Method for treating soil contaminated by heavy metal ions and arsenic

Abstract

The invention discloses a method for treating soil contaminated by heavy metal ions and arsenic, comprising the following steps: adjusting the soil pH, and dissolving heavy metal ion arsenate into heavy metal cations and arsenate anions after the alkalinity increases; oxidizing the dissolved arsenate anions with an oxidant to oxidize As III with high toxicity in the contaminated soil into As V with low toxicity and adsorbed by iron salts; using flocculent amorphous Fe(OH)3 gel generated in situ by water-soluble iron salts in alkaline soil solution to adsorb the dissolved and oxidized arsenic complex; using phosphate calcium salts to precipitate heavy metal ions with enhanced activity after dissolution to convert them into stable heavy metal ion complexes; the arsenic complexes adsorbed, dissolved and oxidized by the Fe(OH)3 gel and the stable heavy metal ion complexes are cured and buried in the soil to complete soil treatment.

Description

Technical Field

[0001] The invention relates to the technical field of contaminated soil treatment, and in particular to a treatment method for soil contaminated by heavy metal ions and arsenic. Background Art

[0002] At present, the remediation of soil pollution in agricultural land mainly adopts technologies such as plant absorption, in-situ passivation of heavy metals in soil, imported soil method, and deep plowing method. The in-situ passivation technology of heavy metals in soil refers to adding passivators to heavy metal-contaminated soil, and converting heavy metals in the soil into chemically inactive forms by adjusting the physical and chemical properties of the soil and a series of reactions such as adsorption, precipitation, ion exchange, and oxidation-reduction, thereby reducing their biological effectiveness and preventing the migration and accumulation of heavy metals in the soil from the roots of crops to the aboveground parts. The in-situ passivation technology of heavy metals in soil is widely used because of its small impact on the surrounding environment and quick results.

[0003] Chinese patent CN 113828628B discloses a method for remediating soil contaminated by cadmium and arsenic, which includes three steps: step one, using sodium percarbonate to oxidize the contaminated soil to oxidize the highly toxic and bioavailable As(III) to As(V); step two, adding Fe2O3 and calcium-based compounds to adsorb and fix As(V); step three, adding the chelating agent 3-mercaptopropyltrimethoxysilane to chelate and adsorb the heavy metal ion cadmium. In this way, the purpose of treating cadmium and arsenic in contaminated soil is achieved through three steps. Obviously, when actually applied to the treatment of large quantities of contaminated soil, the three mixing and curing steps will bring a heavy burden on manpower, equipment, and capital investment, with low efficiency and poor benefits. In addition, 3-mercaptopropyltrimethoxysilane is very easy to hydrolyze and condense in the alkaline soil solution created by calcium-based compounds, loses the chelating effect, and results in poor cadmium adsorption effect. If step one is eliminated, the treatment effect is not ideal, especially the stabilization effect of arsenic is poor. If step one is combined with step two, the CO3 produced by the decomposition of sodium percarbonate will be 2- Significantly affects Fe 3+ The adsorption effect of cadmium and the chelation effect of cadmium and chelating agent result in poor treatment effect.

[0004] The Chinese patent with application number 202210435552.X discloses an iron-based modified nano-hydroxyapatite material and its preparation method and application in the remediation of Cd-contaminated soil. In an alkaline solution, through a three-stage heating reaction, (NH4)2HPO4, Ca(NO3)2·4H2o and FeCl3·6H2O are used to in-situ generate hydroxyapatite while adsorbing iron salts to prepare iron-based modified nano-hydroxyapatite materials, which have achieved good results in the remediation of Cd-contaminated soil. When iron-based hydroxyapatite is used to treat soil contaminated by heavy metal ions and arsenic, the iron salt is wrapped inside the hydroxyapatite and cannot fully contact the contaminated soil. The large specific surface area and strong adsorption effect of the iron salt cannot be fully exerted, and anions such as arsenic cannot be fully adsorbed, and the treatment effect is not significant.

[0005] Based on the existing technology, iron salts have a strong adsorption effect on anionic pollutants such as arsenic, and hydroxyapatite, phosphates, etc. have good adsorption or precipitation effects on various heavy metal cations. However, in the one-step treatment technology that directly mixes iron salts, hydroxyapatite or phosphates with contaminated soil, the iron salts have precipitated with hydroxyapatite or phosphate before adsorbing anionic pollutants and become ineffective, and the purpose of simultaneously treating anionic pollutants such as arsenic and heavy metal cation pollutants cannot be achieved. Summary of the invention

[0006] In view of the above-mentioned deficiencies in the current treatment of soil contaminated by heavy metal ions and arsenic, the present invention provides a method for treating soil contaminated by heavy metal ions and arsenic, which achieves the purpose of treating soil contaminated by heavy metal ions and arsenic through a few simple steps.

