Treatment method for separating and recovering heavy metals As and Zn from lithium slag

Abstract

The invention relates to the technical field of heavy metal treatment, in particular to a treatment method for separating and recovering heavy metals As and Zn from lithium slag. According to the method, the decisive effect of factors such as matrix structure suitability and binding energy difference on As and Zn attachment behaviors is determined from the atomic scale for the first time, a precise theoretical basis is provided for target leaching agent type selection and process parameter optimization, and blindness of experience trial and error of a traditional process is avoided. Based on the closed-loop design of theoretical revelation-process optimization-experimental verification, the bottleneck of existing lithium slag treatment is effectively solved, specifically, the efficiency of targeted leaching of As by NaOH reaches 92% or above, and the efficiency of subsequent leaching of Zn by sulfuric acid is not lower than 90% and is far higher than that of a traditional process; the residual quantity of As and Zn in the leaching tailings meets the national standard, the heavy metal-containing leaching solution is single in component, the double targets of harmlessness and recycling are achieved, and the agent consumption is reduced by 30% or above compared with that of a traditional process.

Description

Technical Field

[0001] This invention relates to the field of heavy metal treatment technology, and in particular to a method for separating and recovering heavy metals As and Zn from lithium slag. Background Technology

[0002] With the rapid development of the new energy industry, spodumene and lepidolite, as core raw materials for lithium extraction, are generating a surge in lithium slag emissions during their processing. Lithium slag is an industrial solid waste produced during lithium extraction from spodumene or lepidolite, containing heavy metals such as As and Zn. Currently, the mainstream heavy metal treatment technologies for lithium slag are mainly divided into two categories: chemical solidification and biological mineralization. Chemical curing methods often use calcium-containing compounds (such as calcium hydroxide, calcium carbonate, tricalcium silicate, etc.) as curing agents to reduce the risk of heavy metal leaching through adsorption, precipitation and other processes. Biomineralization utilizes the metabolic activities of microorganisms to alter the pH value and redox environment of the system, thereby promoting the formation of stable mineral phases from heavy metals.

[0003] While the above methods can reduce leaching risks, they lack a systematic analysis of atomic-level interactions, resulting in common problems such as low solidification efficiency and high processing costs for some heavy metals, making it difficult to meet the needs of large-scale industrial applications.

[0004] 1. The lack of understanding of the atomic-level interaction mechanism leads to low curing efficiency and high cost. The solidification process of heavy metals (such as As³⁺ and Zn²⁺) is essentially a process of forming a stable chemical bond between them and the active components of the solidifying agent (such as compounds of Ca²⁺) or the lithium slag matrix (silicate structure). This involves the construction of various chemical bonds, including ionic bonds, covalent bonds, and coordinate bonds, ultimately achieving harmlessness by reducing the migration of heavy metal ions. This process is regulated by coordination chemistry: functional groups (such as -H, -OH, etc.) in the lithium slag matrix and solidifying agent coordinate with heavy metal ions, and the stability of the coordination structure depends on key parameters such as coordination number, bond length, charge distribution, and spatial configuration. If the bond energy (such as the coordination bond energy between Zn²⁺ and carboxyl groups) and spatial configuration (such as tetrahedral or octahedral coordination) are not clearly defined, it is impossible to screen for stable mineral structures, resulting in excessively long reaction times and increased costs.

[0005] 2. The lack of crystal structure matching between heavy metals and the matrix leads to secondary pollution. In traditional lithium slag heavy metal leaching processes, technical solutions often focus on improving the macroscopic leaching rate. This typically involves using strong acids (such as sulfuric acid and hydrochloric acid) or strong alkalis (such as sodium hydroxide) to adjust the system's pH value, or employing high-temperature intensification to promote the leaching of heavy metals (Ni, Cr, Zn, As, Pb, etc.). However, these processes have a fatal flaw: they fail to consider the compatibility of the heavy metals with the crystal structure of the lithium slag matrix (spodumene, SiO2) at the atomic level. This results in unstable leaching performance and a high risk of secondary pollution.

[0006] Lithium spodumene (LiAlSi2O6) has a typical chain silicate crystal structure, in which Al-O tetrahedra and Si-O chains are arranged alternately in its lattice, forming a large number of coordination vacancies with a pore size of 0.2-0.3 nm. SiO2, as the main component of lithium slag (accounting for more than 60%), has a core structure of Si-O tetrahedral network, with a surface hydroxyl (Si-OH) density of 5-8 per nm², and also has strong hydrogen bonding sites. Traditional leaching processes do not have parameters designed to address the aforementioned structural characteristics. Due to the strong compatibility of heavy metal ions such as As³⁺ with Al-O coordination vacancies, they are not completely desorbed, or they are reattached due to electrostatic adsorption with the SiO2 tetrahedral network. This results in the residual heavy metal content in the leachate exceeding the limits specified in the "Identification Standard for Hazardous Waste" (GB 5085.3—2007). If the heavy metals are directly discharged or simply solidified in subsequent treatment, they are easily re-migrated with rainwater infiltration or changes in environmental pH, causing secondary pollution of soil and water bodies. At the same time, excessive leaching agents can also damage the matrix structure and generate new harmful byproducts.

