Preparation method and application of heavy metal adsorption material based on lead-zinc tailings

Abstract

The invention relates to the technical field of heavy metal adsorption, in particular to a preparation method and application of a heavy metal adsorption material based on lead-zinc tailings, and the preparation method comprises the following steps: S1, grinding the lead-zinc tailings until the particle size is less than 75 microns, and drying; s2, putting the lead-zinc tailings treated in the step S1 into a microwave reactor, and carrying out microwave thermal modification treatment for 5-15 minutes at the power of 600-1000W; s3, the lead-zinc tailings subjected to microwave treatment are soaked in a sodium sulfide solution with the mass concentration being 0.5%-2%, and surface vulcanization treatment is conducted; and S4, heating the lead-zinc tailings subjected to sulfuration treatment to 800-950 DEG C at the speed of 3-10 DEG C / min under the protection of nitrogen, calcining for 1-3 hours, cooling, washing and drying to obtain the heavy metal adsorption material. The adsorption material with a good heavy metal treatment effect is synthesized through microwave thermal modification assisted by surface vulcanization treatment and high-temperature sintering of the lead-zinc tailings.

Description

Technical Field

[0001] The present invention relates to the technical field of heavy metal adsorption, and particularly relates to a preparation method and application of a heavy metal adsorption material based on lead-zinc tailings. Background Art

[0002] Heavy metal pollution in wastewater is a serious problem faced by the world today. Especially the wastewater containing a large amount of heavy metals generated in industrial production and agricultural activities is likely to accumulate in organisms when entering the environment, and has toxicity, carcinogenicity, mutagenicity and teratogenicity. Among them, excessive Cu 2+ will cause cytotoxicity to aquatic animals and damage the homeostasis of the aquatic system, hindering the growth and development of organisms and damaging the structure of the ecosystem. Cd 2+ is a highly toxic and carcinogenic element that will damage the functions of the kidneys and lungs; the Itai-Itai disease that occurred in Japan last century was caused by cadmium-containing wastewater discharged from a zinc smelter polluting the surrounding cultivated land and water sources. Thus, it can be seen that treating the excessive heavy metals Cu 2+ and Cd 2+ in wastewater is very important for the environment and humans.

[0003] At present, various methods for treating heavy metals in wastewater have been proposed at home and abroad, such as chemical precipitation method, microbial remediation method and adsorption method, etc. Among them, the adsorption method is considered to be the method with the most application prospects and economic benefits. Because there are various choices of adsorption materials with low cost, good treatment effect and reusable, and the technology application has developed to a relatively mature stage. There are many common adsorption materials at present, such as compounds MOFs with metal-organic framework structures; biochar (agricultural waste and plants, etc.); natural clay minerals (bentonite, diatomite, etc.).

[0004] Tailings-based solid wastes are used as adsorption materials by more and more scholars due to their rich functional groups and developed porosity. Wang calcined and compounded copper tailings and ginkgo leaves at different temperatures to form a magnetic adsorption material. The various functional groups possessed by the tailings themselves combine with biochar to form chemical bonds with strong adsorption energy, and the effect is obvious in single and binary adsorption systems. The adsorption rates of Cd and As can reach more than 90%. A large amount of metal elements such as Fe and Mn make the material have strong magnetism and improve the adsorption capacity of the material; Cheng calcined rare earth tailings to synthesize highly crystalline zeolite A, forming a three-dimensional crystalline aluminosilicate lattice of tetrahedral units. Through the ion exchange action between a large number of cations, its adsorption effect is improved by about 30% compared with ordinary zeolite; Wei sintered iron tailings to prepare porous ceramsite. The rich pores in the ceramsite are conducive to cation exchange, Pb 2+The charge attraction with the anionic groups on the ceramsite leads to its deposition and coverage on the particle surface. The formed Pb-O and Si-O-Pb bonds are also stably adsorbed on the surface, and this material exhibits excellent adsorption performance in an acidic environment. Xu prepared a high specific surface area adsorption material from iron tailings and chitosan by the sol-gel method. A large number of active sites are increased and fully exposed on the surface, and Zn 2+ and Pb 2+ show good adsorption effects.

[0005] A large amount of solid waste, namely lead-zinc tailings, will be produced during the beneficiation process of lead-zinc ore. This kind of tailings is mainly composed of components such as silicates, aluminates and iron oxides. Since a certain amount of heavy metal elements remain in the tailings, if directly stacked or discharged, it may seep into the surrounding environment through rain leaching, causing secondary pollution. Nevertheless, the mineral composition and surface characteristics of lead-zinc tailings endow it with a certain adsorption capacity. Especially after appropriate modification, its adsorption performance can be significantly improved. Thermal modification is a common physico-chemical treatment method. By high-temperature treatment, the crystal structure, specific surface area and surface active sites of the tailings can be changed, thereby enhancing its adsorption effect on heavy metal ions. During the thermal modification process, some mineral phases in the tailings will undergo phase transformation or decomposition to form new active substances. For example, the decomposition of carbonate minerals under high-temperature conditions can increase the porosity of the tailings, while the reduction of iron oxides may generate magnetic substances with stronger adsorption capacity. At the same time, thermal modification can also effectively remove organic impurities in the tailings, improve its surface cleanliness, and thus expose more adsorption sites. These changes work together, making the lead-zinc tailings after thermal modification treatment exhibit excellent performance in adsorbing heavy metal ions. Through thermal modification, the adsorption capacity of lead-zinc tailings has been significantly improved. High-temperature treatment not only changes the physical structure of the tailings, but also enhances its chemical activity, enabling it to more effectively adsorb heavy metal ions in wastewater. In addition, thermal modification can also improve the stability and regeneration performance of the tailings, making it more feasible in practical applications. In short, thermal modification is an effective method to improve the adsorption performance of lead-zinc tailings. Through high-temperature treatment, the physico-chemical properties of the tailings have been significantly improved, showing good application potential in the treatment of heavy metal wastewater.

[0006] In the present invention, an adsorption material is prepared by microwave thermal modification combined with surface sulfidation and sintering of a lead-zinc tailing with high carbonate and silicate contents. Through toxicity leaching and mineral composition analysis, the feasibility of using the lead-zinc tailing as an adsorption material is determined. Under different conditions of pH, time, temperature and concentration, the adsorption material is explored for its adsorption of Cu 2+ and Cd 2+The adsorption performance was studied by fitting adsorption kinetics and adsorption isotherm models, and the adsorption mechanism was explored by means of SEM, FTIR and XPS characterization. This method can not only realize the resource utilization of tailings, but also provide an economic and environmental solution for heavy metal pollution control. Summary of the Invention

[0007] The object of the present invention is to provide a preparation method and application of a heavy metal adsorption material based on lead-zinc tailings. By means of microwave thermal modification supplemented by surface sulfidation treatment, an adsorption material with good heavy metal treatment effect was synthesized by high-temperature sintering of lead-zinc tailings.

