Ferrothermal dual-modified phosphorite material capable of synchronously adsorbing cadmium and arsenic as well as preparation method and application of ferrothermal dual-modified phosphorite material

Abstract

The invention discloses a ferro-thermal dual-modified phosphorite material capable of synchronously adsorbing cadmium and arsenic as well as a preparation method and application of the ferro-thermal dual-modified phosphorite material aiming at arsenic and cadmium pollution treatment requirements. According to the technical scheme disclosed by the invention, phosphorite waste containing fluorine-containing calcium phosphate and calcium magnesium carbonate is taken as a raw material, a tailing material generated by a phosphorite flotation process is preferably selected, and a novel functional material is prepared by a thermal modification-iron modification combined method. Main iron minerals loaded on the iron-heat dual-modified phosphorite material are hematite and iron phosphate. The iron-heat dual-modified phosphorite material has relatively high adsorption performance on heavy metal cations and inorganic arsenic pollutants, can efficiently adsorb and remove cadmium ions, arsenate ions and arsenite ions in a water body, and also can be used for passivating and repairing arsenic and cadmium pollution of soil; particularly, a material is provided for repairing cadmium-arsenic combined pollution in a water body or a soil environment.

Description

Technical Field

[0001] The present invention relates to the field of environmental protection, and particularly to an iron-thermally dual-modified phosphate rock material for synchronously adsorbing cadmium and arsenic, a preparation method thereof, and an application thereof. Background Art

[0002] Due to the significant differences in the properties of arsenic and cadmium pollutants, the treatment of soil arsenic-cadmium combined pollution has become a challenge. The passivation and remediation technology uses remediation materials to adsorb heavy metal pollutants in the soil, reducing the mobility and bioavailability of the pollutants. However, the existing commercially available passivation materials have poor synchronous adsorption capacity for arsenic and cadmium pollutants. The high-efficiency remediation materials for arsenic-cadmium combined pollution are mainly in the laboratory research stage, and most research results are difficult to be popularized and applied due to factors such as the small stock of raw materials and high preparation costs. There is an urgent need to continue to explore a preparation method for high-efficiency and low-cost arsenic-cadmium combined pollution remediation materials.

[0003] China is a major producer of phosphate fertilizers, and phosphate fertilizers mainly come from phosphate rock mining. However, phosphate rock mining will produce various solid wastes such as phosphate tailings, with a huge daily output. The annual output of phosphate tailings exceeds 7 million tons, and most of them are in a stockpiled state, bringing various environmental impacts. At the same time, the domestic phosphate rocks are mainly medium- and low-grade phosphate rocks. With the gradual mining of medium-grade phosphate rocks, the effective utilization of the remaining large amount of low-grade phosphate rocks has become a difficult problem.

[0004] Low-grade phosphate rocks and phosphate rock wastes still contain a certain amount of fluorapatite and dolomite minerals, and have the potential for application in the field of soil pollution remediation after activation and modification. For example, phosphate agents are one of the high-efficiency materials for fixing heavy metal pollutants such as cadmium ions. The fluorapatite minerals in low-grade phosphate rocks and phosphate rock wastes can release a large amount of phosphate ions after being activated by physical / chemical processes, which helps to fix heavy metal pollutants in the environment. Patent 202010510129.2 proposes an ammonium oxalate modification method for phosphate tailings, using organic acid salt reagents to activate the fluorapatite of the material, increasing the effective phosphorus content, and improving the fixing effect of the material on heavy metal pollutants such as cadmium, lead, and copper. Patent 202011184522.3 proposes a thermal modification method for phosphate rock flotation tailings, effectively utilizing the thermodynamic characteristics of the dolomite component in phosphate rock flotation tailings. Through thermal modification, dolomite is promoted to decompose into calcium carbonate and magnesium oxide, improving the alkalinity of the material and enhancing the interaction mechanism between the material and cation pollutants such as cadmium and lead, expanding the possibility of applying phosphate rock flotation tailings to the treatment of soil heavy metal pollution. However, by analyzing the action mechanisms of these technical solutions, it can be found that none of them can improve the adsorption capacity of phosphate rock materials for arsenite ions / arsenate ions, and the disclosed new materials lack the application prospects in the treatment of arsenic-cadmium combined pollution.

