of acid-extractable As (a) and acid-extractable Cd (b) in the soil after stabilization and remediation for 60 days with different addition amounts of arsenic-containing multi-metal co-contaminated soil remediation agent (SC) in Example 3 of the present invention.

[0055] Figure 6 The results show the change of As in water-extractable soil (a) and Cd in water-extractable soil (b) after stabilization and restoration of flooded soil for 365 days with different addition amounts of arsenic-containing multi-metal co-contaminated soil remediation agent (SC) in Example 5 of the present invention.

[0056] Figure 7 (a) is the change of the leached state of As and the change of the leached state of Cd under the ferrous catalytic conditions of arsenic-containing multi-metal co-contaminated soil remediation agent (SC) in Example 6 of the present invention; Figure 7 (b) is the XRD diagram of the arsenic-containing multi-metal co-contaminated soil remediation agent (SC) under ferrous catalysis conditions in Example 6 of the present invention. DETAILED DESCRIPTION

[0057] Experimental Materials:

[0058] Ferrous sulfate (FeSO4·7H2O) and 30wt% hydrogen peroxide were purchased from Beijing Zhongke Guotong Environmental Engineering Technology Co., Ltd.; sodium hydroxide was purchased from Jiangsu Fuzhan Pharmaceutical Co., Ltd.; calcium carbonate powder was purchased from Suput Agricultural Technology Co., Ltd.; cadmium nitrate (Cd(NO3)2·4H2O) and acetic acid were purchased from China National Pharmaceutical Group Chemical Reagent Co., Ltd.; sodium arsenite (NaAsO2) was purchased from Sigma Olerich Co., Ltd.; 6 mol / L HCl was purchased from Nanjing Chemical Reagent Co., Ltd.

[0059] Preparation Example 1

[0060] This embodiment discloses a method for preparing a soil remediation agent containing arsenic and multiple metals co-contaminated, comprising the following steps:

[0061] Dissolution step: weigh 250kg FeSO4·7H2O and dissolve it in water, stirring continuously to obtain Fe2+ Ferrous sulfate solution with a concentration of 25 g / L;

[0062] Mineralization step: 30 wt% hydrogen peroxide was introduced into the ferrous sulfate solution at a flow rate of 25 L / h for 3 hours, and NaOH was added every half an hour during the addition of hydrogen peroxide to adjust the pH of the ferrous sulfate solution to 2.5, accompanied by stirring at a speed of 80-100 rpm for 24 hours;

[0063] Adjustment step: After the mineralization step is completed, NaOH is added to the system to adjust the pH to 7 and then plate and frame filter is performed;

[0064] Mixing step: After the filter cake is air-dried, the Schreiberite is obtained. The Schreiberite is crushed and ground through a 100-mesh sieve, and then mixed with calcium carbonate in a mass ratio of 1:1 to obtain a solid powder, namely, an arsenic-containing multi-metal co-contaminated soil remediation agent.

[0065] like Figure 1 The figure shows the XRD pattern of the Schmidtite (S) synthesized by the mineralization of ferrous sulfate and 30wt% hydrogen peroxide. The Schmidtite (Fe8O8(OH) 8-2x (SO4) x ) also contains iron oxyhydroxide (FeOOH). After the Schmidtite was completely dissolved in 6 mol / L HCl, the iron and sulfur contents per unit mass were measured to be 538.7 mg / g and 74.2 mg / g, respectively. According to the calculation that all sulfur comes from the Schmidtite component, the chemical formula of the Schmidtite is Fe8O8(OH) 3.56 (SO4) 2.22 , that is, the content of iron oxyhydroxide mineral in Schreiber mineral is 112.57 mg / g. In other words, the mass ratio of iron oxyhydroxide mineral to Schreiber mineral is about 1:8.9.

[0066] like Figure 2 As shown, the soil remediation agent obtained by crushing and grinding the Schmidt mineral and mixing it with calcium carbonate in a mass ratio of 1:1 is a gray-brown powder.

