Porous lightweight aggregates made from high-salinity heavy metal contaminated sediment and their preparation method

Abstract

This invention provides a porous lightweight granular material, which is obtained by combining recycled glass with high-salinity heavy metal contaminated sediment and performing a vitrification reaction using electromagnetic induction heating. The crystalline phase of this porous lightweight granular material contains at least quartz and mullite, and its density is between 0.4 and 0.8 g / cm³, with a water absorption rate between 30% and 60%. The porous lightweight granular material of this invention has passed granular material specification tests and can be used as various reuse materials to improve the economic efficiency of waste glass, waste oyster shells, and contaminated soil. It gives new life to hazardous waste and transforms it into products needed for human life, replacing the natural stone that would otherwise need to be mined, protecting the natural environment, and promoting a circular economy.

Description

Technical Field

[0001] The present invention relates to a porous lightweight granular material, in particular to a porous lightweight granular material obtained by vitrifying high-salinity heavy metal contaminated sediment and a production method thereof. Prior Art

[0002] With the rapid advancement of technology, people's lives have become more convenient. This continuous use of limited natural resources, accompanied by the generation of large amounts of waste, has led to a decrease in available resources. This linear consumption economy cannot be sustainable indefinitely. The key to the future development of a circular economy is how to combine waste that should be recycled with waste that should be treated, and utilize innovative technologies to transform it into valuable bulk materials. This will not only significantly reduce waste generation but also lower the rate of resource depletion, ultimately achieving the goal of sustainable economic and social development.

[0003] Sediment is the organic and inorganic material at the bottom of water bodies, including clay, silt, sand, gravel, shells, and decaying organic matter. It plays a vital role in Earth's ecosystems, such as supporting river self-purification, providing habitats for plankton and benthic organisms, and serving as a feeding and breeding ground for fish. However, river sediment is currently severely contaminated by organic compounds and heavy metals. According to official statistics, 59.9% of river sediments are contaminated above the regulatory lower limit, and 7.3% are above the upper limit. Therefore, sediment remediation is imperative. Heavy metal contamination, due to the inability of organisms to degrade it, can accumulate in the environment, then accumulate in plants and animals through the food chain, ultimately affecting humans at the top of the food chain and causing serious illnesses. This highlights the need for rapid and cost-effective sediment remediation technologies.

[0004] There are many methods for sediment remediation. The most common method is dredging. This involves removing high-concentration sediment from a contaminated site and transporting it to a qualified treatment plant for final disposal. However, this method often causes sediment to be blown up during dredging, and high-concentration pollution can attach to small particles. These particles are then carried downstream by river water, causing the pollutants to spread (Köthe, 2003).

[0005] Currently, the most commonly used method abroad is in-situ capping, which involves laying a capping material over the contaminated area to reduce bioaccessibility and prevent further spread of the contamination. However, because the bottom of the water is usually anaerobic, microorganisms produce gas, causing the capping material to bulge and rupture, rendering it ineffective. Furthermore, this method requires anchoring in areas with wide and slow-moving rivers. However, Taiwan's rivers are relatively turbulent and are frequently hit by typhoons. Therefore, Taiwan's climate and topography are not suitable for these commonly used methods abroad.

[0006] Vitrification is a thermal process that heats a material to a molten state, which then forms a glassy material upon cooling. High temperatures destroy organic compounds and bind heavy metals within the glassy structure. Treatment methods include Joule heating (Dellisanti et al., 2009), plasma heating (Wang et al., 2010), and electromagnetic induction heating. Electromagnetic induction heating utilizes high-frequency current conversion and magnetic field fluctuations to induce current in magnetic materials, thereby heating the material. Its energy conversion efficiency reaches as high as 90%. Using electromagnetic induction heating for vitrification can shorten processing time and reduce energy consumption.

[0007] Waste glass is a government-designated recyclable waste. Approximately 500,000 to 600,000 tons of waste glass are generated annually, nearly 50% of which goes unused. Furthermore, Taiwan produces an average of 190,000 tons of discarded oyster shells annually, of which 26,000 tons are improperly disposed of. Oyster shells are primarily composed of calcium carbonate, which, upon sintering, produces calcium oxide and carbon dioxide, which are useful for the production of porous materials. Waste glass can be remade into products with varying properties and porous properties, depending on the sintering temperature and the addition of different reagents. These materials can be remade into lightweight aggregates, soundproofing materials, eco-friendly pumice stones, thermal insulation materials, and filter materials.

[0008] Combining different waste streams and transforming them into valuable resources is a current international trend. If heavy metal-contaminated sediments can be used alongside recycled waste glass and oyster shells as raw materials, the porous materials produced can simultaneously treat the heavy metal-contaminated sediments, effectively addressing hazardous waste while also saving on raw material costs, creating a win-win situation. Summary of the Invention

[0009] In light of this, the present inventors have diligently researched and explored various possible solutions to the aforementioned problems of conventional technologies. They have combined electromagnetic induction heating to transform high-salinity, heavy metal-contaminated sediment into a valuable porous material. This not only eliminates the pollution problem but also extends the lifespan of soil resources, turning them into a valuable material, in line with the principles of a circular economy.

[0010] Specifically, this invention utilizes heavy metal-contaminated sediments, already exceeding pollution control standards, with high salinity and appropriate additives to perform a foaming-type vitrification process. This results in the production of porous, lightweight aggregates with low specific gravity and high porosity, suitable for applications such as breathable stone and lightweight aggregate, while complying with regulatory standards. Furthermore, this method of reproducing porous, lightweight aggregates from heavy metal-contaminated sediments is a one-step production process, superior to the conventional method of first heating the contaminated sediment to 1400°C to fully vitrify it, then grinding the vitrified product and mixing it with a foaming agent before further heating to form the porous medium. This method significantly saves energy, time, and money compared to the conventional two-stage process.