[0005] In summary, there is still a lack of technical solutions that can simultaneously improve the adsorption capacity of phosphate rock materials for cadmium ions, arsenite ions, and arsenate ions. There is still a lack of effective methods for the application of phosphate rock materials such as low-grade phosphate rock / phosphate rock waste in the treatment of arsenic-cadmium combined pollution. Summary of the Invention

[0006] In view of the above deficiencies, the present invention provides a thermally and ferrous dual-modified phosphate rock material for synchronous adsorption of cadmium and arsenic, a preparation method thereof, and an application thereof.

[0007] The preparation method of the thermally and ferrous dual-modified phosphate rock material is as follows:

[0008] (1) Collect phosphate rock materials, grind them through a 100-mesh sieve, and perform thermal modification under aerobic conditions to obtain a thermally modified product.

[0009] (2) Prepare an iron salt solution, disperse the thermally modified product in the iron salt solution, and magnetically stir at 700 rpm for 10 min at room temperature.

[0010] (3) While maintaining the conditions of room temperature and magnetic stirring at 700 rpm, gradually add an alkali solution until the pH reaches 12 ± 0.2.

[0011] (4) Allow natural sedimentation for 48 h, place it in a reactor for thermal reaction to achieve the transformation of the iron mineral phase.

[0012] (5) Take out the above product, elute the free iron ions until the pH value of the eluate is less than 9.5 and the difference in the pH values of the two eluates is less than 0.5 unit. Take out the solid and freeze-dry it.

[0013] The phosphate rock material is a phosphate rock waste containing calcium fluorophosphate and calcium magnesium carbonate, with a phosphorus content requirement of 2% - 5%, the proportion of available phosphorus in the total phosphorus not exceeding 5‰, and an Fe content lower than 1%. The phosphate rock material is preferably the tailing material produced by the phosphate rock flotation process.

[0014] The thermal modification temperature of the phosphate rock material is 600 - 800 °C; the thermal modification time of the phosphate rock material is 2 - 4 h. Preferably, the thermal modification temperature of the phosphate rock material is 650 °C and the thermal modification time is 2 h.

[0015] The iron salt is ferric nitrate or ferric chloride, with a concentration of 0.2 - 1.0 mol / L. The alkali solution is sodium hydroxide solution or potassium hydroxide solution, with a concentration of 5 - 10 mol / L. Preferably, the concentration of the iron salt solution is 0.4 mol / L and the concentration of the alkali solution is 5 mol / L.

[0016] The mixing ratio of the thermally modified product to the iron salt solution is 1 g of thermally modified product: 25 mL of iron salt solution.

[0017] The thermal reaction temperature is 80 - 100 °C. The thermal reaction time is 12 - 24 h. Preferably, the thermal reaction temperature is 90 °C and the thermal reaction time is 16 h.

[0018] The iron-thermally dual-modified phosphate rock material is any material obtained according to the above preparation method.

[0019] The iron minerals loaded on the iron-thermally dual-modified phosphate rock material are mainly hematite and iron phosphate.

[0020] The present invention claims the application of the iron-thermally dual-modified phosphate rock material in adsorbing cadmium ions, arsenate ions and arsenite ions.

[0021] The present invention claims the use of the iron-thermally dual-modified phosphate rock material for repairing heavy metal-polluted soil or water body, characterized in that the heavy metal pollution is single cadmium or arsenic pollution or combined pollution containing cadmium and arsenic.

[0022] The technical solution of the present invention can also be applied to low-grade phosphate rock materials meeting the requirements of mineral phase composition.

[0023] The present invention is further described below:

[0024] The present invention proposes a modification and enhancement scheme for phosphate rock materials containing calcium fluorophosphate and calcium carbonate magnesium components. Through thermal modification, part of calcium carbonate magnesium is promoted to be converted into magnesium oxide, calcium oxide and calcium carbonate, increasing the alkalinity of the material and activating the phosphate groups, thereby enhancing the adsorption capacity of the material for cadmium ions. Subsequently, by reacting iron salts with the modified material in a strongly alkaline environment, the synthesis and loading of iron minerals are realized, while ensuring the high adsorption capacity of the material for cadmium ions, the adsorption performance of the material for inorganic arsenic is enhanced; the regulation of the mineral components of the material in the previous thermal modification step also increases the alkalinity of the material, reduces the alkali input required to maintain the strongly alkaline environment for iron loading, and reduces the material preparation cost.