[0067] Example 1

[0068] The three remediation materials, namely, the schreberite (S), calcium carbonate (C) and the arsenic-containing multi-metal co-contaminated soil remediation agent (SC) of the present invention, were selected in Preparation Example 1, and As (Ш) and Cd (II) adsorption tests were carried out in 30 mL of 2-morpholineethanesulfonic acid (MES) buffer solution (pH = 6.5):

[0069] The initial As(III) concentration was set at 10-500 mg / L, the initial Cd(II) concentration was set at 1-120 mg / L, and the amount of the repair agent was 1.0 g / L.

[0070] After arsenic (As) and cadmium (Cd) were adsorbed by three kinds of repair agents for 24 hours to reach equilibrium, the supernatant was filtered with a filter membrane with a pore size of 0.45 μm, and the concentrations of As and Cd in the supernatant were determined by inductively coupled plasma mass spectrometry (ICP-MS). The adsorption isotherms were fitted with the Langmuir model. The Langmuir model formula is as follows:

[0071]

[0072] Where C0 is the initial concentration of the solution (mg / L), C t is the instantaneous concentration of the solution at time t (mg / L), q t is the amount of heavy metal adsorbed on the adsorbent at time t (mg / g), V is the volume of the solution (L), and m is the mass of the adsorbent (g).

[0073] The results are as follows Figure 3 As shown in Table 1, the adsorption data fit well with the Langmuir isotherm. The adsorption capacities of S, SC and C for a series of As(Ш) at pH = 6.5 are shown in Figure 3 As shown in (a), the correlation coefficient (R 2 ) is above 0.9. According to the Langmuir model, the maximum adsorption of As is calculated as follows: 160.4 mg / g (Schmidtite) > 128.0 mg / g (soil remediation agent of the present invention) > 13.7 mg / g (calcium carbonate); on the other hand, the adsorption capacity of S, SC and C for a series of Cd(II) at pH = 6.5 is as follows Figure 5 As shown in (b), the correlation coefficient R 2 >0.98. The maximum adsorption amounts of Cd calculated according to the Langmuir model are: 48.28 mg / g (soil remediation agent of the present invention) > 36.76 mg / g (Schmidtite) > 25.67 mg / g (calcium carbonate). In summary, the arsenic-containing multi-metal co-contaminated soil remediation agent of the present invention has a good passivation effect on As and Cd, and the combined use of S and C can produce an effective synergistic effect, further improving the passivation effect of SC on As and Cd.

[0074] Table 1 Langmuir model fitting parameters of adsorption isotherms of As(Ш) and Cd(II) by Schroeder mineral, calcium carbonate and soil remediation agent

[0075]

[0076]

[0077] Example 2

[0078] This embodiment provides an application of an arsenic-containing multi-metal co-contaminated soil remediation agent (SC) in arsenic-containing multi-metal co-contaminated soil, and uses the arsenic-containing multi-metal co-contaminated soil remediation agent to stabilize and remediate the arsenic-containing multi-metal co-contaminated soil:

[0079] Weigh 200.0 g of surface soil from a site contaminated with As-Cd in Chengzhong District, Liuzhou City, Guangxi, China (the total As and total Cd contents in the soil were 1659 mg / kg and 32.26 mg / kg, respectively, and the soil particle size was <1 mm).

[0080] 1%, 3%, and 5% (w / w) of the arsenic-containing multi-metal co-contaminated soil remediation agent obtained in Preparation Example 1 were added respectively and mixed thoroughly with the soil. Distilled water was added to maintain the water content of the soil mixture at 30%, and soil stabilization and remediation began.

[0081] The samples were incubated at 25±2℃, and sampling and analysis were carried out on the 10th, 20th, 30th and 60th days after the start of soil stabilization and remediation according to the extraction steps of "Solid Waste Leaching Toxicity-Horizontal Vibration Method" (HJ 557-2010, China), specifically, heavy metals in the soil were extracted with pure water for 18 hours; the extract was collected with a 0.45μm pore size filter membrane; and the concentrations of As and Cd in the extract (i.e., the concentrations of water-extractable heavy metals) were determined.

