Magnetic iron mineral-phosphate tailing material and application thereof in treatment of arsenic and cadmium pollution

Abstract

The invention discloses a magnetic iron mineral and phosphate tailing material and application thereof in treatment of arsenic and cadmium pollution. A low-cost phosphate tailing material is taken as an object, and an environmental functional material loaded with magnetic gamma-Fe2O3 and other iron minerals is prepared by adopting a method of'rapid thermal activation-primary addition of a modifying agent-mineral phase conversion '. The magnetic iron mineral and phosphate tailing material can efficiently adsorb cadmium ions, arsenate ions and arsenite ions, has a synchronous adsorption effect on coexisting cadmium ions and inorganic arsenic, and can be used as an efficient passivation repair material for arsenic-cadmium combined polluted soil. The material also has magnetism, is easy to separate and recover, and also can be combined with a magnetic separation technology to serve as a material for synchronously removing arsenic and cadmium pollutants in a water body or soil.

Description

Technical Field

[0001] The present invention relates to the field of environmental pollution remediation materials, and particularly relates to a magnetic iron mineral@phosphorus tailings material and its use for treating arsenic and cadmium pollution. Background Art

[0002] Cadmium and arsenic are two typical (quasi-)heavy metal pollutants. Due to geological background problems or the influence of industrial and mining activities, cadmium pollution, arsenic pollution, and cadmium-arsenic combined pollution may exist in the environment, posing a risk to the health and safety of residents and the quality of the ecological environment. Cadmium pollutants mainly exist as divalent cadmium ions, and arsenic pollutants mainly exist as negatively charged arsenate ions or arsenite ions. The forms and valence states of the two types of pollutants vary greatly, and conventional functional materials are difficult to efficiently adsorb cadmium and arsenic pollutants simultaneously, bringing huge challenges to the treatment and remediation of cadmium-arsenic combined pollution.

[0003] The iron modification method can improve the adsorption capacity of functional materials for arsenic pollutants. By screening suitable functional materials and optimizing the iron modification method, materials that can simultaneously adsorb cadmium and arsenic pollutants can be prepared. For example, Patent 201610644164.7 uses acid-washed clinoptilolite as a carrier, and through iron salt soaking, surfactant mixing, and sodium borohydride reaction, a nano-iron material-modified zeolite is prepared, which can remove arsenic, cadmium, and lead pollutants in the environment. Patent 2020108284581 uses biochar as a carrier, and through steps such as heat treatment starch coating, dysprosium salt modification, and iron salt compounding, a soil remediation agent that can treat arsenic and cadmium combined pollution is obtained. However, there are rich types of iron minerals, and there are significant differences in the adsorption effects of different iron minerals on pollutants. Moreover, the types and properties of iron minerals loaded by the iron modification method vary depending on the raw material type and modification process, and the loading effects of different iron minerals will significantly affect the interaction efficiency and reaction mechanism between the modified material and the pollutants. At the same time, the technical solutions of many current patents are relatively complex. For example, the existing methods basically adopt the operation steps of finely adjusting the pH of the reaction system drop by drop. These complex operations result in high preparation costs of the materials, and the large-scale production and application prospects of the materials are limited.

[0004] Phosphorus tailings are solid wastes generated from phosphorus ore mining, with a huge daily output and a lack of effective disposal methods. The tailings piles cover a large area and pose various potential environmental risks. There is an urgent need to expand the resource utilization ways of phosphorus tailings. If phosphorus tailings are used as raw materials for environmental functional materials, it is expected to provide low-cost repair materials for environmental pollution control and promote the resource utilization of waste. At present, the application of phosphorus tailings in the field of soil pollution repair is still in its infancy. The existing reports mainly propose optimization schemes for the effect of phosphorus tailings on adsorbing cadmium and lead pollutants (such as patents 202010510129.2 and 202011184522.3). Due to the possible competitive adsorption between phosphate and arsenate, there is little attention in the existing literature on the removal of arsenic pollution by phosphorus-based materials, and there is a lack of research on the influence of methods such as iron modification on the removal of arsenic pollution by phosphorus tailings. There is still a lack of technical solutions that can simultaneously improve the adsorption performance of phosphorus tailings for cadmium and arsenic pollutants. Summary of the Invention

[0005] The present invention provides a magnetic iron mineral@phosphorus tailings material, which can simultaneously adsorb cadmium and arsenic pollutants, and the material has magnetism and is easy to separate and recycle, providing a solution for the treatment of cadmium-arsenic combined pollution.