[0011] That is, the present invention provides a method for producing porous lightweight pellets using high-salinity heavy metal contaminated sediment, which comprises the following steps:

[0012] The sintering step comprises mixing dried contaminated sediment, glass, oyster shell powder, and water, followed by heating to a specific temperature and maintaining the temperature for 3 to 10 minutes; the weight ratio of the contaminated sediment to the glass is between 1:1 and 1:4; the weight percentage concentration of the oyster shell powder is between 1wt% and 10wt%; and the weight percentage concentration of the water is between 1wt% and 20wt%.

[0013] According to one aspect of the present invention, the specific temperature is generally between 750 and 950°C; more preferably between 800 and 950°C; and most preferably 950°C.

[0014] According to one aspect of the present invention, the water-free portion of the contaminated sludge contains more than 40 wt% of silicon dioxide and more than 10 wt% of aluminum oxide.

[0015] According to one aspect of the present invention, the heavy metals contained in the sludge include at least one of arsenic, cadmium, chromium, copper, mercury, nickel, lead, and zinc; preferably, they include at least one of chromium, copper, nickel, lead, and zinc.

[0016] According to one aspect of the present invention, a salt removal step is further included before the sintering step, which reduces the salt content in the contaminated sludge to a specific concentration.

[0017] According to one aspect of the present invention, the crystalline phase of the porous lightweight aggregate contains at least quartz and mullite, and the density of the porous lightweight aggregate is between 0.4 and 0.8 g / cm 3 and the water absorption rate is between 30 and 60%.

[0018] Furthermore, the present invention can also provide a porous lightweight pellet produced from high-salinity, heavy metal-contaminated sludge, characterized in that the crystalline phase of the porous lightweight pellet contains at least quartz and mullite, and the porous lightweight pellet has a density between 0.1 and 2.0 g / cm3, a porosity between 30% and 90%, and a water absorption rate below 80%.

[0019] According to one aspect of the present invention, the surface dry saturation specific gravity of the porous lightweight granular material after crushing is between 1.5 and 2.0.

[0020] According to one aspect of the present invention, the chloride ion concentration of the porous lightweight granules after crushing is below 50 ppm.

[0021] According to one aspect of the present invention, the 28-day compressive strength of the porous lightweight granular material is greater than 255 kgf / cm2.

[0022] According to one aspect of the present invention, the porous lightweight aggregate is suitable for fine aggregate in concrete.

[0023] According to one aspect of the present invention, the porous lightweight granular material is suitable for use as a construction material, a gardening planting material, or a filter material. Simple diagram description

[0024] FIG. 1 is a factor response diagram showing the water absorption rate of the porous lightweight granules S1 to S9 in Examples 1 to 9. FIG. 2 is a factor response diagram showing the density difference percentage of the porous lightweight pellets S1 to S9 in Examples 1 to 9. FIG. 3A to 3E are factor response diagrams showing the stabilization rates of various heavy metals for the porous lightweight granules S1 to S9 in Examples 1 to 9. FIG. 4A and 4B are graphs showing XRD analysis results of porous lightweight pellets S1 to S9. FIG5 is a graph showing a comparison of the compressive strength of standard sand and porous lightweight aggregate in a compressive strength test. Implementation Method

[0025] The present invention is further described below with reference to the following examples and accompanying drawings. However, the following description is for illustrative purposes only and is not intended to limit the scope of the present invention or the scope of the claims. Unless otherwise defined herein, scientific and technical terms used herein have the same meanings as those commonly understood and used by persons skilled in the art in the art to which this invention belongs.

[0026] In addition, those with ordinary skill in the art should understand that the present invention is certainly not limited to these examples, and other identical or equivalent functions and step sequences can also be used to implement the present invention.

[0027] In this document, the numerical values ​​and parameters used to define the scope of the present invention are inherently subject to standard deviations due to individual testing methods, and therefore are often expressed as approximate numerical values. However, in the specific examples, the relevant numerical values ​​are presented as accurately as possible. In this document, "about" is generally determined by one of ordinary skill in the art to which the present invention belongs, and generally means that the actual value falls within an acceptable standard error of the mean, for example, the actual value is within ±10%, ±5%, ±1%, or ±0.5% of a particular value or range.

[0028] First, the various detection methods used in the embodiments of the present invention are described below. Heavy Metal Concentration Analysis

[0029] To ensure that the vitrified sediment samples can effectively solidify heavy metals, a heavy metal digestion and dissolution experiment was conducted on the vitrified samples in the embodiments of the present invention to verify that no heavy metals were leached from the samples after vitrification. The digestion and dissolution method was based on the "Metal Detection Method for Waste and Sediment - Acid Digestion Method (NIEAM 353.02C)" provided by the Environmental Protection Administration, Executive Yuan, and was combined with the parameters of the equipment used. The digestion steps are as follows: First, weigh 1.0g of dry solid sample, add 2.0ml of low-mercury nitric acid (HNO3:H2O = 1:1) and 5.0ml of low-mercury hydrochloric acid (HCl:H2O = 1:1). The mixture was mixed with solids (a 1:4 ratio of 2O) and placed in a digester for 30 minutes at a heated digestion temperature of 95°C. After half an hour, the mixture was allowed to cool for 20 minutes. Immediately, 2.0 ml of 30% hydrogen peroxide was added and allowed to react for 10 minutes. The mixture was then placed in a digester (set to 85°C) for another 30 minutes. After the mixture cooled for 10 minutes, 2.0 ml of 30% hydrogen peroxide was added and allowed to react for 10 minutes. Finally, the mixture was placed in a digester (set to 85°C) for another 30 minutes. Deionized water was then added for quantitative dilution. Digestion and dissolution results were analyzed using an inductively coupled plasma emission spectrometer (Optima™ 7000DV, ICP-OES). Heavy Metal Stability Analysis

[0030] Immobilization Percentage (IP) is used to indicate the degree to which a sample immobilizes heavy metals and prevents them from being dissolved (Yang et al., 2014). The calculation method is as follows: Where C0 is the concentration of heavy metals dissolved before vitrification, and C1 is the concentration of heavy metals dissolved after vitrification. Physical Property Analysis of Porous Lightweight Granular Materials

[0031] 1. Volume measurement

[0032] First, the volume of porous, lightweight granular materials was measured using the displacement method. To ensure accurate volume measurements, the material was first soaked in water to allow the material to absorb water completely. Excess surface moisture was then wiped away, resulting in a saturated surface dry (SSD) state before measurement. Volume was measured using a homemade empty plastic can connected to a water pipe. The can was filled with water, allowing the water above the pipe to flow out naturally, creating a uniform water level. Once the water level stabilized, the material to be measured was slowly lowered into the water to minimize fluctuations. The weight of the water that flowed out was collected on a precision scale and multiplied by the density of water to obtain the volume.

