Progressive Freezing-Thawing Method For Boron Removal And Seawater Desalination

In the background of global water shortage,seawater desalination technology has developed rapidly in the past decade or so,among which the most common desalination technologies are thermal method and membrane method.These two desalination methods are costly and ineffective in removing boron,making the boron exceedance in desalinated water more serious.It has been shown that excessive intake of boron in humans can cause slow neurotoxicity,damage the central nervous system,affect the development of the fetus and cause fertility diseases;excessive boron in irrigation water can inhibit photosynthesis and respiration of plants,causing leaf curling and yellow leaves and accelerated fruit decay.In this paper,the migration law of boron in the two phases of ice and water under different freezing conditions(freezing time,freezing temperature,initial concentration)and different melting metho ds(natural melting,oscillatory melting,ultrasonic melting)was investigated;on this basis,the effects of different freezing conditions(freezing time,freezing temperature)and different melting methods(natural melting,oscillatory melting and ultras onic melting)on the actual seawater during the progressive freezing process were studied.The effects of desalination were investigated.It is expected to provide a new idea for seawater desalination and boron treatment,thus this study is of direct relevance.The study found that:1.The gradual freezing experiment of boron solution found that 90% of boron in the solution could be concentrated in the ice water during the freezing process,and only a small part remained in the ice.With the increase of initial boron concentration and freezing time,the migration ability of boron to ice water decreases gradually;With the decrease of freezing temperature,the migration ability of boron to ice water first increases and then decreases.Therefore,considering comprehensively,the freezing temperature is-15 ?,the freezing time is 48 h,and the initial concentration is 12 mg/L.2.The experimental study of natural melting,ultrasonic melting and oscillatory melting found that boron migrated from ice to molten water during the melting process,and showed a large number of concentrated migration in the early stage of melting and a small amount of stable release in the middle and late stage of melting.In the first 30% of meltwater,46.04% boron is transfer red by natural melting,88.97% boron is transferred by ultrasonic melting,and 91.12% boron is transferred by oscillatory melting.Therefore,the migration capacity of boron is oscillatory melting > ultrasonic melting > natural melting.3.The progressive freezing experiment of the actual seawater found that the freezing process can concentrate more than 50% of the pollutants in the seawater in the subglacial water,and with the decrease of the freezing temperature and the increase of the freezing time,the effect of the progressive freezing desalination of the actual seawater becomes worse and worse.Therefore,it is necessary to comprehensively consider the icing rate and material removal rate.The freezing temperature selected in the ac tual seawater freezing experiment is-20 ? and the freezing time is 44 h.4.The melting experiment of sea ice shows that the pollutants in sea ice are melted out in the early stage of melting.When the melting water ratio of natural melting method is 50%,the boron in the remaining ice body meets the boron limit(0.5 mg/L)in the hygienic standard for drinking water(GB5749-2006).In the sea ice treated by oscillatory melting method,it meets the standard when the melting water ratio is 25%;The salt ion concentration of the remaining ice in the natural melting method is still much higher than that in the hygienic standard for drinking water(GB5749-2006)when the melting water ratio is 75%.The ultrasonic melting method meets the standard when the melting water ratio is 75%,and the oscillating melting method meets the standard when the melting water ratio is 50%.