Method for preparing sintered bricks from heavy metal contaminated soil

Abstract

The invention relates to the technical field of soil remediation, and particularly discloses a method for preparing sintered bricks from heavy metal contaminated soil, and the method comprises the following steps: mixing the heavy metal contaminated soil with coal gangue, fly ash and desulfurized gypsum, and carrying out crushing, aging, compression molding and high-temperature sintering to prepare the sintered bricks. Through single factor and orthogonal test optimization, the optimal process parameters are determined as follows: the additive amount of the polluted soil is 40%, the sintering temperature is 800 DEG C, and the heat preservation time is 10 h. The sintered brick prepared by the invention can effectively fix heavy metals such as Cd, As, Pb and the like in soil, the leaching concentration of the sintered brick is far lower than the GB / T 35605-2017 limit value of Wall Materials for Evaluation of Green Products, and safe disposal and resource utilization of the heavy metal contaminated soil are realized.

Description

Technical Field

[0001] This invention relates to the field of soil remediation technology, specifically to a method for preparing sintered bricks using soil contaminated with heavy metals. Background Technology

[0003] Existing soil heavy metal pollution treatment technologies can be mainly categorized into four types: physical remediation, chemical remediation, and physicochemical remediation. Physical remediation methods primarily utilize soil replacement and thermal desorption, offering advantages such as rapid effectiveness and wide applicability, but suffer from high energy consumption and high costs. Chemical remediation mainly employs soil washing and ambient temperature fixation stabilization techniques; these methods are simple to operate and highly efficient, but have high carbon emission loads, which do not align with the current trend towards low-carbon and green pollution remediation. Physicochemical remediation combines physical and chemical methods, such as electrokinetic remediation (EMR), but for large-scale soil pollution areas, EMR requires significant equipment and engineering investment, resulting in long construction periods and high costs.

[0004] Therefore, it is necessary to develop a new method for treating heavy metal contaminated soil in order to reduce the leaching of heavy metals from contaminated soil. Summary of the Invention

[0005] To develop a novel method for treating heavy metal-contaminated soil, this invention provides a method for preparing sintered bricks using heavy metal-contaminated soil. The sintered bricks prepared by this invention can effectively immobilize heavy metals such as Cd, As, and Pb in the soil, with leaching concentrations far below the limits (Cd < 0.1 mg / L, As < 0.6 mg / L, Pb < 2 mg / L) in GB / T 35605-2017, the "Green Product Evaluation Wall Materials" standard, thus achieving the safe disposal and resource utilization of heavy metal-contaminated soil.

[0006] This invention provides a method for preparing sintered bricks using heavy metal contaminated soil, comprising the following steps: Heavy metal contaminated soil, coal gangue, and a solidifying agent are crushed to below 60 mesh and mixed at a mass ratio of 10~50:45~89:1~5 to obtain a mixed raw material; the solidifying agent is a combination of fly ash and desulfurized gypsum. Water is added to the mixed raw materials until the moisture content is 8%~12%, and then the mixture is aged to obtain aged raw materials; The aged raw materials are pressed into shape to obtain brick blanks; The brick blanks are sintered to obtain sintered bricks.

[0007] The sintered bricks prepared by this invention can effectively fix heavy metals such as Cd, As, and Pb in the soil. Their leaching concentration is far below the limit of GB / T 35605-2017 "Green Product Evaluation Wall Materials", realizing the safe disposal and resource utilization of heavy metal contaminated soil.

[0008] Furthermore, the mass ratio of the fly ash to the desulfurized gypsum is 1~4:4~1.

[0009] Further, the desulfurized gypsum and fly ash are mixed and then treated at a high temperature of 1100℃~1300℃ for 1 h~3 h to obtain the curing agent.

[0010] Further, the aging process involves placing the mixed raw materials in an environment with a temperature of 15℃~25℃ and a humidity of 25%~35% for 22 h~26 h.

[0011] Furthermore, the sintering temperature is 600℃~1000℃.

[0012] Furthermore, the sintering time is 8 h to 10 h.

[0013] Furthermore, the dimensions of the pressing mold are 240 mm × 115 mm × 53 mm.

[0014] The present invention also provides a sintered brick prepared by any of the methods described herein.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention optimizes the sintering process and curing agent combination, resulting in leaching concentrations of key heavy metals Cd, As, and Pb in the final sintered brick product that are far below the stringent limits (Cd<0.1 mg / L, As<0.6 mg / L, Pb<2 mg / L) of the "Green Product Evaluation Wall Materials" (GB / T 35605-2017). Under optimal conditions, the leaching concentration of As can be as low as 54.1 μg / L, with extremely high fixation efficiency.

[0016] The method for preparing sintered bricks from heavy metal-contaminated soil provided by this invention not only treats the contaminated soil but also disposes of a large amount of other solid wastes such as fly ash, desulfurization gypsum, and coal gangue, achieving "waste treatment with waste" and significantly reducing raw material and environmental remediation costs. Furthermore, through process optimization, this invention increases the amount of contaminated soil added from the theoretically optimal 10% to 40%, quadrupling the treatment efficiency. This significantly reduces the equipment operating cycle, energy consumption, and labor costs required to treat the same amount of contaminated soil. Moreover, this method can be directly upgraded using existing sintered brick production processes and equipment, eliminating the need for huge investments in constructing entirely new dedicated treatment facilities, resulting in significant economic benefits.