[0007] To achieve the above object, the present invention is implemented by the following technical solutions:

[0008] The method for treating soil contaminated by heavy metal ions and arsenic comprises the following steps:

[0009] Adjust the soil pH, and after the alkalinity increases, the heavy metal ion arsenate dissolves into heavy metal cations and arsenate anions;

[0010] The dissolved arsenate anions are oxidized by an oxidant to oxidize the more toxic AsIII in the contaminated soil into less toxic AsV adsorbed by iron salts. The flocculent amorphous Fe(OH)3 gel generated in situ by water-soluble iron salts in alkaline soil solution adsorbs the dissolved and oxidized arsenic complexes.

[0011] Utilize calcium phosphates to precipitate heavy metal ions whose activity is enhanced after dissolution, and convert them into stable heavy metal ion complexes;

[0012] The Fe(OH)3 gel adsorbs, dissolves, and oxidizes the arsenic complex and the stable heavy metal ion complex, which are then preserved and buried in the soil to complete soil treatment.

[0013] Furthermore, the soil pH is adjusted by adding CaO, the oxidant includes water-soluble iron salt and Na2S2O8, the oxidant and CaO are pre-mixed into the soil, and after curing at room temperature for a first set time, phosphate calcium salt is added and cured at room temperature for a second set time.

[0014] Furthermore, the molar ratio of the water-soluble iron salt, CaO and Na2S2O8 mixture is 1: (2.5-3.5): 0.02, wherein the water-soluble iron salt is Fe 3+ Mole ratio.

[0015] Furthermore, the step of adjusting the soil pH is specifically to increase the soil alkalinity through the reaction of CaO and water until the pH is adjusted to 9-13.

[0016] Furthermore, the water-soluble iron salt is FeCl3 and / or Fe2(SO4)3.

[0017] Furthermore, the weight of the mixture of water-soluble iron salt, CaO and Na2S2O8 is 0.2%-0.8% of the mass of the contaminated soil to be treated.

[0018] Furthermore, the method also includes adjusting the moisture content of the contaminated soil to be treated, specifically, before adjusting the soil pH, adjusting the moisture content of the contaminated soil to be treated to 20%-30%.

[0019] Furthermore, the calcium phosphate salt is at least Ca(H2PO4)2, Ca(H2PO4)2·CaHPO4, Ca 10 One of (PO4)6(OH)2.

[0020] Furthermore, the amount of the phosphate calcium salt is (PO4) 3- By mass, it is 0.14% to 0.22% of the mass of the contaminated soil to be treated.

[0021] Furthermore, the step of curing at room temperature for a set time specifically includes covering with a plastic film and curing at room temperature, the first set time specifically is 3-5 days, and the second set time specifically is 10-12 days.

[0022] Furthermore, the heavy metal is at least one of lead, cadmium or copper.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. Under the action of water in the soil, CaO generates Ca(OH)2, the soil alkalinity increases, and the heavy metal ion arsenate is dissolved into heavy metal cations and arsenate anions. At the same time, iron salts generate flocculent amorphous Fe(OH)3 gel in the alkaline soil solution, which has a large surface area and strong adsorption capacity, and can strongly adsorb arsenate ions. According to literature data, near-edge X-ray absorption spectroscopy (XANES) and extended X-ray absorption spectroscopy (EXAFS) show that this part of the arsenic in the soil forms inner mononuclear or binuclear monodentate or bidentate complexes with iron / manganese / aluminum oxides and hydroxides in the soil, which are strongly adsorbed and belong to the strongly adsorbed arsenic, and its bioavailability and migration ability are greatly weakened.