[0007] Therefore, how to reveal the essential laws of arsenic adhesion and desorption on the surface of spodumene and zinc on the surface of SiO2 from the microscopic atomic and coordination level, clarify the intrinsic relationship between "crystal structure-coordination-leaching efficiency" and establish a corresponding model, and then optimize the type, concentration and reaction process parameters of leaching agent in a targeted manner to achieve stepwise selective and efficient separation and recovery of arsenic and zinc in lithium slag with low secondary pollution has become a core technical problem that urgently needs to be solved in this field. Summary of the Invention

[0008] To address the above problems, this invention provides a method for separating and recovering heavy metals As and Zn from lithium slag, achieving stepwise selective and efficient separation and recovery of arsenic and zinc, and reducing secondary pollution.

[0009] The technical solution of this invention is: A method for separating and recovering heavy metals As and Zn from lithium slag includes the following steps: Step 1: Construct the matrix model and heavy metal morphology model S1.1, Constructing the spodumene model Using simulation software, a 1×1×1 unit cell was constructed based on the single crystal structure of spodumene. S1.2 Constructing the SiO2 model Using simulation software, a 1×1×1 supercell was constructed based on the SiO2 single crystal structure. S1.3 Constructing a heavy metal morphology model The distribution of heavy metal As and Zn in the lithium slag leaching system was constructed by simulation software, the dominant forms of As and Zn were determined, and DFT was used to perform geometric optimization of the two forms. Step 2, DFT adsorption behavior calculation S2.1 Using the 1×1×1 spodumene unit cell constructed in step S1.1 and the 1×1×1 SiO2 supercell constructed in step S1.2 as the adsorption substrate, the subsequent surface relaxation calculation is performed using their crystal structure and lattice parameters. S2.2 The preferred form of heavy metal optimized in step S1.3 is used as the adsorbate; S2.3 Calculation parameter settings and basis model adaptation: The exchange correlation energy is calculated using the PBE functional in the generalized gradient approximation, and spin polarization is calculated throughout the process. A stable electronic structure is obtained through self-consistent iteration. S2.4 Atom Optimization and Adsorption Simulation Atom positions and horizontal lattice parameters are optimized using a conjugate gradient algorithm, while vertical lattice parameters are fixed during the optimization process to simulate surface relaxation states. The AsO4 determined in step one 3- and Zn 2+ H is attached to the topological active sites on the spodumene and SiO2 crystal planes, respectively, by introducing H onto the surface. + and OH - Simulate acidic and alkaline environments with different pH levels; S2.5 binding energy calculation Using the binding energy formula: Eb = Etot - Etom, the binding energy was calculated for different matrices (spodumene, SiO2) and different heavy metals (Zn). 2+ AsO4 3- The binding energy of ) Where Etot is the total energy of the adsorption system formed by the substrate and adsorbate constructed in step one; Etom is the sum of the total energy of the isolated substrate and the total energy of the isolated adsorbate, with the van der Waals interaction energy between the substrate and the adsorbate deducted during the calculation. Step 3: Selective adsorption and separation of AsO4³⁻ and Zn²⁺ in solution S3.1 Selection of Matrix Material Spodumene and SiO2 were selected as adsorption matrices, respectively. S3.2 Target Heavy Metal Adsorption The spodumene and SiO2 selected in step S3.1 are respectively added into a mixture containing AsO4. 3- and Zn 2+ In water, the coordination vacancies of Al-O tetrahedra on the spodumene surface interact with AsO4. 3- The tetrahedral structure forms a geometrically matched stable coordination structure, achieving AsO4 coordination bonds. 3- Selective adsorption; simultaneously, the hydrogen bonding sites and bridging oxygen structures of Si-OH on the SiO2 surface interact with weak coordination bonds with Zn via electrostatic interactions. 2+ The combination of Zn-O covalent bonds and electrostatic interactions enables the control of Zn. 2+ Selective adsorption; S3.3 Acid-base environment regulation Based on AsO4 in water bodies 3- With Zn 2+ The content ratio of the adsorption agent is adjusted by regulating the pH value of the water to control the adsorption effect. S3.4 Separation after adsorption After adsorption reaches equilibrium, spodumene and SiO2 in the water are separated to achieve AsO4. 3- With Zn 2+ Selective separation and recovery; Step 4: Leaching of heavy metals from lithium slag S4.1 Lithium slag pretreatment: The lithium slag containing arsenic and zinc obtained from the previous adsorption separation process is ground and sieved to control the lithium slag particle size within a preset initial range to obtain pretreated lithium slag. S4.2 Selective leaching of arsenic: Pretreated lithium slag is added to sodium hydroxide solution and leached with stirring under preset initial process parameters. After leaching, solid and liquid are separated to obtain arsenic-containing leachate and arsenic-removed filter residue. S4.3 Selective leaching of zinc: The arsenic-removed filter residue obtained in step S4.2 is added to a sulfuric acid solution and leached with stirring under preset initial process parameters. After leaching, solid and liquid are separated to obtain zinc-containing leachate and leaching tail residue. S4.4 Process Parameter Optimization: Based on the binding characteristics and leaching behavior correlation of As, Zn with spodumene and SiO2 revealed by the previous adsorption process, the key process parameters in steps S2 and S3 were optimized through single-factor experiments and response surface methodology. The key process parameters include leaching time, lithium slag particle size, leaching agent concentration, and leaching temperature, to obtain the optimal parameter combination for arsenic and zinc leaching.

[0010] Specifically, the lattice parameters of the unit cell are a=5.19Å, b=8.54Å, c=9.18Å, α=90.00°, β=102.63°, and γ=90.00°.

[0011] Specifically, the lattice parameters of the supercell are a=13.79Å, b=4.84Å, c=8.74Å, α=90.00°, β=128.98°, and γ=90.00°.