[0008] To achieve the above technical objectives and effects, the present invention is realized through the following technical solutions:

[0009] A preparation method of a heavy metal adsorption material based on lead-zinc tailings, comprising the following steps:

[0010] S1: Grind the lead-zinc tailings to a particle size less than 75 μm and perform drying treatment;

[0011] S2: Place the lead-zinc tailings treated in step S1 in a microwave reactor and perform microwave thermal modification treatment at a power of 600-1000 W for 5-15 minutes;

[0012] S3: Immerse the microwave-treated lead-zinc tailings in a sodium sulfide solution with a mass concentration of 0.5%-2% for surface sulfidation treatment;

[0013] S4: Under the protection of nitrogen, heat the sulfide-treated lead-zinc tailings to 800-950 °C at a heating rate of 3-10 °C / min and calcine for 1-3 hours. After cooling, wash and dry to obtain a heavy metal adsorption material.

[0014] Further, in step S2, the microwave power is 800 W and the treatment time is 10 minutes;

[0015] Further, in step S3, the mass concentration of the sodium sulfide solution is 1% and the sulfidation treatment time is 1-3 hours.

[0016] Further, in step S4, the calcination temperature is 850 °C and the heating rate is 5 °C / min.

[0017] On the other hand, the present invention proposes a method for treating wastewater containing Cu 2+ and Cd 2+ by the above heavy metal adsorption material, comprising the following steps:

[0018] S1: Adjust the pH of the wastewater to 4-8;

[0019] S2: Add the adsorbent material at a solid-liquid ratio of 1:10 - 1:50, and oscillate for adsorption at 15 - 35 °C for 60 - 240 minutes;

[0020] S3: Separate the material after adsorption to complete the wastewater treatment.

[0021] On the other hand, the present invention proposes the application of the above heavy metal adsorbent material in environmental remediation for removing Cu 2+ , Cd 2+ and their combined pollution in industrial wastewater, mine leachate or agricultural irrigation water.

[0022] Advantages of the present invention:

[0023] Through the synergistic effect of microwave thermal modification, surface sulfidation and high-temperature calcination, the present invention significantly improves the adsorption capacity of lead-zinc tailings for heavy metal ions. Microwave thermal modification utilizes the selective heating characteristics of high-frequency electromagnetic fields to rapidly activate the decomposition of carbonate minerals (such as dolomite) in the tailings, generating a composite framework of calcium oxide and magnesium oxide with high porosity ( Figure 10 k-n SEM shows optimized pore structure), significantly increasing the specific surface area and providing abundant physical adsorption sites for heavy metal ions. Surface sulfidation treatment causes the residual metal elements Fe, Pb, etc. in the tailings to combine with sulfide ions to form metal sulfides, and the sulfur-based functional groups on its surface form stable Me-S bonds with Cu 2+ , Cd 2+ through chemical complexation. At the same time, the Si-O bonds in the silicate framework displace Ca 2+ / Mg 2+ by ion exchange to fix heavy metals. The synergistic effect of physical pore adsorption, sulfide complexation and ion exchange enables the material to reach a leading level in the saturated adsorption capacity for Cu 2+ and Cd 2+ , and the competitive adsorption efficiency for the two ions in the mixed system is stable, breaking through the bottleneck of low adsorption capacity and poor selectivity of traditional tailings materials.

[0024] During the modification process, high-temperature calcination promotes the transformation of unstable heavy metals in lead-zinc tailings into residual forms, and the silicate phase formed by the reconstruction of the mineral lattice wraps the heavy metals in a stable structure, greatly reducing their bioavailability. After adsorption, heavy metal ions are firmly fixed through the dual mechanisms of sulfide complexation and silicate encapsulation. Leaching toxicity tests show that the heavy metal leaching concentrations of the treated material and adsorption products are far lower than the environmental safety limits, completely avoiding the risk of secondary pollution of tailings. In addition, the material still maintains structural stability under acidic conditions, can adapt to complex water quality environments such as mine leachate, and solves the problem that traditional biochar materials are prone to failure in acidic media.

[0025] The present invention uses lead-zinc tailings as raw materials, and realizes the full-quantification utilization of solid waste through microwave treatment for 10 minutes, low-temperature sulfidation and controlled calcination. The production cost is less than 2% of that of commercial activated carbon. The rapid heating and selective heating characteristics of microwave thermal modification greatly reduce energy consumption. The surface sulfidation uses low-concentration reagents to avoid secondary pollution, and the nitrogen protection calcination inhibits the generation of harmful gases. The overall process is green and efficient. After the material is recycled five times, due to the mechanical stability of the silicate skeleton and the chemical regenerability of the sulfide, the adsorption rate still remains at an excellent level, and the regeneration performance is significantly better than that of conventional adsorbents. The present invention transforms lead-zinc tailings from an environmental burden into a high-value-added functional material, providing an integrated solution that can be scaled up and promoted for the resource utilization of mine solid waste and the treatment of heavy metal pollution.

[0026] Of course, it is not necessary for any product implementing the present invention to simultaneously achieve all the above-mentioned advantages. Brief Description of the Drawings

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0028] Figure 1 It is a diagram of the mineral composition and content of lead-zinc tailings;

[0029] Figure 2 It is an analysis diagram of mineral particles of dolomite (left), pyrite (middle) and quartz (right);

[0030] Figure 3 It is a BSE image of lead-zinc tailings;

[0031] Figure 4 It is an XRD image of lead-zinc tailings;

[0032] Figure 5 It is a TG-DSC curve of lead-zinc tailings in the range of 0-1000 °C;

[0033] Figure 6 It is an XRD image of lead-zinc tailings sintered at different temperatures;

[0034] Figure 7 It is a diagram of the adsorption performance of lead-zinc tailings sintered at different temperatures for heavy metals;

[0035] Figure 8 It is a comparison diagram of the bioavailability of lead-zinc tailings and LZT850; (a) lead-zinc tailings; (b) LZT 850 ;

[0036] Figure 9N2 adsorption - desorption curves and pore size distribution diagrams of lead - zinc tailings and LZT850;

[0037] Figure 10 (a) Scanning electron microscope image of lead - zinc tailings; (b - j) Energy - dispersive spectroscopy images of lead - zinc tailings; (k - n) Scanning electron microscope images of lead - zinc tailings sintered at different temperatures;

[0038] Figure 11 (a) TEM image of LZT 850 ; (b - f) HRTEM images of LZT 850 ;

[0039] Figure 12 Adsorption rates of heavy metals by LZT 850 under different adsorption conditions: (a) pH; (b) Zeta potential diagram; (c) Adsorption time; (d - f) Adsorption temperature and concentration;

[0040] Figure 13 Fitting diagrams of adsorption kinetic models; (a) Pseudo - first - order kinetic model; (b) Pseudo - second - order kinetic model;

[0041] Figure 14 Fitting diagrams of adsorption kinetic models: (a) Intra - particle diffusion model; (b) Elovich model;

[0042] Figure 15 Fitting diagrams of adsorption isotherm models; (a - b) Adsorption isotherm fitting of Cu; (c - d) Adsorption isotherm fitting of Cd;

[0043] Figure 16 XRD images of LZT850 before and after heavy metal adsorption;

[0044] Figure 17 FTIR images of LZT850 before and after adsorption;

