Reduction and Immobilization of Movable Cu 2+ Ions in Soils by Fe 78 Si 9 B 13 Amorphous Alloy

: The Fe-based amorphous alloy (Fe 78 Si 9 B 13AP ) is applied to the remediation of copper contaminated soil for the ﬁrst time. The dynamic process of conversion of movable Cu to immobilized forms in the soil system is analyzed. In addition, the dynamic process of form transformation of Cu 2+ ions in the soil system is analyzed. The morphology and phase composition of the reaction products are characterized by scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD). Finally, the feasibility of recovering residual stabilizer particles and attached immobilized copper by the magnetic separation process is discussed. The results show that the apparent reaction rate constant of Fe 79 Si 9 B 13AP with Cu 2+ ions is higher than that of zero valent iron (ZVI) at all the experimental temperatures. According to the Arrhenius formula, the apparent activation energy of the reaction of Fe 78 Si 9 B 13AP and ZVI with Cu 2+ ions is 13.24 and 19.02 kJ/mol, respectively, which is controlled by the diffusion process. The lower apparent activation energy is one of the important reasons for the high reaction activity of Fe 78 Si 9 B 13AP . After 7 days of reaction, a continuous extraction of the experimental soil shows that the main form of copper in the immobilized soil is Cu and copper combined with iron (hydroxide) oxide, and there is almost no soluble copper with a strong mobility, which effectively reduced the bioavailability of copper in the soil. The magnetic separation results of the treated soil show that the recovery rates of immobilized copper in Fe 78 Si 9 B 13AP and soil are 47.23% and 21.56%, respectively, which reduced the content of iron and copper in the soil to a certain extent. The above experimental results show that Fe 78 Si 9 B 13AP is a promising new material for the remediation of heavy metal contaminated soils, and provides more new references for the application of amorphous alloys in the ﬁeld of remediation of water and soil contaminated by heavy metals and organic matter.


Introduction
Soil heavy metal pollution has a large base and strong mobility, which has become an important factor restricting national sustainable development and endangering human health. Copper is one of the essential trace elements for the human body, but the high content of copper has adverse effects on animals, plants, and the human body. Baryla et al. [1] found that excessive copper can cause the concentration difference between the two sides of the plasma membrane, resulting in the flow of potassium ions out of the cell membrane, thus damaging the plasma membrane of plant roots. Dijendra et al. [2] reported that when mice were fed with a diet containing copper (15 mg/kg), their liver morphology and function would show symptoms of poisoning, and the decrease of superoxide dismutase activity would lead to mitochondrial dysfunction, and eventually lead to the death of hepatocytes. Choudhary et al. [3] reported that under the stress of heavy metals such as Cu, the growth of cyanobacteria is inhibited by the increase in the amount of proline, malondialdehyde, and superoxide dismutase. The main source of copper pollution is exogenous copper, such as waste water discharged from mining and the storage of waste As 5+ from the groundwater. As 5+ is reduced to As 3+ by Fe 79 Si 13 B 8 AR and then combined with S 2− to form the As 2 S 3 precipitation. The removal rate of As 5+ is more than 95% after 60 min. Some scholars attribute the high reactivity of MGs to the fact that the metastable structure of disordered arrangement of atoms makes the surface diffusion rate of MGs millions of times higher than that of the bulk phase [26,27].
Inspired by the previous research results, the Fe 79 Si 13 B 8 AP is applied to the immobilization and remediation of copper contaminated soil for the first time in this paper. The kinetic process of conversion of movable Cu to immobilized forms in soil and the effect of product morphology on the reaction rate are studied. Then, the feasibility of recovering residual Fe 79 Si 13 B 8 AP particles and copper immobilized on their surfaces by the magnetic separation process is explored. Providing more new references for the application of MGs in the field of environmental pollutant degradation is expected.