[0012] Specifically, in step S1.3, after geometric optimization, the As-O bond length of AsO4³⁻ is 1.68 Å, and the ionic radius of Zn²⁺ is 0.74 Å.

[0013] Specifically, in step S2.2, the adsorbate of As is AsO4³⁻ with an As-O bond length of 1.68 Å, and the adsorbate of Zn is Zn²⁺ with an ionic radius of 0.74 Å.

[0014] Specifically, in step S2.3, the plane wave cutoff energy of the wave function is set to 400 eV, where: The k-point of the spodumene model was sampled using a 3×2×2 Monkhorst-Pack grid. The k-point of the SiO2 model was sampled using a 2×4×3 Monkhorst-Pack grid, and the sampling density was determined based on the cell size and atomic arrangement density of the model in step one.

[0015] Specifically, in step S2.4, the energy convergence criterion is set to 1.0 × 10⁻⁶. -5 eV, with the force convergence criterion set to 0.02 eV / Å.

[0016] Specifically, in step S3.1, the spodumene has a particle size of 50-200 μm, the SiO2 has a particle size of 100-300 μm, and the specific surface area of ​​both matrix materials is not less than 50 m² / g.

[0017] Specifically, the spodumene and AsO4-containing materials mentioned in step S3.2 3- Zn 2+ The solid-liquid ratio of the water body is 1:50-1:200, with SiO2 and AsO4-containing substances... 3- Zn 2+ The solid-liquid ratio of the water is 1:30-1:150. The adsorption process is carried out at a temperature of 25-45℃, for a time of 2-8 hours, and with a stirring rate of 100-300 r / min.

[0018] Specifically, in step S3.3, when it is necessary to enhance the treatment of AsO4... 3- Adsorption and weakening of Zn 2+ During adsorption, the water is controlled to be weakly alkaline, and adsorption is achieved through the reaction of OH⁻ with Zn. 2+ Formation of hydroxyl complexes, reducing Zn 2+ The binding energy with the SiO2 matrix disrupts the spatial configuration of the Zn-O bonds; When it is necessary to strengthen the Zn 2+Adsorption and weakening of AsO4 3- During adsorption, the water body is controlled to be weakly acidic, and H+ is used to... + It preferentially binds to the Si-O sites on the SiO2 surface, reducing the AsO4 content. 3- The binding energy with the matrix weakens the electron cloud density of the As-O bond.

[0019] This invention designs a leaching process based on the heavy metal adhesion mechanism revealed by density functional theory (DFT), achieving a unity of theoretical innovation and application value. By constructing crystal structure models of spodumene and SiO2 through DFT calculations, and combining heavy metal morphology optimization and adsorption energy analysis, this invention, for the first time at the atomic scale, clarifies the decisive role of factors such as matrix structure compatibility and binding energy differences in the adhesion behavior of As and Zn. This provides a precise theoretical basis for the selection of targeted leaching agents and the optimization of process parameters, avoiding the blindness of traditional "trial and error" processes. Based on a closed-loop design of "theoretical revelation—process optimization—experimental verification," it effectively solves the bottlenecks in existing lithium slag treatment: the efficiency of NaOH targeted leaching of As reaches over 92%, and the efficiency of subsequent sulfuric acid leaching of Zn is no less than 90%, far exceeding that of traditional processes; the residual As and Zn in the leaching tailings meet national standards, and the heavy metal-containing leachate has a single composition, achieving the dual goals of "harmlessness + resource utilization," and reducing reagent consumption by more than 30% compared to traditional processes. Meanwhile, the cross-scale paradigm of "DFT theoretical calculation - mineral processing technology" established by this invention can be applied to the treatment of solid wastes such as tailings and smelting slag, providing the industry with a brand-new technical path and having important value for promoting the resource utilization of solid waste and environmental protection. Attached Figure Description

[0020] Figure 1 It is a crystal structure diagram of heavy metals (As, Zn) attached to a matrix (spodumene, SiO2); Figure 2 It is H + Figure showing the bond length variation of As in SiO2 under different conditions; Figure 3 It is OH − The bond length variation of Zn in SiO2 under the specified environment. Detailed Implementation

[0021] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0022] The following is for reference. Figure 1-3 Describe the present invention; A method for separating and recovering heavy metals As and Zn from lithium slag includes the following steps: Step 1: Construct the matrix model and heavy metal morphology model S1.1, Constructing the spodumene model Using Materials Studio simulation software, a 1×1×1 unit cell was constructed based on the single crystal structure of spodumene (space group P21 / c). The lattice parameters of the unit cell are a=5.19Å, b=8.54Å, c=9.18Å, α=90.00°, β=102.63°, and γ=90.00°. S1.2 Constructing the SiO2 model Using Materials Studio simulation software, a 1×1×1 supercell was constructed based on the SiO2 single crystal structure (space group C2 / c). The lattice parameters of the supercell are a=13.79Å, b=4.84Å, c=8.74Å, α=90.00°, β=128.98°, and γ=90.00°. The relevant parameters of crystal structures of different mineral phases are shown in Table 1: Table 1: S1.3 Constructing a heavy metal morphology model The speciation of heavy metals As and Zn in a lithium slag leaching system (pH=2-12) was constructed using Materials Studio simulation software. The dominant speciation of As was determined to be AsO4³⁻ (tetrahedral structure) and the dominant speciation of Zn was determined to be Zn²⁺ (isolated ion). DFT was used to optimize the geometry of the two speciations. After optimization, the As-O bond length of AsO4³⁻ was 1.68 Å and the ionic radius of Zn²⁺ was 0.74 Å. The optimizations include the following: (1) Atomic coordinate optimization: Adjust the three-dimensional spatial coordinates (x, y, z) of each atom in the system so that the net force on the atom approaches 0; (2) Optimization of lattice parameters: Adjust the lattice parameters (a, b, c) and lattice angles (α, β, γ) of the crystal to make the stress tensor of the lattice approach 0; (3) Stress tensor optimization: When the system needs to simulate actual working conditions, optimize the lattice parameters to meet the specified external pressure (such as 0 GPa (normal pressure) or 5 GPa (service pressure)) so that the system stress is balanced with the external pressure.

