The invention discloses a method for extracting
chitosan from
oyster shells. The method includes the steps of firstly, using
clean water to clean waste
oyster shells to remove
silt and impurities on the surfaces of the
oyster shells; secondly,
drying and crushing the
oyster shells obtained in the first step to obtain oyster shell
powder; thirdly, sequentially performing low-temperature freezing and low-temperature lyophilization, and then using
liquid nitrogen as the
grinding medium to perform low-temperature crushing under the temperature from minus 80 DEG C to minus 120 DEG C by using an ultralow-temperature
crusher; fourthly, adding
purified water into materials obtained in the third step, evenly mixing, and
processing in a high-pressure homogenizing
machine; fifthly, performing
acid treatment, to be more specific, soaking materials obtained in the fourth step into diluted
hydrochloric acid, washing until neutrality is achieved, centrifuging, and
drying to obtain
chitin; sixthly, performing deacetylation, and
drying to obtain the
chitosan. The method has the advantages that the whole working
procedure time is shortened, black impurities in the intermediate working procedure are avoided, and the obtained
chitosan is pure white.