[0006] The raw material of the magnetic iron mineral@phosphorus tailings material is phosphorus tailings, and the main iron minerals loaded are magnetic γ-Fe 2 O 3 、magnetic ε-Fe 2 O 3 as well as α-Fe 2 O 3 , iron oxyhydroxide and iron phosphate 。

[0007] The preparation method of the magnetic iron mineral@phosphorus tailings material includes the following steps:

[0008] (1) Collect phosphorus tailings, grind them through 100 meshes, and thermally activate them under aerobic conditions.

[0009] (2) Mix the thermally activated product with iron salt solution and alkali solution in proportion, add water to adjust the solid-liquid ratio, place it in a reactor for heat treatment, and carry out mineral phase loading-conversion.

[0010] (3) Take out the above product, elute the free iron ions until the pH of the eluate is 10 ± 0.5, and freeze-dry.

[0011] In step (1), the main components of the phosphorus tailings are fluorapatite, dolomite and quartz, the pH is 7.2 - 7.7, the P 2 O 5 content is 5% - 15%, the Fe content is less than 1%, and the temperature range of thermal weight loss is 600°C - 1000°C.

[0012] In step (1), the thermal activation temperature of the phosphorus tailings is 600 - 800 °C, preferably 650 °C; the high-temperature activation time is 1 - 4 h, preferably 2 h.

[0013] In step (2), the iron salt is ferric chloride or ferric nitrate, preferably ferric nitrate; the iron concentration in the iron salt solution is 0.2 - 1 mol / L. The alkali solution is a potassium hydroxide solution with a concentration of 1 - 5 mol / L.

[0014] In step (2), the mixing ratio of the thermally activated product, the iron salt solution and the alkali solution is 1 g of thermally activated product: 5 - 20 mmol of iron element: 50 - 150 mmol of alkali, preferably 1 g of thermally activated product: 10 mmol of iron element: 90 mmol of alkali.

[0015] In step (2), the final solid-liquid ratio of the thermally activated product and the solution mixture is 1 g: 200 mL.

[0016] In step (2), the heat treatment temperature is 60 - 80 °C, preferably 70 °C; the heat treatment time is 48 h - 72 h, preferably 60 h.

[0017] The magnetic iron mineral@phosphorus tailings material is any material obtained according to the above preparation method.

[0018] The present invention claims to protect the use of the magnetic iron mineral@phosphorus tailings material for adsorbing and removing cadmium ions, arsenate ions, and arsenite ions singly or in combination in water bodies.

[0019] The present invention claims to protect the use of the magnetic iron mineral@phosphorus tailings material for passivating and remediating single cadmium or arsenic pollution or cadmium-arsenic combined pollution in soil.

[0020] The present invention also claims to protect the use of the magnetic iron mineral@phosphorus tailings material for removing cadmium and arsenic pollutants singly or in combination in soil.

[0021] The magnetic iron mineral@phosphorus tailings material proposed by the present invention also has the effect of improving soil acidity and reducing the stress of exchangeable acid and exchangeable aluminum on plant growth, and can be used as a soil improvement material for soils with acidification-heavy metal combined pollution.

[0022] The technical solution proposed by the present invention has the following advantages and positive effects:

[0023] Taking the low-cost phosphorus tailings material as the object, based on medium-temperature and rapid thermal activation, the "modified reagent one-time addition - mineral phase transformation" method is adopted to prepare an adsorption material loaded with magnetic iron minerals, and the preparation method is simpler than the traditional iron modification technical solution. This technical solution utilizes the reaction of the surface functional groups of the material after thermal activation with the iron salt in the alkaline environment jointly formed by the activated material and the alkali solution to generate magnetic γ-Fe 2 O 3 and magnetic ε-Fe2 O 3 and a small amount of α-Fe 2 O 3 iron minerals such as goethite, ferric oxyhydroxide, and iron phosphate, which are significantly different from the iron mineral materials (pure goethite) synthesized without added materials according to the same preparation steps; the alkaline mineral components generated in the thermal activation step also reduce the amount of alkali input required for iron mineral synthesis, contributing to cost reduction in preparation.