[0023] The optimization method employs the conjugate gradient method (CG): it searches along the conjugate direction of the energy gradient, gradually approximating the energy minimum, without needing to store the Hessian matrix. The optimization steps include: (1) Preprocessing: Structure building and document preparation Download crystal structures from crystal databases (such as ICSD, COD) or build models using Materials Studio or VESTA; prepare input files (INCAR, POSCAR, POTCAR, KPOINTS).

[0024] (2) Iterative optimization: phased relaxation Coarse optimization (fast relaxation); fine optimization (high-precision relaxation).

[0025] (3) Result verification: Optimization rationality judgment Check the total energy change in the OUTCAR file to ensure that the energy decreases monotonically and tends to stabilize (without oscillations or increases) during the iteration process.

[0026] Step 2, DFT adsorption behavior calculation To determine the leaching behavior of heavy metals Zn and As in acidic and alkaline solutions in lithium slag samples and to support experimental research, density functional theory (DFT) was used to conduct computational simulations using projected fused wave (PAW) pseudopotentials in the VASP package. The core substrate and adsorbate of the computational system were directly modeled using the model constructed and optimized in step one. S2.1 Using the spodumene 1×1×1 unit cell (lattice parameters a=5.19Å, b=8.54Å, c=9.18Å, α=90.00°, β=102.63°, γ=90.00°) constructed in step S1.1 and the SiO2 1×1×1 supercell (lattice parameters a=13.79Å, b=4.84Å, c=8.74Å, α=90.00°, β=128.98°, γ=90.00°) constructed in step S1.2 as the adsorption substrate, the subsequent surface relaxation calculations are performed using their crystal structure and lattice parameters; S2.2 The preferred heavy metal form optimized in step S1.3 is used as the adsorbate, that is, the adsorbate of As is AsO4³⁻ (tetrahedral structure) with an As-O bond length of 1.68 Å, and the adsorbate of Zn is Zn²⁺ (isolated ion) with an ionic radius of 0.74 Å. The optimized geometric structure is used as the initial adsorption configuration. S2.3 Calculation parameter settings and basis model adaptation: The exchange correlation energy is calculated using the PBE functional in the generalized gradient approximation (GGA), and spin polarization is calculated throughout the process. A stable electronic structure is obtained through self-consistent iteration. The plane wave cutoff energy of the wave function is set to 400 eV, where: The k-point of the spodumene model was sampled using a 3×2×2 Monkhorst-Pack grid. The k-point of the SiO2 model is sampled using a 2×4×3 Monkhorst-Pack grid, and the sampling density is determined based on the optimization of the cell size and atomic arrangement density of the model in step one. S2.4 Atom Optimization and Adsorption Simulation Atomic positions and horizontal lattice parameters were optimized using a conjugate gradient algorithm; Specifically, using the conjugate gradient algorithm (with IBRION=2 and ISIF=3 in VASP), the three-dimensional Cartesian coordinates (x, y, z) of each atom in the system, as well as the side lengths (a, b, c) and lattice angles (α, β, γ) of the horizontal lattice, are iteratively adjusted to ensure that the net three-dimensional interaction force between atoms is ≤0.01 eV / Å and the lattice stress approaches 0. Ultimately, the total energy of the system is reduced to the thermodynamic minimum, resulting in a stable structure with reasonable bond lengths, bond angles, and lattice morphology. During the optimization process, the lattice parameters in the vertical direction are fixed to simulate the surface relaxation state, and the energy convergence criterion is set to 1.0 × 10⁻⁶. -5 eV (self-consistent iterative convergence), the force convergence criterion is set to 0.02 eV / Å (atomic relaxation convergence, taking the absolute value); The AsO4 determined in step one 3- and Zn 2+ H is attached to the topological active sites on the spodumene and SiO2 crystal planes, respectively, by introducing H onto the surface. + (Concentration of 0.01-1 mol / L corresponds to 1-5 H+ ions) + / cell) and OH - (Concentration of 0.01-1 mol / L corresponds to 1-5 OH groups) - / cell) to simulate acid-base environments with different pH values ​​(2-12), where H + and OH - The initial adsorption sites are pre-screened based on the crystal structure features of the matrix model in step one (such as the inter-chain gaps of spodumene and the distribution of Si-OH groups on the SiO2 surface) and the crystal field stabilization energy calculation. Based on crystal structure characteristics and crystal field stabilization energy (CFSE) calculations, the screening steps are as follows: ① Identify candidate adsorption sites with electronegativity matching (H⁺ matches negative potential sites, OH⁻ matches positive potential sites) from the crystal structures of spodumene (interchain interstitial sites, surface charge unsaturated Li⁺ / O²⁻ sites) and SiO2 (Si-OH groups, Si-O-Si bridging oxygen sites); ② Construct adsorption models for each candidate site and calculate the CFSE of the coordination environment after adsorption; ③ Select sites with larger absolute values ​​of CFSE (more stable coordination) as initial adsorption sites for H⁺ and OH⁻ to ensure consistency with the adsorption thermodynamic trend under acid and alkaline conditions.