[0045] Figure 18 (a) SEM image of LZT 850 ; (b) SEM image of LZT 850 after Cu adsorption; (c) SEM image of LZT 850 after Cd adsorption;

[0046] Figure 19 XPS elemental valence state change diagrams of LZT850 before and after adsorption; (a) C 1s; (b) S2p; (c) Si2p; (d) Fe2p; (e) Cu 2p; (f) Cd 3d;

[0047] Figure 20 (a) LZT 2+ after Cu adsorption 850Bioavailability; (b) Adsorption of Cd 2+ After LZT 850 Bioavailability;

[0048] Figure 21 Is the adsorption performance diagram of LZT850 in the mixed system;

[0049] Figure 22 Is the adsorption performance diagram of the regeneration cycle of LZT850. Specific implementation mode

[0050] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

[0051] Example 1

[0052] A preparation method of a heavy metal adsorption material based on lead-zinc tailings described in this embodiment includes the following steps:

[0053] S1: Grind the lead-zinc tailings to a particle size less than 75 μm and perform a drying treatment;

[0054] S2: Place the lead-zinc tailings treated in step S1 in a microwave reactor and perform microwave thermal modification treatment at a power of 600 - 1000 W for 5 - 15 minutes;

[0055] S3: Immerse the microwave-treated lead-zinc tailings in a sodium sulfide solution with a mass concentration of 0.5% - 2% for surface sulfidation treatment;

[0056] S4: Under the protection of nitrogen, heat the sulfide-treated lead-zinc tailings to 800 - 950 °C at a heating rate of 3 - 10 °C / min for 1 - 3 hours, cool and then wash and dry to obtain the heavy metal adsorption material.

[0057] In this embodiment, the microwave power in step S2 is 800 W and the treatment time is 10 minutes; the calcination temperature in step S4 is 850 °C and the heating rate is 5 °C / min.

[0058] In this embodiment, the mass concentration of the sodium sulfide solution in step S3 is 1% and the sulfidation treatment time is 1 - 3 hours.

[0059] On the other hand, the present invention proposes a method for treating wastewater containing Cu 2+ and Cd 2+ using the above heavy metal adsorption material, including the following steps:

[0060] S1: Adjust the pH of the wastewater to 4 - 8;

[0061] S2: Add the adsorption material at a solid - liquid ratio of 1:10 - 1:50, and oscillate and adsorb at 15 - 35 °C for 60 - 240 minutes;

[0062] S3: Separate the adsorbed material to complete the wastewater treatment.

[0063] In this example, the pH of the wastewater is 6, the adsorption temperature is 25 °C, the adsorption time is 120 - 180 minutes, and the saturated adsorption capacities of Cu 2+ and Cd 2+ are 126.01 mg / g and 149.52 mg / g respectively.

[0064] In this example, the adsorption process conforms to the pseudo - second - order kinetic model and the Langmuir isothermal adsorption model, and the adsorption mechanism includes ion exchange, chemical complexation, and electrostatic adsorption.

[0065] In this example, the competitive adsorption efficiency of the adsorption material for Cu 2+ and Cd 2+ in the mixed system is ≥ 80%, and the adsorption rate remains above 82% after 5 - cycle use.

[0066] On the other hand, the present invention proposes the application of the above - mentioned heavy - metal adsorption material in environmental remediation for removing Cu 2+ , Cd 2+ and their combined pollution in industrial wastewater, mine leachate, or agricultural irrigation water.

[0067] Example 2

[0068] Experimental raw materials

[0069] The lead - zinc tailings used in the experiment were collected from the Lumaolin lead - zinc tailings reservoir in Jichangpo Township, Puding County, Anshun City, Guizhou Province. The mining and dressing scale of the lead - zinc tailings in the field area is 150,000 - 300,000 t / a, and the mined - out area is about 275,800 m 3 / a. Grind the retrieved tailings and dry them in an oven at 60 °C for 48 hours. After passing through a 200 - mesh sieve (75 μm), store them in a sealed manner in a dark place. All the reagents used in the experiment were purchased from the Chemical Reagent Network.

[0070] Experimental method

[0071] Mineral analysis of lead - zinc tailings

[0072] To explore the mineral composition of lead-zinc tailings, the elemental composition of various minerals, the distribution of elements in minerals, and the occurrence characteristics of various minerals, a fully automatic mineral analysis system (AMICS) was used to analyze the lead-zinc tailings. AMICS combines high-resolution BSE with high-energy EDS. By collecting data from a scanning electron microscope, it automatically identifies and classifies mineral phases, obtaining the mineral distribution map and chemical composition data of the lead-zinc tailings.

[0073] Synthesis of Adsorbent Materials

[0074] In a microwave reactor, heat treatment was carried out for a short time of 10 min at a specific power of 800 W. Utilizing the selective heating property of microwaves, the active sites on the surface of the tailings were rapidly activated to form a porous structure. Subsequently, the microwave-treated lead-zinc tailings were placed in a 1% sodium sulfide solution for surface sulfidation treatment, causing metal sulfides such as PbS, ZnS, and FeS to form on the surface of the tailings. These sulfides have a strong affinity for heavy metal ions. Finally, the sulfide layer was stabilized by calcination at different temperatures to further enhance the adsorption performance of the material. Prepare 20 g of microwave-sulfided lead-zinc tailings (<0.075 mm) respectively, put them into a tubular furnace with a nitrogen atmosphere (N2 flow rate 200 ml / min), heat at a rate of 5 °C / min, and heat to 600 °C, 700 °C, 800 °C, 850 °C, 900 °C, and 950 °C respectively and hold for one hour, then cool naturally to room temperature. Take out the materials, wash them with ultrapure water, and then put them in an oven at 60 °C to dry for 24 hours, and store them sealed. They are respectively named LZT 600 、LZT 700 、LZT 800 、LZT 850 、LZT 900 、LZT 950 。 This method combines the high efficiency of microwave rapid heating and the selective adsorption advantage of sulfidation treatment, can significantly improve the adsorption capacity of lead-zinc tailings for various heavy metal ions, and at the same time reduce energy consumption and treatment time. It is a potential new modification method.

[0075] Toxicity Leaching Experiment

[0076] The TCLP leaching method and sulfuric acid leaching method were used to study the leaching toxicity of LZT and LZT 850 。

[0077] Heavy Metal Species Distribution

[0078] The Tessier five-step sequential extraction method was used to quantitatively analyze LZT and LZT 850The changes in the morphological distribution of heavy metals before and after adsorption. The heavy metal forms can be divided into five forms: exchangeable state (F1), carbonate-bound state (F2), iron and manganese oxide-bound state (F3), organic matter and sulfide-bound state (F4), and residual state (F5). Determine the degree to which each heavy metal can be utilized by organisms in LZT 850 and then prove the environmental harmlessness of LZT 850 when used as an adsorbent material, as well as its stability after adsorbing heavy metals.