[0082] like Figure 4 As shown in (a), when the SC dosage increased to 5%, the As leaching concentrations in the soil at the 10th, 20th, 30th, and 60th days were 144.7 μg / L, 144.7 μg / L, 138.4 μg / L, and 109.8 μg / L, respectively, which were all reduced by more than 78.2% compared with the treatment without SC addition. Figure 4 As shown in (b), the leaching concentration of Cd in the soil dropped from 130.2 μg / L before remediation to 7.9 μg / L (10 days of remediation using 1% (w / w) SC). When the SC dosage was greater than 1%, the leaching concentration of Cd in the soil remained below 5 μg / L within 10 days, meeting the third-level remediation standard (5 μg / L) for Cd specified in China (GB 3838-2002). Moreover, as the stabilization and remediation time increased, the Cd leaching concentration in the soil stabilized and remediated with high doses (3%, 5% (w / w)) of SC was always below 5 μg / L. Figure 4 It can be seen that the concentrations of As and Cd gradually decreased, and As and Cd did not reactivate over time to cause secondary pollution.

[0083] The heavy metal stabilization efficiency (W) index is used to evaluate the stability of heavy metals in soil, and its calculation formula is:

[0084]

[0085] Among them, C0 and C i They refer to the leaching concentrations of heavy metals in soils without passivators and with passivators, respectively, calculated based on the water extraction horizontal vibration method.

[0086] It has been calculated that during the entire remediation process, the stabilization efficiency of As in the soil after SC stabilization treatment reached 57.3%-82.9%, and the stabilization efficiency of SC for Cd was always maintained above 77%.

[0087] In summary, the arsenic-containing multi-metal co-contaminated soil remediation agent of the present invention can stably reduce the activity of heavy metals As and Cd in the soil in a long-term manner.

[0088] Example 3

[0089] This embodiment provides an application of an arsenic-containing multi-metal co-contaminated soil remediation agent (SC) in arsenic-containing multi-metal co-contaminated soil, and uses the arsenic-containing multi-metal co-contaminated soil remediation agent to stabilize and remediate the arsenic-containing multi-metal co-contaminated soil:

[0090] Weigh 200.0 g of surface soil from a site contaminated with As-Cd in Chengzhong District, Liuzhou City, Guangxi, China (the total As and total Cd contents in the soil were 1659 mg / kg and 32.26 mg / kg, respectively, and the soil particle size was <1 mm).

[0091] 1%, 3%, and 5% (w / w) of the arsenic-containing multi-metal co-contaminated soil remediation agent obtained in Preparation Example 1 were added respectively and mixed thoroughly with the soil. Distilled water was added to maintain the water content of the soil mixture at 30%, and soil stabilization and remediation began.

[0092] The samples were incubated at 25±2℃, and sampling and analysis were carried out on the 60th day after the start of soil stabilization and remediation. Specifically, the heavy metals in the soil were extracted with acetic acid solution (pH value was 2.88±0.05) for 18 hours; the extract was collected with a 0.45μm pore size filter membrane; and the TCLP method was used to determine the concentrations of As and Cd in the acetic acid extract (i.e., the concentrations of acid-extractable heavy metals, recorded as TCLP-As and TCLP-Cd, respectively).