[0017] The final product of this invention is a green wall material that meets national standards and can be directly used in construction projects. Compared to chemical remediation methods that generate high carbon emissions, this method achieves carbon sequestration and permanent resource conversion by transforming heavy metal-contaminated soil into sustainable building materials, aligning with the green and low-carbon development direction. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 The effect of the amount of heavy metal added to contaminated soil on the leaching concentration of heavy metals from sintered bricks; In the figure, A represents the effect of the amount of heavy metal contaminated soil added on the Cd leaching concentration of sintered bricks; B represents the effect of the amount of heavy metal contaminated soil added on the As leaching concentration of sintered bricks; C represents the effect of the amount of heavy metal contaminated soil added on the Pb leaching concentration of sintered bricks.

[0020] Figure 2 The effect of sintering temperature on the leaching concentration of heavy metals from sintered bricks; In the figure, A represents the effect of sintering temperature on the Cd leaching concentration of sintered bricks; B represents the effect of sintering temperature on the As leaching concentration of sintered bricks; C represents the effect of sintering temperature on the Pb leaching concentration of sintered bricks.

[0021] Figure 3 The effect of heat preservation time on the leaching concentration of heavy metals in sintered bricks; In the figure, A represents the effect of heat preservation time on the Cd leaching concentration of sintered bricks; B represents the effect of heat preservation time on the As leaching concentration of sintered bricks; C represents the effect of heat preservation time on the Pb leaching concentration of sintered bricks.

[0022] Figure 4 The effect of fly ash addition on the leaching concentration of heavy metals in sintered bricks; In the figure, A represents the effect of fly ash addition on the Cd leaching concentration of sintered bricks; B represents the effect of fly ash addition on the As leaching concentration of sintered bricks; C represents the effect of fly ash addition on the Pb leaching concentration of sintered bricks.

[0023] Figure 5The effect of CaO addition on the leaching concentration of heavy metals in sintered bricks; In the figure, A represents the effect of CaO addition on the Cd leaching concentration of sintered bricks; B represents the effect of CaO addition on the As leaching concentration of sintered bricks; C represents the effect of CaO addition on the Pb leaching concentration of sintered bricks.

[0024] Figure 6 The effect of Fe2SO4 addition on the leaching concentration of heavy metals in sintered bricks; In the figure, A represents the effect of Fe2SO4 addition on the Cd leaching concentration of sintered bricks; B represents the effect of Fe2SO4 addition on the As leaching concentration of sintered bricks; C represents the effect of Fe2SO4 addition on the Pb leaching concentration of sintered bricks.

[0025] Figure 7 The effect of direct addition of desulfurization gypsum and fly ash on the leaching concentration of heavy metals in sintered bricks; In the figure, A represents the effect of direct addition of desulfurized gypsum and fly ash on the Cd leaching concentration of sintered bricks; B represents the effect of direct addition of desulfurized gypsum and fly ash on the As leaching concentration of sintered bricks; C represents the effect of direct addition of desulfurized gypsum and fly ash on the Pb leaching concentration of sintered bricks.

[0026] Figure 8 The effect of adding desulfurized gypsum after high-temperature treatment on the leaching concentration of heavy metals in sintered bricks; In the figure, A represents the effect of adding desulfurized gypsum after high-temperature treatment on the Cd leaching concentration of sintered bricks; B represents the effect of adding desulfurized gypsum after high-temperature treatment on the As leaching concentration of sintered bricks; C represents the effect of adding desulfurized gypsum after high-temperature treatment on the Pb leaching concentration of sintered bricks.

[0027] Figure 9 The effect of adding desulfurized gypsum and fly ash after high-temperature treatment on the leaching concentration of heavy metals in sintered bricks; In the figure, A represents the effect of adding desulfurized gypsum and fly ash after high-temperature treatment on the Cd leaching concentration of sintered bricks; B represents the effect of adding desulfurized gypsum and fly ash after high-temperature treatment on the As leaching concentration of sintered bricks; C represents the effect of adding desulfurized gypsum and fly ash after high-temperature treatment on the Pb leaching concentration of sintered bricks. Detailed Implementation

[0028] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise specified, the experimental methods described in the embodiments of the present invention are conventional methods, and the materials and reagents used in the following embodiments are commercially available unless otherwise specified.

[0029] Example 1: A method for preparing sintered bricks using soil contaminated with heavy metals.

[0030] I. Experimental Methods 1. Sintering heavy metal-contaminated soil for brick making The heavy metal contaminated soil was taken from a Pb / Zn smelter, the coal gangue and desulfurization gypsum were provided by Jiangsu Zhenfeng Environmental Protection Group, and the fly ash was provided by Xuzhou Huarun Power Plant.