[0079] Adsorption experiment

[0080] For the adsorption experiment, adsorption solutions with a concentration of 10 mg / L were prepared using heavy metal standard solutions of Cu and Cd. The solid-liquid ratio of the adsorbent material to the adsorption solution was 1 g / L. The mixed solution (adsorbent material + adsorption solution) was oscillated in a horizontal shaker at 200 rpm for 180 min, and then centrifuged at 4000 r / min for 10 min. The supernatant was filtered through a 0.45 μm filter and then the heavy metal concentration was measured. Under different conditions of pH, time, temperature, and concentration, explore the adsorption performance of LZT 850 for Cu 2+ and Cd 2+ . Fit the adsorption results using adsorption kinetic models and adsorption isotherm models.

[0081] (1) Analyze the influence of adsorption pH;

[0082] (2) The influence of adsorption time and adsorption kinetics;

[0083] (3) The influence of adsorption concentration and temperature and adsorption isotherm;

[0084] In this experiment, two heavy metal standard solutions with concentration gradients of 10, 20, 40, 60, 80, 100, 120, 150, 200, 300, and 400 mg / L were prepared. The pH of the mixed solution was adjusted to 6, and adsorption experiments were carried out at 15 °C, 25 °C, and 35 °C. After oscillation, centrifugation, taking the supernatant, filtering, the heavy metal concentration was measured and the adsorption capacity was calculated. The Langmuir and Freundlich isothermal adsorption models were used to fit the adsorption process. The formulas are as follows:

[0085] Langmuir isothermal adsorption model:

[0086]

[0087] Freundlich isothermal adsorption model:

[0088]

[0089] In the formula, Q m (mg / g) represents the maximum adsorption capacity of the adsorbent at adsorption equilibrium; Ce (mg / L) represents the concentration of the solution after equilibrium; K L (L / mg) represents the Langmuir constant related to the adsorption energy; K F (L / mg) represents the Freundlich constant; 1 / n represents the Freundlich intensity parameter.

[0090] (4) Adsorption experiment of the mixed system.

[0091] In this experiment, the adsorption material was added to the mixed solution of Cu and Cd with a concentration of 30 - 50 mg / L at a solid-liquid ratio of 1 g / L. After oscillation and centrifugation, the supernatant was taken for filtration, and the concentrations of the two heavy metals were measured and the adsorption rate was calculated.

[0092] (5) Adsorption-desorption experiment.

[0093] In this experiment, the adsorption material was added to 50 ml standard solutions of Cu and Cd with concentrations of 10, 20, 30, 40, and 50 mg / L at a solid-liquid ratio of 1 g / L. They were oscillated for 180 and 120 min respectively, centrifuged and filtered to measure the concentration of the supernatant, and the adsorption rate was calculated. 50 ml of 1 mol / L HCl solution was added to the precipitate to desorb the material, and it was oscillated at 200 rpm for 24 h to displace the adsorbed heavy metal ions. Then it was centrifuged and filtered to measure the concentration of the supernatant, and the desorption rate was calculated. The desorbed adsorption material was washed with ultrapure water and then put into the same standard solution to test its adsorption performance. The above steps were repeated 5 times.

[0094] Material characterization

[0095] In order to more clearly understand the physical and chemical properties of the material, inductively coupled plasma mass spectrometry (ICP-MS) was used in the research to detect the composition of lead-zinc tailings and the concentrations of heavy metals in the toxic leaching solution, as well as the changes in heavy metal concentrations before and after adsorption. The automatic mineralogical analysis system for quantitative analysis (AMICS) was used to determine the mineral composition of lead-zinc tailings and the characteristic parameters of the main minerals. The crystal structure of the powder was characterized by Cu Kα radiation x-ray diffraction (XRD). The surface morphology and microstructure of the samples were observed by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). Thermogravimetry-differential scanning calorimetry (TG-DSC) was used to analyze the weight changes during the sintering process of lead-zinc tailings, so as to analyze the substance reactions corresponding to different temperatures in this process. The specific surface area and porosity of the prepared adsorption material were analyzed by a fully automatic specific surface area and porosity analyzer (BET). Fourier transform infrared spectroscopy (FTIR) was used to analyze the changes in functional groups and chemical bonds of the adsorption material before and after adsorption. X-ray photoelectron spectroscopy (XPS) was used to detect the elemental binding energy analysis, surface chemical composition analysis, and valence state analysis of the adsorption material before and after adsorbing heavy metals.

[0096] Mineral Composition and Characteristics of Lead-Zinc Tailings

[0097] Figure 1 The mineral composition of lead-zinc tailings is shown, mainly including minerals such as dolomite, pyrite, quartz, and calcite. Dolomite is a carbonate mineral, including ankerite and kutnohorite. Its crystal structure is like that of calcite and often appears as a rhombohedron. Some dolomite emits orange-red light under cathode ray irradiation. Dolomite is the main mineral component of dolomite rock and dolomitic limestone. The most common crystals of pyrite are hexahedron, octahedron, and pentagonal dodecahedron. There are fine stripes on the crystal faces of the hexagonal crystals. Sometimes many crystals combine together to form various complex crystals. Sometimes it is golden yellow, sometimes brass-colored, and has a bright metallic luster. Quartz sand is a hard, wear-resistant, and chemically stable silicate mineral.

[0098] Occurrence Characteristics among Main Minerals in Lead-Zinc Tailings

[0099] The occurrence characteristics among the main minerals in lead-zinc tailings are as Figure 2 shown. The molecular formula of dolomite is CaMg(CO3)2, and its content is as high as 82.29%. Combining Figure 3 with the backscattered scanning electron microscope image, it can be seen that the dissemination grain size of dolomite is relatively coarse, and its symbiotic relationship with other main minerals is relatively close. Except for some simple intergrowth relationships with other minerals, most dolomite contains metal mineral particles such as pyrite, galena, quartz, and sphalerite with different grain sizes. The grain sizes of some metal mineral particles are extremely fine and difficult to identify; some dolomite contains barite, pyroxene, and calcite particles.

[0100] Physicochemical Properties and Characterization of Lead-Zinc Tailings and LZT 850

[0101] The leaching results of lead-zinc tailings by the TCLP method and the sulfuric acid-nitric acid method are shown in Table 1. The leaching concentrations are compared with the determination thresholds of the US Environmental Protection Agency (USEPA) and the "Identification Standard for Hazardous Wastes - Identification of Leaching Toxicity" (GB5085.3-2007). The leaching concentrations of various heavy metals in both leaching methods are lower than the standard limits. Among them, the highest leaching concentrations of Pb and Zn are 4.5225 and 3.7175 mg / L respectively, and the leaching concentrations of other heavy metals are lower than 1 mg / L.

[0102] Table 1 Leaching Toxicity of Lead-Zinc Tailings

[0103]

[0104]

[0105] ​The ICP analysis results of the lead-zinc tailings are shown in Table 2. The lead-zinc tailings mainly contain elements such as Ca, Mg, Si, Fe, and S. The contents of Ca and Mg are as high as 210435 and 112416 mg / kg respectively, and the contents of Si, Fe, and S are 32534, 25971, and 17624 mg / kg respectively. It belongs to alkaline carbonate and alkaline silicate minerals.