Soil Sample Collection
Surface loess soil without copper contamination was collected from Lanzhou suburb of Gansu Province (36 • 03 N, 103 • 49 E) and sifted through a 2 mm sieve. After screening, it was washed with distilled water three times to remove soluble compounds and suspended particles. The washed soil was air-dried and then passed through the 2 mm sieve again, and the obtained soil was put into a sample bag for backup.

Preparation of Contaminated Soil
The soil environmental quality standard of the People's Republic of China stipulates that the upper limit of copper contaminated soil is 200 mg/kg [28]. In addition, the maximum content of copper in the soil around the Baiyin copper smelter, known as "Copper City of China", is 658 mg/kg [29]. As a result, the content of copper in the contaminated soil was determined to be 600 mg/kg. The specific steps were as follows: Mixing a 1 L CuSO 4 ·5H 2 O solution of 60 mg/L with 100 g washed soil and then mechanically stirring until air-dried. In order to determine the uniformity of Cu in soil when different volumes of water were added to soil samples of the same quality. The concentration of Cu 2+ ions were inversely proportional to the volume of distilled water, indicating that Cu has been uniformly dispersed in the soil.

Immobilization of Cu 2+ Ions in the Soil: Batch Test
The immobilization effect of Fe 79 Si 13 B 8 AP and ZVI on Cu 2+ ions in the soil was evaluated under the experimental temperature of 293, 303, 313, and 323 K. In order to remove the surface oxide layer as much as possible, the stabilizer was leached with 2% HNO 3 before each batch of test. Each group of experiments was carried out in a series of 100 mL jars, and the preparation of slurry in each jar was as follows: 5 g of copper contaminated soil was mixed with 50 mL deionized water, then shaken in a water bath shaker for 5 min to completely wet the soil to form a soil suspension. According to the method of Shaaban et al. [30], the initial pH of the reaction system was adjusted to 6 by HCl and NaOH. In general, increasing the amount of stabilizer is beneficial to the immobilization of heavy metal ions [31]. However, when the content of iron in the soil is more than 5%, it will inhibit the growth of plants [32]. As a result, the dosage of Fe 78 Si 9 B 13 AP and ZVI was selected as 5% of the soil mass, that is, 0.25 g was added to the jar. When the soil reacted for 1,2,4,8,16,24,36, and 48 h, it was continuously extracted according to the method of Ure et al. [33]. The content of Cu 2+ ions in each extract was determined by inductively coupled plasma atomic emission spectrometry (ICP-AES). After the remaining two slurries continued to react for 7 days, one of them was continuously extracted according to the above-mentioned method. The other slurry carried out magnetic separation of the treated soil according to the method described by Guan [34] to separate the immobilized products and stabilizer particles. Table 1 shows all the reagents of the continuous extraction method. In order to accurately analyze the copper in the immobilization reaction and the rate control process of the reaction of Fe 78 Si 9 B 13 AP and ZVI with Cu 2+ ions in soil. The experimental results were fitted by the pseudo-first-order kinetic Equation (1) linear fitting: where t is the reaction time (h); C t is the concentration of SE at the current time (mg/kg); C 0 is the concentration of SE at the initial time (mg/kg); and k obs is the observed pseudofirst-order reaction rate constant. The reaction activation energy (∆E) is an important parameter to characterize the kinetic process of the chemical reaction. ∆E can be obtained according to the Arrhenius-type equation (Equation (2)): where k T is the k obs obtained by Equation (1) at different temperatures. R is the gas constant, R = 8.314 J/(mol·K); A is the constant.

Characterization Techniques
The surface morphology changes of Fe 78 Si 9 B 13 AP and ZVI before and after the reaction were observed by the scanning electron microscope (SEM, JSM-6700, JEOL, Akishima, Japan). The structural characterizations of the stabilizer and the composition of the reaction product were identified by X-ray diffraction (XRD, D8 ADVANCE, BRUKER, Karlsruhe, Germany) with Cu-Kα radiation (40 kV, 150 mA).