[0093] like Figure 5As shown in Figure 2, the addition of SC significantly reduced the concentrations of TCLP-As and TCLP-Cd in the soil compared with the control group without SC addition. After adding 1% (w / w) SC, the concentration of TCLP-As in the soil decreased by 62.4%. Moreover, as the amount of SC increases, the concentration of TCLP-As further decreases. When the amount of SC reaches 5% (w / w), the concentration of TCLP-As decreases from 1.10 mg / L in the control group to 0.16 mg / L, a decrease of 85.5%. Compared with the control group without SC, after adding 1%-5% (w / w) SC, the concentration of TCLP-Cd in the soil is significantly reduced by 91.6%-93.7%, that is, from 3.82 mg / L in the control group to 0.32 mg / L (1% (w / w) SC dosage), 0.26 mg / L (3% (w / w) SC dosage) and 0.24 mg / L (5% (w / w) SC dosage), which are in line with the upper limit value (1.0 mg / L) specified by the US Environmental Protection Agency. In summary, the arsenic-containing multi-metal co-contaminated soil remediation agent of the present invention can effectively reduce the effect of pH on As and Cd after passivation, and avoid the reactivation and migration of As and Cd.

[0094] Example 4

[0095] This embodiment provides an application of an arsenic-containing multi-metal co-contaminated soil remediation agent (SC) in arsenic-containing multi-metal co-contaminated soil, and uses the arsenic-containing multi-metal co-contaminated soil remediation agent to stabilize and remediate the arsenic-containing multi-metal co-contaminated soil:

[0096] Weigh 200.0 g of As- and Cd-contaminated sludge from the Jiehe River in Zhaoyuan, Shandong (the total As and Cd contents in the sludge were 91.4 mg / kg and 40.0 mg / kg, respectively, and contained quartz sand of different particle sizes).

[0097] 10% (w / w) of the arsenic-containing multi-metal co-contaminated soil remediation agent obtained in Preparation Example 1 was added and mixed thoroughly with the soil. Distilled water was added to maintain the water content of the soil mixture at 30%, and soil stabilization and remediation began.

[0098] The samples were incubated at 25±2℃, and sampling and analysis were carried out on the 30th day after the start of soil stabilization and remediation according to the extraction steps of "Solid Waste Leaching Toxicity-Horizontal Vibration Method" (HJ 557-2010, China), specifically, heavy metals in the soil were extracted with pure water; the extract was collected with a 0.45μm pore size filter membrane; and the concentrations of As and Cd in the extract (i.e., the concentrations of water-extractable heavy metals) were determined.

[0099] As shown in Table 2, the concentrations of water-extractable As and water-extractable Cd in the contaminated sediment after the arsenic-containing multi-metal co-contaminated soil remediation agent were reduced to 4.93 μg / L and 11.5 μg / L. Compared with the control group without SC addition, the water-extractable As and water-extractable Cd were reduced by 92.0% and 57.4%, respectively. The arsenic-containing multi-metal co-contaminated soil remediation agent of the present invention can effectively passivate As and Cd in river sludge.

[0100] Table 2 Leaching concentrations of As and Cd in sediment after 30 days of stabilization (water extraction method)

[0101]

[0102] Example 5

[0103] The four groups of soil stabilized for 60 days in Example 2 were transferred to anaerobic bottles, sealed with butyl rubber stoppers and hollow aluminum caps, and placed in a 25°C incubator for 365 days of flooding. Specifically, during the incubation period, a 2-3 cm water layer was maintained above the soil surface, and three replicate experiments were set for each group of soil. Among them, the control group without SC was recorded as CK, and the treatment groups with 1% (w / w), 3% (w / w), and 5% (w / w) SC were recorded as SC-1%, SC-3%, and SC-5%, respectively.

[0104] 30 mL of the water layer solution above the soil was extracted, and the concentrations of As and Cd in the supernatant were determined using inductively coupled plasma mass spectrometry (ICP-MS).

[0105] like Figure 6 As shown in the figure, compared with the CK group, the treatment groups with 3% (w / w) and 5% (w / w) SC addition can significantly reduce the soil extractable As content to 4.35 mg / L and 2.15 mg / L, respectively, which are both lower than the limit value of As (5 mg / L) in the "Hazardous Waste Identification Standard GB5085.3-2007". On the other hand, the concentration of extractable As in the soil decreased significantly with the increase in the amount of SC added. Compared with the CK group, the As concentration released from the soil in the treatment group with 5% (w / w) SC addition decreased by 74.7%. Similarly, as the amount of SC increased, its stabilization effect on Cd became better. Compared with the CK group, the Cd concentration in the soil of the 5% (w / w) SC treatment group was significantly reduced by about 86.7%. It further shows that the remediation effect of SC on As and Cd under flooding reduction conditions has long-term stability, reducing the potential toxic effects in changing environmental conditions, so as to be suitable for more demanding application scenarios.

