TWI761775B - Method for recycling waste foundry sand - Google Patents

Abstract

The invention relates to a method for recycling waste foundry sand and applying it to a ceramsite lightweight aggregate production system. The focus of his method is to use foundry waste sand as an auxiliary raw material for the production of ceramsite and mix it with the main raw material of natural clay, such as the Shimen reservoir silt. Then through the production process of ceramsite granulation and rotary kiln roasting. Manufacture of lightweight aggregate with high strength structure. In this production process, iron-containing components such as Fe₂O₃ and FeO in the waste foundry sand are used as fluxes and expansion agents in the ceramsite roasting process. The ceramsite produced by this method is more energy-saving, lightweight, heat-insulating and earthquake-resistant. It can be further widely used in green building materials, agricultural horticultural media materials, water purification filter materials and other fields. Achieving the purpose of a sustainable circular economy.

Description

Waste foundry sand resource treatment method

The invention relates to a method for recycling waste foundry sand, which is characterized in that after mixing waste foundry sand and silt clay, granulation and roasting are performed to prepare ceramsite.

Generally speaking, waste foundry sand is defined as: waste foundry sand produced in the foundry process of the metal basic industry, metal product manufacturing industry or machinery and equipment manufacturing repair industry and the foundry sand powder collected in dust collection equipment. The components are silicon dioxide (SiO ₂ ), aluminum oxide (Al ₂ O ₃ ) and iron oxide (Fe ₂ O ₃ ). According to the "Notification of Waste Codes for Recycling or Reuse" stipulated by the Environmental Protection Agency, waste foundry sand is a recyclable waste (R-1201).

According to statistics from the Environmental Engineering Society, the Industrial Bureau of the Ministry of Economic Affairs and the Environmental Protection Agency, the average annual output of waste casting sand in my country in recent years is about 1.5 million tons. At present, the main resource reuse pipelines are buried soil, roadbed materials, and building fillers for earth engineering; concrete fillers and cement additives in civil materials; fertilizer additives for agricultural products, etc. However, although there are many pipelines for resource reuse in the past, it is still unable to effectively digest the output of waste casting sand which increases year by year.

Therefore, according to the above-mentioned waste casting sand decontamination pipeline and the current bottleneck of decontamination, the inventors of the present invention Then try to use waste foundry sand as an additive for ceramsite raw materials. In addition to increasing the decontamination pipeline of waste foundry sand, the production of ceramsite is carried out in a greener and more environmentally friendly way by changing the properties of raw materials after blending waste foundry sand. and improvement.

After decades of research on the mechanism of the formation mechanism of ceramsite, the following viewpoints can be considered:

Three-phase changes in physics: There are two necessary components for the roasting of ceramsite. One is that the ceramsite slowly melts from a solid state to a liquid state during the high-temperature roasting process. As the roasting time becomes longer, part of the liquid material turns into a gaseous state. And gradually increase the internal pressure, and at the same time, the molten state of the ceramsite surface must generate enough viscosity to prevent the internal gas from escaping. When the two necessary factors occur at the same time, they can be cooled in a timely manner, that is, a ceramsite lightweight aggregate with a dense and smooth surface and numerous pores inside is formed.

Chemical composition of raw materials and their thermochemical reactions: According to the research of Charles.M.Riley (1951), who was commissioned by the Bureau of Minerals of the US Department of the Interior to find suitable raw materials for mass production of ceramsite from all over the United States, analyzed the 81 pieces of clay and shale from all over the United States. Thirty-nine of the samples were found to swell and 42 of them did not. Through the analysis of chemical properties of mineral samples and the results of statistical summary, it is found that although the higher content of alumina (Al ₂ O ₃ ) will increase the melting point of the raw material, it will increase the plasticity of the ceramsite and the strength of the generated ceramsite during the calcination process. . The higher the content of silicon dioxide (SiO ₂ ), the lower the melting point of the raw material, but the lower the strength of the generated ceramsite. While ferrous oxide (FeO), iron oxide (Fe ₂ O ₃ ), calcium oxide (CaO), magnesium oxide (MgO), sodium oxide (Na ₂ O), potassium oxide (K ₂ O) have low melting points, in addition to the composition In addition to the flux in the process of ceramsite formation, it is also the main component of the expanding gas of ceramsite.