[0033] 2. Density and density difference percentage

[0034] The density of each sample group was calculated using the following formula and then compared to the benchmark (the density of glass and sediment (approximately 2.5)). The percentage difference in density was calculated as follows. A greater density difference indicates a lower density, a larger volume, and more pores. This provides a preliminary assessment of the impact of different conditions on porosity.

[0035] 3. Water absorption

[0036] Water absorption is defined as the amount of water absorbed by a dry material until it reaches saturated surface dryness (SSD). The weight of water absorbed is usually expressed as a percentage of dry weight, as shown below. The sample is placed in water at room temperature for 24 ± 4 hours. The sample is then removed, the surface wiped dry, and the weight is accurately weighed until saturated surface dryness is achieved. The sample is then removed and dried in an oven at 105 ± 5°C for 24 hours to obtain the oven-dried weight.

[0037] 4. Porosity

[0038] When the volume of pores is included in the volume of the material, the resulting specific gravity is called volumetric specific gravity. It is calculated as the ratio of the weight per unit volume of the material in air at a specific temperature to the weight of the same volume of distilled water in air at that temperature. The ratio of a particle's pore volume to its total volume (particle volume plus pore volume) is called porosity.

[0039] 5. XRD characteristic analysis

[0040] High-resolution X-ray diffractometer (HRXRD) was used to observe structural changes in the material, exploring the changes in the glass before and after heating and the impact on the pellets. This experiment commissioned the National Chung Hsing University Research and Development Office, a subsidiary of the Ministry of Science and Technology, to provide valuable equipment for testing. To maximize accuracy, the sample was crushed to less than 100 meshes, with a detection rate of 1.5° / min. Raw material pretreatment

[0041] The waste glass used in this invention is transparent waste glass commonly found in households, such as wine bottles, milk bottles, and pickle jars. After removing the paper labels from the bottles, the bottles are cleaned with a neutral detergent and water. After being air-dried, they are crushed with a hammer and the glass powder that passes through a 50-mesh screen is collected.

[0042] Oyster shells were purchased from Wuqi Fishing Port. The surface and internal meat residue of the oyster shells were cleaned with a steel brush, soaked in bleach for 24 hours to rinse off the residual bleach on the oyster shells, and placed in an oven to dry at 105 ± 5℃ for 24 hours. After drying and cooling, the shells were crushed and sieved with 100 mesh.

[0043] The sediment used in this invention comes from the confluence of the Erren River and the Sanyegong River in Tainan City. From the 1970s to the early 2000s, Erren River was home to factories specializing in the recycling and refining of scrap metals. These factories used numerous toxic, acidic chemical solvents and dumped their wastewater into the river without proper treatment, resulting in significant water pollution. As a result, the river contains high concentrations of heavy metals, exceeding regulatory standards even after adding other raw materials.

[0044] After collecting the contaminated sediment, remove any rocks and weeds. Place the sediment on an iron tray covered with aluminum foil and place in an oven at 105 ± 5°C for 24 hours. Once dry, cool to room temperature, and collect any sediment that passes through a 50-mesh sieve. Analysis of the sediment sample's composition using energy-dispersive X-ray spectroscopy revealed 44.46 wt% silicon dioxide, 16.03 wt% aluminum oxide, and 7.7 wt% iron oxide.

[0045] Alternatively, the salinity of the contaminated sediment can be reduced to a specific concentration (less than 10% of seawater salinity) before proceeding to the subsequent sintering step. For example, the contaminated sediment can be soaked in running water or mixed with low-salinity soil. Alternatively, sediment that has been replanted can be used. Examples 1 to 3

[0046] Contaminated sediment and glass powder were mixed uniformly at weight ratios of 0.25:1, 0.5:1, and 1:1, respectively. Then, based on a 10g sample, 1wt% oyster powder and 1wt% water were added. The sample was then placed in a graphite crucible (60mm outer diameter, 50mm inner diameter, 60mm height, and coil inner diameter approximately 70mm; supplier: Jinglong Special Carbon Technology Co., Ltd.). The sample was then electromagnetically heated to 950°C for 5 minutes using a solid-state semiconductor high-frequency generator (supplier: Feifan Thermal Technology International Co., Ltd., model: SP-30KW). After heating, the crucible was moved aside and allowed to cool to room temperature, yielding porous lightweight pellets W1 to W3.

[0047] Next, a toxicity dissolution test was conducted on the porous lightweight pellets W1 to W3, and the heavy metal stability rates of the porous lightweight pellets W1 to W3 were calculated and recorded in Table 1.