Characterization of Fe 78 Si 9 B 13
AP and ZVI Figure 1 shows the structural and morphological differences between Fe 79 Si 13 B 8 AP and ZVI before the soil remediation experiments. In Figure 1a, the crystalline α-Fe phase is observed in the X-ray diffraction spectrum of ZVI, and there is no crystallization peak of iron oxide, indicating that the purity of ZVI is high and the surface is not oxidized. There is a diffuse scattering peak in the X-ray diffraction spectrum of Fe 79 Si 13 B 8 AP around 45 • , and there is no crystallization peak in the rest of the X-ray diffraction spectrum, indicating that it is amorphous. Since there are no lattice fringes and lattice diffraction spots in the TEM and SAED images in Figure 1b, this conclusion is further confirmed. Figure 1c,d shows the SEM images of Fe 79 Si 13 B 8 AP and ZVI, respectively. The two kinds of powders have a spherical structure with a smooth surface and there is no adhesion between the particles. The particle size of Fe 78 Si 9 B 13 AP is 10-20 µm, and that of ZVI is 1-3 µm. is a diffuse scattering peak in the X-ray diffraction spectrum of Fe79Si13B8 AP around 45°, and there is no crystallization peak in the rest of the X-ray diffraction spectrum, indicating that it is amorphous. Since there are no lattice fringes and lattice diffraction spots in the TEM and SAED images in Figure 1b, this conclusion is further confirmed. Figure 1c,d shows the SEM images of Fe79Si13B8 AP and ZVI, respectively. The two kinds of powders have a spherical structure with a smooth surface and there is no adhesion between the particles. The particle size of Fe78Si9B13 AP is 10-20 μm, and that of ZVI is 1-3 μm.  Figure 2a,b shows the exponential decay curve of the normalized concentration of Cu 2+ reacting with Fe78Si9B13 AP and ZVI at different temperatures. The reaction of each experimental group basically ended within 10 h, and there is no secondary dissolution after 10 h, indicating that the reduction products could stably exist in the reaction system. Figure 2c shows the kobs obtained by fitting the quasi-first-order kinetic equation (Equation (1)). With the increase of the reaction temperature from 293 to 323 K, the kobs of each experimental group shows an upward trend. The kobs of Fe78Si9B13 AP increases from 0.955 to 1.568 h −1 . The kobs of ZVI is significantly lower than that of Fe78Si9B13 AP . Generally speaking, the smaller the particle size and the higher the content of the reactant, the more conducive it is to speeding up the reaction [35,36]. However, in this experiment, the kobs of ZVI with a relatively small particle size and higher iron content reacting with Cu 2+ are lower than Fe78Si9B13 AP with a relatively large particle size and lower iron content, which may be due to the metastable state of MGs caused by the structure.