[0025] 2. Fe 3+ , Na2S2O8 are strong oxidants and can oxidize As(III) in contaminated soil to As(V), and Fe a+ It can also be used as an activator of Na2S2O8 to further stimulate and improve the activity of Na2S2O8, and reduce the dosage of Na2S2O8. As(V) is much less toxic than As(III) and is more easily oxidized by Fe 3+ Salt adsorption;

[0026] 3. The activity of heavy metal ions dissolved in the soil increases, and they can quickly react with Ca(H2PO4)2, Ca(H2PO4)2·CaHPO4, Ca 10 (PO4)6(OH)2 undergoes precipitation and adsorption, and is converted into a stable state. Ca(H2PO4)2 and Ca(H2PO4)2·CaHPO4 are the main components of phosphate fertilizers. 10 The main components of (PO4)6(OH)2 are also calcium ions, phosphate ions, etc., which will not cause secondary pollution of the soil, will not affect the subsequent use of farmland and orchard soil, and can also improve the fertility of farmland and orchard soil at the same time.

[0027] 4. The present invention has a significant effect of reducing the treatment of heavy metal ions such as copper, cadmium, lead and arsenic by more than 90%. The leaching concentrations of lead, copper, cadmium and arsenic in the contaminated soil after treatment meet the requirements of agricultural water in the "Surface Water Environmental Quality Standard". The two-step treatment process is efficient and economical. DETAILED DESCRIPTION

[0028] In order to better understand the present invention, the technical solution of the present invention is further described in detail below in conjunction with embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, and the present invention is not limited to the following embodiments.

[0029] The following examples describe in more detail the treatment of soil contaminated by heavy metal ions and arsenic according to the method of the present invention, and these examples are given in an illustrative manner, but these examples do not limit the scope of the present invention.

[0030] The method for treating soil contaminated by heavy metal ions and arsenic in the present invention comprises the following steps: adjusting the soil pH, and after the alkalinity increases, dissolving the heavy metal ion arsenate into heavy metal cations and arsenate anions; the heavy metal ion arsenate in the present invention mainly refers to lead arsenate, copper arsenate, etc., and the present invention is mainly aimed at treating pesticides such as lead arsenate and copper arsenate.

[0031] The dissolved arsenate anions are oxidized by an oxidant, and the more toxic As(III) in the contaminated soil is oxidized to As(V) with lower toxicity and adsorbed by iron salts. The flocculent amorphous Fe(OH)3 gel generated in situ by water-soluble iron salts in alkaline soil solution is used to adsorb the dissolved and oxidized arsenic complexes.

[0032] In this embodiment, water-soluble iron salt and Na2S2O8 are selected as oxidants, which are then pre-mixed with CaO into the soil, and then cured at room temperature for a first set time, and then phosphate is added to cure at room temperature for a second set time. Compared with a single oxidant, the oxidant and water-soluble iron salt in this embodiment have Fe 3+ , Na2S2O8 are strong oxidants and can oxidize As(III) in contaminated soil to As(V), and Fe 3+ It can also be used as an activator of Na2S2O8 to further stimulate and improve the activity of Na2S2O8, and reduce the dosage of Na2S2O8. As(V) is much less toxic than As(III) and is more easily oxidized by Fe 3+ Salt adsorption;

[0033] Specifically, the molar ratio of the water-soluble iron salt, CaO and Na2S2O8 mixture is 1: (2.5-3.5): 0.02, wherein the water-soluble iron salt is Fe 3+ In this embodiment, CaO is more, the purpose is to react with water, Fe 3+ After the reaction generates Fe(OH)3 gel, it is still in excess, providing an alkaline environment for the soil. Specifically, when adjusting the pH, the soil alkalinity is increased by the reaction of CaO and water until the pH is adjusted to 9-13.

[0034] In this embodiment, the weight of the mixture of water-soluble iron salt, CaO and Na2S2O8 is 0.2%-0.8% of the mass of the contaminated soil to be treated. In this embodiment, 0.2%-0.8% can meet the treatment requirements. If it is too low, the treatment effect is not good. If it is too high, the economic benefit is not good and the soil remediation agent is polluted.

[0035] Using phosphate to precipitate heavy metal ions whose activity is enhanced after dissolution, so as to convert them into stable heavy metal ion complexes;

[0036] The arsenic complexes dissolved and oxidized by Fe(OH)3 gel are cured and buried in the soil to complete soil treatment.

[0037] In this embodiment, full use is made of the fresh flocculent amorphous Fe(OH)3 gel rapidly generated in situ by water-soluble iron salts in the alkaline soil solution to improve the adsorption of arsenic and the efficiency of soil pollution treatment.