[0048] Table 1 Example Ratio of contaminated sediment and glass powder Heavy metal stability rate As Cd Cr Cu Hg Ni Pb Zn 1 0.25:1 NA 58.49 83.65 29.81 NA 20.26 70.72 99.12 2 0.5:1 NA 87.48 86.52 20.31 NA 22.72 61.86 98.71 3 1:1 NA 100 90.05 13.20 NA 21.95 69.61 98.06

[0049] From the results in Table 1 above, it can be seen that the porous lightweight aggregate W1 obtained in Example 1 has the highest stability rate of the three heavy metals. Therefore, the subsequent examples will be tested with the bottom mud and glass ratio of 0.25:1 in Example 1. Examples 4 to 12

[0050] Contaminated sediment and glass powder were mixed uniformly at a weight ratio of 0.25:1. Using a 10g sample as the base, the samples were divided into nine groups using the Taguchi test method, with the sediment moisture content, calcium carbonate addition, heating temperature, and holding time as variable factors. Oyster powder was added to the samples in the proportions shown in Table 2 below and placed in a graphite crucible. Using a solid-state semiconductor high-frequency generator, the nine groups of samples were subjected to electromagnetic induction heating at 750°C, 850°C, and 950°C for 3, 5, and 10 minutes, respectively. After heating, the crucible was moved aside and allowed to cool to room temperature, yielding porous lightweight pellets S1 to S9.

[0051] Next, the density difference percentage and water absorption rate of the porous lightweight pellets S1 to S9 were analyzed, and the results are recorded in Table 2.

[0052] Table 2 Example 4 Example 5 Example 6 Example 7 Example 8 Example 9 Example 10 Example 11 Example 12 Heating temperature (℃) 750 750 750 850 850 850 950 950 950 Oyster powder (wt%) 1 5 10 1 5 10 1 5 10 Water (wt%) 1 10 20 10 20 1 20 1 10 Holding time (min) 3 5 10 10 3 5 5 10 3 porous and lightweight Granules S1 S2 S3 S4 S5 S6 S7 S8 S9 Finished product properties Water absorption rate (%) 33 43 35 58 53 58 46 50 56 density Difference rate (%) 57 60 57 54 48 47 72 73 67 *ND means the concentration is below the minimum detectable concentration (10 ppb) at 20-fold dilution.

[0053] The water absorption results show that all experimental groups achieved a water absorption rate of over 30%, with Examples 7 and 9 achieving the highest, reaching 58%. Next, based on the results in Table 2, a factor-effect table for water absorption was calculated, and a factor-response diagram was then plotted.

[0054] Table 3 Water absorption factor effect table temperature Oyster powder added Water addition Maintenance time Level 1 37.0 45.4 47.1 47.2 Level 2 56.3 48.9 52.2 48.8 Level 3 50.5 49.5 44.6 47.8 E1-2 19.3 3.5 5.1 1.6 E2-3 -5.8 0.6 -7.5 -1.0 Range 19.3 4.1 7.5 1.6 Rank 1 3 2 4

[0055] Please refer to Table 3 and Figure 1 above. Figure 1 shows the factor-response diagram for the water absorption of porous lightweight aggregates S1 to S9. The Rank values ​​in Table 3 indicate that the most significant control factors are, in order, temperature, water addition, oyster powder addition, and holding time. Water in the sample structure is primarily due to externally connected pores, connections between pores, and capillary action on the surface, which traps water within the pores. Dense pores facilitate capillary action. Temperature has the most significant influence. Samples heated at 750°C, due to their low temperature, have a loose and brittle structure, resulting in a decrease in water absorption. Samples heated at 950°C, due to the higher temperature, expand the gas more and more, resulting in larger pores or covering the pore structure, which is not conducive to water absorption. Proper temperature control is essential to achieve high water absorption, with 850°C being the optimal temperature among these three.

[0056] At 100°C, water begins to dissipate gradually. The escaping water vapor increases the porosity of the raw material particles. As the glassy structure begins to melt, it encapsulates the pores created by the gas, creating dense pores. However, excessive water content can lead to excessive gas dissipation, so an appropriate amount of water must be added, with 10wt% being the optimal amount. Oyster powder, primarily composed of calcium carbonate, begins to decompose at 600°C, producing gas. The glassy structure encapsulates this gas, creating pores. This capillary effect significantly increases water absorption. Prolonged heating causes the gas to expand, interconnecting and enlarging the pores. As the pores become larger, the capillary effect becomes less pronounced, resulting in a decrease in water absorption. Therefore, the optimal conditions for water absorption are a temperature of 850°C, a high dosage of oyster powder, 10% water, and a holding time of 5 minutes.

[0057] Next, analyze the results of the density difference percentage. Based on the results of Table 2 above, calculate the factor effect table of the density difference percentage and then draw the factor response diagram.

[0058] Table 4 Density difference percentage factor effect table temperature Oyster powder added Water addition Maintenance time Level 1 0.58 0.61 0.59 0.57 Level 2 0.50 0.60 0.60 0.60 Level 3 0.71 0.57 0.59 0.61 E1-2 -0.08 -0.01 0.01 0.02 E2-3 0.21 -0.03 -0.01 0.02 Range 0.21 0.04 0.01 0.04 Rank 1 3 4 2

[0059] Please refer to Table 4 and Figure 2 above. Figure 2 shows the factor response diagram for the density difference percentage of porous lightweight pellets S1 to S9. The Rank values ​​in Table 4 indicate that the most significant control factors are, in order, temperature, holding time, oyster powder addition, and water addition. At a temperature of 950°C, more gas is generated, and the density difference percentage increases. A higher holding time allows for a longer gas reaction time and more uniform sintering. Greater gas expansion and increased gas production also increase the density difference percentage. The amount of oyster powder added and the amount of water added are not significantly different. A higher oyster powder addition increases the gas reaction, preventing gas from escaping and being trapped in the glassy structure, preventing pore formation. Water addition also affects gas generation, so it is important to add it in appropriate amounts, with 10 wt% water being the optimal amount. Furthermore, the factor response diagram for the density difference percentage shown in Figure 2 shows that the optimal conditions for the density difference percentage are 950°C, a low oyster powder dosage, a 10 wt% water addition, and a holding time of 10 minutes.

[0060] Next, toxicity dissolution tests were conducted on the porous lightweight pellets S1 to S9, and the results are recorded in Table 5.