[0024] The magnetic iron mineral @phosphorus tailings material proposed in this solution has a significantly higher adsorption capacity for cadmium ions, arsenate ions, and arsenite ions than the phosphorus tailings raw material. When there are combined cadmium and arsenic pollutants in the water body or soil environment, the material can efficiently adsorb cadmium and arsenic pollutants simultaneously, and there is a synergistic adsorption effect of the material on cadmium ions and arsenic pollutants, that is, the adsorption amounts of cadmium and arsenic pollutants by the material under the condition of combined pollution are higher than those in a single pollution system.

[0025] The magnetic iron mineral @phosphorus tailings material proposed in this technical solution can react with cadmium and arsenic pollutants through multiple mechanisms. The main mechanisms include: the material can undergo surface adsorption, complexation, precipitation, and coprecipitation with cadmium ions through phosphate, carbonate, and oxide mineral components; the material has a certain alkalinity, which can promote the adsorption and precipitation processes of cadmium ions in a high-pH environment; the magnetic iron minerals contained on the surface of the material can adsorb arsenate ions and arsenite ions through mechanisms such as surface adsorption, monodentate complexation, and bidentate complexation; the calcium and magnesium ions contained on the surface of the material can adsorb cadmium ions through ion exchange and fix arsenate ions and arsenite ions through precipitation or coprecipitation mechanisms.

[0026] The loading of magnetic iron minerals provides good magnetism for the material, making the material easy to separate and recycle, and expanding the uses of the material.

[0027] After the material is applied to contaminated soil, it can increase the soil pH, reduce the soil exchangeable acidity, and at the same time can immobilize arsenic and cadmium pollutants. It can be used for passivation and remediation of soil arsenic, cadmium, and arsenic-cadmium combined pollution, reducing the mobility and bioavailability of heavy metals, and realizing the safe utilization of contaminated soil; combined with magnetic separation technology, this material can also be used as a functional material for simultaneously removing arsenic and cadmium pollutants from soil. Description of the Drawings

[0028] Figure 1 are the scanning electron microscope and transmission electron microscope test results of the phosphorus tailings material and the preparation product in Example 1.

[0029] Figure 2 is the hysteresis curve of the magnetic iron mineral @phosphorus tailings material in Example 1.

[0030] Figure 3Is the adsorption isotherm of the magnetic iron mineral @phosphorus tailings material for cadmium ions, arsenate ions, and arsenite ions in Example 3.

[0031] Figure 4 Is the adsorption result of the magnetic iron mineral @phosphorus tailings material for the composite pollutant of cadmium ions and arsenite ions in Example 4.

[0032] Figure 5 Is the adsorption result of the magnetic iron mineral @phosphorus tailings material for the composite pollutant of cadmium ions and arsenate ions in Example 5.

[0033] Figure 6 Is the influence of the magnetic iron mineral @phosphorus tailings material on soil pH, Eh, and the availability of cadmium and arsenic in Example 6.

[0034] Figure 7 Is the influence of the magnetic iron mineral @phosphorus tailings material on soil pH, Eh, and the availability of cadmium and arsenic in Example 7. Detailed implementation manners

[0035] The technical solutions of the present invention will be further described below in conjunction with specific implementation methods.

[0036] The following examples are only used to illustrate the present invention, but are not used to limit the protection scope of the present invention. Unless otherwise specified, the reagents and technical means used in the examples are all conventional means well known to those skilled in the art.

[0037] Example 1

[0038] Collect the phosphorus tailings material (F), the pH of the material is 7.63, P 2 O 5 The content is 12%, the Fe content is 0.72%, and the main components are fluorapatite, dolomite, and quartz. The thermogravimetric analysis results show that the temperature range of the thermal weight loss of the material is 600°C - 800°C.

[0039] The phosphorus tailings material was ground to pass through a 100-mesh sieve and thermally activated at 650 °C for 2 h under aerobic conditions to obtain a thermally activated product (F650). 1 g of the thermally activated product was mixed with 10 mL of 1 mol / L iron nitrate solution and 18 mL of 5 mol / L potassium hydroxide solution, and the mixing ratio of the substances was 1 g of thermally activated product: 10 mmol Fe: 90 mmol base. Water was added to adjust the total solid-liquid ratio to 1 g: 200 mL. The mixture was heated and reacted at 70 °C for 60 h to promote the synthesis and loading of iron minerals on the surface of the thermally activated product. It was taken out, and the free iron ions were eluted until the pH of the eluate was 10, and then freeze-dried to obtain a magnetic iron mineral@phosphorus tailings material (Fe@F650). At the same time, 10 mL of 1 mol / L iron nitrate solution and 18 mL of 5 mol / L potassium hydroxide solution were mixed, water was added to 200 mL, heated and reacted at 70 °C for 60 h, the free iron ions were eluted until the pH of the eluate was 10, and then freeze-dried to prepare a control iron material (FeOOH-1).