[0031] Crushing and Mixing: According to preliminary test results, when the raw materials are crushed and passed through a sieve smaller than 60 mesh, the fired bricks exhibit significant quality defects, including surface cracks, loose structure, and spontaneous breakage over time, failing to meet molding requirements. However, after crushing the coal gangue raw materials and passing them through a 60-mesh sieve (particle size <0.250 mm), the quality of the fired bricks is significantly improved. The bricks have a uniform brick-red appearance, no cracks or efflorescence, and a dense and hard structure. Therefore, heavy metal contaminated soil, coal gangue, fly ash, and desulfurized gypsum are crushed and uniformly passed through a 60-mesh sieve (i.e., <0.250 mm). The sieved heavy metal contaminated soil, coal gangue, fly ash, and desulfurized gypsum are then mixed to obtain a mixed raw material.

[0032] Water aging: Add water to the mixed raw materials until the moisture content is 10%, let it stand naturally (temperature 20℃, humidity 30%) for 24 hours to obtain aged raw materials.

[0033] Pressing and molding: 10 g of aged raw material is added to a mold (mold size 240×115×53mm). An electronic universal testing machine (Jilin Guanteng Automation Technology Co., Ltd., WDW-100) is used to press the material in the mold for 10 seconds at a pressure of 15 MPa to obtain the brick body. The brick body is then air-dried naturally for 12 hours to prevent cracking or fine cracks caused by excessive drying. It is then placed in an oven at 60℃ for 5 hours to obtain the brick blank. Three parallel samples are made each time to eliminate errors.

[0034] High-temperature sintering: The brick blanks are placed in a muffle furnace and sintered at 800℃. After holding at this temperature for 8 hours, they are removed from the muffle furnace and allowed to cool naturally to obtain sintered bricks.

[0035] 2. Single-factor experiment Single-factor experiments were conducted to determine the relative optimal conditions for key factors such as the amount of heavy metal contaminated soil added, sintering temperature, heat preservation time, and solidifier ratio, which were then used for process optimization in subsequent orthogonal experiments.

[0036] 2.1 Selection of sintering parameters A three-factor, five-level experiment was designed (Table 1). The addition amounts of heavy metal contaminated soil were 10%, 20%, 30%, 40%, and 50%, respectively. The addition amount of solidifying agent (a mixture of desulfurized gypsum and fly ash at a mass ratio of 4:1, held at 1200℃ for 2 h) was 5%, with the remainder being coal gangue. The sintering temperatures were 600℃, 700℃, 800℃, 900℃, and 1000℃, and the holding times were 6 h, 7 h, 8 h, 9 h, and 10 h, respectively. The addition amounts are percentages of the total mass.

[0037] Table 1 Single-factor control experimental design 2.2 Selection of Curing Agent Fly ash, CaO, and Fe2SO4 were selected as curing agents, and the relatively optimal curing agents and their addition amounts were screened. Five levels were designed for each of the three curing agents (Table 2): fly ash addition amounts of 1%, 2%, 3%, 4%, and 5%; calcium oxide addition amounts of 1%, 2%, 3%, 4%, and 5%; and ferrous sulfate addition amounts of 1%, 2%, 3%, 4%, and 5%. For heavy metal contaminated soil, the addition amount was 30%, with the remainder being coal gangue. The holding time was 8 hours, and the sintering temperature was 800℃. The addition amounts are percentages of the total mass.

[0038] Table 2 Curing agent screening test design Fly ash and desulfurized gypsum were subjected to high-temperature treatment, and the resulting mixture was used as a curing agent to further optimize the curing agent combination and its dosage. A three-factor, five-level experiment was designed (Table 3). The addition ratios of desulfurized gypsum and fly ash were 4:1, 3:2, 1:1, 2:3, and 1:4. The addition amounts of desulfurized gypsum after high-temperature treatment were 1%, 2%, 3%, 4%, and 5%, respectively. The addition ratios of desulfurized gypsum and fly ash after high-temperature treatment were 4:1, 3:2, 1:1, 2:3, and 1:4. For heavy metal contaminated soil, the addition amount was 30%, with the remainder being coal gangue. The holding time was 8 hours, and the sintering temperature was 800℃. The addition amounts are percentages of the total mass.

[0039] Table 3. Optimization Experimental Design of Curing Agent Note: The ratio of desulfurized gypsum to fly ash in the table refers to the mass ratio of desulfurized gypsum to fly ash when the total addition is 5%. For example, 4:1 means that 4% of desulfurized gypsum is added and 1% of fly ash is added, and 1:1 means that 2.5% of desulfurized gypsum is added and 2.5% of fly ash is added.

[0040] 3. Orthogonal experiment A three-factor, three-level orthogonal experiment was designed to determine the optimal conditions for the amount of heavy metal contaminated soil added, sintering temperature, and holding time using a mixture of desulfurized gypsum and fly ash treated at high temperature as a solidifying agent (Table 4). The amount added is a percentage of the total mass.