[0106] Example 6

[0107] This example further studies the stability of arsenic-containing multi-metal co-contaminated soil remediation agent (SC) in anaerobic environment through ferrous catalysis test.

[0108] 0.5g of the arsenic-containing multi-metal co-contaminated soil remediation agent (SC) of the present invention was added to 500mL of MES buffer solution containing As and Cd (As and Cd concentrations were 10mg / L and 1mg / L, respectively) and mixed and shaken for 24h (28°C); after the reaction, the sample suspension was separated into solid and liquid using a 0.45μm filter membrane, and the As and Cd concentrations in the liquid phase were determined using inductively coupled plasma mass spectrometry (ICP-MS), and the solid phase was washed 3 times with deionized water to remove the unadsorbed As and Cd; freeze-dried, crushed, and ground through a 100-mesh sieve to obtain SC adsorbed with As-Cd. According to the remaining As and Cd concentrations in the solution, the adsorption amounts of As and Cd by the arsenic-containing multi-metal co-contaminated soil remediation agent (SC) of the present invention were 7.62mg / g and 0.72mg / g, respectively.

[0109] The above 0.03 g of SC containing As-Cd and 30 mL of deoxygenated MES buffer solution were mixed in a 100 mL vial, the pH was adjusted to 6.5, and the vial was sealed with a butyl rubber stopper and a hollow aluminum cap; nitrogen was introduced into the vial to create an anaerobic environment in the vial; under anaerobic conditions, Fe(II) stock solution (FeCl2·4H2O) was added to the vial to make the Fe(II) concentration in the system 1 mM, and the vial was transferred to a shaker for cultivation.

[0110] The sacrificial method was used to take samples at different reaction times (0.5d, 1d, 3d, 5d, and 10d). The sample suspension was separated into solid and liquid using a 0.45μm filter membrane. The changes in the concentrations of As and Cd in the liquid phase were determined using inductively coupled plasma mass spectrometry (ICP-MS). After the solid phase was washed, centrifuged and freeze-dried, its mineral structure was analyzed using X-ray diffraction (XRD).

[0111] like Figure 7 As shown in (a), the As concentration released by SC increased rapidly to 0.99 mg / L within 12 h, and the amount of As released was 13% of the As content fixed by SC in the early stage. As the ferrous catalysis time increased, the As concentration in the solution slowly decreased, and by the 10th day it had dropped to 0.46 mg / L, with about half of the As being re-fixed. Similarly, the Cd concentration in the solution first increased and then gradually decreased, and finally the Cd concentration in the solution was maintained at 0.01 mg / L. This indicates that during the ferrous catalysis process, some of the As and Cd adsorbed and passivated by SC will be re-released into the environment and then fixed again, which may be one of the reasons why SC has long-term stability in remediating As and Cd-contaminated soils. In addition, Figure 7 As shown in (b), after ferrous catalytic conversion, the peak intensity of lepidocrocite is enhanced, and no new mineral phase is generated. Therefore, SC has a strong mineral phase stability and can effectively exert the continuous passivation effect of SC on As and Cd.

[0112] The above content is a schematic description of the present invention and its implementation methods, which is not restrictive. What is shown in the embodiment is only one of the implementation methods of the present invention, and the actual implementation method is not limited thereto. Therefore, if a person of ordinary skill in the art is inspired by it and designs implementation methods and embodiments similar to the technical solution without creative design without departing from the purpose of the invention, they should all fall within the scope of protection of the present invention.