[0106] Table 2 Elemental composition of lead-zinc tailings

[0107]

[0108] The XRD characterization results of the lead-zinc tailings are as Figure 4 shown. It can be seen that the main component of the lead-zinc tailings is dolomite, which is consistent with the PDF card of [CaMg(CO3)2]. Secondly, the characteristic peaks of pyrite (FeS2) and quartz (SiO2) can be observed, corresponding to the AMICS mineral analysis results.

[0109] The thermogravimetric-differential scanning calorimetry (TG-DSC) analysis of the lead-zinc tailings was carried out, and the results are as Figure 5 shown. The TG curve of the lead-zinc tailings has two obvious weight loss intervals. The mass loss is about 2.5% between 500 °C and 600 °C. In this temperature range, the tailings lose crystal water, hydroxyl groups, and the decomposition of organic impurities in the tailings. After 600 °C, there is a large mass loss, and the weight loss is about 37.5%. This is because a large amount of carbonate minerals such as dolomite and calcite begin to decompose, and the generated CO2 gas escapes until the mass tends to be balanced at 800 °C. In the DSC curve in this temperature range, two exothermic peaks appear. Combining with the XRD pattern after thermal modification, it is inferred that ( Figure 6 ), the decomposed CaO and MgO react with SiO2 by heating to form CaSiO3 and MgSiO3 respectively. A small amount of pyrite contained in the tailings may undergo oxidation reaction at high temperature, resulting in mass change.

[0110] According to the thermogravimetric analysis results, the lead-zinc tailings were thermally modified at 600 °C, 700 °C, 800 °C, 850 °C, 900 °C, and 950 °C. It can be seen from the XRD patterns of the lead-zinc tailings calcined at different temperatures that the diffraction peaks of dolomite gradually decrease from 600 °C to 800 °C, and CaMg(CO3)2 gradually decomposes into CaCO3, CaO, and MgO, but their contents are all small. Starting from 850 °C, the diffraction peaks of each alkaline oxide become more obvious. However, compared with 900 °C and 950 °C, the materials calcined at 850 °C have the coexistence of CaCO3, CaO, and MgO in three phases and relatively high contents, which will generate a large number of loose pores, providing an escape channel for the CO2 decomposed by calcination and more adsorption sites. A small amount of clay mineral illite carried by the lead-zinc tailings plays a bonding role, making the material structure more stable.

[0111] LZT 600 、LZT 700 、LZT 800 、LZT 850 、LZT 900 、LZT 950 The adsorption rates for Cu 2+ and Cd 2+ are as shown Figure 7 The adsorption rates of uncalcined lead-zinc tailings and the adsorbents prepared from lead-zinc tailings calcined at 600 °C - 800 °C for Cu 2+ and Cd 2+ gradually increase, from 4% and 34.58% to 59.57% and 77.18% respectively. This may be because the carbonates and organic matters in the lead-zinc tailings at 800 °C decompose incompletely, resulting in fewer surface active sites and limited adsorption capacity. As the temperature rises to 850 °C, the adsorption effect of the adsorbent is significantly improved. This may be due to the decomposition of calcium carbonate into calcium oxide, and at the same time, more pores and active sites are formed inside the material, enhancing its adsorption capacity for Cu 2+ and Cd 2+ . However, at higher temperatures (900 °C and 950 °C), the adsorption effect decreases. This may be because high temperature causes the material to sinter, and part of the pore structure collapses, resulting in a decrease in the specific surface area of the material, thus reducing the adsorption performance. Therefore, the lead-zinc tailings thermally modified at 850 °C show the best adsorption effect and can more effectively remove Cu 2+ and Cd 2+ from the aqueous solution.

[0112] For the lead-zinc tailings thermally modified at 850 °C, the heavy metal concentrations in their TCLP and acid leaching by sulfuric acid and nitric acid methods are significantly lower than those of the uncalcined tailings, as shown in Table 3. This is mainly due to multiple physicochemical effects occurring during the calcination process. First, high-temperature calcination promotes the transformation of unstable mineral phases in the lead-zinc tailings. For example, minerals such as sulfides and carbonates decompose or recombine under high-temperature conditions to form more stable oxides or silicates. Taking lead and zinc as examples, their sulfides (galena and sphalerite) are oxidized to oxides such as PbO and ZnO during the calcination process, and the solubility of these oxides in acidic media is significantly reduced, thus effectively inhibiting the leaching of heavy metals.

[0113] Table 3 Leaching toxicity of LZT 850

[0114]

[0115] Secondly, sintering or solid-phase reactions may occur during the calcination process, forming a densified mineral structure or glass phase. These new phases have stronger resistance to acid erosion. Meanwhile, high-temperature conditions may also cause some heavy metal elements (such as Pb) to volatilize, thus directly reducing the total content of heavy metals in the tailings. In addition, calcination may also fix heavy metal ions in a stable mineral lattice, forming a more chemically inert bound state, further restricting their migration and release under acidic conditions. This process not only improves the stability of lead-zinc tailings but also provides an effective technical path for heavy metal pollution control.

[0116] The Tessier sequential extraction results are as Figure 8 shown, and the Tessier bioavailability of heavy metals in LZT 850 is significantly lower than that of untreated lead-zinc tailings, which is mainly attributed to the transformation of heavy metal forms and chemical properties under high-temperature environments. According to the classification of the Tessier sequential extraction method, the forms of heavy metals can be divided into exchangeable state, carbonate-bound state, iron-manganese oxide-bound state, organic matter-bound state, and residual state. In untreated lead-zinc tailings, the first two forms of heavy metals Pb, Cu, and Cd account for a relatively high proportion. These forms have high biological activity and are easily taken up by plants and microorganisms, and then accumulate through the food chain, posing potential risks to the ecosystem and human health. While in LZT 850 there are huge changes in the various internal heavy metal forms. High temperature promotes the decomposition of carbonates in the tailings, generating carbon dioxide. At the same time, heavy metals undergo solid-phase reactions with minerals such as silicates to form more stable silicate minerals or glass phases. This newly formed mineral structure firmly locks heavy metals in the lattice, transforming them from the exchangeable state and carbonate-bound state with high biological activity to the iron-manganese oxide-bound state and organic matter-bound state with lower bioavailability, and the residual state with almost no biological activity. The solubility of residual-state heavy metals is extremely low and is not easily absorbed by organisms, thus significantly reducing their bioavailability. In addition, high-temperature treatment may also promote the combination of heavy metals with iron-manganese oxides or aluminosilicates to form more stable compounds. These compounds exhibit extremely high chemical stability in the natural environment and are not easily decomposed by acids, alkalis, or microorganisms, further weakening the migration ability and bioavailability of heavy metals.

[0117] The BET curves of lead-zinc tailings and LZT 850 are as Figure 9 shown. After calcination, the specific surface area of the material increases from 2.3454 m 2 / g to 5.4633 m 2 / g, and the average pore volume increases from 0.009196 cm 3 / g to 0.038162 cm 3 / g, with a pore size between 2 - 50 nm, belonging to mesoporous materials. LZT 850 The type of N2 adsorption - desorption curve of LZT is type Ⅳ adsorption isotherm, and an adsorption hysteresis loop appears, indicating that the material has a capillary condensation system. The pores of the material are slit pores formed by the accumulation of ribbon - shaped particles, which is convenient to provide more adsorption sites during the adsorption process and is conducive to giving full play to the adsorption performance of the material.