[0061] Table 5 sample As Cd Cr Cu Hg Ni Pb Zn Standard upper limit

[33] [2.49]

[0233]

[0157] [0.87]

[80]

[0161]

[0184] Standard lower limit 11 0.65 76 50 0.23 twenty four 48 140 oyster flour NA 0.02 0.75 22.48 NA 0.48 0.37 4.53 glass bottom mud NA 0.34 78.24 242.66 NA 38.16 63.23 218.49 S1 NA 0.01 42.61 107.81 NA 31.06 9.51 50.58 S2 NA NA 33.83 134.83 NA 27.99 7.11 32.89 S3 NA NA 33.49 148.98 NA 27.20 12.19 44.68 S4 NA NA 21.46 128.94 NA 27.18 8.18 11.33 S5 NA NA 27.95 133.72 NA 26.97 8.04 31.19 S6 NA NA 23.91 124.56 NA 22.99 5.36 22.08 S7 NA 0.02 13.23 143.97 NA 22.10 12.39 5.86 S8 NA 0.03 13.52 106.41 NA 18.42 4.28 5.43 S9 NA NA 19.14 109.17 NA 19.72 4.43 11.58 Note: NA means the concentration is below the minimum detectable concentration (10 ppb) at a 20-fold dilution.

[0062] Table 5 shows that the contaminated sediment and glass mixtures exceeded the upper limit of the sediment quality standard for copper and zinc. Chromium, nickel, and lead fell between the upper and lower limits, while cadmium met regulatory standards. This indicates that the sediment contamination in Erren Creek is quite severe; even when glass is mixed with sediment, it still exceeds the upper limit. Arsenic, cadmium, and mercury volatilize at 950°C, making their concentrations undetectable. A downward trend in contaminant concentrations was observed after firing, but copper still exceeded the regulatory limit.

[0063] Next, based on the results in Table 5 above, the factor effect table of heavy metal stability rate was calculated, and then the factor response diagram was drawn.

[0064] Table 6 Effect of stability factor of heavy metal copper temperature Oyster powder added Water addition Maintenance time Level 1 46.2 47.7 53.5 51.8 Level 2 46.8 48.5 48.8 44.6 Level 3 50.6 47.4 41.4 47.2 E 1-2 0.6 0.8 -4.7 -7.2 E 2-3 3.8 -1.1 -7.4 2.6 Range 4.4 1.1 12.1 7.2 Rank 3 4 1 2

[0065] Table 7 Effect of stability factor of heavy metal chromium temperature Oyster powder added Water addition Maintenance time Level 1 53.2 67.1 65.9 61.8 Level 2 68.8 67.9 68.3 69.8 Level 3 80.4 67.4 68.2 70.8 E 1-2 15.6 0.9 2.4 8.0 E 2-3 11.7 -0.5 -0.1 1.1 Range 27.3 0.9 2.4 9.0 Rank 1 4 3 2

[0066] Table 8 Effect of stability factor of heavy metal lead temperature Oyster powder added Water addition Maintenance time Level 1 84.8 84.1 89.9 88.4 Level 2 88.6 89.8 89.6 86.9 Level 3 88.9 88.4 82.8 87.0 E 1-2 3.8 5.6 -0.3 -1.5 E 2-3 0.3 -1.3 -6.8 0.1 Range 4.1 5.6 7.1 1.5 Rank 3 2 1 4

[0067] Table 9 Stability Factor Effect of Heavy Metal Nickel temperature Oyster powder added Water addition maintenance time Level 1 24.7 29.8 36.7 32.1 Level 2 32.6 35.9 34.6 36.2 Level 3 47.4 38.9 33.4 36.4 E 1-2 8.0 6.1 -2.1 4.1 E 2-3 14.8 3.0 -1.2 0.2 Range 22.7 9.1 3.3 4.3 Rank 1 2 4 3

[0068] Table 10 Effect of stability factor of heavy metal zinc temperature Oyster powder added Water addition Maintenance time Level 1 80.4 89.7 88.1 85.8 Level 2 90.1 89.4 91.5 90.7 Level 3 96.5 88.0 87.5 90.6 E 1-2 9.7 -0.3 3.4 5.0 E 2-3 6.4 -1.3 -4.0 -0.1 Range 16.1 1.6 4.0 5.0 Rank 1 4 3 2

[0069] Tables 6 through 10 present the factor response tables for each heavy metal, and Figures 3A through 3E present the factor response graphs for the stability rates of each heavy metal. The ranking values ​​for the copper factor response table indicate that the most significant control factors are, in order, water addition, holding time, temperature, and oyster powder addition. The optimal conditions for the copper factor response graph are 950°C, medium oyster powder addition, 1 wt% water addition, and a holding time of 3 minutes. The ranking values ​​for the chromium factor response table indicate that the most significant control factors are, in order, temperature, holding time, water addition, and oyster powder addition. The optimal conditions for the chromium factor response graph are 950°C, medium oyster powder addition, 10 wt% water addition, and a holding time of 10 minutes. The ranking values ​​for the lead factor response table indicate that the most significant control factors are, in order, water addition, oyster powder addition, temperature, and holding time. The optimal conditions for the lead factor response graph are 950°C, medium oyster powder addition, 1% water addition, and a holding time of 3 minutes. The Rank values ​​of the nickel factor response table indicate that the most significant control factors are, in order, temperature, oyster powder addition, holding time, and water addition. The nickel factor response graph shows that the optimal conditions are 950°C, high oyster powder addition, 1% water addition, and a holding time of 10 minutes. The Rank values ​​of the zinc factor response table indicate that the most significant control factors are, in order, temperature, holding time, water addition, and oyster powder addition. The zinc factor response graph shows that the optimal conditions are 950°C, low oyster powder addition, 10% water addition, and a holding time of 5 minutes.

[0070] Because local pollution often involves multiple heavy metals, optimal conditions cannot be determined based on a single heavy metal. Therefore, the five heavy metals are ranked according to their level of change, and the rankings of the factor response graphs and signal-to-noise ratio graphs are summed and recorded in Tables 11 and 12, respectively.