Cu 2+ immobilization by Fe78Si9B13 AP and ZVI
As we all know, the activation energy (ΔE) reflects an important kinetic parameter of the difficulty of the chemical reaction [37]. On the basis of the above kobs, the ΔE difference between crystalline and amorphous iron-based materials is further analyzed. The illustrations in Figure 2a,b are shown as straight lines fitted by the Arrhenius-type equation (Equation (2)) for the kobs which was reacted by Fe78Si9B13 AP and ZVI with Cu 2+ at different temperatures. The correlation coefficients R 2 are all above 0.99. The ΔE of 3.2. Cu 2+ immobilization by Fe 78 Si 9 B 13 AP and ZVI Figure 2a,b shows the exponential decay curve of the normalized concentration of Cu 2+ reacting with Fe 78 Si 9 B 13 AP and ZVI at different temperatures. The reaction of each experimental group basically ended within 10 h, and there is no secondary dissolution after 10 h, indicating that the reduction products could stably exist in the reaction system. Figure 2c shows the k obs obtained by fitting the quasi-first-order kinetic equation (Equation (1)). With the increase of the reaction temperature from 293 to 323 K, the k obs of each experimental group shows an upward trend. The k obs of Fe 78 Si 9 B 13 AP increases from 0.955 to 1.568 h −1 . The k obs of ZVI is significantly lower than that of Fe 78 Si 9 B 13 AP . Generally speaking, the smaller the particle size and the higher the content of the reactant, the more conducive it is to speeding up the reaction [35,36]. However, in this experiment, the k obs of ZVI with a relatively small particle size and higher iron content reacting with Cu 2+ are lower than Fe 78 Si 9 B 13 AP with a relatively large particle size and lower iron content, which may be due to the metastable state of MGs caused by the structure.
As we all know, the activation energy (∆E) reflects an important kinetic parameter of the difficulty of the chemical reaction [37]. On the basis of the above k obs , the ∆E difference between crystalline and amorphous iron-based materials is further analyzed. The illustrations in Figure 2a,b are shown as straight lines fitted by the Arrhenius-type equation (Equation (2)) for the k obs which was reacted by Fe 78 Si 9 B 13 AP and ZVI with Cu 2+ at different temperatures. The correlation coefficients R 2 are all above 0.99. The ∆E of Fe 78 Si 9 B 13 AP is 13.24 kJ/mol, while the ∆E of ZVI which is significantly higher than that of Fe 78 Si 9 B 13 AP is 19.02 kJ/mol. In other words, Fe 78 Si 9 B 13 AP needs less energy to transform from a normal state to an active state where chemical reactions easily occur. This is due to the higher Gibbs free energy of MGs than crystalline alloys [38]. It also explains why the k obs of Fe 78 Si 9 B 13 AP is higher than that of ZVI. The ∆E of the general chemical reaction is between 60-250 kJ/mol. The ∆E of the reaction between iron-based materials and Cu 2+ is lower than that of 60 kJ/mol [39]. According to the diffusion theory, when ∆ E is within the range of 8-22 kJ/mol, the reaction is controlled by an external diffusion [40]. The ∆E of the two materials is in this range, indicating that the adsorption of soil to Cu 2+ hinders the effective contact between Cu 2+ and the reaction surface.
Fe78Si9B13 AP is 19.02 kJ/mol. In other words, Fe78Si9B13 AP needs less energy to transform a normal state to an active state where chemical reactions easily occur. This is due t higher Gibbs free energy of MGs than crystalline alloys [38]. It also explains why the of Fe78Si9B13 AP is higher than that of ZVI. The ΔE of the general chemical reactio between 60-250 kJ/mol. The ΔE of the reaction between iron-based materials and Cu lower than that of 60 kJ/mol [39]. According to the diffusion theory, when Δ E is w the range of 8-22 kJ/mol, the reaction is controlled by an external diffusion [40]. The Δ the two materials is in this range, indicating that the adsorption of soil to Cu 2+ hinder effective contact between Cu 2+ and the reaction surface.

The Fractions of Different Cu Forms in Soil after a 200 h Treatment
The existing form of heavy metals in soil is one of the important indicators fo environmental risk assessment. In order to determine the content of each compone the four forms of copper in soil after Fe78Si9B13 AP and ZVI treatment, the method of U al. [32] is used to extract the soil continuously. Figure 2d shows the influenc temperature on the fractions of different Cu forms after a 200 h treatment. The frac of soluble and exchangeable (SE) in untreated soil is the highest, accounting for 68.94 the total copper content. The second is the reducible state (OX) accounting for 16.50% fractions of oxidizable state (OM) and residual state (RE) is 9.14% and 5.41%, respecti There is almost no SE in soil after Fe78Si9B13 AP and ZVI treatment. Cu 2+ is converted to and OM by the reduction and adsorption of iron-based materials. The source of OX i Cu 2+ combined with iron oxide with high surface energy and low coordination num [41]. The fractions of OX1 in soil treated with Fe78Si9B13 AP at different temperatur 28.23%, 25.52%, 23.54%, and 22.36%, respectively. The fractions of OX2 in the soil after

