问皮江法提炼Mg的反应原理

http://www.baidu.com/s?ie=gb2312&bs=%B3%F5%D6%D0%D3%EF%CE%C4%BD%CC%CA%A6%BF%BC%CA%D4%CC%E2&sr=&z=&cl=3&f=8&wd=%C6%A4%BD%AD%B7%A8%CC%E1%C1%B6Mg%B5%C4%B7%B4%D3%A6%D4%AD%C0%ED&ct=0