[0025] The iron-thermally dual-modified phosphate rock material proposed by this technical solution is mainly loaded with iron phosphate and hematite minerals, while the iron minerals synthesized in a pure solution system without phosphate rock material according to the above iron modification step are pure goethite, indicating that significant chemical reactions occur between iron salts and the mineral components of the phosphate rock material during the preparation process, thus changing the synthesis type of iron minerals. Further, this change in mineral phase also improves the adsorption performance of the material for pollutants: traditional phosphate rock materials are mainly used to adsorb cadmium and lead pollutants, and goethite materials are mainly used to remove arsenic pollutants, but the iron-thermally dual-modified phosphate rock material proposed by this technical solution can adsorb both cadmium and arsenic pollutants, providing a new material.

[0026] The iron-thermally dual-modified phosphate rock material proposed by the present invention has a significantly higher adsorption capacity for cadmium ions, arsenate ions, and arsenite ions than phosphate rock materials or mixtures of phosphate rock materials and goethite. When there are combined cadmium and arsenic pollutants in the environment, the material can efficiently adsorb cadmium and arsenic pollutants simultaneously; at the same time, 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, providing a functional material for the treatment of water and soil environments.

[0027] This material can react with cadmium and arsenic pollutants through multiple mechanisms. The main action 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 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.

[0028] In dryland soil and flooded soil systems, the application of the iron-thermally dual-modified phosphate rock material can reduce the available contents of cadmium and arsenic simultaneously, reducing the environmental risks of pollutants, indicating that the application scope of this material is relatively wide, providing a material for the treatment and remediation of polluted soils of different utilization types. At the same time, this technical solution uses abundant stockpiles of phosphate rock waste or low-grade phosphate rock as raw materials, providing the possibility of large-scale production of the material. Description of the Drawings

[0029] Figure 1 are the scanning electron microscope and transmission electron microscope test results of the iron-thermally dual-modified phosphate rock material and the prepared product in Example 1.

[0030] Figure 2 are the adsorption isotherms of the iron-thermally dual-modified phosphate rock material for cadmium ions, arsenate ions, and arsenite ions in Example 3.

[0031] Figure 3 is the adsorption result of the iron-thermally dual-modified phosphate rock material for the combined pollutant of cadmium ions and arsenite ions in Example 4.

[0032] Figure 4 is the adsorption result of the iron-thermally dual-modified phosphate rock material for the combined pollutant of cadmium ions and arsenate ions in Example 5.

[0033] Figure 5 is the influence of the iron-thermally dual-modified phosphate rock material on soil pH, Eh, and the availability of cadmium and arsenic in Example 6.

[0034] Figure 6It is the influence of the iron-thermal double-modified phosphate rock material in Example 7 on soil pH, Eh, and the availability of cadmium and arsenic. Specific implementation mode

[0035] The technical solution of the present invention will be further described below in combination 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 Preparation and characterization of iron-thermal double-modified phosphate rock material

[0038] Collect the waste produced by the flotation process in phosphate rock mining (abbreviated as phosphate tailing material (F)), which mainly contains calcium fluorophosphate (fluorapatite), calcium magnesium carbonate (i.e., dolomite), and silicon dioxide (i.e., quartz); the P content is 3.98%, the available P content is 55 mg / kg, and the Fe content is 0.72%.

[0039] Grind the material through 100 meshes and thermally activate it at 650 °C for 2 h under aerobic conditions to obtain a thermally modified product (F650). Mix 6 g of the thermally modified product with 150 mL of 0.4 mol / L ferric nitrate solution and stir magnetically at 700 rpm at room temperature for 10 min. Subsequently, under the conditions of room temperature and magnetic stirring at 700 rpm, gradually dropwise add 5 mol / L potassium hydroxide solution until the pH is 12, and a large amount of red flocs are formed in the solution. Let it settle naturally for 48 h, put it into a reactor and react thermally at 90 °C for 16 h to achieve the mineral phase transformation of iron. Take out the above product, elute the free iron ions until the pH value of the eluate is ~9.1 and the difference in pH values of the two eluates is less than 0.5 units, and freeze-dry to prepare an iron-thermal double-modified phosphate rock material (Fe90@F650). At the same time, under the condition of no phosphate tailing material, carry out the titration-thermal reaction of iron salt to prepare a control iron material (FeOOH).