[0041] Table 4 Orthogonal Experimental Design Desulfurized gypsum and fly ash were mixed at a mass ratio of 2:3 and then subjected to high-temperature treatment at 1200℃ for 2 hours. The treatment product was used as an additive at a concentration of 5%, and a three-factor, three-level orthogonal experiment was conducted. The addition amounts for heavy metal contaminated soil were 10%, 25%, and 40% (the balance being coal gangue), the sintering temperatures were 600℃, 800℃, and 1000℃, and the holding times were 7 hours, 8.5 hours, and 10 hours. All working conditions were performed in triplicate.

[0042] 4. Determination of heavy metal leaching concentration A mixture of concentrated sulfuric acid and concentrated nitric acid (2:1 mass ratio) was added to water (2 drops of the mixture per L of water) to adjust the pH to 3.2, thus obtaining the extractant. 15 g of sintered brick, passed through a 9.5 mm sieve, was weighed and placed in a centrifuge bottle. 150 mL of the extractant was added at a liquid-to-solid ratio of 10:1 (mL / g). The centrifuge bottle was tightly capped and fixed on a tilting shaker. The shaker was set to 30 r / min and operated at 23°C for 18 h for extraction (if gas is generated during shaking, the extraction bottle should be opened periodically in a fume hood to release excessive pressure), yielding the extract. The extract was then filtered through a 0.45 μm filtration device after rinsing with dilute nitric acid to obtain the test solution. The test solution was acidified with nitric acid to pH < 2 and stored at 4°C.

[0043] The content of heavy metals Cd, As, and Pb in the test solution was determined by inductively coupled plasma mass spectrometry (ICP-MS), which is the heavy metal leaching concentration of the sintered brick.

[0044] 5. Data Processing Data processing and preliminary analysis were performed using Excel 2016, orthogonal experimental analysis was performed using Orthogonal Experiment Assistant V3.1, and the final data results were plotted and expressed using Originpro 2024 software.

[0045] II. Test Results 1. Effects of different sintering parameters on the leaching concentration of heavy metals from sintered bricks 1.1 Amount of heavy metals added to contaminated soil When the amount of heavy metal added to the contaminated soil was 10%, 20%, 30%, 40%, and 50%, the Cd leaching concentrations of the sintered bricks were 0.043 μg / L, 0.023 μg / L, 0.099 μg / L, 0.080 μg / L, and 0.060 μg / L, respectively. Figure 1 The Cd leaching concentrations (A) were all lower than the 0.1 mg / L limit for wall materials in the "Evaluation of Green Products" (GB / T 35605-2017), with the lowest Cd leaching concentration (0.023 μg / L) when the addition amount was 20%.

[0046] When the amount of heavy metal added to the contaminated soil was 10%, 20%, 30%, 40%, and 50%, the As leaching concentrations of the sintered bricks were 872.221 μg / L, 1372.172 μg / L, 524.544 μg / L, 158.409 μg / L, and 34.951 μg / L, respectively. Figure 1 The As leaching concentration met the 0.6 mg / L limit in the "Green Product Evaluation Wall Materials" when the addition amount was 30%, 40% and 50%, with the lowest As leaching concentration (34.951 μg / L) when the addition amount was 50%.

[0047] When the amount of heavy metal added to the contaminated soil was 10%, 20%, 30%, 40%, and 50%, the Pb leaching concentration of the sintered bricks was 0 μg / L, 0 μg / L, 0.039 μg / L, 0.448 μg / L, and 0.846 μg / L, respectively. Figure 1 The concentrations of Pb (C) were all lower than the 2 mg / L limit for Pb in the "Evaluation of Green Products for Wall Materials". The lowest Pb leaching concentrations (0 μg / L) were observed when the addition amounts were 10% and 20%.

[0048] To balance the amount of soil added and the effect of heavy metal fixation, a 30% heavy metal contaminated soil addition was selected for subsequent single-factor experiments.

[0049] 1.2 Sintering Temperature When the sintering temperatures are 600℃, 700℃, 800℃, 900℃, and 1000℃, the Cd leaching concentrations of the sintered bricks are 1.085 μg / L, 0.058 μg / L, 0.84 μg / L, 0.140 μg / L, and 0.100 μg / L, respectively. Figure 2 The Cd leaching concentrations (A) were all lower than the 0.1 mg / L limit for Cd in the "Green Product Evaluation of Wall Materials". The lowest Cd leaching concentration (0.058 μg / L) was observed when the sintering temperature was 700℃.

[0050] When the sintering temperatures are 600℃, 700℃, 800℃, 900℃, and 1000℃, the As leaching concentrations of the sintered bricks are 1303.599 μg / L, 856.230 μg / L, 507.984 μg / L, 756.31 μg / L, and 3406.063 μg / L, respectively. Figure 2 Of the B, the lowest As leaching concentration (507.984 μg / L) was observed at a sintering temperature of 800℃, which is lower than the As limit of 0.6 mg / L in the "Green Product Evaluation Wall Materials".