[0038] The present invention is mainly used for the treatment of agricultural land pollution. Compared with the soil remediation technology in the prior art, the present invention makes full use of the adsorption performance of the fresh Fe(OH)3 gel generated in situ to make it adsorb arsenate ions, and at the same time selects a variety of oxidants with strong oxidizing properties to increase the activity of one of the oxidants and reduce its usage. At the same time, CaO is used to increase the alkalinity of the contaminated soil, thereby dissolving heavy metal ion arsenate, increasing the activity of heavy metal ions, and then converting them into a stable state, which will not cause secondary soil pollution, will not affect the subsequent use of farmland and orchard soil, and can also improve the fertility of farmland and orchard soil at the same time.

[0039] In this embodiment, before adjusting the pH, the water content of the contaminated soil to be treated is also adjusted. Specifically, before adjusting the pH of the soil, the water content of the contaminated soil to be treated is adjusted to 20%-30%. The water content is selected to be 20%-30% in order to provide a good migration environment for various ions to accelerate ion adsorption and precipitation.

[0040] In this embodiment, when performing normal temperature curing, specifically covering with a plastic film for normal temperature curing, the first set time is specifically 3-5 days, and the second set time is specifically 10-12 days.

[0041] In this embodiment, the water-soluble iron salt is FeCl3 and / or Fe2(SO4)3.

[0042] Furthermore, the phosphate is at least Ca(H2PO4)2, Ca(H2PO4)2·CaHPO4, Ca 10 One of (PO4)6(OH)2. The purpose of selecting this type of phosphate is to precipitate heavy metal ions without causing secondary soil pollution, and to improve the fertility of farmland and orchard soil at the same time.

[0043] In the present invention, the following 15 embodiments are specifically added. In the following embodiments: Embodiments 1-5 are soils contaminated by lead and arsenic; Embodiments 6-10 are soils contaminated by lead, copper and arsenic; Embodiments 11-15 are soils contaminated by lead, copper, cadmium and arsenic.

[0044] Example 1

[0045] The method for treating soil contaminated by heavy metal ions and arsenic in the present invention specifically comprises two steps: step 1, adjusting the moisture content of the soil to 20%, adding 0.2wt% of a mixture of FeCl3, CaO and Na2S2O8 in a molar ratio of 1:2.5:0.02 to the contaminated soil, mixing the mixture with the contaminated soil, covering the mixture with a plastic film and curing at room temperature for 3 days; step 2, adding 0.14wt% of (PO4) to the soil cured in step 1 3- The weight of Ca(H2PO4)2 is mixed evenly with the contaminated soil and then cured for 10 days to complete the treatment of the soil contaminated by heavy metal ions and arsenic.

[0046] Example 2

[0047] The method for treating soil contaminated by heavy metal ions and arsenic in this embodiment specifically includes two steps. Step 1: adjusting the moisture content of the soil to 25%, adding 0.4wt% of a water-soluble iron salt (a mixture of FeCl3 and Fe2(SO4)3 in a molar ratio of 2:1), CaO and Na2S2O8 in a molar ratio of 1:3:0.02 to the contaminated soil, mixing the mixture with the contaminated soil, and then covering with a plastic film and curing at room temperature for 3 days; Step 2: adding 0.16wt% of (PO4) to the soil cured in step 1. 3- Gravimetric Ca(H2PO4)2 and Ca 10 (PO4)6(OH)2 mixture (Ca(H2PO4)2 and Ca 10 (PO4)6(OH)2 is mixed in a molar ratio of 3:1), mixed evenly with the contaminated soil and cured for 10 days to complete the treatment of the soil contaminated by heavy metal ions and arsenic.

[0048] Example 3

[0049] The method for treating soil contaminated by heavy metal ions and arsenic in this embodiment specifically includes two steps. Step 1: adjusting the soil moisture content to 30%, adding 0.6 wt% of Fe2(SO4)3 (Fe2SO4)3 in a molar ratio of 1:3:0.02) to the contaminated soil. 3+ molar ratio), a mixture of CaO and Na2S2O8, and the contaminated soil are mixed evenly, covered with a plastic film and cured at room temperature for 3 days; step 2, adding 0.16wt% (PO4) to the soil cured in step 1 3-Ca(H2PO4)2·CaHPO4 and Ca 10 (PO4)6(OH)2 mixture (Ca(H2PO4)2·CaHPO4 and Ca 10 (PO4)6(OH)2 is mixed in a molar ratio of 2:1), mixed evenly with the contaminated soil and cured for 10 days to complete the treatment of the soil contaminated by heavy metal ions and arsenic.