[0118] The SEM images and EDS spectra of lead - zinc tailings are as Figure 10 (a - j) shown. It can be clearly seen that Ca and Mg elements cover most of the area; the distribution areas of Si and O almost overlap, proving the existence of quartz; Fe and S are indeed present in the same mineral (pyrite); heavy metals Pb and Zn are present in a small amount of galena and sphalerite. This is consistent with the results shown in the BSE images of lead - zinc tailings above. The SEM images of lead - zinc tailings calcined at different temperatures are as Figure 10 (k - n) shown. With the increase of the heat treatment temperature, rich pores and cracks gradually form on the surface of the tailings, the particle structure is significantly damaged, a large number of irregular fragments and fine particles are generated, and agglomeration phenomena occur, and a dense massive structure is formed in local areas. Generally speaking, the surface morphology of the tailings gradually changes from the initial dense and smooth state to a porous and loose feature, reflecting the dynamic evolution of the mineral structure during the thermal modification process. Among them, the lead - zinc tailings calcined at 850℃ have better looseness and more pores can be observed on the surface.

[0119] As Figure 11 (a) shown of the LZT 850 TEM image. After thermal modification, the particle size of LZT 850 becomes smaller and the distribution tends to be uniform, and the surface shows significant porous and loose characteristics. The HRTEM image further reveals that the 850 material lattice fringes of LZT are clear, the crystallinity is improved, and an amorphous structure appears in local areas. It is speculated that this is caused by the decomposition of substances such as carbonates at high temperature. The FFT images of figures (c) and (d) correspond to regions Ⅰ and Ⅱ respectively. The number of diffraction spots of LZT 850 increases, and the distribution order means that the crystal structure has been optimized. The lattice spacing images of figures (e) and (f) show that the lattice spacing of LZT 850 significantly increases in some areas. Among them, 0.215 nm and 0.153 nm correspond to the (113) and (027) crystal planes of carbonate, which is closely related to the pore structure formed after the decomposition of carbonate. This loose structure not only expands the specific surface area of the material but also creates more active adsorption sites, thus greatly enhancing the adsorption ability of heavy metal ions. It can be seen that the thermally modified lead - zinc tailings have more advantages as efficient heavy metal adsorption materials due to their looser structure and stronger adsorption performance.

[0120] Heavy metal adsorption experiment

[0121] Effect of pH on LZT 850 The influence on adsorption performance is as follows Figure 12 (a) shows that in a strong acid environment with pH of 2 and 4, the adsorption rates of Cu 2+ and Cd 2+ are both lower than 50%. Because there are a large number of H + with a radius smaller than that of heavy metal ions, which are more likely to occupy the adsorption sites. The surface functional groups of LZT 850 are prone to combine with H + , making the surface positively charged and repelling cationic metals, resulting in poor adsorption performance. As the pH increases to 6, the adsorption rate of LZT 850 increases to about 95%. When the pH is in an alkaline environment, the adsorption rate of LZT 850 is close to 100%. Figure 12 (b)'s Zeta potential diagram reflects the positive and negative charge values on the material surface at different pH values. When the material adsorbs Cu 2+ and Cd 2+ at pH of 2 and 4, the charge values are +10.71mv / +15.53mv and +3.65mv / +3.22mv; at pH of 5 and 6, the charge values are +1.26mv / +0.82mv and +0.21mv / -5.51mv; at pH of 8 and 10, the charge values are -3.18mv / -11.27mv and -3.9mv / -12.05mv. It shows that the positive charge value of the material is indeed higher in a strong acid environment, and the repulsion between cations is stronger; in a weak acid environment, the charge value is around 0mv, and the electrostatic adsorption effect of the material on heavy metal cations is stronger; in an alkaline environment, the charge values are all less than 0mv, and the adsorption effect is good. However, considering that there are a large number of OH - that will combine with Cu 2+ and Cd 2+ to form precipitates and various complexes, which affects the judgment of the material's adsorption performance, so the pH of the subsequent experiment is set to 6.

[0122] Effect of adsorption time on LZT 850 The influence on adsorption performance is as follows Figure 12 (c) shows that in the first 60 minutes of the adsorption process, the adsorption rates of LZT 850 for Cu 2+ and Cd 2+ increase rapidly, reaching 56% and 88% respectively. It can be seen that the adsorption rate of the material for Cd is 1.57 times that of Cu. As the time increases, the adsorption rate gradually slows down and reaches the adsorption equilibrium at 120 minutes and 180 minutes respectively. The material adsorbs 10mg / L Cu 2+ and Cd2+ The adsorption capacities of the solution are 9.58 mg / g and 9.95 mg / g respectively. However, because the concentration of heavy metal ions is too low, not all adsorption sites of the material are fully occupied, and there is still remaining adsorption capacity.

[0123] The effect of adsorption temperature on LZT 850 on the adsorption performance is as Figure 12 (d - f) shows that for LZT 850 the removal rates of the two heavy metals both increase with the increase of adsorption temperature. At the same solid - liquid ratio and solution concentration, from 15 °C to 35 °C, the adsorption capacity of LZT 850 increases by 3 mg / g. This may be because the increase in temperature intensifies the kinetic energy of heavy metal ions in the solution, increasing the probability of collision with surface adsorption sites. At the same time, it shows that the adsorption process of LZT 850 is an endothermic reaction, and appropriate temperature increase is beneficial to the adsorption of heavy metals.

[0124] The effect of the initial concentration of heavy metals on LZT 850 on the adsorption performance is as Figure 12 (d - f) shows that when the concentrations of heavy metal solutions are 10 mg / L and 20 mg / L, the adsorption rates of LZT 850 for Cu 2+ and Cd 2+ can reach more than 90%. With the increase of adsorption concentration, the adsorption efficiency gradually decreases, and the adsorption capacity gradually increases. When the concentration is in the range of 50 mg / L - 100 mg / L, the decrease in adsorption efficiency slows down, and the higher the temperature, the more it slows down. This may be because the concentrations of Cu 2+ and Cd 2+ are moderate, and the increase in temperature has an obvious effect on the adsorption efficiency. As the concentration continues to increase, the adsorption sites of LZT 850 are occupied in large quantities, and the adsorption efficiency decreases. When the concentrations of Cu 2+ and Cd 2+ solutions reach 400 mg / L, LZT 850 reaches the maximum adsorption capacities, which are 126.01 mg / g and 149.52 mg / g respectively. Further increasing the concentration, the adsorption capacity hardly changes, indicating that the adsorption capacity has reached saturation.

[0125] Adsorption kinetics

[0126] Table 4 The adsorption amounts of LZT 850 at different times

[0127]

[0128] The adsorption amounts of LZT 850 at different times are shown in Table 4. The pseudo - first - order and pseudo - second - order kinetic models are used to fit the adsorption of LZT 850 for Cu2+ and Cd 2+ adsorption process, and the results are as Figure 13 (a - b) shown. The correlation coefficients of the pseudo-first-order and pseudo-second-order kinetic model fittings are shown in Table 5. After fitting the pseudo-second-order kinetic equation, R 2 are 0.97641 and 0.99896 respectively, both higher than the R 2 of the pseudo-first-order kinetic equation, and are more in line with the adsorption process of LZT 850 for Cu 2+ and Cd 2+ . It shows that in addition to a small part of physical adsorption, the adsorption methods of Cu 2+ and Cd 2+ on the material surface are mainly chemical adsorption (such as electrostatic adsorption, ion exchange, and chemical bond adsorption, etc.).