[0071] Table 11 Ranking of factor response diagrams for each heavy metal Temperature (℃) Oyster powder added (%) Water addition (%) Maintenance time (minutes) 750 850 950 1 5 10 1 10 20 3 5 10 Cr 3 2 1 3 1 2 3 1 2 3 2 1 Cu 3 2 1 2 1 3 1 2 3 1 3 2 Ni 3 2 1 3 2 1 1 2 3 3 2 1 Pb 3 2 1 3 1 2 1 2 3 1 3 2 Zn 3 2 1 1 2 3 2 1 3 3 1 2 total 15 10 5 12 7 11 8 8 14 11 11 8

[0072] Table 12 SNR ranking of heavy metals Temperature (℃) Oyster powder added (%) Water addition (%) Maintenance time (minutes) 750 850 950 1 5 10 1 10 20 3 5 10 Cr 3 2 1 3 1 2 3 1 2 3 2 1 Cu 3 2 1 2 1 3 1 2 3 1 3 2 Ni 3 2 1 3 2 1 1 2 3 3 2 1 Pb 3 2 1 3 1 2 1 2 3 1 3 2 Zn 3 2 1 1 2 3 2 1 3 3 1 2 total 15 10 5 12 7 11 8 8 14 11 11 8

[0073] Table 11 shows that the rankings for water additions of 1 wt% and 10 wt% are identical. However, since the 1 wt% addition was optimal for all three heavy metals, the 1 wt% addition was selected. Table 12 shows that both the oyster powder addition and the holding time had identical rankings. However, compared to the factor response diagram ranking, the higher level (5% oyster powder addition and 10-minute holding time) was selected. Both the factor response diagram ranking and the signal-to-noise ratio ranking yielded identical results, with the optimal conditions being a temperature of 950°C, a 5% oyster powder addition, a 1% water addition, and a 10-minute holding time.

[0074] Furthermore, since the copper concentrations in porous lightweight aggregates S1 to S9 still exceeded the regulatory lower limit after testing using the Acid Digestion Method for Metal Detection in Waste and Sediment (NIEA M353.02C), extraction was performed using the Toxicity Characteristic Leaching Procedure for Industrial Waste (NIEA R201.15C) before testing. The test results are shown in Table 13.

[0075] Table 13 Group chromium copper nickel lead zinc S1 NA 0.88 NA NA NA S2 NA 1.23 NA NA NA S3 NA 0.15 NA NA NA S4 NA 0.78 NA NA NA S5 NA 0.91 NA NA NA S6 NA 0.49 NA NA NA S7 NA 1.03 NA NA NA S8 NA 0.35 NA NA NA S9 NA 0.44 NA NA NA Note: NA means that the concentration is lower than the minimum detectable concentration (10 ppb) at 50-fold dilution.

[0076] The results in Table 13 show that after the industrial waste toxicity characteristic dissolution test, the heavy metal concentrations in the porous lightweight pellets S1 to S9 all passed the regulatory standards. Therefore, the porous lightweight pellets of the present invention can be subsequently reused.

[0077] In addition, porous lightweight pellets S1 to S9 were subjected to XRD analysis. The results are shown in Figures 4A and 4B. Figure 4A shows the XRD analysis results for porous lightweight pellets S1 to S6, and Figure 4B shows the XRD analysis results for porous lightweight pellets S7 to S9. The results in Figures 4A and 4B show that porous lightweight pellets S1 to S9 all contain mullite and quartz crystal phases, while the formation of other crystal phases decreases with increasing temperature. Porous lightweight pellets S1 to S3, produced using a lower temperature process, exhibit a richer variety of crystal phases. In addition to the quartz and mullite phases common to the other porous lightweight pellets, more wollastonite and diopside crystal phases are observed. Diopside facilitates sintering and the formation of a viscous layer. Analysis of the applicability of porous lightweight aggregates

[0078] Table 13 shows the particle size distribution of the porous lightweight pellets prepared under Taguchi's optimal conditions after crushing. Since fired samples are difficult to obtain and can only be mass-produced in small quantities, hammer crushing tends to produce smaller particle sizes. Therefore, samples with a mesh size of less than 200 were also included in the test. If the addition of 200 mesh also meets regulatory standards, there will be no problem in practical application.

[0079] Table 13 Particle size (mesh) Particle size distribution (%) 4-8 5.16 8-16 21.75 16-30 17.09 30-50 17.32 50-100 25.22 100-200 8.69 Below 200 4.77

[0080] When porous lightweight aggregate is made into concrete, it is necessary to determine the surface dry saturation specific gravity to facilitate the calculation of aggregate addition to the concrete screed. The water absorption of fine aggregate will also differ from that of bulk materials. Basic testing items include surface dry saturation, specific gravity, water absorption rate, and chloride ion content.

[0081] The analysis method of surface dry saturation specific gravity and water absorption rate is as follows:

[0082] Crush the sample and soak it in water for 24 ± 4 hours to allow it to completely absorb water. Carefully pour off any excess water to prevent loss. Spread the sample flat on a non-absorbent surface and dry it evenly with a fan, stirring occasionally, until the sample is free-flowing and saturated. This facilitates gravity-based specific gravity testing. Surface moisture content can be determined using a cone mold and a tamping rod to determine if the sample has reached saturation. To test for surface moisture content, place the cone mold on a non-absorbent surface and fill it with the sample until it reaches the top. Lift the tamping rod 5 mm above the sample and tap it several times in a free-fall motion. Then, fill it again until it reaches the top and tap again. Repeat this several times, then lift the cone mold vertically. If there is still moisture on the surface and the fine aggregate maintains the shape of the cone mold, or if there is slight collapse, the sample is saturated.