[0051] When the sintering temperatures are 600℃, 700℃, 800℃, 900℃, and 1000℃, the Pb leaching concentrations of the sintered bricks are 0.435 μg / L, 0.645 μg / L, 0.480 μg / L, 0.077 μg / L, and 0.023 μg / L, respectively. Figure 2 The Pb concentrations (C) were all below the 2 mg / L limit for Pb in the "Green Product Evaluation of Wall Materials", with the lowest Pb leaching concentration (0.023 μg / L) at a sintering temperature of 1000℃.

[0052] To meet the heavy metal leaching standards as much as possible, a sintering temperature of 800℃ was selected for subsequent single-factor experiments.

[0053] 1.3 Insulation Time When the heat preservation time was 6 h, 7 h, 8 h, 9 h, and 10 h, the Cd leaching concentration of the sintered bricks was 0.029 μg / L, 0.042 μg / L, 0.070 μg / L, 0.055 μg / L, and 0.066 μg / L, respectively. Figure 3 The Cd leaching concentrations (A) were all below the 0.1 mg / L limit for wall materials in the "Evaluation of Green Products". The lowest Cd leaching concentration (0.029 μg / L) was observed when the insulation time was 6 h.

[0054] When the heat preservation time was 6 h, 7 h, 8 h, 9 h, and 10 h, the As leaching concentration of the sintered bricks was 41.331 μg / L, 146.454 μg / L, 469.279 μg / L, 792.274 μg / L, and 684.380 μg / L, respectively. Figure 3 The As leaching concentration was lower than the 0.6 mg / L limit in the "Green Product Evaluation Wall Materials" when the heat preservation time was 6 h, 7 h and 8 h, with the lowest As leaching concentration (41.331 μg / L) when the heat preservation time was 6 h.

[0055] When the heat preservation time was 6 h, 7 h, 8 h, 9 h, and 10 h, the Pb leaching concentration of the sintered bricks was 0.442 μg / L, 0.465 μg / L, 0.293 μg / L, 0.067 μg / L, and 0.062 μg / L, respectively. Figure 3 The concentrations of Pb (C) were all lower than the 2 mg / L limit for Pb in the "Evaluation of Green Products for Wall Materials". The lowest Pb leaching concentration (0.062 μg / L) was observed when the insulation time was 10 h.

[0056] To balance the strength of sintered bricks and the heavy metal leaching standard, an 8-hour heat preservation time was selected for subsequent single-factor experiments.

[0057] 2. Effects of curing agent type and dosage on heavy metal leaching concentration in sintered bricks 2.1 Fly ash addition amount When the fly ash addition amount was 1%, 2%, 3%, 4%, and 5%, the Cd leaching concentration of the sintered bricks was 0.024 μg / L, 0.026 μg / L, 0.109 μg / L, 0.130 μg / L, and 0.052 μg / L, respectively. Figure 4 The Cd leaching concentrations (A) were all lower than the 0.1 mg / L limit for wall materials in the "Evaluation of Green Products". The lowest Cd leaching concentration (0.024 μg / L) was found when the fly ash content was 1%.

[0058] When the fly ash addition amount was 1%, 2%, 3%, 4%, and 5%, the As leaching concentration of the sintered bricks was 1869.770 μg / L, 1752.201 μg / L, 1471.057 μg / L, 733.953 μg / L, and 57.814 μg / L, respectively. Figure 4 Among the B), the lowest As leaching concentration (57.814 μg / L) was achieved when the fly ash addition was 5%, which is lower than the As limit of 0.6 mg / L in the "Green Product Evaluation Wall Materials".

[0059] When the fly ash addition amount was 1%, 2%, 3%, 4%, and 5%, the Pb leaching concentration of the sintered bricks was 0.039 μg / L, 0.036 μg / L, 0.078 μg / L, 0.280 μg / L, and 0.252 μg / L, respectively. Figure 4 The Pb leaching concentrations were all lower than the 2 mg / L limit in the "Green Product Evaluation Wall Materials" standard, with the lowest Pb leaching concentration (0.036 μg / L) observed when the fly ash addition was 2%.

[0060] 2.2 CaO addition amount When the CaO addition amount is 1%, 2%, 3%, 4%, and 5%, the Cd leaching concentration of the sintered bricks is 0.026 μg / L, 0.042 μg / L, 0.034 μg / L, 0.047 μg / L, and 0.036 μg / L, respectively. Figure 5 All of them (A) are lower than the Cd limit of 0.1 mg / L in the "Green Product Evaluation Wall Materials". The Cd leaching concentration is the lowest (0.026 μg / L) when the CaO addition is 1%.

[0061] When the CaO addition amount was 1%, 2%, 3%, 4%, and 5%, the As leaching concentration of the sintered bricks was 1368.566 μg / L, 101.920 μg / L, 13.276 μg / L, 2.918 μg / L, and 1.094 μg / L, respectively. Figure 5 (B) When the CaO addition is 2%~5%, the As leaching concentration is lower than the 0.6 mg / L limit in the "Green Product Evaluation Wall Materials". Among them, the As leaching concentration is the lowest (1.094 μg / L) when the CaO addition is 5%.