[0040] The characterization results show that: there are significant differences in the colors of the four materials. The iron-thermal double-modified phosphate rock material changes from the gray color of the phosphate tailing material and its thermally modified product to dark brown, while the control iron material is yellow.

[0041] The results of electron microscopy analysis showed that the iron-thermally dual-modified phosphate rock material had spherical and rod-shaped iron minerals loaded on the surface of the original phosphate tailings material. The EDX results showed a relatively high content of iron elements on the material. The results of mineral composition analysis showed that: after preparation, the Fe90@F650 material still contained the original fluorapatite, dolomite and quartz, and at the same time calcium carbonate and various iron minerals were formed; while in the thermally activated product F650 of the phosphate tailings material, in addition to the original fluorapatite, dolomite and quartz, mainly new magnesium oxide, calcium carbonate and calcium oxide substances were formed. Among them, magnesium oxide and calcium oxide did not appear in Fe90@F650, mainly because they were removed by the alkali solution added during the iron mineral synthesis stage through neutralization reactions; in the control iron material FeOOH, its XRD pattern had a high degree of matching with the goethite card, so mainly high-purity goethite was synthesized during the preparation of this material. The results of Mössbauer spectroscopy characterization further proved that the iron-thermally dual-modified phosphate rock material was mainly loaded with hematite (α-Fe 2 O 3 ) and iron phosphate (FePO 4 ), and contained a small amount of iron oxyhydroxide (α-FeOOH).

[0042] The pH of Fe90@F650 was 9.22, higher than that of the F material (7.63) and lower than that of F650 (11.00). The specific surface area of Fe90@F650 was 122 cm 2 / g, 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 was beneficial to the fixation of pollutants such as cadmium ions, and the high specific surface area was also beneficial to the adsorption of various pollutants by the material. The total iron content of Fe90@F650 increased from 7.20 g / kg of the F material to 245.62 g / kg.

[0043] Table 1 Analysis results of the main iron minerals on the Fe90@F650 material by Mössbauer spectroscopy Compound IS(mm / s) QS(mm / s) Γ(mm / s) H(T) α-FeO23 0.17 0.010 0.94 49.7 α-FeOOH 0.23 0.097 0.92 45.0 FePO4 0.23 0.69 0.56 —

[0044] Example 2

[0045] Using 0.01 mol / L sodium nitrate solution as the substrate, prepare cadmium nitrate or sodium arsenite pollution solutions with cadmium or arsenic concentrations of 100 mg / L, and adjust the pH of the solutions to 5.0 ± 0.2. Weigh the F, F650 and Fe90@F650 prepared in Example 1, mix them with the pollution solutions according to a solid-liquid ratio of 1 g:500 mL, and oscillate 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 amount of the material for 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.

[0046] The results show that the adsorption capacities of Fe90@F650 for cadmium ions and arsenite ions are significantly higher than those of the F material, with the adsorption capacities being 37.64 mg / g and 32.87 mg / g respectively, while the adsorption capacities of F are only 4.07 mg / g and 1.68 mg / g. For F650 that is only thermally activated, the adsorption capacities for cadmium ions and arsenite ions are 42.61 mg / g and 13.75 mg / g respectively, and its adsorption capacity for arsenic pollutants is significantly lower than that of Fe90@F650.

[0047] Example 3

[0048] Using a 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 Fe90@F650 prepared in Example 1, mix them with the contaminated solutions at a solid-liquid ratio of 1 g : 500 mL, and shake at 150 rpm at room temperature for 72 h. Filter, dilute, determine the cadmium or arsenic concentration by ICP-OES, calculate the adsorption capacity of the materials for the pollutants, and plot the adsorption isotherms of the materials for cadmium ions, arsenate ions or arsenite ions. 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.

[0049] Figure 2 The results show that the adsorption capacities of Fe90@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 Fe90@F650 for cadmium ions, arsenite ions and arsenate ions are 132 mg / g, 99.5 mg / g and 48.4 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.

[0050] Example 4

[0051] Using a 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 Fe90@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 determine the cadmium or arsenic concentration by ICP-OES, and calculate the adsorption capacity of the material for the composite pollutants. 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.

