In the production process of alumina, mineral is firstly broken into pieces to make sure their radius is smaller than 1 mm. Feed strong sodium hydroxide solution to the system with high temperature and high pressure . Only aluminum and soluble silicon can be dissolved in this highly corrosive liquid, while impurities will not to be dissolved.   Add anionic polyacrylamide flocculant to the primary thickening tank to obtain clarified overflow is an very important process,in which aluminum is recovered.Thus,the overflow in the primary thickening tank rich in aluminum are to be processed(filtering,cooling,precipitating) to obtain aluminium.