Claims

1. A method for preparing an arsenic-containing multi-metal co-contaminated soil remediation agent, characterized in that: The following steps are involved: Dissolution step: ferrous sulfate is dissolved in water to obtain Fe 2+ Ferrous sulfate solution with a concentration of 20-30 g / L; Mineralization step: adding hydrogen peroxide to the ferrous sulfate solution and maintaining the pH value at 2-4 during the addition process. 2+ The molar ratio is 1:(0.8-1.5); Adjustment step: adjusting the pH value of the mixed solution obtained in the mineralization step to 6-8, stirring evenly and then performing plate and frame filter pressing; Compounding step: drying the filter cake obtained in the adjustment step to obtain Schroeder mineral, and uniformly mixing the Schroeder mineral with calcium carbonate in a mass ratio of 1:(0.5-2) to obtain an arsenic-containing multi-metal co-contaminated soil remediation agent.

2. The method for preparing the arsenic-containing multi-metal co-contaminated soil remediation agent according to claim 1, characterized in that: In the compounding step, the particle sizes of the Schroeder mineral and calcium carbonate are less than or equal to 0.3 mm.

3. The method for preparing the arsenic-containing multi-metal co-contaminated soil remediation agent according to claim 2, characterized in that: The Schmidt mineral also contains iron oxyhydroxide mineral, and the iron oxyhydroxide mineral accounts for 1 / 9 to 1 / 7 of the total mass of the Schmidt mineral.

4. The method for preparing the arsenic-containing multi-metal co-contaminated soil remediation agent according to any one of claims 1 to 3, characterized in that: In the mineralization step, the flow rate of adding hydrogen peroxide is 20 to 30 L / h; A stirring step is performed in the mineralization step, wherein the stirring speed in the stirring step is 80 to 100 rpm and the stirring time is not less than 24 hours.

5. A soil remediation agent for arsenic-containing and multi-metal co-contaminated soil, characterized in that: The invention is prepared by the preparation method of the arsenic-containing multi-metal co-contaminated soil remediation agent according to any one of claims 1 to 4.

6. The arsenic-containing multi-metal co-contaminated soil remediation agent according to claim 5, characterized in that: The arsenic-containing multi-metal co-contaminated soil remediation agent has an adsorption capacity of 100 mg / g to 180 mg / g for arsenic and an adsorption capacity of 30 mg / g to 70 mg / g for cadmium; The arsenic-containing multi-metal co-contaminated soil remediation agent has a stabilization efficiency of greater than or equal to 50% for arsenic and a stabilization efficiency of greater than or equal to 75% for cadmium.

7. Use of the arsenic-containing multi-metal co-contaminated soil remediation agent according to claim 5 or 6 in soil remediation, characterized in that: The arsenic content in the soil is 10-1800 mg / kg, and the cadmium content is 1-40 mg / kg.

8. The use of the arsenic-containing multi-metal co-contaminated soil remediation agent according to claim 7 in soil remediation, characterized in that: The moisture content of the soil is 25% to 35%; The particle size of the soil is less than 1 mm; The pH value of the soil is 2 to 8; The amount of the arsenic-containing multi-metal co-contaminated soil remediation agent added is 2.25 kg / m 2 ~11.25kg / m 2 .

9. The use of the arsenic-containing multi-metal co-contaminated soil remediation agent according to claim 7 in soil remediation, characterized in that: The soil is riverbed mud; The water content of the riverbed mud is 25% to 35%; The riverbed mud contains quartz sand of different particle sizes; The amount of the arsenic-containing multi-metal co-contaminated soil remediation agent added is 18kg / m 2 ~27kg / m 2 .

10. The use of the arsenic-containing multi-metal co-contaminated soil remediation agent according to claim 7 in soil remediation, characterized in that: The soil surface has a water layer of at least 2 cm; The amount of the arsenic-containing multi-metal co-contaminated soil remediation agent added is 2.25 kg / m 2 ~11.25kg / m 2 ; The continuous action time of the arsenic-containing multi-metal co-contaminated soil remediation agent is 3 to 12 minutes.

Images