[0027] S2.5 binding energy calculation Using the binding energy formula: Eb = Etot - Etom, the binding energy was calculated for different matrices (spodumene, SiO2) and different heavy metals (Zn). 2+ AsO4 3- The binding energy of ) Etot refers to the substrate (spodumene or SiO2) and adsorbate (Zn) constructed in step one. 2+ or AsO4 3- The total energy of the adsorption system formed; Etom is the sum of the total energy of the isolated substrate and the total energy of the isolated adsorbate, with the van der Waals interaction energy between the substrate and the adsorbate deducted during the calculation. Step 3: Selective adsorption and separation of AsO4³⁻ and Zn²⁺ in solution Based on the binding energy (Eb) calculation results in step two, by comparing different matrices (spodumene, SiO2) with different heavy metals (Zn)... 2+ AsO4 3- The difference in binding energy (Eb) between the adsorption and separation ions, combined with the variation of Eb under acid-base conditions, allows for adjustment of the water's pH to regulate the adsorption effect and achieve post-adsorption separation; specifically including: S3.1 Selection of Matrix Material Spodumene and SiO2 were selected as the adsorption matrix, respectively. Spodumene has a chain silicate structure, which consists of [SiO4] tetrahedral chains and [AlO6] octahedral chains connected by Li... + The links form a sandwich-like rod chain with low inter-chain bond density and large gaps, and coordination vacancies exist in the Al-O tetrahedra on its surface; the SiO2 has a Si-O tetrahedral network structure, in which interlayer domains and Si-OH surface groups exist. The spodumene particle size in step S3.1 is 50-200 μm, the SiO2 particle size is 100-300 μm, and the specific surface area of ​​both matrix materials is not less than 50 m² / g.

[0028] Target heavy metal adsorption The spodumene and SiO2 selected in step S3.1 are respectively added into a mixture containing AsO4. 3- and Zn 2+ In water, the coordination vacancies of Al-O tetrahedra on the spodumene surface interact with AsO4. 3- The tetrahedral structure forms a geometrically matched stable coordination structure, achieving AsO4 coordination bonds. 3- Selective adsorption; simultaneously, the hydrogen bonding sites and bridging oxygen structures of Si-OH on the SiO2 surface interact with weak coordination bonds with Zn via electrostatic interactions. 2+ The combination of Zn-O covalent bonds and electrostatic interactions enables the control of Zn.2+ Selective adsorption; The spodumene and AsO4-containing materials mentioned in step S3.2 3- Zn 2+ The solid-liquid ratio of the water body is 1:50-1:200, with SiO2 and AsO4-containing substances... 3- Zn 2+ The solid-liquid ratio of the water is 1:30-1:150. The adsorption process is carried out at a temperature of 25-45℃, for a time of 2-8 hours, and with a stirring rate of 100-300 r / min.

[0029] Acid-base environment regulation Based on AsO4 in water bodies 3- With Zn 2+ The content ratio of [specific component] is adjusted to regulate the pH value of the water to control the adsorption effect, specifically as follows: When it is necessary to strengthen the control of AsO4 3- Adsorption and weakening of Zn 2+ During adsorption, the water is controlled to be weakly alkaline, and adsorption is achieved through the reaction of OH⁻ with Zn. 2+ Formation of hydroxyl complexes, reducing Zn 2+ The binding energy with the SiO2 matrix disrupts the spatial configuration of the Zn-O bonds; When it is necessary to strengthen the Zn 2+ Adsorption and weakening of AsO4 3- During adsorption, the water body is controlled to be weakly acidic, and H+ is used to... + It preferentially binds to the Si-O sites on the SiO2 surface, reducing the AsO4 content. 3- The binding energy with the matrix weakens the electron cloud density of the As-O bond; The pH range of the weakly alkaline water body in step S3 is 8.0-10.0, and the pH range of the weakly acidic water body is 4.0-6.0.

[0030] Separation after adsorption After adsorption reaches equilibrium, spodumene and SiO2 in the water are separated to achieve AsO4. 3- With Zn 2+ Selective separation and recovery; The separation method described in step S3.4 is filtration or centrifugation. The filtration uses a filter membrane with a pore size of 0.22-0.45 μm, and the centrifugation speed is 3000-5000 r / min.

[0031] Based on the Eb calculation results, it can be seen that AsO4 3- The Eb on the surface of spodumene is significantly higher than that on the surface of SiO2, Zn 2+The Eb value of the SiO2 surface is higher than that of the spodumene surface, confirming the selectivity of the attachment site. The chain silicate structure of spodumene consists of [SiO4] tetrahedral chains and [AlO6] octahedral chains connected by Li + The chains connect to form sandwich-like rod chains with low inter-chain bond density and large gaps. The coordination vacancies of Al-O tetrahedra on the surface and the dominant As form AsO4 3- (Tetrahedral structure) forms a geometrically matched stable coordination structure, becoming the main attachment sites for As; the Si-O tetrahedral network of SiO2 contains interlayer domains and Si-OH surface groups, and the hydrogen bonding sites and bridging oxygen structures of Si-OH adsorb Zn through electrostatic interactions and weak coordination bonds. 2+ (Isolated ions) form a relatively loose attachment structure.