[0040] The characterization results showed that there were significant differences in the colors of the four materials. The magnetic iron mineral@phosphorus tailings material changed from the gray color of the phosphorus tailings material and its thermally activated product to dark brown, while the control iron material was yellow. The results of electron microscopy analysis ( Figure 1 ) showed that the magnetic iron mineral@phosphorus tailings material was loaded with spherical and rod-shaped minerals on the surface of the original phosphorus tailings material, and the EDX results showed a high content of iron element on the material.

[0041] The results of mineral composition analysis showed that the prepared magnetic iron mineral@phosphorus tailings material still contained the original fluorapatite, dolomite and quartz, and at the same time, calcium carbonate and various iron minerals were generated; in the mineral composition of the thermally activated product of the phosphorus tailings material, in addition to the original fluorapatite, dolomite and quartz, mainly new magnesium oxide, calcium carbonate, calcium oxide substances were generated; in the control iron material, its XRD pattern had a high degree of matching with the goethite card, and the mineral phase was goethite with a high purity. The results of Mössbauer spectroscopy characterization proved that the magnetic iron mineral@phosphorus tailings material was loaded with γ-Fe 2 O 3 and ε-Fe 2 O 3 magnetic substances, and at the same time, it also contained α-Fe 2 O 3 , iron phosphate, and iron oxyhydroxide (Table 1).

[0042] The hysteresis curve ( Figure 2 ) showed that the magnetic iron mineral@phosphorus tailings material had strong magnetism, while the other three materials did not have magnetism; the γ-Fe 2 O 3 and ε-Fe 2 O 3 substances loaded by the magnetic iron mineral@phosphorus tailings material were the main sources of magnetism.

[0043] The physicochemical characterization results show that the pH of Fe@F650 is 8.07, higher than that of F and F650 (7.63 and 11.00 respectively). The specific surface area of Fe@F650 is 127 cm 2 / g, significantly higher than that of F and F650 (3.93 cm 2 / g and 4.49 cm 2 / g respectively). The high pH of the material is beneficial to the fixation of pollutants such as cadmium ions, and the high specific surface area is also beneficial to the adsorption of various pollutants by the material. The total iron content of Fe@F650 increases from 7.20 g / kg of the F material to 252.06 g / kg.

[0044] Table 1 Mössbauer spectroscopy characterization results of main iron minerals on Fe@F650 Compound IS (mm / s) H (KOe) QS (mm / s) LW (mm / s) <![CDATA[γ-Fe 2 O 3 > 0.48 51.4 -0.044 0.36 <![CDATA[ε-Fe 2 O 3 > 0.40 40.2 0.054 0.44 <![CDATA[α-Fe 2 O 3 > 0.37 48.2 -0.050 0.58 <![CDATA[FeP0 4 > 0.34 / 0.61 0.55 α-FeOOH 0.46 33.6 0.054 0.39

[0045] Example 2

[0046] Using 0.01 mol / L sodium nitrate solution as the substrate, three kinds of simulated pollution solutions were prepared, including cadmium nitrate pollution solution (cadmium concentration is 500 mg / L), disodium hydrogen arsenate pollution solution (arsenic concentration is 200 mg / L) and sodium arsenite pollution solution (arsenic concentration is 200 mg / L), and the pH of the solution was adjusted to 5.0 ± 0.2. Weigh F650, FeOOH-1 and Fe@F650 prepared in Example 1, and mix them with the pollution solution according to the solid-liquid ratio of 1 g:500 mL, and oscillate at 150 rpm for 72 h at room temperature. At the same time, weigh FeOOH-1 and F650 prepared in Example 1 and mix them according to the mass ratio of 1:1, and then mix them with the pollution solution according to the solid-liquid ratio of 1 g:500 mL, and oscillate at 150 rpm for 72 h at room temperature. Filter and dilute the two groups of experimental samples respectively, and measure the cadmium or arsenic concentration by ICP-OES to calculate the adsorption amount of the material to the pollutants. In the experiment, the adsorption amounts of arsenate ions and arsenite ions were both converted to the adsorption amount of arsenic element per unit material.