[0050] Example 4

[0051] The method for treating soil contaminated by heavy metal ions and arsenic in this embodiment specifically includes two steps. Step 1: adjusting the moisture content of the soil to 30%, adding 0.8wt% of a mixture of FeCl3, CaO and Na2S2O8 with a molar ratio of 1:3:0.02 to the contaminated soil, mixing it evenly with the contaminated soil, covering it with a plastic film and curing it at room temperature for 3 days; Step 2: adding 0.20wt% of (PO4) to the soil cured in step 1 3- Ca by weight 10 (PO4)6(OH)2, after being evenly mixed with the contaminated soil and cured for 10 days, the treatment of the soil contaminated by heavy metal ions and arsenic is completed.

[0052] In this embodiment, Ca(H2PO4)2·CaHPO4 can also be used alone to replace Ca 10 (PO4)6(OH)2.

[0053] Example 5

[0054] The method for treating soil contaminated by heavy metal ions and arsenic in this embodiment specifically includes two steps. Step 1: adjusting the moisture content of the soil to 25%, adding 0.4wt% of a water-soluble iron salt (a mixture of FeCl3 and Fe2(SO4)3 in a molar ratio of 2:1), CaO and Na2S2O8 in a molar ratio of 1:3:0.02 to the contaminated soil, mixing the mixture with the contaminated soil, and then covering with a plastic film and curing at room temperature for 3 days; Step 2: adding 0.22wt% of (PO4) to the soil cured in step 1. 3- A mixture of Ca(H2PO4)2 and Ca(H2PO4)2·CaHPO4 (Ca(H2PO4)2 and Ca(H2Po4)2·CaHPO4 are mixed in a molar ratio of 3:2) by weight is evenly mixed with the contaminated soil and cured for 10 days, thereby completing the treatment of the soil contaminated with heavy metal ions and arsenic.

[0055] Embodiment 6-10

[0056] Examples 6-10 are soils contaminated with lead, copper and arsenic. The treatment steps are the same as those of Examples 1-5, except that copper is added to the soil as a pollutant.

[0057] Examples 11-15

[0058] Examples 11-15 are soils contaminated with lead, copper, cadmium and arsenic, with more soil pollutants, and the treatment steps are the same as those of Examples 1-5.

[0059] The metal ion and arsenic composite contaminated soil before treatment and after treatment in Examples 1-15 was subjected to pollutant leaching according to the Horizontal Oscillation Method for Toxicity Leaching of Solid Waste (HJ 557-2010). 2+ 、Cd 2+ , Pb 2+ The content of heavy metal cations was determined by inductively coupled plasma atomic emission spectrometry (ICP-AES), and the content of arsenic was determined by hydride generation atomic absorption spectrometry (HG-AAS). The specific test results are shown in Table 1-3.

[0060] Table 1 shows the treatment results of lead and arsenic compound contaminated soil in Examples 1-5

[0061] Table 1

[0062]

[0063] Table 2 shows the results of treating the soil contaminated by lead, copper and arsenic in Examples 6-10

[0064] Table 2

[0065]

[0066] Table 3 shows the results of the treatment of lead, copper, cadmium and arsenic compound contaminated soil in Examples 11-15

[0067] Table 3

[0068]

[0069] As can be seen from Tables 1-3, the treatment method for heavy metal ion and arsenic composite contaminated soil provided by the present invention can reduce the treatment effect of heavy metal ions such as lead, copper, cadmium and arsenic by more than 90%, whether it is for single heavy metal ion and arsenic composite contaminated soil or for multiple heavy metal ions and arsenic composite contaminated soil, and the treatment effect is remarkable. The leaching concentrations of lead, copper, cadmium and arsenic in the contaminated soil after treatment all meet the requirements of agricultural water in the "Surface Water Environmental Quality Standard". Moreover, the two-step treatment procedure is efficient and economical.