[0062] When the CaO addition amount is 1%, 2%, 3%, 4%, and 5%, the Pb leaching concentration of the sintered bricks is 0.030 μg / L, 0.179 μg / L, 0.309 μg / L, 2.247 μg / L, and 115.048 μg / L, respectively. Figure 5 The C values ​​were all lower than the 2 mg / L Pb limit in the "Green Product Evaluation Wall Materials" standard, with the lowest Pb leaching concentration (0.030 μg / L) when the CaO addition was 1%.

[0063] 2.3 Fe2SO4 addition amount When the Fe2SO4 addition amount was 1%, 2%, 3%, 4%, and 5%, the Cd leaching concentration of the sintered bricks was 0.049 μg / L, 0.045 μg / L, 0.052 μg / L, 0.034 μg / L, and 0.026 μg / L, respectively. Figure 6 All of them (A) were lower than the Cd limit of 0.1 mg / L in the "Green Product Evaluation Wall Materials". The Cd leaching concentration was the lowest (0.026 μg / L) when the Fe2SO4 addition was 5%.

[0064] When the Fe2SO4 addition amount was 1%, 2%, 3%, 4%, and 5%, the As leaching concentration of the sintered bricks was 1893.322 μg / L, 2367.828 μg / L, 2250.993 μg / L, 1356.430 μg / L, and 595.387 μg / L, respectively. Figure 6Among the B), the lowest As leaching concentration (595.387 μg / L) was achieved when the Fe2SO4 addition was 5%, which is lower than the As limit of 0.6 mg / L in the "Green Product Evaluation Wall Materials".

[0065] When the Fe2SO4 addition amount was 1%, 2%, 3%, 4%, and 5%, the Pb leaching concentration of the sintered bricks was 0.714 μg / L, 0.097 μg / L, 0.113 μg / L, 0.310 μg / L, and 0.565 μg / L, respectively. Figure 6 The Pb leaching concentration was lower than the 2 mg / L limit in the "Green Product Evaluation Wall Materials" standard, with the lowest Pb leaching concentration (0.097 μg / L) when the Fe2SO4 addition was 2%.

[0066] 3. Effect of high-temperature curing agent treatment on the leaching concentration of heavy metals in sintered bricks The experimental results of the above-mentioned curing agents show that Fe2SO4 has a slightly worse effect on As fixation than fly ash and CaO, and its price is also higher, so Fe2SO4 was excluded. CaO and fly ash both showed good As fixation effects, and the As fixation effect significantly improved with the increase of their addition amount. Therefore, desulfurized gypsum was used to replace CaO in subsequent experiments to study the effect of high-temperature treatment of desulfurized gypsum and fly ash on the leaching concentration of heavy metals in sintered bricks.

[0067] 3.1 Desulfurization gypsum and fly ash are added directly. When the ratio of desulfurized gypsum to fly ash was 4:1, 3:2, 1:1, 2:3, and 1:4, the Cd leaching concentrations of the sintered bricks were 0.006 μg / L, 0.014 μg / L, 0.009 μg / L, 0.023 μg / L, and 0.046 μg / L, respectively. Figure 7 The concentrations of Cd in the A-values ​​were all below the 0.1 mg / L limit for Cd in the "Evaluation of Green Products for Wall Materials". The lowest Cd leaching concentration (0.006 μg / L) was observed when the addition ratio was 4:1.

[0068] When the ratio of desulfurized gypsum to fly ash was 4:1, 3:2, 1:1, 2:3, and 1:4, the As leaching concentrations of the sintered bricks were 1375.249 μg / L, 1748.856 μg / L, 1288.650 μg / L, 734.575 μg / L, and 250.458 μg / L, respectively. Figure 7 The lowest As leaching concentration (250.458 μg / L) was observed when the addition ratio was 1:4, which is lower than the As limit of 0.6 mg / L in the "Green Product Evaluation Wall Materials".

[0069] When the ratio of desulfurized gypsum to fly ash was 4:1, 3:2, 1:1, 2:3, and 1:4, the Pb leaching concentrations of the sintered bricks were 0.013 μg / L, 0.024 μg / L, 0.086 μg / L, 0.237 μg / L, and 0.157 μg / L, respectively. Figure 7 The concentrations of Pb (C) were all lower than the 2 mg / L limit for Pb in the "Evaluation of Green Products for Wall Materials". The lowest Pb leaching concentration (0.013 μg / L) was observed when the addition ratio was 4:1.

[0070] 3.2 Added after high-temperature treatment of desulfurized gypsum When the addition amount of desulfurized gypsum after high-temperature treatment was 1%, 2%, 3%, 4%, and 5%, the Cd leaching concentration of the sintered bricks was 0.039 μg / L, 0.023 μg / L, 0.031 μg / L, 0.054 μg / L, and 0.040 μg / L, respectively. Figure 8 The Cd leaching concentrations (A) were all below the 0.1 mg / L limit for wall materials in the "Evaluation of Green Products". The lowest Cd leaching concentration (0.023 μg / L) was observed when the addition amount was 2%.

