| With the development of science and technology, there are many wastewater treatment methods available, such as adsorption, chemical oxidation, ion exchange, biochemical treatment, electro-dialysis and flocculation sedimentation and so on. As an effective pre-treatment method, Flocculation sedimentation has the widest applicable range,the lowest treatment cost and the best flocculation efficiency. Flocculation effect of flocculant directly determines the regular working of operational unit, treatment cost and the effluent water quality. At present, the widest application is inorganic polymeric flocculant, which mainly includes two kinds: polyaluminum salt flocculant and polyferric salt flocculant.Polyaluminum salt flocculant and its hydrolysate have the following disadvantages: its flocs sedimentation is slow,sludge produced is loose and large amount,its decolourity effect is not good and residual alum is harmful to human body; polyferric salt flocculant and its hydrolysate are used to treat wastewater with the following flocculation phenomena: forming compact and strong flocs,good precipitation and dewatering effect,wide applicable range of pH value,low treatment cost. In addition, wastewater quality influence on its flocculation efficiency is slim, but ferric salt flocculant haas strong erosion action to treatment equipment and residual ferric will make Wastewater to be treated yellow to affect the effluent quality. However, polyaluminum ferric chloride (PAFC) is a new kind of high-effective inorganic polymeric flocculant developed on basis of polyaluminum and polyferric flocculants. It has the advantages of polyaluminum and polyferric, at the same time, it can make up their weak points, particularly, it is used to dispose low temperature and low turbidity,low temperature and high turbidity wastewater, better flocculation efficiency can be achieved. It can be widely used to treat drinking water,urban water and industrial wastewater.Low concentration bauxite means the mineral its Al2O3 concentration ranges from 25% to 40% and total Fe concentration is over 2%. There are many these kinds of low concentration bauxites in China. It can be neither used as raw materials of industrial alum production nor used as refractory. However, the conventional extraction method, such as baler method and agglomeration method, their requirements to alum concentration are strict and high, in general, bauxite is regarded as waste solid and can't be used if its Al2O3 concentration is below 45%; The main constituent of waste gas discharging from electrochemical factory is HCl, if the low concentration bauxite and waste gas were released into environment, it not only brings huge pressure to environment but also wastes lots of valuable resources, therefore, it is demonstrated to be necessary to carry out study on preparation of PAFC by using the bauxite and recycled waste gas, which has important society and economy profit.This research adopts two-step method to prepare PAFC by using bauxite,calcium aluminate and waste acid recycled from waste gas as main raw materials. At first, bauxite should be calcined at muffle stove at temperature of 800℃for 2 hours, and then cooling and comminuting to 0.25mm. In the first step, adding right amount of mixed hydrochloric acid, bauxite and water to vessel reacting some time in order to extract fully Al2O3 and Fe from bauxite. In the process of PAFC preparation, without adding additional ferric to mixed solution because bauxite itself contains amounts of ferric, what needs to do is to add calcium aluminate in the second step. Addition of calcium aluminate can both adjust Al2O3/Fe concentration ratio and enhances basicity of PAFC product. Stirring and heating for 7 hours, the product PAFC can be achieved after another 24 hours sedimentation. Experiment results show that:In the acid dissolution experiment of bauxite, adding 300ml 15% mixed hydrochloric acid and 110ml H2O into four outlet flask, then heating up to 80℃and putting 150g bauxite into the mixed solution react 3 hours under stirring condition, the reaction temperature was controlled at 105℃, after the end of reaction, Al2O3 and Fe concentration were investigated in order to calculate their dissolution rate. Experiment result showed that dissolution rate of Al2O3 and Fe can be up to 80.84% and 92.15% respectively. In the second step, 142ml 15% mixed hydrochloride acid,140ml H2O and 60g calcium aluminate were put into the acid dissolution solution reacting for 7 hours at 105℃, In the process of polymerization reaction,vapor was inpoured into the reaction solution to increase reaction temperature and to accelerate proceeding of polymerization reaction。The factors which affect the flocculation efficiency of PAFC product and the optimum conditions were investigated, such as dosage and concentration of mixed acid, reaction temperature, reaction time and dosage of calcium aluminate. After the end of polymerization reaction,cooling reaction solution and sedimentation for 24 hours in the air, the product PAFC was prepared. Its parameters are listed below: concentration of Al2O3 and Fe is 9.73% and 1.62% respectively, basicity is 79.4%.The self-prepared PAFC flocculant was analyzed by infrared spectrum and scanning electrode microscope and result showed that its micro-structure is alike to neither that of polyaluminum chloride nor that of polyferric. It has large molecular structure to form net so that its flocculation efficiency is better than that of other flocculants.The self-prepared polyaluminum ferric chloride flocculant (PAFC) was used to treat practical wastewater with large and compact flocs formed, fast sedimentation and wide range of applicable pH value. colourity,turbidity,chemical oxygen demand can be removed effectively. Good flocculation effect can be achieved to treat washing wastewater,printing and dyeing wastewater,paper making wastewater and cotton spinning wastewater. In comparison with other flocculations, its flocculation efficiency is superior to that of similar product in the current market.
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