[0083] Then fill the empty hydrometer with water and put the cap on to allow excess water to overflow, wipe the bottle dry and record the weight on the precision scale; then fill the hydrometer with one-third of water, put in a saturated sample of known weight of dry dough, eliminate bubbles, and let it stand overnight to allow small particles to settle, to prevent small particles from flowing out with the water after filling with water; after the small particles have completely settled, carefully fill the bottle with water along the wall to prevent small particles from being lifted up, cover the bottle cap to allow excess water to overflow, and then wipe the bottle dry and record the weight on the precision scale.

[0084] Finally, calculate with the following formula: Drying relative density (specific gravity) Sd = A / (B + S - C) Saturated relative density (specific gravity) Ss = S / (B + S - C) Apparent relative density (apparent specific gravity) Sa = A / (A + B - C) Water absorption As = 100[(S - A) / A](%) Where A = mass of the dried sample (g); B = mass of water in the pycnometer (g); C = mass of the pycnometer filled with sample and topped up with water (g); S = saturated test mass within the dry surface (g)

[0085] The chloride ion content of porous lightweight aggregates is for reference only. Referencing the test method for water-soluble chloride ion content in fine aggregates (CNS13407), a 30-g sample is added to 30 mL of water and allowed to soak for 24 hours. The sample is then shaken three times, top and bottom, approximately every five minutes to extract the salts. After a period of stagnant water, the supernatant is collected and tested for chloride ion content using ion chromatography (IC). The regulatory maximum allowable concentration is 0.012%.

[0086] The analysis results are recorded in Table 14.

[0087] Table 14 Porous lightweight granules Standard sand Saturated ratio of dry surface 1.92 2.6 Water absorption 8.15 1%~3% Chloride ion concentration (ppm) 42.38 <12

[0088] Crushed porous lightweight aggregate exposes internal pores, resulting in a decrease in water absorption. Chloride ion testing meets the regulatory standard of 0.012%, allowing it to be used as recycled aggregate. According to the N and H coarse aggregate classification standards, the porous lightweight aggregate of this invention is classified as a basic N grade. Since it is not a high-grade aggregate, its intended use is in secondary structural concrete. Recycled Concrete Test

[0089] The porous lightweight aggregate of the present invention is mixed with cement to form cement slurry according to the mechanical mixing method of hydraulic cement plastic viscous cement slurry and plaster (CNS3655).

[0090] Then, the potential alkali reactivity test method for the combination of cement and aggregate (cement mortar bar method CNS13619) and hydraulic mixed cement (CNS15286) were used to examine whether the combination of cement and aggregate is prone to expansion reaction with alkali (sodium and potassium) hydroxides. The alkali for expansion reaction usually comes from cement, and in some cases it may also come from the outside or other components of concrete. The alkali reactivity of aggregate can be divided into two forms: (1) Reaction of alkali with silica: including certain siliceous rocks, minerals, and natural or artificial glass. (2) Reaction of alkali with carbonate: including certain calcite dolomite and dolomitic limestone and other dolomite systems. This test method is less suitable for detecting the reaction of type (2) because the expansion of cement mortar bars caused by the reaction of alkali with carbonate is usually much smaller than that caused by the reaction of alkali with silica.

[0091] This test was commissioned by the Concrete Testing and Research Center of Taiwan Power Company. Accelerated testing was conducted using the CNS1258 Portland Cement Hot Expansion Test Method. The cement mortar mix ratio was the same as that used in the compressive strength test. A 25x25x285 mm square cylindrical specimen mold was used. The effective gauge length of the specimen was 250 mm (the length between the innermost points of the metal plug). The mold was constructed of steel or a hard metal that is not susceptible to corrosion by cement slurry. All components should fit tightly and be securely fastened together, and all sides should be sufficiently rigid to prevent bulging or distortion.

[0092] After the specimen is completed and the cement has dried and formed, it can be removed from the mold and immediately placed in a 23°C curing cabinet for 24.0 ± 0.5 hours. Remove the specimen from the curing cabinet and measure its length using an elongation tester. The elongation tester must be calibrated with a calibration rod before use. The specimen is then placed in a high-pressure cooking furnace for cooking. The high-pressure cooking furnace must be locked to prevent explosions caused by high pressure. Air must be expelled during initial heating. The outlet valve should be opened until steam is emitted, saturating the interior with water vapor. The switch should then be closed. The temperature inside the high-pressure cooking furnace should rise at such a rate that the pressure reaches 20.8 kgf / cm² within 45-75 minutes of turning on the heating switch. After 3 hours, the heating switch should be turned off and the cooking furnace should be allowed to cool. After 1.5 hours of cooling, the pressure should drop below 0.7 kgf / cm². For the remaining pressure, the outlet valve should be slightly opened until the pressure equalizes with the outside pressure. After taking out the specimen, immediately place it in hot water with a temperature above 90℃. Add cold water to evenly lower the temperature of the specimen. Reduce the water temperature to 23℃ within 15 minutes and maintain the water temperature for 15 minutes. Wipe the surface of the specimen dry before measuring the length again.

[0093] The thermal expansion coefficient can be calculated according to the following formula:

[0094] Table 15 Before cooking (mm) After cooking (mm) Expansion rate (%) Porous lightweight granules-1 2.131 2.620 0.196 Cement-1 2.128 2.330 0.081

[0095] The results of length measurements after autoclaving are shown in Table 15. The porous lightweight aggregate in the table represents mortar bars made under optimal conditions, while the cement represents standard concrete mortar bars. Both tests were repeated twice. The calculation results show high repeatability across the two replicates, and the expansion ratio exceeds the 0.8% standard. This indicates that the porous lightweight aggregate of the present invention reacts less with the alkaline substances in cement, is less likely to expand, and can be used as a fine aggregate to replace sand. Compressive Strength Test

[0096] The compressive strength test of hydraulic cement paving was conducted according to the test method for the compressive strength of hydraulic cement paving (CNS1010). A 50 mm cubic specimen was used to measure the compressive strength of hydraulic cement paving. Compressive strength specimens were prepared using porous lightweight aggregate prepared under Taguchi's optimal conditions and standard sand as fine aggregate for comparison. Three specimens were prepared at each age, 7 days and 28 days. The average compressive strength values ​​are recorded in Table 16 and plotted in Figure 5.

