Research On Alkalify Flocculation Seawater Pretreatment And Byproduct Magnesium Hydroxide

The reverse osmosis desalination is becoming an effective approach in seawater desalination to solve the shortage of freshwater resource.High-quality seawater after being pretreated feeding to the Reverse Osmosis(RO) is a key point for the successful seawater desalination.A kind of economic plant for seawater pretreatment was investigated in this study. The lime milk, as important auxiliaries for alkalify flocculation desalination pretreatment, its quality is crucial for the effect of desalination pretreatment. We will divide the technology of curing lime milk into dosage two phases to get the best conditions for curing under different conditions. Under the necessity of alkalify flocculate desalination pretreatment, this thesis respectively states how to cure the lime milk with clear water and sea water and compare the functions of alkalinization under different curing conditions. Turbidity is the most important factor of feed water of reverse osmosis desalination, and turbidity removal is a difficulty of desalination pretreatment. The alkalify flocculation desalination pretreatment technology is a cheap and effective way to reduce the turbidity of seawater. The flocculant, polyaluminiumferric chloride(PAFC), is an important additive for alkalify flocculation desalination pretreatment, and the dosage is crucial for the effect of desalination pretreatment. According to our experimental data and analysis, alkalized seawater by6g/L lime milk, flocculated by9ml/L PAFC and3ml/L starch solution, turbidity reduced to0.8NUT and meet the requirement of feed water of reverse osmosis desalination. The structure of magnesium hydroxide in floccule was regular from observed by scanning electron microscope and content improved with addition of starch from thermogravimetric analysis. The experimental results were analyzed in terms of the SDI value, the turbidity, the residual chlorine and the iron content and the floes breakage was found to follow the first model of floes breskage. The results are as follows:when the flow rate of PAFC was5.71x10-7m/s and water was design standard, the turbidity is bellow0.2NTU; the SDI value is below4. The residual chlorine in the water outlet is about0.030mg/L, and the iron content is about1.0μg/L. The results show that the water sample, which flows out of this economic equipment, integrated flocculation and sedimentation, can completely meet the demand of the water feeding into the plant of RO desalination.