[0047] The results show that: in the cadmium ion - contaminated solution system with an initial concentration of 500 mg / L, Fe@F650 can adsorb 109 mg / g of cadmium ions, while the adsorption capacity of pure FeOOH - 1 for cadmium ions is less than 1 mg / g, the adsorption capacity of F650 for cadmium ions is 124 mg / g, and the adsorption capacity of the mixture of FeOOH - 1 and F650 for cadmium ions is 71 mg / g. In the arsenite or arsenate - contaminated solution system with an initial arsenic concentration of 200 mg / L, Fe@F650 can adsorb 32 mg / g of arsenite ions and 27 mg / g of arsenate ions respectively. While the adsorption capacity of pure FeOOH - 1 for both arsenite ions and arsenate ions is less than 10 mg / g, the adsorption capacity of pure F650 for both arsenite ions and arsenate ions is less than 7 mg / g, and the adsorption capacities of the mixture of FeOOH - 1 and F650 for arsenite ions and arsenate ions are 7.7 mg / g and 8.9 mg / g respectively. Therefore, the magnetic iron mineral @ phosphorus tailings material has better adsorption performance for arsenic pollutants than the simple phosphorus tailings thermally activated material, goethite and their compound products, and its adsorption performance for cadmium pollutants is also higher than that of the compound product of the simple phosphorus tailings thermally activated material and goethite, indicating that this modification process can improve the adsorption capacity of the material for pollutants by generating different mineral phase structures.

[0048] Example 3

[0049] Using 0.01 mol / L sodium nitrate solution as the substrate, prepare cadmium nitrate, disodium hydrogen arsenate or sodium arsenite - contaminated solutions, and adjust the pH of the solutions to 5.0 ± 0.2. Weigh the F and Fe@F650 prepared in Example 1, mix them with the contaminated solutions at a solid - liquid ratio of 1 g:500 mL, and oscillate at 150 rpm for 72 h at room temperature. Filter, dilute, measure the cadmium or arsenic concentration by ICP - OES, calculate the adsorption capacity of the material for pollutants, and draw the adsorption isotherms of the material for cadmium ions, arsenate ions or arsenite ions. In the experiment, the adsorption capacities of both arsenate ions and arsenite ions are converted to the adsorption capacity of arsenic element per unit material.

[0050] Adsorption isotherm results ( Figure 3 ) show that: the adsorption capacities of Fe@F650 for cadmium ions, arsenate ions and arsenite ions are significantly higher than those of the F material. The fitting results of the Langmuir adsorption isotherm model show that: the saturated adsorption capacities of Fe@F650 for cadmium ions, arsenite ions and arsenate ions are 108 mg / g, 111 mg / g and 65.6 mg / g respectively, while the adsorption capacities of the F material are only 5.27 mg / g, 7.06 mg / g and 7.60 mg / g.

[0051] Example 4

[0052] Using 0.01 mol / L sodium nitrate solution as the base, prepare a cadmium nitrate and sodium arsenite composite pollution solution, and adjust the pH of the solution to 4.0 ± 0.2. Weigh the Fe@F650 prepared in Example 1, mix it with the pollution solution at a solid-liquid ratio of 1 g:500 mL, and shake it at 150 rpm for 72 h at room temperature. Filter, dilute, and measure the cadmium or arsenic concentration by ICP-OES to calculate the adsorption capacity of the material for the composite pollutant. The pollution solutions include: (1) Cd pollution solution with a Cd concentration of 112 mg / L; (2) As(III) pollution solution with an As(III) concentration of 75 mg / L; (3) Cd&As(III) pollution solution with a Cd concentration of 112 mg / L and an As(III) concentration of 75 mg / L; (4) H-Cd&As(III) pollution solution with a Cd concentration of 224 mg / L and an As(III) concentration of 75 mg / L; (5) Cd&H-As(III) pollution solution with a Cd concentration of 112 mg / L and an As(III) concentration of 150 mg / L. In the experiment, the adsorption capacities of arsenate ions and arsenite ions are both converted to the adsorption capacity of arsenic element per unit material.

