Study On Pretreatment Of Seawater And Boron Removal From Seawater

In recent years, with the growth of population, the development of economic and industry, human have the demand for fresh water is increasing. Seawater is the most abundant and steady water sourse, exploiting seawater is imperative under the situation. Currently, the reverse osmosis (RO) is still the main desalination technology, the membrane needs better water quality, if seawater enter RO device directly without being pretreated, the membrane will be polluted seriously, so the pretreatment of seawater is very indispensable before desalination. Due to seawater contains excessive of boron, it have great harm to the plant, animals and human, the World Health Organization (WHO) demand the content of boron in the irrigation water is less than1mg/L, and in the drinking water does not exceed0.3mg/L, therefore, study on boron removal is very indispensable.Boron removal from Bohai seawater by alkalization-flocculation have been investigated. The influences of main single factors such as the types of alkalizer and flocculant, pH, temperature, the dosage of flocculant, slow stirring time and stirring time on the boron removal have been explored, and do the orthogonal experiment for the alkalizer, Al and Fe flocculants, the optimal process conditions have been determined. The results showed that the best alkalizer is NaOH, the rate of boron removal obtained79.9%, and81.0%was obtained in the orthogonal experiment, the remaining amount of boron was0.96mg/L. When the flocculants were applied in the boron removal, the best flocculant was polyaluminium chloride silicate magnesium (PACSM) in the A1flocculants, the rate of boron removal was86.8%, and87.5%was obtained in the orthogonal experiment, the remaining amount of boron was0.63mg/L; the best Fe flocculant was poly aluminium ferrumiron chloride silicate (PAFCS), the rate of boron removal was92.7%, and93.6%was obtained in the orthogonal experiment, the remaining amount of boron obtained0.32mg/L.In addition, adsorption thermodynamic and kinetic properties of boron adsorption by Mg(OH)2which was the intermediate of alkalization-flocculation process have been explored. The results showed:Mg(OH)2had a strong boron adsorption capacity, and the process agreed with the Langmuir adsorption isotherm model, Freundlich adsorption isotherm model and the Lagergren pseudo-second kinetic model, and the adsorption process was an exothermic process, boron of seawater was adsorbed by Mg(OH)2easily at low temperature.