Experimental Study On The Process Of Fluoride Removal From Drinking Water

A prevalent progress of treating the fluoride containing drink water is using activated alumina as adsorbent and aluminum sulfate as regenerant. It is a safe and reliable progress for removing fluorine from water, also it is simple and easy to catch on. Two problems exist when aluminium sulfate is used as regenerant. The first is aggregation of activated alumina causing lower rate of activated alumina and the second is lower actified efficiency which causes larger fluoride aggragation in the activated alumina and affects the sequent absorption cycle. This paper studied the recover capacity of sodium hydroxide for the activated alumina with large fluorine deposition.The maximum desorption experiments demonstrated that the desorbing capacity of sodium hydroxide is superior to aluminium sulfate. Under the experiment condition:0.8% sodium hydroxide solution, a liquid-to-solid ratio of 1/100,24h shaking at a certain temperature,the desorbing capacity of different concentration sodium hydroxide solutions are between 8.1mg/g and 12.7mg/g.the largest desorbing capacity is 12.7mg/g when the concentration of sodium hydroxide solution is 0.8%.The desorbing capacity accounts for about 90%-95% of the aggregation of activated alumina. Under the same condition,the desorbing capacity of different concentration aluminium sulfate solutions are between 2.6mg/g-4.1mg/g.The smaller the liquid-to-solid ratio,the larger the concentration of fluorine in the regeneration solution after regeneration process finished.But the desorbing capacity of unit mass activated aluminium decrease.So the adsorption space of activated aluminium get less recovery.When liquid-to-solid ratio is 64:40 and sodium hydroxide solution concentration is 0.8%, the largest desorbing capacity is 0.42mg/g,4.7% of liquid-to-solid ratio is 100:1.Thus,it need large volume regeneration liquid to completely regenerate the activated aluminium with large fluorine deposition. The experiments of flowdesorption show that the utilization rate of sodium hydroxide medicine reach the highest that per gram medicine desorb ahout 52mg F- when it is formed to 0.4% sodium hydroxide solution.The desorbing capacity of sodium hydroxide solution is proportionate to its concentration.The higher the concentration of sodium hydroxide solution,the larger the desorptive rate is.when sodium hydroxide solution concentration is higher than 0.8%,the desorptive rates is almost a fixed value.Combining with desorptive rate and utilization rate of sodium hydroxide medicine,1% sodium hydroxide solution is used in the regeneration of water plants. In the whole regenerative period, the desorbing capacities of filtrations are between 380 and 550kg except filtration No.10. The desorbing capacity of unit mass activated aluminium is 10-14mg/g accounting for about 60%-70% of the fluorine aggregation.Because of solution hydroxide is strongly alkaline solution, the filter can not operate effectively unless neutralized with acid and washed with water until the pH value in the effluent was about 6.5. This regeneration progress is tedious and the medicament inputs are big,so it is not suitable to be used as convention regeneration process. Suggested that the conventional regeneration uses the aluminium sulfate regeneration, every other about 6 months, use the sodium hydroxide to carry on regenerate completely. The adsorption filter uses one kind newfilter using adverse current, air operated regeneration. The adverse current air operated regeneration ensure the regeneration fluid and the adsorption material full contact and response. So the regenerant is used fully, the amount used obviously reduces, and can guarantee that the bottom metafiltration material obtains the full regeneration.