[0071] When the addition amount of desulfurized gypsum after high-temperature treatment was 1%, 2%, 3%, 4%, and 5%, the As leaching concentration of sintered bricks was 640.959 μg / L, 831.914 μg / L, 302.919 μg / L, 134.665 μg / L, and 56.403 μg / L, respectively. Figure 8 The As leaching concentration of B was lower than the 0.6 mg / L limit in the "Green Product Evaluation Wall Materials" when the addition amount was 3% to 5%, with the lowest As leaching concentration (56.403 μg / L) when the addition amount was 5%.

[0072] When the addition amount of desulfurized gypsum after high-temperature treatment was 1%, 2%, 3%, 4%, and 5%, the Pb leaching concentration of the sintered bricks was 0.255 μg / L, 0.204 μg / L, 0.274 μg / L, 0.265 μg / L, and 0.340 μg / L, respectively. Figure 8 The concentrations of Pb (C) were all lower than the 2 mg / L limit for Pb in the "Evaluation of Green Products for Wall Materials". The lowest Pb leaching concentration (0.204 μg / L) was found when the addition amount was 2%.

[0073] The above results indicate that, compared to adding desulfurized gypsum and fly ash directly after mixing, desulfurized gypsum treated at 1200℃ has a certain improvement in the fixation effect of As.

[0074] 3.3. Add desulfurized gypsum and fly ash after high-temperature treatment When the addition ratio of desulfurized gypsum and high-temperature treated fly ash was 4:1, 3:2, 1:1, 2:3, and 1:4, the Cd leaching concentrations of the sintered bricks were 0.041 μg / L, 0.030 μg / L, 0.057 μg / L, 0.031 μg / L, and 0.051 μg / L, respectively. Figure 9 The Cd leaching concentrations (A) were all below the 0.1 mg / L limit for wall materials in the "Evaluation of Green Products". The lowest Cd leaching concentration (0.030 μg / L) was observed when the addition ratio was 3:2.

[0075] When the addition ratio of desulfurized gypsum and high-temperature treated fly ash was 4:1, 3:2, 1:1, 2:3, and 1:4, the As leaching concentrations of the sintered bricks were 113.449 μg / L, 252.313 μg / L, 157.159 μg / L, 72.295 μg / L, and 51.647 μg / L, respectively. Figure 9 The concentrations of As (B) were all below the 0.6 mg / L limit for As in the "Evaluation of Green Products for Wall Materials". The lowest As leaching concentration (51.647 μg / L) was observed when the addition ratio was 1:4.

[0076] When the addition ratio of desulfurized gypsum and high-temperature treated fly ash was 4:1, 3:2, 1:1, 2:3, and 1:4, the Pb leaching concentrations of the sintered bricks were 0.193 μg / L, 0.185 μg / L, 0.324 μg / L, 0.182 μg / L, and 0.412 μg / L, respectively. Figure 9 The concentrations of Pb (C) were all lower than the 2 mg / L limit for Pb in the "Evaluation of Green Products for Wall Materials". The lowest Pb leaching concentration (0.182 μg / L) was observed when the addition ratio was 2:3.

[0077] The above results indicate that using desulfurized gypsum and fly ash treated at 1200℃ as curing agents significantly improves the fixation effect on As, and all five gradients meet the limits specified in the "Green Product Evaluation of Wall Materials". Although the As fixation effect is best at a desulfurized gypsum:fly ash ratio of 1:4, the leaching concentrations of Cd and Pb both show an increasing trend. Therefore, an orthogonal experiment was conducted using a desulfurized gypsum:fly ash ratio of 2:3.

[0078] 4. Optimization of sintering process for heavy metal contaminated soil 4.1 Determination of Orthogonal Experiment Parameters The above test results show that under all conditions, the leaching concentrations of Cd and Pb in the sintered bricks are far below the limits specified in the "Green Product Evaluation of Wall Materials," but the leaching concentration of As only meets the limits under certain conditions. The As leaching concentration is generally positively correlated with the holding time and sintering temperature. After the holding time exceeds 8 hours, the As leaching concentration exceeds the limit, and the sintering temperature exceeds the limit except for 800℃. Based on the actual working conditions of enterprises and laboratory results, the amount of heavy metal contaminated soil added, sintering temperature, and holding time were identified as influencing factors and optimized to maximize soil treatment capacity and ensure brick performance while ensuring that the soil leaching concentration meets environmental standards. The gradients for the amount of heavy metal contaminated soil added were 10%, 25%, and 40%; the gradients for sintering temperatures were 600℃, 800℃, and 1000℃; and the gradients for holding times were 7 h, 8.5 h, and 10 h. The amount of curing agent (desulfurized gypsum: fly ash in a ratio of 2:3) used after high-temperature treatment was 5%, with the remainder being coal gangue. The test index was the heavy metal leaching concentration.

[0079] 4.2 Results of Orthogonal Experiments The orthogonal experimental design is a three-factor, three-level design; therefore, L9(3) is selected. 4 The experiment was conducted using an orthogonal array, and the results are shown in Table 5. The range analysis is shown in Table 6.