Thermal changes of mineralogy structure: During the high temperature roasting process of general mineral raw materials, If the temperature exceeds the melting point of the mineral, due to thermal dehydroxylation, the mineral will undergo a series of mineral phase transformations from the original stable crystal structure to generate a new crystal structure. It is known from the past literature that the main raw materials for ceramsite firing are mostly clay minerals.

Whether it is waste foundry sand or silt clay, it is a reusable resource that needs to be dealt with urgently in our country. Therefore, the motivation of the present invention is to use silt clay as the main raw material and waste foundry sand as the auxiliary raw material, and recycle them into resources for production. After the ceramsite product is formed, it can be used in construction (including structural and non-structural cement concrete aggregate raw materials), gardening (soil machine medium raw material) and water purification (filter material raw material), so that the reused resources can be included in sustainable use In addition to the cycle, through the improvement of the production fuel efficiency, the fuel consumption can also be effectively reduced, and the effect of energy saving and carbon reduction can be achieved.

The main purpose of the present invention is to provide a method for treating waste foundry sand as a resource, which can effectively optimize the blending of waste foundry sand and silt clay. It can effectively reduce the roasting temperature when producing ceramsite, so as to achieve the effect of energy saving and carbon reduction.

Therefore, in order to achieve the purpose of the present invention, the present invention provides a method for recycling waste foundry sand, comprising the following steps:

Composition analysis of waste foundry sand: Before the waste foundry sand enters the factory, its element composition, content analysis and moisture content must be measured; drying, magnetic separation and grinding: the waste foundry sand after entering the factory is placed in a rotary drying kiln Medium drying, and electromagnets are used to separate and remove the magnetic metal components in the waste casting sand, and then grind and sieve through a screen to ensure that the particle size of the waste casting sand is less than 150μm; adding water and stirring: according to the results of component analysis , after mixing the silt clay and waste casting sand in proportion, add water into the Stirring uniformly; granulation of raw granules: after mixing, the raw granules are obtained by extrusion granulation, spheronization and fine sieving; calcined in a ceramsite rotary kiln: the raw granules are passed through the preheating section of the ceramsite rotary kiln. After the water is removed, the raw granules are calcined into finished ceramsite products through the calcining section of the ceramsite rotary kiln at a high temperature of 900 to 1,200°C.

Using waste foundry sand as a mineral additive to produce ceramsite through the above steps does have the following advantages, which are detailed as follows:

1. In line with the spirit of recycling waste resources and incorporating them into a sustainable economic cycle.

2. Reducing the amount of fuel (the sintering temperature of ceramsite after adding waste casting sand is reduced by about 25°C), which not only reduces the fuel cost, but also effectively improves the energy efficiency and achieves the environmental protection spirit of energy saving and carbon reduction.

3. After adding waste foundry sand, it can effectively improve the connected pores of ceramsite, make it have higher drainage, and expand the scope of application of its products, such as gardening, water purification and other fields.

4. The ceramsite after adding waste casting sand not only conforms to the concept and relevant regulations of green building materials, but also can improve the added value of its raw materials and products.

S1: Composition analysis of waste foundry sand

S2: Drying, Magnetic Separation and Grinding

S3: add water and stir

S4: Granulation of raw pellets

S5: Roasting in ceramsite rotary kiln

FIG. 1 is a flow chart of the steps of the method for recycling waste foundry sand according to the present invention.

The present invention includes any combination of the following steps, and the embodiments are shown in the following examples:

Please refer to Figure 1 for the process of making ceramsite, including the following steps:

Component analysis step S1 of waste foundry sand:

The composition of waste foundry sand will vary with different basic metal industries, metal product manufacturing or machinery equipment manufacturing and repairing industries, different casting procedures, smelting processes and different dust collection equipment methods. Therefore, before each batch of waste foundry sand enters the factory, X-ray fluorescence analyzer (X-ray Fluorescence, XRF) must be used to analyze the silicon dioxide (SiO ₂ ), aluminum oxide (Al2O3) in the waste foundry sand. The composition and content of elements such as Al ₂ O ₃ ), iron oxide (Fe ₂ O ₃ ) and other elements are analyzed, and the water content in the waste casting sand is measured by an oven. As shown in Table 1:

Drying, magnetic separation, grinding step S2:

The waste casting sand after entering the factory is placed in a rotary drying kiln for drying, and the heat of the rotary drying kiln originates from the dry and wet seasons. In the dry season, a blower is used to extract the waste heat from the production line into the rotary drying kiln to dry the waste casting sand; in the wet season, the waste casting is carried out by an open flame through the combustion equipment attached to the kiln head of the rotary drying kiln and the exhaust equipment at the kiln tail. Sand drying. After drying, the waste casting sand is removed by electromagnets to remove the magnetic metal components in it, and then it is ground by a pulverizer.