[0032] The attachment core of As is the As-O coordination bond, which corresponds to a high Eb value and Al on the substrate surface. 3+ Si 4+ The strong coordination ability is directly related; the adhesion of Zn depends on the Zn-O covalent bond and electrostatic interaction, and its Eb value reflects the strength of the bonding. When H is present in the environment... + When OH⁻ is present, coordination competition is triggered, and the Eb value increases with H⁻. + OH - Concentration changes exhibit regular fluctuations: H + Preferentially binding to Si-O sites on the SiO2 surface, As reduces the Eb value of the matrix and weakens the electron cloud density of the As-O bond; OH - With Zn 2+ The formation of more stable hydroxyl complexes reduces the Eb value of Zn and the matrix, disrupts the spatial configuration of Zn-O bonds, and leads to chemical bond elongation and reduced bond energy.

[0033] Step 4: Leaching of heavy metals from lithium slag Based on the coordination mechanism between the matrix and heavy metals in lithium slag, a stepwise selective leaching strategy is adopted to achieve efficient separation and recovery of arsenic and zinc, including the following steps: S4.1 Lithium slag pretreatment: The lithium slag containing arsenic and zinc obtained from the previous adsorption separation process is ground and sieved to control the lithium slag particle size within a preset initial range to obtain pretreated lithium slag. S4.2 Selective leaching of arsenic: Pretreated lithium slag is added to a sodium hydroxide solution and leached with stirring under preset initial process parameters. The OH- in the sodium hydroxide solution... - On the one hand, it interacts with the Al on the surface of spodumene in lithium slag. 3+ Forming stable hydroxyl complexes, replacing silicon-oxygen bonds and coordinating water molecules; on the other hand, reacting with SiO2 on the surface of lithium slag. 4+Stable Si-OH coordination bonds are formed, which change the surface charge of SiO2 (from positive to negative) by replacing Si-O-Si bridging oxygen, weak adsorbed species and heavy metal binding sites. Finally, the adhesion of arsenic is destroyed through electrostatic repulsion, steric hindrance, coordination competition and precipitation, so that As enters the leachate in a soluble form. After leaching, solid and liquid are separated to obtain arsenic-containing leachate and arsenic-removed filter residue. OH - Si on the SiO2 surface 4+ The stable Si-OH coordination bonds formed have a higher bonding strength than the original Si-O-Si bridging oxygen and heavy metal binding sites on the SiO2 surface. This allows for efficient site substitution. After the surface charge changes from positive to negative, it can form electrostatic repulsion with the soluble form of arsenic, further enhancing the desorption effect of arsenic.

[0034] S4.3 Selective Leaching of Zinc: The arsenic-removed filter residue obtained in step S4.2 is added to a sulfuric acid solution, and leaching is carried out with stirring under preset initial process parameters. The H+ ions in the sulfuric acid solution protonate the bridging oxygen on the SiO2 surface of the filter residue to form Si-OH2⁺, weakening the bond energy of the Zn-O bond. The bond energy decreases from 3.2 eV to 1.8 eV, thereby promoting the selective leaching of Zn. 2+ Desorption allows Zn to enter the leachate in a soluble form; after leaching, solid-liquid separation is performed to obtain zinc-containing leachate and leaching tailings. S4.4 Process Parameter Optimization: Based on the binding characteristics and leaching behavior correlation of As, Zn with spodumene and SiO2 revealed by the previous adsorption process, the key process parameters in steps S2 and S3 were optimized through single-factor experiments and response surface methodology. The key process parameters include leaching time, lithium slag particle size, leaching agent concentration, and leaching temperature, to obtain the optimal parameter combination for arsenic and zinc leaching.

[0035] Single-factor experiments: A single parameter was controlled (e.g., other parameters were fixed while only the NaOH concentration was changed) to determine the leaching rates of As and Zn at different levels, thus screening the effective range of each parameter; as shown in Table 2, the experimental parameters for heavy metal leaching from lithium slag are as follows: Table 2: Response surface methodology: Based on the results of single-factor experiments, parameters that have a significant impact on the leaching rate (such as leaching agent concentration and temperature) are selected to construct a quadratic regression model. The interaction between parameters is determined through statistical analysis (such as the synergistic effect of temperature increase on the leaching of Zn by high-concentration sulfuric acid). Finally, the optimal parameter combination is obtained (such as "NaOH concentration 5mol / L + temperature 60℃ + leaching time 150min" corresponds to an As leaching rate of 92%).

[0036] Example 1: The mineral composition of solid waste also determines the leaching behavior. As mentioned earlier, the main phases of untreated lithium slag are spodumene, lithium mother rock, lepidolite, and quartz, as well as abundant chemical components such as Al2O3, CaO, Na2O, and K2O. This embodiment takes spodumene (LiAl(SiO3)2) and SiO2 as examples and uses density functional theory calculations to systematically study the leaching mechanism of As and Zn ions in the lithium slag mineral phases. The crystal structures of heavy metals (As, Zn) attached to the matrix (spodumene, SiO2) show that the space group of spodumene is P21 / c and the space group of SiO2 is C2c.