The Fractions of Different Cu Forms in Soil after a 200 h Treatment
The existing form of heavy metals in soil is one of the important indicators for an environmental risk assessment. In order to determine the content of each component of the four forms of copper in soil after Fe 78 Si 9 B 13 AP and ZVI treatment, the method of Ure et al. [32] is used to extract the soil continuously. Figure 2d shows the influence of temperature on the fractions of different Cu forms after a 200 h treatment. The fractions of soluble and exchangeable (SE) in untreated soil is the highest, accounting for 68.94% of the total copper content. The second is the reducible state (OX) accounting for 16.50%. The fractions of oxidizable state (OM) and residual state (RE) is 9.14% and 5.41%, respectively. There is almost no SE in soil after Fe 78 Si 9 B 13 AP and ZVI treatment. Cu 2+ is converted to OX and OM by the reduction and adsorption of iron-based materials. The source of OX is the Cu 2+ combined with iron oxide with high surface energy and low coordination number [41]. The fractions of OX 1 in soil treated with Fe 78 Si 9 B 13 AP at different temperatures is 28.23%, 25.52%, 23.54%, and 22.36%, respectively. The fractions of OX 2 in the soil after ZVI treatment at different temperatures is 44.24%, 42.25%, 39.24%, and 36.20%, respectively. It can be seen that the fractions of OX 2 are significantly higher than that of OX 1 at all temperatures. This is due to the fact that the particle size of ZVI is much smaller than that of Fe 78 Si 9 B 13 AP , which provides more active sites for the adsorption reaction and is more conducive to the binding of Cu 2+ ions. Since the extraction of OM is carried out in acidic H 2 O 2 , this process can not only oxidize the organic matter, but also reoxidize the reduced Cu 0 to Cu 2+ ions. Therefore, OM includes organically bound copper and elemental copper. The fractions of OM 1 in the soil after Fe 78 Si 9 B 13 AP treatment is 64.62%, 68.04%, 70.59%, and 71.37%, respectively. The fractions of OM 2 in soil treated with ZVI is 47.62%, 51.26%, 55.27%, and 57.34%, respectively. With the increase in temperature, the fractions of OM 1 and OM 2 show an upward trend, and the values of each group of OM 1 are higher than OM 2 . Since the organic bound state does not participate in the immobilization process of Cu 2+ , the increase of OM fraction is caused by the conversion of Cu 2+ ions to Cu 0 . As a result, the ability of Fe 78 Si 9 B 13 AP to reduce Cu 2+ ions is higher than that of ZVI. Once the Cu 2+ ions are reduced to Cu 0 , they cannot be dissolved even if they are leached by acid rain for a long time. Combined with the change of OX fraction, it can be determined that the process of immobilization and remediation of copper contaminated soil by two kinds of iron-based materials is mainly the reduction and adsorption reaction, and the increase in temperature is beneficial to the reduction and immobilization. The fraction of RE in the soil is about 6% before and after the treatment. This is due to the fact that the process of replacing silicon, aluminum, and other atoms in the soil lattice by copper is too slow to occur in this experiment.

Reaction Mechanism Analysis
According to the previous kinetic analysis, it is known that the reduction of Cu 2+ ions by Fe 78 Si 9 B 13 AP and ZVI is controlled by the diffusion process. Therefore, the morphology and phase of the surface products directly affect the movement of Cu 2+ ions to the reaction interface. The morphology and phase composition of the surface products before and after the reaction are analyzed by SEM and XRD. Figure 3a shows the morphology of the product on the surface of Fe 78 Si 9 B 13 AP . The originally smooth surface is seriously corroded and the product layer on the surface is thin. In order to observe the morphology of the product more clearly, the B region is magnified and displayed in Figure 3b. The product layer presents a three-dimensional flower-like structure composed of nano-lamellar intercalation perpendicular to the reaction interface, and the interstitial pores provide a channel for the diffusion of Cu 2+ ions to the reaction interface. Figure 3c observed that ZVI is completely surrounded by a dense product layer. Some of the products fall off from the matrix, which is difficult to extract in the later magnetic separation process. Figure 3d shows a highresolution image of the product layer overlaid on the ZVI. The morphology of the product is dendritic and grows randomly in all directions, which hinders the contact between Cu 2+ ions and ZVI, which is the main reason for the low activity of ZVI. With regard to the explanation that the morphology of the products of amorphous and crystalline alloys affects the reaction rate, some scholars think that there is an active "liquid-like" layer on the surface of the amorphous alloy [42]. Figure 4 shows a Bragg peak of Cu 0 in the XRD pattern of soil treated with Fe 78 Si 9 B 13 AP and ZVI. The products of Cu 2+ ions reduction by two kinds of iron-based alloys are Cu 0 . Since the standard electrode potential of copper E(Cu/Cu 2+ ) is higher than the standard electrode potential of hydrogen E(H 2 /H + ), even long-term acid rain leaching cannot dissolve Cu 0 again, effectively reducing the potential risk of copper in the soil.