[0053] As Figure 4 shown, in the cadmium-arsenic composite pollution solution system, Fe@F650 can adsorb cadmium ions and arsenic pollutants simultaneously. When arsenite ions are present in the solution, the adsorption capacity of Fe@F650 for cadmium ions increases significantly. When cadmium ions are present in the solution, the adsorption capacity of Fe@F650 for arsenite ions increases significantly; the increase in the initial cadmium ion concentration will improve the adsorption capacity of the material for arsenic, indicating the existence of a synergistic adsorption effect.

[0054] Example 5

[0055] Using a 0.01 mol / L sodium nitrate solution as the base, a composite pollution solution of cadmium nitrate and disodium hydrogen arsenate was prepared, and the pH of the solution was adjusted to 4.0 ± 0.2. Weigh the Fe@F650 prepared in Example 1, and mix it with the pollution solution at a solid-liquid ratio of 1 g:500 mL. Oscillate at 150 rpm for 72 h at room temperature. Filter, dilute, and determine the cadmium or arsenic concentration by ICP-OES, and calculate the adsorption capacity of the material for the composite pollutant. The pollution solutions include: (1) Cd pollution solution with a Cd concentration of 112 mg / L; (2) As(V) pollution solution with an As(III) concentration of 75 mg / L; (3) Cd&As(V) pollution solution with a Cd concentration of 112 mg / L and an As(V) concentration of 75 mg / L; (4) H-Cd&As(III) pollution solution with a Cd concentration of 224 mg / L and an As(V) concentration of 75 mg / L; (5) Cd&H-As(V) pollution solution with a Cd concentration of 112 mg / L and an As(V) concentration of 150 mg / L. In the experiment, the adsorption capacities of arsenate ions and arsenite ions were both converted to the adsorption capacity of arsenic element per unit material.

[0056] As Figure 5 shown, in the cadmium-arsenic composite pollution solution system, Fe@F650 can simultaneously adsorb cadmium ions and arsenic pollutants. When cadmium ions are present in the solution, the adsorption capacity of Fe@F650 for arsenate ions increases significantly, indicating the existence of a synergistic adsorption effect.

[0057] Example 6

[0058] Weigh two materials, F and Fe@F650, prepared in Example 1, and mix them with the polluted soil respectively; the dosage of the materials is 2% or 5% (mass fraction). Add deionized water to adjust the soil moisture content to 70% of the saturated water holding capacity to simulate the dryland soil reaction system. Place the samples in a constant temperature incubator and incubate at 25 °C for 30 days. Take out, freeze-dry, and analyze the soil physical and chemical properties and the availability of cadmium, arsenic, etc.

[0059] The results show that:

[0060] After adding F, the soil pH increased from 4.79 in the control group to 6.67 - 6.68, and the soil Eh decreased from 256 mV to 161 mV - 181 mV. In the Fe@F650 treatment group, the soil pH increased to 6.93 - 7.53, and the soil Eh was 199 mV - 255 mV; the soil pH and Eh increased with the increase in the dosage of the material.

[0061] After adding F, the concentration of available cadmium extracted by calcium chloride in the soil decreased from 0.127 mg / kg in the control group to 0.009 mg / kg - 0.013 mg / kg, a decrease of 89.5% - 92.7%. The concentration of arsenic extracted in the solution decreased from 0.698 mg / kg in the control group to 0.433 mg / kg - 0.444 mg / kg, a decrease of 36.4% - 38.0%. The chromium concentration decreased by 17.73% - 25.61%, the cobalt concentration decreased by 84.12% - 84.18%, the nickel concentration decreased by 57.73% - 61.72%, the copper concentration decreased by 82.01% - 81.63%, the zinc concentration decreased by 96.22% - 96.23%, and the lead concentration decreased by 98.13% - 98.31%. At the same time, the concentration of available arsenic extracted by sodium dihydrogen phosphate in the soil was 6.90 mg / kg - 7.56 mg / kg, a decrease of -2.78% - 6.24%.

[0062] After adding Fe@F650, the concentration of available cadmium extracted by calcium chloride in the soil decreased to 0.004 mg / kg - 0.008 mg / kg, a decrease of 94.1% - 96.6%. The concentration of arsenic extracted in the solution decreased by 94.1% - 96.6%, the chromium concentration decreased by 43.93% - 46.65%, the cobalt concentration decreased by 89.87% - 91.84%, the nickel concentration decreased by 60.86% - 68.31%, the copper concentration decreased by 86.86% - 89.07%, the zinc concentration decreased by 96.68% - 97.25%, and the lead concentration decreased by 98.63% - 98.83%. At the same time, the concentration of available arsenic extracted by sodium dihydrogen phosphate in the soil decreased to 3.46 mg / kg - 5.40 mg / kg, a decrease of 26.6% - 53.0%. The Fe@F650 material effectively and synchronously immobilized pollutants such as cadmium and arsenic in the soil.

