| The oyster is the largest economic shellfish.A major problem with this profitable industry is the disposal of oyster shells.More than 1 000 000 tons of oyster shells are disposed annually without recycling for further use.The disposal of large quantities of oyster shells leads to serious environmental problems.Thus,some innovative methods of recycling the waste oyster shell have to be designed.In this thesis,the chemical components,phase structure,thermal stability,anti-bacterial and absorbing properties of the oyster shells were studied by ICP-MS,XRD,FTIR,TG and ESEM.Based on these studies,the oyster shell’s superfine powder was prepared and applied to the processing of agricultural products and environmental protection.The main results are as follows:(1)The main component(94.3%)of oyster shell powder is calcium carbonate with biosynthesis.The oyster shell powder contains 39.8%calcium and only 0.089%phosphorus in macro elements,2631 mg/kg strontium in trace elements.The oyster shell powder contains 17 kinds of amino acids,of which aspartic acid is the greatest,up to 1800 mg/kg.These features of oyster shell must be carefully considered in recycling.(2)The oysters shell powder with more fine can be obtained by wet milling pulverization method than high-frequency vibration milling method,but the soluble substances may partly be lost.Materials fill rate and moisture content of oyster shell are greatly affected by its particle size.(3)The oyster shell powder can significantly inhibit Escherichia coli,Staphyloccocus aureus Rosenbach,Bacillus subtilis(Ehrenberg)Cohn),Penicillium,Aspergillus niger and Rhizopus,but the water extract of oyster shell powder has no such inhibiting effects.(4)Since the oyster shell powder is rich in calcium carbonate,its usages of food processing are being paid attention to.In kimchi production,it can decrease acid content and enhance fragility.When it is used as an addictive in the juice fermentation,the oyster shell powder not only decrease acid content but also increase clarity,and alcohol content can increasing 60%.Besides,when it was used as konjac tofu coagulant,it can improve water retention and gel strength of konjac tofu increasing by 9.36%and 55.1%respectively.(5)Due to its porous structure with a large specific surface area and good adsorption,oyster shell powder can be applied to agricultural processing and environmental governance.The oyster shell powder can absorb ethylene during the storage of bananas and prolong the preservation of bananas by 33%.Besides,its usages in environmental protection are proved.The removal rate can reach 74.2%of dye from methyl orange in aqueous solutions under the optimums conditions.The removal rate can reach 98.23%of the trivalent chromium in the treatment of waste water containing chromium.Used as desulfurization agent during the coal combustion process,it can reduce 80%of the concentration of sulfur dioxide emissions.To solve the problem of economic efficiency in those plants,the ideas of multi-step utilization of oyster shells were promoted.So the results showed that oyster shell has antibacterial,adsorbing properties and other unique function of aggregation,and oyster shell superfine powder by wet milling pulverization has broad application prospects both in agricultural products processing and in environmental protection.It can be used widely and effectively so that a source of pollution will be eliminated. |
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