[0080] Table 5. Results of the orthogonal experiment Throughout the orthogonal experiment, the leaching concentrations of Cd and Pb were significantly lower than the limits of 0.1 mg / L and 2 mg / L respectively in the "Green Product Evaluation of Wall Materials". As leachate concentrations were also lower than the limit of 0.6 mg / L under some conditions. Therefore, the selection of subsequent conditions primarily focused on the leaching concentration of As. Comparison of the range (R) of As leaching concentrations under each factor showed RC > RB > RA, with factor C exhibiting the largest range (R = 6346.580), indicating its significant regulatory effect on the index changes. Factor A had the lowest k1 value (2748.064), factor B had the lowest k3 value (2379.863), and factor C had the lowest k1 value (952.000). Based on this, the theoretically optimal parameter combination was: 10% addition of heavy metal contaminated soil, sintering temperature of 600℃, and holding time of 10 h. Under this combination, all factors were at their corresponding minimum k values.

[0081] However, under practical conditions, economic benefits and brick strength must also be considered. In terms of economic benefits, the higher the amount of heavy metal-contaminated soil in the bricks, the larger the amount that can be treated at one time, and the fewer treatment sessions required, thus saving on equipment and labor costs. The value of level k1 for factor A is 2748.064, and the value of level k3 is 2972.753. The difference between the two is not significant, so 40% is chosen as the condition for the amount of heavy metal-contaminated soil added, as it offers better economic benefits. Regarding brick strength, sintering temperature and brick strength are generally positively correlated. The required brick strength cannot be achieved at 600℃, and the As leaching concentration is too high at 1000℃ (k3=7298.580). Therefore, considering both factors, 800℃ is chosen as the sintering temperature.

[0082] In summary, after combining theory and practice, the optimized sintering process parameters obtained by this invention are: 40% heavy metal contaminated soil addition, sintering temperature of 800℃, and holding time of 10 h. Under these conditions, the leaching concentrations of Cd, As, and Pb are 0.067 μg / L, 54.100 μg / L, and 1.141 μg / L, respectively, which are far lower than the limits of 0.1 mg / L, 0.6 mg / L, and 2 mg / L in the "Green Product Evaluation of Wall Materials". This indicates that the sintered bricks produced under these process parameters can be used as green wall materials in actual construction scenarios.

[0083] Table 6 Range Analysis of Orthogonal Experiments Note: In the table, the amount of heavy metal contaminated soil added, the holding time, and the sintering temperature are factors A, B, and C, respectively. The k1, k2, and k3 values ​​for factor A represent the average leaching concentrations of heavy metal ions when the amount of heavy metal contaminated soil added is 10%, 25%, and 40%, respectively; the k1, k2, and k3 values ​​for factor B represent the average leaching concentrations of heavy metal ions when the holding time is 7 h, 8.5 h, and 10 h, respectively; the k1, k2, and k3 values ​​for factor C represent the average leaching concentrations of heavy metal ions when the sintering temperature is 600℃, 800℃, and 1000℃, respectively; R is the result of subtracting the minimum value from the maximum value among k1, k2, and k3.

[0084] Although preferred embodiments of the invention have been described, those skilled in the art, once they have learned the basic inventive concept, can make other changes and modifications to these embodiments.

[0085] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for preparing sintered bricks using heavy metal-contaminated soil, characterized in that, Includes the following steps: Heavy metal contaminated soil, coal gangue, and a solidifying agent are crushed to below 60 mesh and mixed at a mass ratio of 10~50:45~89:1~5 to obtain a mixed raw material; the solidifying agent is a combination of fly ash and desulfurized gypsum. Water is added to the mixed raw materials until the moisture content is 8%~12%, and then the mixture is aged to obtain aged raw materials; The aged raw materials are pressed into shape to obtain brick blanks; The brick blanks are sintered to obtain sintered bricks.

2. The method for preparing sintered bricks from heavy metal-contaminated soil according to claim 1, characterized in that, The mass ratio of fly ash to desulfurized gypsum is 1~4:4~1.

3. The method for preparing sintered bricks from heavy metal-contaminated soil according to claim 2, characterized in that, The desulfurized gypsum and fly ash are mixed and then treated at a high temperature of 1100℃~1300℃ for 1 h~3 h to obtain the curing agent.

4. The method for preparing sintered bricks from heavy metal-contaminated soil according to claim 1, characterized in that, The aging process involves placing the mixed raw materials in an environment with a temperature of 15℃~25℃ and a humidity of 25%~35% for 22 h~26 h.

5. The method for preparing sintered bricks from heavy metal-contaminated soil according to claim 1, characterized in that, The sintering temperature is 600℃~1000℃.

6. The method for preparing sintered bricks from heavy metal-contaminated soil according to claim 1, characterized in that, The sintering time is 8 h to 10 h.

7. The method for preparing sintered bricks from heavy metal-contaminated soil according to claim 1, characterized in that, The dimensions of the pressing mold are 240 mm × 115 mm × 53 mm.

8. A sintered brick, characterized in that, Prepared by the method described in any one of claims 1 to 7.

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