[0037] Theoretically, a single-chain silicate mineral's basic structure consists of [SiO4] tetrahedra and [AlO6] octahedra. The [SiO4] tetrahedra are connected by oxygen atoms sharing corners to form extended silicon-oxygen tetrahedral chains, while the [AlO6] octahedra are connected by sharing edges to form extended octahedral chains. These two chains are further connected by lithium, ultimately forming a 2:1 sandwich-like rod chain. Due to the low bond density and weak bonding between the ring chains, large gaps exist during the connection process, which can be occupied by heavy metals. Quartz, being a silicon-oxygen tetrahedral structure, possesses certain interlayer domains within its structural space, providing entry points for heavy metals and facilitating their adsorption. Furthermore, different minerals exhibit different adsorption characteristics for heavy metal ions, which can be well understood at the molecular and even atomic scales through DFT calculations. By definition, the larger the absolute value of the binding energy (|Eb|), the easier it is for heavy metal atoms to be incorporated into the structure. The absolute values ​​of the binding energies between spodumene and As in lithium slag are significantly higher than those between spodumene and Zn. Similarly, the absolute values ​​of the binding energies between SiO2 and As are also higher than those between SiO2 and Zn. This indicates that the heavy metal As is more readily soluble in the lithium slag structure, while Zn is more easily leached. Overall simulations show that calculating the binding energies between minerals can reveal the ease with which heavy metals leach from minerals, laying a foundation for future experiments. (Binding energy of heavy metals adhering to the matrix |E) b As shown in Table 3: Table 3: Example 2 This embodiment constructs a concentration gradient model for H⁺ and OH⁻ using density function theory (DFT), providing direct evidence at the atomic scale to reveal the influence mechanism of acid-base environment on the leaching behavior of heavy metals in lithium slag, and providing experimental basis for the selection and concentration optimization of leaching agents.

[0038] The experiment used SiO2 as the research object, focusing on monitoring the changes in bond lengths between As and O, and Zn and O, under different acid and alkali concentrations. Bond length is a key parameter reflecting the strength of chemical bonds—the longer the bond length, the weaker the chemical bond energy, the easier it is to break, and the easier it is for heavy metals to desorb and leach from the substrate surface. In an H⁺ environment, the effect of H⁺ concentration gradients from 2 mol / L to 8 mol / L on As leaching was simulated: when the H⁺ concentration was 2 mol / L, the As-O bond length was 2.146 Å; as the H⁺ concentration increased to 4 mol / L, the bond length extended to 2.248 Å; when the H⁺ concentration further increased to 6 mol / L and 8 mol / L, the bond lengths reached 2.337 Å and 2.384 Å, respectively. The core reason for this change is that H⁺ competes with the Si-O sites on the SiO2 surface for adsorption, weakening the interaction between As and O, leading to the gradual elongation of the As-O bond. In an OH⁻ environment, the effect of OH⁻ concentration gradients from 1 mol / L to 9 mol / L on Zn leaching was simulated: at an OH⁻ concentration of 1 mol / L, the Zn-O bond length was 2.119 Å; when the concentration increased to 3 mol / L, the bond length extended to 2.362 Å; at OH⁻ concentrations of 5 mol / L, 7 mol / L, and 9 mol / L, the bond lengths increased to 2.391 Å, 2.433 Å, and 2.454 Å, respectively. The essence of this phenomenon is that OH⁻ coordinates with Zn, and this coordination competition disrupts the Zn-O covalent bonds between Zn and the bridging oxygen on the SiO₂ surface, causing the Zn-O bonds to continuously lengthen. Overall experimental results show that with the increase of acid and base concentration, the bond lengths of As-O and Zn-O bonds both show a significant elongation trend, and the chemical bond strength weakens accordingly, making them easier to break in the end. This significantly promotes the desorption and leaching of As and Zn from the SiO2 matrix surface. This conclusion is highly consistent with the heavy metal adhesion mechanism revealed in step three, and also provides direct experimental support for step four, which selects NaOH (providing OH⁻) as the leaching agent for As and sulfuric acid (providing H⁺) as the leaching agent for Zn.

[0039] Table 4. Changes in bond lengths of As and Zn in SiO2 under different acid and alkali concentrations. This case transforms the atomic-level attachment / desorption mechanisms revealed in step three (such as "coordination competition between OH⁻ and Al³⁺" and "weakening effect of H⁺ on Zn-O bonds") into operable process parameters, establishing a complete logical chain of "theoretical calculation → mechanism analysis → process optimization," thus avoiding the blindness of traditional leaching processes that rely on trial and error based on experience.

[0040] Regarding the information disclosed in this case, the following points need to be clarified: (1) The accompanying drawings of the embodiments disclosed in this case only involve the structures involved in the embodiments disclosed in this case. Other structures can refer to the general design. (2) Where there is no conflict, the embodiments and features disclosed in this case can be combined with each other to obtain new embodiments; The above are merely specific embodiments disclosed in this case, but the scope of protection of this disclosure is not limited thereto. The scope of protection disclosed in this case shall be determined by the scope of protection of the claims.