Adding water and stirring step S3:

After the waste casting sand has been processed in the above steps, a belt conveyor is used with a meter to make the waste casting sand After the sand and silt clay are mixed in proportion, they are mixed with a double-shaft mixing mixer, and at the same time, appropriate water is added to make the soil plastic conditions suitable for granulation.

The blending ratio is adjusted according to the component analysis data after the detection of waste foundry sand and clay. The component analysis data of a silt clay sample obtained by the present invention are shown in Table 2:

5~30% of the waste foundry sand (sample A) with the composition shown in Table 1 and 70~95% of the clay (sample B) with the composition shown in Table 2 are used for blending and mixing. Silicon oxide (SiO ₂ ) accounts for about 50~80%, alumina (Al ₂ O ₃ ) content accounts for about 10~25%, and the flux components are alkaline earth metal oxides (CaO+MgO) and alkali metal oxides (Na _{2 )} . The total content of O+K ₂ O) accounts for 5~25%.

Raw pellet granulation step S4:

The mixed mixture is subjected to extrusion granulation of raw granules by a counter-roll granulator, and rounded by a spheronizer to obtain raw granules.

Ceramsite rotary kiln roasting step S5:

The raw material needs to pass through the preheating section of the ceramsite rotary kiln to remove the moisture to prevent the cracking caused by the rapid evaporation of water during the high-temperature roasting process. The pellets are roasted into finished ceramsite products, which are then cooled by a cooling machine to prevent the cold cracking of the finished ceramsite products from affecting the strength due to rapid cooling. points to facilitate grading and subsequent quality control.

Through the above steps, the embodiment of the present invention can indeed achieve the expected effect, and the disclosed manufacturing process and products have not been seen in similar technical fields, nor have they been disclosed before the application. The above is only an example to illustrate the present invention. The composition of the invention is not intended to limit the scope of protection of the present invention, and creations based on modifications or alterations of this embodiment are also deemed to be included in the scope of the rights of the present invention.

Claims (1)

A method for recycling waste foundry sand, comprising any combination of the following steps: component analysis of the waste foundry sand Step S1: in this step, an X-ray fluorescence analyzer (X-ray Fluorescence, XRF) is used to perform chemical analysis of the waste foundry sand and mineral composition content analysis, and use an oven to measure the water content of the waste foundry sand; drying, magnetic separation and grinding step S2: the drying process of this step uses a rotary drying kiln for drying; the magnetic separation process of this step uses an electromagnet to The magnetic metal components in the casting sand are separated and removed; in the grinding process of this step, a pulverizer is used for grinding, and a screen is used for sieving to ensure that the particle size of the waste casting sand is less than 150 μm; adding water and stirring step S3: this step Use a twin-shaft mixing mixer, take 5~30% of waste foundry sand and 70~95% of silt clay, and add water at the same time to evenly stir to obtain a mixture; raw material granulation step S4: this step is carried out with a pair of roll granulators. For the granulation of raw granules, the raw granules are obtained after granulating the mixture, and the spheronizing screen is used to complete the circle and screen out the crushed mud mass and then enter the step S5. Step S4; calcining step S5 in the ceramsite rotary kiln: this step first removes the moisture of the raw granules through the preheating section of the ceramsite rotary kiln, and then passes through the high-temperature roasting and cooling of the cooling machine in the calcining section of the ceramsite rotary kiln, The raw granules are roasted to make ceramsite finished products. The residence time of ceramsite in the preheating section and the roasting section of the ceramsite rotary kiln is controlled by the rotation speed between 30 and 80 revolutions per minute, and the ceramsite rotary kiln is controlled by a burner. Its flame temperature and flame shape are used to control the temperature of ceramsite calcination to maintain at 900 to 1,200 ℃.

Images