[0063] Further analyzing the changes in the occurrence forms of cadmium and arsenic in the soil, it was found that: the proportions of acid-soluble, reducible, oxidizable, and residual cadmium in the control group soil were 38.42%, 41.76%, 11.43%, and 8.39% respectively. After adding 5% of Fe@F650, the proportions of acid-soluble, reducible, oxidizable, and residual cadmium were 48.81%, 32.83%, 9.14%, and 9.22% respectively. The material promoted the transformation of reducible and oxidizable cadmium in the soil into acid-soluble and residual forms. The proportions of non-specifically adsorbed, specifically adsorbed, weakly crystalline iron and manganese oxide-bound, crystalline iron and manganese oxide-bound, and residual arsenic in the control group soil were 0.88%, 8.89%, 26.46%, 31.87%, and 31.90% respectively. After adding 5% of Fe@F650, the proportions of non-specifically adsorbed, specifically adsorbed, weakly crystalline iron and manganese oxide-bound, crystalline iron and manganese oxide-bound, and residual arsenic were 0.05%, 5.25%, 43.61%, 33.51%, and 17.57% respectively. The material promoted the transformation of adsorbed arsenic in the soil into iron and manganese oxide-bound forms.

[0064] Example 7

[0065] Weigh the two materials, F and Fe@F650, prepared in Example 1 and mix them with the contaminated soil respectively; the dosage of the materials is 2% or 5% (mass fraction). Add deionized water to adjust the soil moisture content to 100% of the saturated water holding capacity, and make a 1 cm water layer appear on the upper layer of the soil to simulate the flooded soil environmental conditions of paddy fields. Place the samples in a constant temperature incubator and incubate at 25°C for 30 days. Take them out, freeze-dry, and analyze the physical and chemical properties of the soil and the availability of cadmium, arsenic, etc.

[0066] The results showed that:

[0067] After adding F, the soil pH increased from 5.33 in the control group to 6.61 - 6.68, and the soil Eh decreased from 221 mV to 173 mV - 177 mV. In the Fe@F650 treatment group, the soil pH increased to 6.81 - 7.38, and the soil Eh was 203 mV - 270 mV, both higher than those in the F treatment group. At the same time, with the increase in the dosage of the Fe@F650 material, both the soil pH value and Eh value showed an increasing trend.

[0068] After adding F, the concentration of available cadmium extracted by calcium chloride in the soil decreased from 0.140 mg / kg to 0.011 mg / kg - 0.015 mg / kg. At the same time, the concentration of arsenic extracted in the solution decreased from 0.881 mg / kg in the control group to 0.311 - 0.469 mg / kg, a decrease of 46.8% - 64.7%; the concentration of available arsenic extracted by sodium dihydrogen phosphate in the soil decreased from 8.31 mg / kg to 7.35 - 7.41 mg / kg.

[0069] After adding Fe@F650, the concentration of available cadmium extracted by calcium chloride in the soil decreased to 0.006 mg / kg - 0.010 mg / kg. At the same time, the concentration of arsenic extracted in the solution decreased to 0.041 mg / kg - 0.104 mg / kg, a decrease of 92.7% - 95.9% and 88.2% - 89.2% respectively. The concentration of available arsenic extracted by sodium dihydrogen phosphate decreased to 3.65 - 5.01 mg / kg, a decrease of 39.7% - 56.1%. While maintaining the passivation effect on cadmium in the soil, the modified material significantly reduced the bioavailability of arsenic in the soil.

[0070] Example 8

[0071] The Fe@F650 material prepared in Example 1 was applied to the cadmium-arsenic co-polluted acidified soil at a ratio of 1%. Chinese cabbage seeds were sown and cultivated for 47 days. After harvesting, plant and soil samples were collected. The test results showed that: the plants in the control group were stressed by soil acidity and cadmium-arsenic pollution, and the above-ground dry biomass was less than 0.06 g / plant. The cadmium and arsenic contents were 10.45 mg / kg and 5.35 mg / kg. After adding Fe@F650, the soil pH increased by 1.31 pH units, and the contents of exchangeable acid and exchangeable aluminum decreased by 0.17 cmol / kg (60.71%) and 0.376 cmol / kg (98.95%) respectively. The above-ground dry biomass reached 0.10 g / plant, and the cadmium and arsenic contents were 3.08 mg / kg and 2.04 mg / kg. Fe@F650 significantly alleviated the stress of the tested soil properties on the growth of Chinese cabbage, and at the same time reduced the cadmium and arsenic uptake in agricultural products, achieving the goal of safe production.

