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At present, many people don't know much about shell powder, and some people who know it will think of shell powder paint and animal feed. In fact, the value of shell powder is much more than that. From the perspective of material sources, shells are formed by the secretion of the mantle of mollusks. They are natural organic-inorganic composite materials. Although their shapes are ever-changing, they are basically composed of 95% CaCO3 crystals and about 5%. Organic matrix composition. As a natural organic-inorganic composite material, the composition and unique microstructure of the shell determine that the material also has a series of excellent characteristics.
Unlike natural calcium carbonate minerals such as limestone, shells have the characteristics of good toughness and high strength, thanks to its multi-scale, multi-level "brick-mud" microstructure. At the same time, the polysaccharides, proteins and other macromolecular substances in the shells have a regulatory and guiding role in the formation of inorganic phases, and can make adjacent lamellas intercalate each other through proliferation mechanisms such as crack deflection, fiber pull-out, and organic matrix bridging. Makes the shells have high strength and toughness. In addition, shells also contain a small amount of inorganic salts of K, Na, Mg, Fe, Zn, and Se elements, which greatly enriches the use value of shell materials. The loose and porous shell powder obtained from shell processing also has many excellent properties, such as good adsorption, antibacterial properties, and affinity for polymer substances. Therefore, shell powder has been widely used in building materials, chemicals, medicine, environmental protection, new materials and other fields in recent years.
Shells contain about 30 kinds of mineral active elements, such as calcium, cobalt, magnesium, strontium, etc., and more than 10 kinds of amino acids, peptides, and collagen. Using shell powder as a feed additive can promote bone growth and blood circulation of livestock and poultry, and improve the quality and output of eggs and milk.
After being eaten, shell powder can stay in the muscles of poultry and livestock for up to several days, and the absorption time is sufficient. The feeding effect is better than limestone powder, eggshell powder and so on. In addition, shell powder also has excellent characteristics such as non-toxicity and dispersibility, and can be used as an excellent carrier for a variety of poultry and livestock medicines.
In addition to being a calcium supplement for poultry and livestock, shell powder can also provide calcium to the human body. The processing of scallop shells into ionic biological calcium can maximize the absorption of calcium by the human body, and its promoting effect on bone growth is significantly better than calcium carbonate.
There are many interconnected pores inside the shell. A large number of 2~10um micropores can be processed to produce a variety of different functional pore structures, so that it has strong adsorption capacity, exchange capacity and catalytic decomposition, etc., can absorb organic phosphorus, Boron, methylene blue, heavy metals and other ingredients, and also has a good water clarification effect. Using shell powder to treat aquaculture water can effectively improve the aquaculture environment and increase the food safety of aquatic products.
It is worth mentioning that in the flue gas purification process, shells and limestone have similar desulfurization performance, but shells have a better microporous structure than limestone, and the utilization of calcium is higher, which is conducive to the complete reaction of the desulfurizer.
At present, the industrial production of biodiesel in Europe and the United States mainly adopts homogeneous catalyzed transesterification reaction. However, compared with homogeneous catalysis, heterogeneous catalyzed transesterification reaction can be separated from the reacted mixture and can be recycled many times. And it can avoid problems such as serious emulsification in homogeneous catalytic reaction. Among the heterogeneous catalysts, CaO-catalyzed transesterification reaction has received widespread attention.
Li Yong et al. catalyzed the synthesis of fatty acid methyl esters using a catalyst prepared by shell powder as a carrier. When the calcination temperature is 600℃ and the active component loading is 20%, the biodiesel yield can reach 98.1%, and the filtered catalyst can be reused10 Times. In addition, studies have found that the synthetic supported alkali catalyst with shell powder as a carrier has the characteristics of large specific surface area, good acid and water resistance, and has high catalytic activity in the synthesis of fatty acid methyl esters, and has broad application prospects. .
In addition, waste shells can also be used in the preparation of shell-based photocatalytic materials. Zou Xiaolan used the pearl oyster shell as the carrier, calcined and activated the nano Cu2O/shell composite material by the hydrolysis method. The composite material has a good absorption effect on ultraviolet light and visible light.
Shells are bactericidal to many bacteria after being calcined at high temperature. Hu Xingjuan and others studied the bactericidal and bacteriostatic effects of the calcined powder of mussels, clams, constrictor shells and other shells on Salmonella, Vibrio parahaemolyticus, Staphylococcus aureus and Escherichia coli. The results showed that all three shells have bactericidal and bacteriostatic effects. Effect, and the effects of each group are not exactly the same. Wu Kaiqiang et al. used micro-nano mussel shell powder, sodium alginate and sodium carboxymethyl cellulose to prepare micro-nano mussel shell powder aquatic preservatives, and studied its preservation performance with hairtail as the research object. The results showed that it can be used to keep hairtail fresh . The main mechanism is to inhibit the oxidation rate of hairtail fat, and inhibit the growth of microorganisms and the production of amine compounds.
The shell powder is rich in CaCO3 and can be used to improve and purify the contaminated soil. The heavy metal ions in the soil can be precipitated in the form of carbonate to achieve the purpose of purifying the soil. Using shell powder as a soil conditioner in combination with organic fertilizer can increase the content of soil organic matter and prevent soil salinization.
As a natural biomineralized material, shell powder has a wide range of applications in the field of building materials. At present, the main uses of shell powder are:
① Shell powder coating, using shell powder as a functional filler to prepare a green multifunctional coating with various characteristics such as alkali resistance, anti-cracking, resistance to washing, and flame retardancy.
②Prepare mortar, replace sand and gravel with shell powder in a certain proportion as fine aggregate, save construction cost without compromising the mechanical strength of materials, or derive new shell powder wall materials.
③Improve the cement base material, and add shell powder to the cement base material in a certain proportion, which significantly improves the hydration effect of the cement, and even obtains more hydration products.
④Sintering cementitious material-lime, the main component of the shell is CaCO3. CaCO3 is decomposed into CaO by high-temperature calcination, and further reacts with water to form Ca(OH)2.
⑤Antibacterial material, the shell product after high-temperature calcination reacts with water, the product is extremely alkaline and has excellent antibacterial effect, so it is widely used in antibacterial materials.
Composite materials combine the excellent properties of inorganic and organic materials and are important new multi-functional materials. The composite material prepared with the shell as the inorganic phase has good mechanical properties. After the shell powder is modified by the surface modifier sodium stearate, the shell powder/polyethylene (PE) composite material can be prepared by the mechanical blending method. The fineness and proportion of the filling shell powder affect the mechanical properties of the composite material. It has a greater impact. When the fineness and proportion are moderate, the impact strength and tensile strength of the material are greatly improved.
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