[0129] Table 5 Fitting parameters of pseudo-first-order and pseudo-second-order kinetic models

[0130]

[0131] The fitting image of the intraparticle diffusion model is as Figure 14 (a) shown. It can be seen that in the first stage, due to the existence of a large number of empty adsorption sites and a high concentration of heavy metal ions, Cu 2+ and Cd 2+ are easily combined with the adsorption active sites in the adsorption material and rapidly diffuse on the material surface, with a high adsorption rate, and the adsorption rate of Cd 2+ is faster; as the adsorption sites are gradually occupied and the concentration of heavy metal ions on the sites also gradually increases, the resistance to the inward diffusion of Cu 2+ and Cd 2+ increases in the second stage, and the intraparticle diffusion rate gradually decreases and tends to equilibrium. The fitting parameters of the intraparticle diffusion model are shown in Table 7. The intraparticle diffusion rate constant k1 > k2 also corroborates the above conclusion. At the same time, the fitting straight line of the intraparticle diffusion model does not pass through the origin of the coordinate, indicating that both surface diffusion and intraparticle diffusion have a certain influence on the adsorption rate.

[0132] Table 6 Fitting parameters of intraparticle diffusion model

[0133]

[0134] The fitting image and fitting parameters of the Elovich kinetic model are as Figure 14 (b) and Table 7 shown. It can be seen that the fitting parameters α and β after adsorbing Cd 2+ are 4.52783 and 0.66103 respectively, both greater than the fitting parameters 0.68181 and 0.44825 after adsorbing Cu 2+ , indicating that Cd 2+ is adsorbed by LZT 850Faster adsorption rate and higher coverage and diffusion degree on the material surface.

[0135] Table 7 Fitting parameters of the Elovich model

[0136]

[0137] Adsorption isotherm

[0138] The fitting images and fitting parameters of the Langmuir model and the Freundlich model are as Figure 15 (a-d) and shown in Table 8. After the material adsorbs Cu 2+ and Cd 2+ , the R 2 fitted by Langmuir is greater than 0.98, while the R 2 fitted by Freundlich is between 0.97 - 0.98, indicating that the adsorption mode of the material is chemisorption and it is monolayer adsorption on homogeneous sites. Adsorption can only occur at a limited number of fixed positions, which are the same and equivalent, and there is no lateral interaction and steric hindrance between the adsorbed molecules.

[0139] Table 8 Fitting parameters of the adsorption isotherm model

[0140]

[0141] Adsorption mechanism

[0142] LZT 850 Adsorbing Cu 2+ and Cd 2+ before and after, the XRD patterns are as Figure 16 shown. After adsorption, the diffraction peaks of CaMg(CO3)2, CaO, and MgO in LZT 850 disappear because carbonate can form precipitates with Cu 2+ and Cd 2+ during the adsorption process. At the same time, basic oxides are prone to combine with Cu 2+ and Cd 2+ to form Cu- and Cd-containing complexes attached to the material surface, such as copper oxides (CuO or Cu2O) and cadmium compounds (such as CdO or CdSiO3). The formation of these new phases is due to the reaction of Cu 2+ and Cd 2+ with active components such as CaO and SiO2 in the tailings to form stable compounds. In addition, CaO and MgO may be partially consumed during the adsorption process, resulting in a decrease in the intensity of their diffraction peaks.

[0143] LZT 850 Adsorbing Cu 2+ and Cd2+ The FTIR spectra before and after are as follows Figure 17 shown. The absorption peaks identified at 3440 and 3650 cm -1 are attributed to the bending vibration of O-H in the water molecules of the material; the two absorption peaks identified near 2900 cm -1 are attributed to the symmetric and antisymmetric stretching vibrations of C-H in the alkyl group; while the absorption peaks identified near 1407 and 875 cm -1 can be respectively attributed to the stretching vibrations of CO3 2- in dolomite and calcite, corresponding to the dolomite and calcite contained in LZT 850 , and the peak value of CO3 2- decreases after adsorption, which also proves that it plays a role in the adsorption process; the absorption peaks identified near 1120 and 600 cm -1 are respectively attributed to the stretching vibrations of S=O and S-S, and their peak values also decrease after adsorption, which also corroborates that the sulfur element in pyrite plays a role during adsorption; the absorption peak identified near 996 cm -1 is the stretching vibration of Si-O, corresponding to the quartz in LZT 850 , but after adsorption, the peak width becomes narrower and the peak value becomes lower, which is consistent with the conclusion of the formation of silicate.

[0144] Through Figure 18 (a-c) The SEM images of LZT 850 before and after adsorption can also show that the surface of the material is covered by many newly emerged strip-shaped and spherical flocs. Therefore, the formation of complexes is also one of the ways for LZT 850 to remove heavy metal ions. Diffraction peaks of CuS2 and CuFeS2 appear in the XRD pattern after adsorbing Cu 2+ , new peaks of CdS and Cd4SiS6 appear after adsorbing Cd 2+ , and the peak intensity of the originally existing FeS2 weakens significantly. It can be seen that the large amount of carbonate radicals contained in dolomite and calcite, as well as the sulfur element carried by pyrite, play a role in adsorption in the material.

[0145] LZT 850 The XPS spectra of LZT 2+ before and after adsorbing Cu 2+ and Cd Figure 19 are as follows Figure 19 (a) It can be seen from the C1s spectrogram that the carbon-containing functional groups in LZT 850 are mainly C-C and CO3 2- , and their binding energies are 284.8 and 289.39 eV respectively. The area percentage of CO3 2- changes significantly after adsorption, indicating that it participates in the adsorption reaction. Figure 19(b) shows the chemical morphological changes of S during the adsorption process. S mainly exists in the form of metal sulfide and SO4 2- in the material. The binding energy of Si is 101.87 eV, and it mainly exists in the form of SiO2 during the reaction. At the same time, there is also a small amount of SiO3 2- formed by oxidation, as shown in Figure 19 (c). After adsorbing Cu 2 + and Cd 2+ , the area percentage of the peak of Fe2p3 / 2 with a binding energy of 710.7 eV in FeS2 decreases from 48.93% to 38.45% and 36.15%, as shown in Figure 19 (d), indicating that part of Fe 2+ is oxidized to Fe 3+ during the reaction, which is identified as Fe2O3, an oxide that also has a certain adsorption effect on heavy metal ions. Therefore, both FeS2 and Fe2O3 play a role in the adsorption process. Figure 19 In the LZT 850 shown in (e), the binding energy of the main peak of Cu is 940.74 eV. According to the XRD pattern, it is judged that Cu exists in the material in its zero-valent form. After adsorbing Cu 2+ , the corresponding binding energy of the main peak of Cu2p3 / 2 is 932.53 eV, existing in the form of divalent copper ions, indicating that Cu 2+ is indeed adsorbed by the material. Combining the Figure 19 spectrum of Cd3d and the XRD pattern after adsorption, it is speculated that Cd exists in the form of CdSO4 with a binding energy of 407.98 eV in LZT 850 . After adsorbing Cd 2+ , the corresponding binding energy of Cd3d5 / 2 is 404.65 eV. After comparing with the XPS standard spectrum, it is determined that it exists in the form of CdS.