[0072] Example 9

[0073] The Fe@F650 material prepared in Example 1 was applied to the cadmium-arsenic co-polluted acidified soil at a ratio of 4%. Chinese cabbage seeds were sown and cultivated for 47 days. After harvesting, plant and soil samples were collected. The test results showed that: the plants in the control group were stressed by soil acidity and cadmium-arsenic pollution, and the above-ground dry biomass was less than 0.06 g / plant. The cadmium and arsenic contents were 10.45 mg / kg and 5.35 mg / kg. After adding Fe@F650, the soil pH increased by 2.40 pH units, and the contents of exchangeable acid and exchangeable aluminum decreased by 0.24 cmol / kg (85.71%) and 0.37 cmol / kg (97.37%) respectively. The above-ground dry biomass reached 0.11 g / plant, and the cadmium and arsenic contents were 1.42 mg / kg and 2.27 mg / kg. Fe@F650 significantly alleviated the stress of the tested soil properties on the growth of Chinese cabbage, and at the same time reduced the cadmium and arsenic uptake in agricultural products, achieving the goal of safe production.

Claims

1. A magnetic iron mineral@phosphorus tailings material, characterized in that, the preparation method of the material comprises the following steps: (1) Collect phosphorus tailings, grind them through 100 meshes, and perform thermal activation under aerobic conditions; (2) Mix the thermally activated product with an iron salt solution and an alkali solution in proportion, add water to adjust the solid-liquid ratio, and place it in a reactor for heat treatment; (3) Take out the heat-treated product, elute the free iron ions until the pH of the eluate is 10 ± 0.5, and freeze-dry to obtain the magnetic iron mineral@phosphorus tailings material.

2. The magnetic iron mineral@phosphorus tailings material according to claim 1, characterized in that: In step (1) of the described material preparation method, the temperature range of the thermal weight loss of the phosphorus tailings is 600°C - 1000°C, and the P 2 O 5 content is 5% - 15%; the thermal activation temperature of the phosphorus tailings is 600 - 700°C, preferably 650°C, and the thermal activation time is 1 - 4 h, preferably 2 h.

3. The magnetic iron mineral@phosphorus tailings material according to claim 1, characterized in that: in step (2) of the material preparation method, the mixing ratio of the thermally activated product, the iron salt solution and the alkali solution is 1 g of thermally activated product: 5 - 20 mmol of iron element: 50 - 150 mmol of alkali, preferably 1 g of thermally activated product: 10 mmol of iron element: 90 mmol of alkali; the solid-liquid ratio of the thermally activated product to the iron salt solution-alkali solution-water mixture is 1 g: 200 mL; the iron salt is ferric chloride or ferric nitrate, preferably ferric nitrate, and the alkali solution is potassium hydroxide solution.

4. The magnetic iron mineral@phosphorus tailings material according to claim 1, characterized in that: in step (2) of the material preparation method, the heat treatment temperature is 60 - 80 °C, preferably 70 °C, and the heat treatment time is 48 h - 72 h, preferably 60 h.

5. The magnetic iron mineral@phosphorus tailings material according to claim 1, characterized in that: The iron minerals loaded on the magnetic iron mineral@phosphorus tailings material contain γ-Fe 2 O 3 and ε-Fe 2 O 3 magnetic iron minerals.

6. The magnetic iron mineral@phosphorus tailings material prepared by the preparation method according to any one of claims 1 - 5.

7. Use of the magnetic iron mineral@phosphorus tailings material according to claim 6 for adsorbing and removing cadmium ions, arsenate ions and arsenite ions singly or in combination present in water.

8. Use of the magnetic iron mineral@phosphorus tailings material according to claim 6 for passivating and repairing single cadmium, arsenic pollution or cadmium-arsenic combined pollution in soil.

9. Use of the magnetic iron mineral@phosphorus tailings material according to claim 6 for removing single or combined cadmium and arsenic pollutants in soil.

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