[0052] As Figure 3 shown, in the cadmium-arsenic composite pollution solution system, Fe90@F650 can simultaneously adsorb cadmium ions and arsenic pollutants. When arsenite ions are present in the solution, the adsorption capacity of Fe90@F650 for cadmium ions increases significantly, indicating that there may be synergistic adsorption. When cadmium ions are present in the solution, the adsorption capacity of Fe90@F650 for arsenite ions increases significantly; the increase in the initial concentration of arsenic pollutants or cadmium ions will both increase the adsorption capacity of the material for arsenic.

[0053] Example 5

[0054] 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 Fe90@F650 prepared in Example 1, and mix it with the pollution solution according to the solid-liquid ratio of 1 g:500 mL, and shake it 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 amount of the composite pollutants by the material. 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 amounts of arsenate ions and arsenite ions were both converted to the adsorption amount of arsenic element per unit material.

[0055] As Figure 4 shown, in the cadmium-arsenic composite pollution solution system, Fe90@F650 can simultaneously adsorb cadmium ions and arsenic pollutants. When arsenate ions exist in the solution, the adsorption amount of Fe90@F650 to cadmium ions decreases. When cadmium ions exist in the solution, the adsorption amount of Fe90@F650 to arsenate ions increases significantly; the increase in the initial concentration of arsenic pollutants or cadmium ions will both increase the adsorption amount of arsenic by the material, indicating that there may be co-adsorption.

[0056] Example 6

[0057] Weigh two materials, F and Fe90@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 culture them 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.

[0058] The results show that:

[0059] 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 Fe90@F650 treatment group, the soil pH increased to 6.83 - 7.54, and the pH value of the soil increased with the increase of the material dosage; the soil Eh was 205 mV - 207 mV, higher than that of the F treatment group.

[0060] After adding F, the concentration of available cadmium extracted by calcium chloride in the soil decreased from 0.127 mg / kg 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 - 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%.

[0061] After adding Fe90@F650, the concentration of available cadmium extracted by calcium chloride in the soil decreased to 0.003 mg / kg - 0.008 mg / kg, a decrease of 86.9% - 94.9%. The concentration of arsenic extracted in the solution decreased by 93.5% - 97.5%, the chromium concentration decreased by 48.87% - 51.42%, the cobalt concentration decreased by 89.94% - 92.51%, the nickel concentration decreased by 65.63% - 71.04%, the copper concentration decreased by 88.27% - 90.83%, the zinc concentration decreased by 96.82% - 97.41%, and the lead concentration decreased by 98.41% - 98.78%. At the same time, the concentration of available arsenic extracted by sodium dihydrogen phosphate in the soil decreased to 3.77 - 5.00 mg / kg, a decrease of 32.1% - 48.8%. While maintaining the passivation effect on cadmium in the soil, the Fe90@F650 material significantly reduces the bioavailability of arsenic in the soil and also has a good immobilization effect on pollutants such as lead.

[0062] Further analysis of the changes in the occurrence forms of cadmium and arsenic in the soil revealed that: in the control group, the proportions of acid-soluble, reducible, oxidizable, and residual cadmium in the soil were 38.42%, 41.76%, 11.43%, and 8.39% respectively. After adding 2% of Fe90@F650, the proportions of acid-soluble, reducible, oxidizable, and residual cadmium were 47.31%, 34.79%, 8.89%, and 9.01% respectively. The material promoted the transformation of reducible and oxidizable cadmium in the soil into acid-soluble and residual cadmium. In the control group, 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 soil were 0.88%, 8.89%, 26.46%, 31.87%, and 31.90% respectively. After adding 2% of Fe90@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 0.14%, 8.55%, 40.54%, 31.32%, and 19.45% respectively. The material promoted the transformation of adsorbed arsenic in the soil into weakly crystalline iron and manganese oxide-bound arsenic.

[0063] Example 7

[0064] Weigh the two materials, F and Fe90@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.

[0065] The results showed that:

[0066] 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 Fe90@F650 treatment group, the soil pH was 6.81 - 7.51, and the soil Eh was 179 mV - 203 mV, both higher than those in the F treatment group. At the same time, with the increase in the dosage of the Fe90@F650 material, both the soil pH value and Eh value showed an increasing trend.