[0146] After being adsorbed by LZT 850 , Cu 2+ and Cd 2+ mainly exist in the form of organic matter and sulfide bound states, as shown in the Figure 20 morphological analysis results, with proportions of 93% and 78% respectively. This bound state of heavy metals is relatively stable, and at the same time, their bioavailability approaches 0, making them not easily absorbed and utilized by organisms in the environment. Existing mainly in the form of sulfide bound state is also consistent with the conclusions of XRD and XPS after adsorption. It also once again proves the environmental harmlessness of lead-zinc tailings as an adsorption material and the stability of the material after adsorbing heavy metals.

[0147] Mixed system and material cyclic adsorption performance

[0148] The adsorption effect after mixing two heavy metals is as shown in Figure 21As shown, compared with the individual adsorption of Cu 2+ and Cd 2+ , when the mixed concentration is between 10 mg / L and 30 mg / L, the adsorption effect does not change much. However, when the mixed concentration reaches 40 mg / L, the adsorption efficiency of LZT 850 for Cu 2+ and Cd 2+ decreases by 2.24% and 1.09% respectively, and as the mixed concentration increases, the adsorption efficiency decreases even more. This is attributed to the limited adsorption sites, and competitive adsorption occurs between the two heavy metals, affecting the adsorption efficiency. However, whether it is separate or mixed adsorption, the adsorption rate and adsorption efficiency of LZT 850 for Cd 2+ are always higher than those of Cu 2+ . This may be because the metal activity of Cd 2+ is stronger than that of Cu 2+ , and it can occupy the adsorption sites faster and more. Moreover, Cd 2+ has a stronger ability to lose electrons and is more easily adsorbed and bound by the surface charge of the material.

[0149] The cyclic regeneration adsorption of LZT 850 is as shown in Figure 22 . It can be seen from the dotted line graph in the figure that the desorption rates of the material after each adsorption of Cu 2+ are 92.56%, 89.28%, 85.21%, 82.05% and 81.56% respectively, and the desorption rates of the material after adsorption of Cd 2+ are 97.37%, 93.65%, 88.17%, 85.21% and 82.96% respectively. Lv found that the presence of CO3 2- and SiO3 2- makes the material easier to desorb. However, the chemical adsorption of heavy metals by LZT 850 will hinder the reversible desorption to a certain extent, and the reduction of adsorption sites leads to the decrease of the adsorption capacity of the material with the increase of the number of repetitions. However, after 5 repetitions, the adsorption rates of LZT 850 for Cu 2+ and Cd 2+ can be maintained at 82.6% and 86.16%, respectively, and it still has good recyclability compared with other tailing materials.

[0150] The present invention synthesizes an adsorption material with good heavy metal treatment effect by combining microwave thermal modification with surface sulfidation treatment and high-temperature sintering of lead-zinc tailings. Lead-zinc tailings are composed of a large amount of alkaline carbonate minerals and silicate minerals. After modification, the existing forms of various heavy metals in them are stable and not easily released into the environment. After 10 minutes of microwave thermal modification at 800 W, treatment with sodium sulfide solution, and high-temperature sintering at 850 °C, the surface of the material mostly shows slit-shaped pores and has a larger specific surface area. The adsorption experiment results show that the adsorption pH, time, temperature, and concentration jointly affect the adsorption efficiency. LZT 850 has the best adsorption effect at pH = 6, for Cu 2+ and Cd 2+ the saturated adsorption amounts are 126.01 mg / g and 149.52 mg / g respectively, and the adsorption equilibrium times are 120 and 180 minutes respectively. Appropriately increasing the temperature is beneficial to the increase of the adsorption capacity. LZT 850 For Cu 2+ and Cd 2+ the adsorption process conforms to the pseudo-second-order kinetic model and the Langmuir isotherm model, belonging to monolayer chemical adsorption on homogeneous sites. The adsorption rate is jointly controlled by surface diffusion and intra-diffusion. LZT 850 mainly adsorbs heavy metals through the exchange action between Ca 2+ , Mg 2+ and heavy metal ions, as well as the bond energy complexation and electrostatic attraction of chemical bonds such as Si-O, C=O, and Fe-S. LZT 850 The adsorption rate for the mixed solution of the two heavy metals can also reach more than 80%. Five-cycle adsorption experiments confirm that LZT 850 has good regeneration ability. This method provides new ideas and references for the resource utilization of other industrial solid wastes.

[0151] The preferred embodiments of the present invention disclosed above are only used to help explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific embodiments described. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments to better explain the principle and practical application of the present invention, so that those skilled in the art in the relevant technical field can well understand and utilize the present invention. The present invention is only limited by the claims and their full scope and equivalents.

Claims

1. A preparation method of a heavy metal adsorption material based on lead-zinc tailings, characterized in that, It includes the following steps: S1: Grind the lead-zinc tailings to a particle size less than 75 μm and conduct drying treatment; S2: Place the lead-zinc tailings treated in step S1 into a microwave reactor and conduct microwave thermal modification treatment at a power of 600 - 1000 W for 5 - 15 minutes; S3: Immerse the microwave-treated lead-zinc tailings in a sodium sulfide solution with a mass concentration of 0.5% - 2% for surface sulfidation treatment; S4: Under the protection of nitrogen, heat the sulfidation-treated lead-zinc tailings to 800 - 950 °C at a heating rate of 3 - 10 °C / min and calcine for 1 - 3 hours. After cooling, wash and dry to obtain a heavy metal adsorption material.

2. The preparation method according to claim 1, characterized in that, In step S2, the microwave power is 800 W and the treatment time is 10 minutes.

3. The preparation method according to claim 1, characterized in that, In step S3, the mass concentration of the sodium sulfide solution is 1% and the sulfidation treatment time is 1 - 3 hours.

4. The preparation method according to claim 1, characterized in that, In step S4, the calcination temperature is 850 °C and the heating rate is 5 °C / min.

5. Method for treating wastewater containing Cu2+ and Cd 2 + by using the heavy metal adsorbent material obtained by the method according to any one of claims 1-4, characterized in that It includes the following steps: S1: Adjust the pH of the wastewater to 4 - 8; S2: Add the adsorption material according to a solid-liquid ratio of 1:10 - 1:50, and oscillate and adsorb at 15 - 35 °C for 60 - 240 minutes; S3: Separate the adsorbed material to complete the wastewater treatment.

6. Use of the heavy metal adsorbent material obtained by the method according to any one of claims 1-4 in environmental remediation, characterized in that, For removing Cu2+, Cd 2 + and its combined pollution in industrial wastewater, mine leachate or agricultural irrigation water.

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