[0097] Table 16 7 days 7-day average 28 days 28-day average Recycled pellets-1 233 235±3.21 276 286±9.54 Recycled pellets-2 239 295 Recycled pellets-3 234 287 Standard sand-1 298 271±28.68 291 278±14.50 Standard sand-2 241 262 Standard sand-3 275 277

[0098] The compressive strength test results are shown in Table 16 and Figure 5. Furthermore, the obtained values ​​were calculated using the following formula to obtain the compressive strength difference and the compressive strength growth rate after 7 days.

[0099] Because the compressive strength is higher at 28 days, the longer the curing time, the higher the compressive strength, but the difference is not significant. Therefore, this experiment used 28 days as the benchmark and observed the growth rate of the samples in the first 7 days. The compressive strength growth rate of the recycled aggregate was approximately 82%, while that of the standard sand was 98%, indicating that the compressive strength growth rate of the recycled aggregate was slower than that of the standard sand. At 7 days, the difference between the recycled aggregate and the standard sand reached 87%, and by 28 days, it exceeded the standard sand by 103%, indicating a higher compressive strength than the standard sand. The results show that the compressive strength of the recycled aggregate meets the regulatory standard of 210 kgf / cm² for secondary structural concrete and the 28-day compressive strength of hydraulic cement of 255 kgf / cm². Replacing fine aggregate in concrete with recycled aggregate is feasible and exhibits good compressive strength. Comprehensive Comparison

[0100] The porous lightweight aggregate of the present invention, standard sand and general traditional aggregate were compared, and the results are shown in Table 17.

[0101] Table 17 project Porous lightweight granules Standard sand General bone material proportion 1.92 2.6 2.3-2.7 Water absorption rate (%) 8.15 2 <3 28-day compressive strength (kgf / cm 2) 286 278 140~350

[0102] The results in Table 7 above show that the porous lightweight aggregate of the present invention has a lower specific gravity than traditional aggregate and standard sand. This lower specific gravity effectively reduces transportation and load. Water absorption affects the properties of concrete. Excessive water absorption can cause concrete expansion or cracking. Therefore, water absorption must be reduced to achieve greater material stability. The compressive strength of the porous lightweight aggregate of the present invention is comparable to that of standard sand and conventional aggregate, demonstrating that the strength of the porous lightweight aggregate produced by the present invention is very good.

[0103] In summary, the present invention has been illustrated by the above embodiments. However, the present invention is not limited to these embodiments. Those skilled in the art may make various modifications and alterations without departing from the spirit and scope of the present invention. For example, the various technical aspects illustrated in the above embodiments may be combined or modified to form new embodiments, which are naturally considered to be within the scope of the present invention. Therefore, the scope of protection sought in this case also includes the scope of the patent application described below and the scope defined therein.

Claims

1. A method for producing porous lightweight granules from high-salinity heavy metal contaminated sediment, comprising the following steps: a salt removal step: reducing the salt content in the contaminated sediment to a specific concentration; and a sintering step: mixing the contaminated sediment treated and dried in the salt removal step, glass, oyster shell powder, and water, then heating it to a specific temperature using electromagnetic induction and maintaining it at that specific temperature for 3 to 10 minutes; wherein the weight ratio of the contaminated sediment to the glass is between 1:1 and 1:4; the weight percentage concentration of the oyster shell powder is between 1 wt% and 10 wt%; the weight percentage concentration of the water is between 1 wt% and 20 wt%; and the specific temperature is between 750 and 950°C.

2. The method for producing porous lightweight aggregate from high-salinity heavy metal contaminated sediment as described in claim 1, wherein the anhydrous portion of the contaminated sediment contains more than 40 wt% silicon dioxide and more than 10 wt% aluminum oxide.

3. The method for producing porous lightweight aggregate from high-salinity heavy metal contaminated sediment as described in claim 1, wherein the heavy metals contained in the contaminated sediment include at least one of arsenic, cadmium, chromium, copper, mercury, nickel, lead, and zinc.

4. The method for producing porous lightweight aggregate from high-salinity heavy metal contaminated sediment as described in claim 1, wherein the crystalline phase of the porous lightweight aggregate contains at least quartz and mullite, and the density of the porous lightweight aggregate is between 0.4 and 0.8 g / cm3, and the water absorption rate is between 30 and 60%.

5. A porous lightweight granular material reprocessed from sediment contaminated with high salinity and heavy metals, which is produced by the method described in claim 1, characterized in that: the crystalline phase of the porous lightweight granular material contains at least quartz and mullite, and the density of the porous lightweight granular material is between 0.4 and 0.8 g / cm3, the porosity is between 30% and 90%, and the water absorption rate is between 30% and 60%.

6. The porous lightweight aggregate reprocessed from high-salinity heavy metal contaminated sediment as described in claim 5, wherein the surface-dry saturated specific gravity of the porous lightweight aggregate after crushing is between 1.5 and 2.

0.

7. The porous lightweight aggregate reprocessed from high-salinity heavy metal contaminated sediment as described in claim 5, wherein the chloride ion concentration of the porous lightweight aggregate after crushing is below 50 ppm.

8. Porous lightweight aggregates reconstituted from high-salinity heavy metal contaminated sediment as described in claim 5, wherein the 28-day compressive strength of the porous lightweight aggregates is greater than 255 kgf / cm2.

9. The porous lightweight aggregate reconstituted from sediment contaminated with high salinity and heavy metals as described in claim 5 is a fine aggregate suitable for concrete.

10. The porous lightweight aggregate reprocessed from high-salinity heavy metal contaminated sediment as described in claim 5 is suitable for use as construction materials, horticultural planting materials, or filter materials.

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