[0070] It can be seen from Example 1 that for the lead and arsenic compound contaminated soil, the lead concentration after treatment was reduced from 1.34 mg / L to 0.08 mg / L, a decrease of 94.0%; the arsenic concentration was reduced from 0.92 mg / L to 0.07 mg / L, a decrease of 92.4%. Example 6 is a lead, copper, and arsenic compound contaminated soil. Compared with the contaminated soil in Example 1, copper ion pollution was added. The treatment method was the same as that in Example 1. It can be seen that after treatment, the lead concentration was reduced from 1.13 mg / L to 0.07 mg / L, a decrease of 93.8%; the copper concentration was reduced from 0.93 mg / L to 0.06 mg / L, a decrease of 93.5%; and the arsenic concentration was reduced from 1.41 mg / L to 0.07 mg / L, a decrease of 95.0%. Example 11 is a soil contaminated with lead, copper, cadmium and arsenic. Compared with the contaminated soil in Example 1, copper ion and cadmium ion pollution are added. The treatment method is the same as that in Example 1. It can be seen that after treatment, the lead concentration is reduced from 1.17 mg / L to 0.07 mg / L, a decrease of 94.0%; the copper concentration is reduced from 1.22 mg / L to 0.08 mg / L, a decrease of 93.4%; the cadmium concentration is reduced from 0.14 mg / L to 0.008 mg / L, a decrease of 94.3%; and the arsenic concentration is reduced from 1.95 mg / L to 0.08 mg / L, a decrease of 95.9%. From the comparison between Example 1, Example 6 and Example 11, it can be seen that the treatment method for soil contaminated with heavy metal ions and arsenic provided by the present invention has a good treatment effect, whether it is for soil contaminated with a single heavy metal ion and arsenic or for soil contaminated with multiple heavy metal ions and arsenic, and the treatment and reduction effect of heavy metals and arsenic is higher than 90%. For different concentrations of arsenic in Example 1, Example 6 and Example 11, the treatment effect of the treatment method provided by the present invention on arsenic is also higher than 90%. The same rule can be seen from comparing Examples 2-5 with Examples 7-10 and Examples 12-15 respectively.

[0071] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A method for treating soil contaminated by heavy metal ions and arsenic, characterized in that: The following steps are involved: Adjust the soil pH, and after the alkalinity increases, the heavy metal ion arsenate dissolves into heavy metal cations and arsenate anions; Before adjusting the pH, the water content of the contaminated soil to be treated is also adjusted. Specifically, before adjusting the pH of the soil, the water content of the contaminated soil to be treated is adjusted to 20%-30%; The dissolved arsenate anions are oxidized by an oxidant to oxidize the more toxic AsⅢ in the contaminated soil into less toxic AsⅤ adsorbed by iron salts. The flocculent amorphous Fe(OH)3 gel generated in situ by water-soluble iron salts in alkaline soil solution is used to adsorb the dissolved and oxidized arsenic complexes. Utilize calcium phosphates to precipitate heavy metal ions whose activity is enhanced after dissolution, and convert them into stable heavy metal ion complexes; The Fe(OH)3 gel adsorbs and dissolves, and the oxidized arsenic complex and the stable heavy metal ion complex are preserved and buried in the soil to complete soil treatment. The heavy metal is at least one of lead, cadmium or copper, and the treatment and reduction effect is more than 90%; The soil pH is adjusted by adding CaO, the oxidant includes water-soluble iron salt and Na2S2O8, the oxidant and CaO are pre-mixed into the soil, and after curing at room temperature for a first set time, phosphate calcium salt is added to the soil and cured at room temperature for a second set time; The molar ratio of the water-soluble iron salt, CaO and Na2S2O8 mixture is 1: (2.5-3.5): 0.02, wherein the water-soluble iron salt is Fe 3+ Mole ratio; The step of curing at room temperature for a set time specifically includes covering with a plastic film and curing at room temperature, the first set time specifically is 3-5 days, and the second set time specifically is 10-12 days.

2. The method for treating soil contaminated by heavy metal ions and arsenic according to claim 1, characterized in that: The step of adjusting the soil pH specifically involves increasing the soil alkalinity through the reaction of CaO with water until the pH is adjusted to 9-13.

3. The method for treating soil contaminated by heavy metal ions and arsenic according to claim 1, characterized in that: The water-soluble iron salt is FeCl3 and / or Fe2(SO4)3.

4. The method for treating soil contaminated by heavy metal ions and arsenic according to claim 1, characterized in that: The mass of the mixture of water-soluble iron salt, CaO and Na2S2O8 is 0.2%-0.8% of the mass of the contaminated soil to be treated.

5. The method for treating soil contaminated by heavy metal ions and arsenic according to claim 1, characterized in that: The calcium phosphate salt is at least Ca(H2PO4)2, Ca(H2PO4)2•CaHPO4, Ca 10 One of (PO4)6(OH)2.

6. The method for treating soil contaminated by heavy metal ions and arsenic according to claim 1, characterized in that: The amount of the phosphate calcium salt is (PO4) 3- By mass, it is 0.14% to 0.22% of the mass of the contaminated soil to be treated.

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