[0067] 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 mg / kg - 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 mg / kg - 7.41 mg / kg.

[0068] After adding Fe90@F650, the concentration of available cadmium extracted by calcium chloride in the soil decreased to 0.005 mg / kg - 0.008 mg / kg, and at the same time, the concentration of arsenic extracted in the solution decreased to 0.036 - 0.092 mg / kg, with a decrease of 94.6% - 96.4% and 89.5% - 95.9% respectively. The concentration of available arsenic extracted by sodium dihydrogen phosphate decreased to 3.69 mg / kg - 4.81 mg / kg, with a decrease of 42.1% - 55.7%. While maintaining the passivation effect on cadmium in the soil, the modified material significantly reduced the bioavailability of arsenic in the soil.

Claims

1. Preparation method of iron-thermal dual-modified phosphate rock material for synchronous adsorption of cadmium and arsenic, characterized in that, the steps are as follows: Collect phosphate rock material, grind it through 100 meshes, and perform thermal modification under aerobic conditions; Prepare an iron salt solution, disperse the thermally modified product in the iron salt solution, and magnetically stir at 700 rpm for 10 min at room temperature; while maintaining the conditions of room temperature and magnetic stirring at 700 rpm, slowly add the alkali solution drop by drop until the pH reaches 12 ± 0.2; let it settle naturally for 48 h, and put it into a reactor for thermal reaction; Take out the above product, wash and elute the free iron ions, and freeze-dry.

2. The preparation method of the iron-thermal dual-modified phosphate rock material for synchronous adsorption of cadmium and arsenic according to claim 1, characterized in that: The phosphate rock material is phosphate rock waste containing calcium fluoride phosphate and calcium carbonate magnesium, the phosphorus content requirement is 2% - 5%, and the proportion of available phosphorus in the total phosphorus is not higher than 5‰; the phosphate rock material is preferably the tailing material produced by the phosphate rock flotation process.

3. The preparation method of the iron-thermal dual-modified phosphate rock material for synchronous adsorption of cadmium and arsenic according to claim 1, characterized in that: The thermal modification temperature of the phosphate rock material in the preparation method is 600 - 800 °C, preferably 650 °C; the thermal modification time is 2 - 4 h, preferably 2 h.

4. The preparation method of the iron-thermal dual-modified phosphate rock material for synchronous adsorption of cadmium and arsenic according to claim 1, characterized in that: The iron salt is ferric nitrate or ferric chloride, with a concentration of 0.2 - 1.0 mol / L, preferably 0.4 mol / L; the alkali solution is sodium hydroxide solution or potassium hydroxide solution, with a concentration of 5 - 10 mol / L, preferably 5 mol / L.

5. The preparation method of the iron-thermal dual-modified phosphate rock material for synchronous adsorption of cadmium and arsenic according to claim 1, characterized in that: The mixing ratio of the thermally modified product to the iron salt solution is 1 g of thermally modified product: 25 mL of iron salt solution.

6. The preparation method of the iron-thermal dual-modified phosphate rock material for synchronous adsorption of cadmium and arsenic according to claim 1, characterized in that: The thermal reaction temperature is 80 - 100 °C, preferably 90 °C; the thermal reaction time is 12 - 24 h, preferably 16 h.

7. An iron-thermal dual-modified phosphate rock material for synchronous adsorption of cadmium and arsenic prepared by the preparation method according to any one of claims 1 - 6.

8. The iron-thermal dual-modified phosphate rock material for synchronous adsorption of cadmium and arsenic according to claim 7, characterized in that: The iron minerals loaded on the iron-thermal dual-modified phosphate rock material include hematite and iron phosphate.

9. Use of the iron-thermal dual-modified phosphate rock material for synchronous adsorption of cadmium and arsenic according to claim 7 for adsorbing cadmium ions, arsenate ions and arsenite ions.

10. Use of the iron-thermal dual-modified phosphate rock material for synchronous adsorption of cadmium and arsenic according to claim 7 for repairing heavy metal contaminated soil or water body.

11. Use of the iron-thermal dual-modified phosphate rock material for synchronous adsorption of cadmium and arsenic according to claim 10 for repairing heavy metal contaminated soil or water body, characterized in that, The heavy metal pollution is single cadmium and arsenic pollution or composite pollution containing cadmium and arsenic.

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