Claims

1. A method for separating and recovering heavy metals As and Zn from lithium slag, characterized in that, Includes the following steps: Step 1: Construct matrix spodumene and SiO2 models, and construct the distribution of heavy metal As and Zn speciation in the lithium slag leaching system. Use DFT to perform geometric optimization on the two speciations. Step 2, DFT adsorption behavior calculation Using spodumene and SiO2 as adsorption substrates, AsO4 3- and Zn 2+ H is attached to the topological active sites on the spodumene and SiO2 crystal planes, respectively, by introducing H onto the surface. + and OH - Acid-base environments with different pH values ​​were simulated; and the binding energy formula Eb=Etot-Etom was used to calculate the binding energy between different matrices of spodumene and SiO2 with different heavy metals Zn. 2+ and AsO4 3- The binding energy; Step 3: Selective adsorption and separation of AsO4³⁻ and Zn²⁺ in solution Lithium spodumene and SiO2, which serve as adsorption matrices, are respectively added to an AsO4-containing substrate. 3- and Zn 2+ In water, the coordination vacancies of Al-O tetrahedra on the spodumene surface interact with AsO4. 3- The tetrahedral structure forms a geometrically matched stable coordination structure, achieving AsO4 coordination bonds. 3- Selective adsorption; simultaneously, the hydrogen bonding sites and bridging oxygen structures of Si-OH on the SiO2 surface interact with weak coordination bonds with Zn via electrostatic interactions. 2+ The combination of Zn-O covalent bonds and electrostatic interactions enables the control of Zn. 2+ Selective adsorption; Based on the AsO43- and Zn in water bodies 2+ The content ratio of spodumene and SiO2 in the water was adjusted to regulate the adsorption effect; after the adsorption reached equilibrium, spodumene and SiO2 in the water were separated to achieve AsO4. 3- With Zn 2+ Selective separation and recovery; Step 4: Leaching of heavy metals from lithium slag S4.1 Lithium slag pretreatment: The lithium slag containing arsenic and zinc obtained by adsorption separation is ground and sieved to control the lithium slag particle size within a preset initial range to obtain pretreated lithium slag; S4.2 Selective leaching of arsenic: The pretreated lithium slag is added to a sodium hydroxide solution and stirred for leaching. After leaching, solid and liquid are separated to obtain arsenic-containing leachate and arsenic-removed filter residue. S4.3 Selective leaching of zinc: The arsenic-removed filter residue obtained in step S4.2 is added to sulfuric acid solution and stirred for leaching. After leaching, solid and liquid are separated to obtain zinc-containing leachate and leaching tail residue. S4.4 Process Parameter Optimization: The key process parameters in steps S2 and S3 were optimized through single-factor experiments and response surface methodology. The key process parameters include leaching time, lithium slag particle size, leaching agent concentration, and leaching temperature to obtain the optimal parameter combination for arsenic and zinc leaching.

2. The method for separating and recovering heavy metals As and Zn from lithium slag according to claim 1, characterized in that, Step one includes: S1.1, Constructing the spodumene model Using simulation software, a 1×1×1 unit cell was constructed based on the single crystal structure of spodumene. The lattice parameters of the unit cell are a=5.19Å, b=8.54Å, c=9.18Å, α=90.00°, β=102.63°, and γ=90.00°.

3. The method for separating and recovering heavy metals As and Zn from lithium slag according to claim 1, characterized in that, Step one includes: S1.2 Constructing the SiO2 model Using simulation software, a 1×1×1 supercell was constructed based on the SiO2 single crystal structure. The lattice parameters of the supercell are a=13.79Å, b=4.84Å, c=8.74Å, α=90.00°, β=128.98°, and γ=90.00°.

4. The method for separating and recovering heavy metals As and Zn from lithium slag according to claim 1, characterized in that, After geometry optimization in step one, the As-O bond length of AsO4³⁻ is 1.68 Å, and the ionic radius of Zn²⁺ is 0.74 Å.

5. The method for separating and recovering heavy metals As and Zn from lithium slag according to claim 1, characterized in that, In step two, Etot represents the total energy of the adsorption system formed by the constructed substrate and the adsorbate. Etom is the sum of the total energy of the isolated substrate and the total energy of the isolated adsorbate, with the van der Waals interaction energy between the substrate and the adsorbate deducted during the calculation.

6. The method for separating and recovering heavy metals As and Zn from lithium slag according to claim 1, characterized in that, In step two, the plane wave cutoff energy of the wave function is set to 400 eV, where: The k-point of the spodumene model was sampled using a 3×2×2 Monkhorst-Pack grid. The k-point of the SiO2 model was sampled using a 2×4×3 Monkhorst-Pack grid, and the sampling density was determined based on the cell size and atomic arrangement density of the model in step one.

7. The method for separating and recovering heavy metals As and Zn from lithium slag according to claim 1, characterized in that, In step two, the energy convergence criterion is set to 1.0 × 10⁻⁶. -5 eV, with the force convergence criterion set to 0.02 eV / Å.

8. The method for separating and recovering heavy metals As and Zn from lithium slag according to claim 1, characterized in that, The spodumene particle size in step three is 50-200 μm, the SiO2 particle size is 100-300 μm, and the specific surface area of ​​both matrix materials is not less than 50 m² / g.

9. The method for separating and recovering heavy metals As and Zn from lithium slag according to claim 1, characterized in that, The spodumene and AsO4-containing materials mentioned in step three 3- Zn 2+ The solid-liquid ratio of the water body is 1:50-1:200, with SiO2 and AsO4-containing substances... 3- Zn 2+ The solid-liquid ratio of the water is 1:30-1:150, the temperature of the adsorption process is 25-45℃, the adsorption time is 2-8h, and the stirring rate of the water is 100-300r / min.

10. The method for separating and recovering heavy metals As and Zn from lithium slag according to claim 1, characterized in that, In step three, it is necessary to strengthen the treatment of AsO4. 3- Adsorption and weakening of Zn 2+ During adsorption, the water is controlled to be weakly alkaline, and adsorption is achieved through the reaction of OH⁻ with Zn. 2+ Formation of hydroxyl complexes, reducing Zn 2+ The binding energy with the SiO2 matrix disrupts the spatial configuration of the Zn-O bonds; When it is necessary to strengthen the Zn 2+ Adsorption and weakening of AsO4 3- During adsorption, the water body is controlled to be weakly acidic, and H+ is used to... + It preferentially binds to the Si-O sites on the SiO2 surface, reducing the AsO4 content. 3- The binding energy with the matrix weakens the electron cloud density of the As-O bond.

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