Magnetic Separation
The above experimental results show that Fe 78 Si 9 B 13 AP and ZVI can effectively reduce the potential risk of copper in the soil. However, when conditions such as soil pH change, the immobilized copper (such as OX) has the possibility of a secondary release. In addition, iron-based alloys added to the soil will have adverse effects on plant growth and microbial community [43]. In this study, the magnetic separation process is used to recover the stabilizer particles with immobilized products attached to the surface. The extraction result is shown in Figure 5. Since the iron content of ZVI is higher than that of Fe 78 Si 9 B 13 AP , the recovery rate of ZVI is relatively high, reaching 68.85%. The recovery rate of Fe 78 Si 9 B 13 AP is slightly lower, only 47.23%. After magnetic separation, the contents of Fe 78 Si 9 B 13 AP and ZVI in soil are 26.36 and 17.07 g/kg, respectively, which are less than the upper limit value. It can be seen that the remediation process does not cause a secondary pollution to the soil. Figure 5b shows that the recovery of copper is not satisfactory. The recovery rate of copper in the soil treated by Fe 78 Si 9 B 13 AP is 21.56%, and the remaining total copper content is 470.64 mg/kg. The recovery rate of copper in the soil treated by ZVI is 32.42%, and the remaining total copper content is 405.48 mg/kg. It is found that the recovery rate of copper in ZVI treated soil is higher than that of Fe 78 Si 9 B 13 AP , which could be explained by the SEM image in Figure 3. The products of ZVI and Cu 2+ ions are attached to the surface of ZVI, while the adhesion amount of Fe 78 Si 9 B 13 AP surface products is less. Since Cu 0 is not ferromagnetic, copper attached to the surface of the Fe-based alloy can only be extracted in the process of magnetic separation. Therefore, the recovery rate of copper in the soil treated with Fe 78 Si 9 B 13 AP is low. It can be seen from Figure 2d that when the temperature is 323 K, the content of OX and Cu 0 in the soil after the Fe 78 Si 9 B 13 AP treatment is 22.36% and 54.87%, respectively. Under ideal conditions, the recovery rate of copper can reach 77.23%, while the experimental value only reaches 42.23%, the difference between the two is 35%. This is due to the shedding of the product layer and the adsorption of copper by the soil. In order to solve the problem of low magnetic separation rate of copper, the combination of strengthening loose products and stabilizers is being considered in the follow-up experiments.

Magnetic Separation
The above experimental results show that Fe78Si9B13 AP and ZVI can effectively reduce the potential risk of copper in the soil. However, when conditions such as soil pH change, the immobilized copper (such as OX) has the possibility of a secondary release. In

Magnetic Separation
The above experimental results show that Fe78Si9B13 AP and ZVI can effectively reduce the potential risk of copper in the soil. However, when conditions such as soil pH change, the immobilized copper (such as OX) has the possibility of a secondary release. In addition, iron-based alloys added to the soil will have adverse effects on plant growth and treatment is 22.36% and 54.87%, respectively. Under ideal conditions, the recovery rate of copper can reach 77.23%, while the experimental value only reaches 42.23%, the difference between the two is 35%. This is due to the shedding of the product layer and the adsorption of copper by the soil. In order to solve the problem of low magnetic separation rate of copper, the combination of strengthening loose products and stabilizers is being considered in the follow-up experiments.

