Study On Preparation Of Modified Clay Defluoridator And The Defluoridation Properties

Fluorine is one of essential trace elements that maintain normal physiological activity. A suitable concentration of fluoride in drinking water is beneficial for the prevention of dental caries. Fluorosis is one of the main endemic diseases in our country. According to statistics, infected areas are all over 28 provinces; the population in the infected areas is about 110,000,000; the sufferers of dental flourosis amount to 37,390,000; the sufferers of skeletal flourosis is about 2,760,000; and the number of sufferers is increasing continuously. The disease is mainly concentrated in the countryside and not in the cities, so domestically fluorisis has been associated with the poor. Therefore, the disease has some social connotationsFluorine-containing groundwater and drinking water sources with low fluorine content are widespread in our country, especially in arid and semi-arid north-west region. High fluoride water pose a serious threat to human health. Presently, the research on defluoridation is more, but the research on defluoridation has many defects, accordingly this limits the actual application. So it is important to investigate the cost-effective methods of defluoridation of drinking water.In this paper, clay is used as raw material, made use of its cheapness, readily, availability, its special characteristic of larger specific surface area, and the characteristics were modified through Al(OH)₃ colloidal solution . As a result, the modified clay defluoridator was finished. Through the study on the defluorination effect on fluorine-containing water to determine the best synthesis conditions: add 2% of NaOH to the Al₂(SO₄)₃ solution that the concentration was 0.3mol / L, until pH reached 6, and this makes an aluminum hydroxide colloidal solution. Then making this solution mix with clay at liquid-solid ratio of 1:3. After mixing uniformly, make the mixture calcine in the muffle furnace at 400℃in 2h. After grinding, taking between 40-60 head of the clay particles, then after using deionized water for washing, using 105℃oven drying to get the defluoridator..The main conclusions have been summarized as follows:(1)At the optimum conditions obtained for the modified clay defluoridator by static and dynamic experiments to study the adsorption properties, the best parameters of operation were determined. In the static experiments, the experiments proved that with the increasing of water, the adsorption capacity of modified clay defluoridator also increased, at the ratio of water-soil was about 200:1, saturation adsorption was reached. Through experiments, defluorination increased with the increasing of soaking time, in the first 3 hours defluoridation was faster, but after 11 hours the adsorption basically showed no further increase, after a certain time the defluorination absorption basically reached equilibrium, that is to mean that saturation absorption capacity had been achieved. When the concentration of fluoride ion solution increased continuously, the saturation adsorption capacity rised continuously as well, indicating that increased concentration gradient results in faster diffusion process., the adsorption process was be promoted. The modified clay defluoridator in the raw water concentration of 1-50mg / L, R² = 0.9922> 0.99, consistenting with the Langmuir-type adsorption isotherm.(2) when the pH≤3, soluble material can be generated easily due to fluoride in acid medium, fluoride ion pattern changed, resulting in the residual fluoride content in solution becoming smaller. General treatment of drinking water must be at pH value between 5-8, this makes it easy to learn from experiment that the absorption of modified clay defluoridator within this pH range was better. When pH=5, adsorption capacity was higher, and at pH 5-8 there was little change, so could be used for general treatment of fluorine-containing water.(3) Groundwater often contains CI^-, SO₄^2-, CO₃^2-, HCO₃^- and other anions, as well as Ca²⁺, Mg²⁺, Fe²⁺, Mn²⁺ and other cations. In this paper, therefore research was on the influence of the above ion on the adsorption capacity of the modified clay. The results showed that: With the Cl^- increasing in solution, fluoride removal efficiency decreased, but not to a great extent, also the concentration of Cl^- was remained essentially the same, basically no reaction occurred between modified clay defluoridator and Cl^-.The adsorbent under these conditions occurred at a certain choice of adsorption characteristics. When SO₄^2- existed in the concentrated solution, SO₄^2- had changed a certain concentration, no matter before or after the adsorption. Adsorption capacity of adsorbents decreased a lot. When CO₃^2- existed in solution, the more CO₃^2- the greater impact on the adsorption properties. The solution containing HCO₃^- had a certain influence on the adsorption properties of adsorbents, though little. When the solution contained Ca²⁺ and Mg²⁺, and since Ca²⁺ and Mg²⁺ and F" form of CaF₂ and MgF₂, this reduced the F^- content in the concentrated solution, so the results from the experimental point of view showed an increasing in the saturation modified clay defluoridator adsorption. When the solution containing Fe²⁺ and Mn²⁺, since Fe²⁺ and Mn²⁺ and F form complexes, which reduced the F^- content in the solution, so that the saturation adsorption of modified clay defluoridator increased slightly.(4)In the dynamic experiment, compounding 5.85 mg/L fluorine water simulating the water sample to be processed , choose a 43 mm diameter glass column, and then put the final product in it. The flow rate was fixed at 4.05 ml/min, settling time was 43 min, this adsorption post handled the water amount of 5832 ml , adsorption amount was 0.2543 mg/g. ,final water aluminium ion contents was 0.068 mg/L <0.2 mg/L , sulfuric acid ion content was 137.57 mg/L <250 mg/L, in accordance with national standards without exception.(5)When the water reached the fluoride ion concentration of 1mg / L, it had already reached the penetration point, the defluoridator could no longer treat anything. At this time there was needed to stop operation in order to allow for adsorbent regeneration. This experiment used static methods of regeneration, regeneration agent was NaOH. The results showed that the best conditions for modification: 2% NaOH, the solid-liquid ratio of 1:5, modification time was 48 hours.Modified clay defluoridator used for fluorine removal is clay used as raw material. Clay has characteristics of abundant resources, low cost, large surface area, easing of modification, regenerating easily. This study broadened the use of the area of the clay, after further study, modified clay defluoridator is expected to replace the original adsorbent. For our country's development and application of soil adsorbent has a certain theoretical significance and application value.