Conclusions
In this paper, ZVI is used to compare and analyze the immobilization remediation effect of Fe78Si9B13 AP on copper contaminated soil. The kinetic process of conversion of movable Cu to immobilized forms in the soil system is studied. The feasibility of the magnetic separation process for removing immobilized copper from the soil is verified. The main results and conclusions are summarized as follows: Compared with the traditional stabilizer ZVI, Fe78Si9B13 AP with a larger particle size and lower iron content can reduce movable copper in the soil more efficiently. According to the fitting analysis of the Arrhenius-type equation, the apparent activation energy of the reaction of Fe78Si9B13 AP and ZVI with Cu 2+ is 13.24 and 19.02 kJ/mol, respectively, which is controlled by the diffusion process.
The main forms of copper in the immobilized soil are OX and OM. There is almost no SE in the immobilized soil. The bioavailability of copper in the soil is effectively reduced.
The difference in the atomic arrangement between Fe78Si9B13 AP and ZVI results in a great difference in the structure of the product layer. The surface products of Fe78Si9B13 AP have a nano-pore structure, which provides a channel for the movement of Cu 2+ to the reaction interface. However, ZVI is wrapped in a dense product layer, which hinders the sustainable progress of the reaction.
The recoveries of Fe78Si9B13 AP and ZVI by the magnetic separation process are 47.23% and 68.85%, respectively, and the recoveries of copper in soil treated by Fe78Si9B13 AP and ZVI are 21.56% and 32.42%, respectively. The content of iron and copper in soil is reduced to a certain extent, which has a certain engineering application value.

Conclusions
In this paper, ZVI is used to compare and analyze the immobilization remediation effect of Fe 78 Si 9 B 13 AP on copper contaminated soil. The kinetic process of conversion of movable Cu to immobilized forms in the soil system is studied. The feasibility of the magnetic separation process for removing immobilized copper from the soil is verified. The main results and conclusions are summarized as follows: Compared with the traditional stabilizer ZVI, Fe 78 Si 9 B 13 AP with a larger particle size and lower iron content can reduce movable copper in the soil more efficiently. According to the fitting analysis of the Arrhenius-type equation, the apparent activation energy of the reaction of Fe 78 Si 9 B 13 AP and ZVI with Cu 2+ is 13.24 and 19.02 kJ/mol, respectively, which is controlled by the diffusion process.
The main forms of copper in the immobilized soil are OX and OM. There is almost no SE in the immobilized soil. The bioavailability of copper in the soil is effectively reduced.
The difference in the atomic arrangement between Fe 78 Si 9 B 13 AP and ZVI results in a great difference in the structure of the product layer. The surface products of Fe 78 Si 9 B 13 AP have a nano-pore structure, which provides a channel for the movement of Cu 2+ to the reaction interface. However, ZVI is wrapped in a dense product layer, which hinders the sustainable progress of the reaction.
The recoveries of Fe 78 Si 9 B 13 AP and ZVI by the magnetic separation process are 47.23% and 68.85%, respectively, and the recoveries of copper in soil treated by Fe 78 Si 9 B 13 AP and ZVI are 21.56% and 32.42%, respectively. The content of iron and copper in soil is reduced to a certain extent, which has a certain engineering application value.
At present, the production technology of the amorphous alloy is quite mature, and the market price is close to that of micron ZVI, which has the basic conditions for an engineering application. The above research results show that the Fe-based amorphous alloy has a high activity in the treatment of copper-contaminated soil, which solves the problem of low treatment efficiency and material waste caused by ZVI passivation. The purpose of this paper is to provide some inspiration for the application of derived amorphous alloys to the field of soil remediation.

Data Availability Statement:
No new data were created or analyzed in this study. Data sharing is not applicable to this article.