Study on Preparation of Bone Char and Properties of DefluoridationFluorine is a essential trace element to human body,distributing in human teeth,bones. nails and hair,particularly in enamel(content about 0.01%～0.02%),mainly existing as CaF2.But it is harmful for human health if there are too low or too much fluoride in drinking water.Excessive fluoride in drinking water greatly endanger the health of local people,which trigger one of China\’s serious endemic.Water-based endemic fluorosis caused by high fluoride drinking water,which is the main type of the endemic fluorosis in our country.This endemic distributed in the 1054 counties(cities. flag) of 29 provinces(autonomous regions and municipalities),mainly in the provinces of north of the Changjiang River.such as Heilongjiang.Jilin,Liaoning,Inner Mongolia,Shanxi,Shaanxi,Gansu,Ningxia,Qinghai,Xinjiang,Hebei,Henan. Shandong.Tianjin.Beijing.There are approximate 120 million population with water-based endemic fluorosis,1,287,000 patients with skeletal fluorosis. and26,381,100 patients with dental fluorosis.As the former criterion for the classification of endemic fluorosis areas promulgated by the office of Endemic Disease. there are 62.072 light endemic fluorosis villages and 45,171 serious endemic fluorosis villages.Therefore.it is urgent for us to preventing and treating endemic fluorosis disease(such as skeletal fluorosis,dental fluorosis,etc.),and improving people\’s health. the available way for soluting this issue is controlling and eliminating the pollution of fluoride in drinking water,researching into economic and practical methods of fluorine-removal agent and fluorine-removal methods.Up to the present,there are many ways to deal with high fluoride drinking water at home and abroad,such as adsorption method,ion exchange method,method of reverse osmosis,flocculation precipitation,electrodialysis and electric coagulation,etc.Adsorption method is letting the fluorine-containing water flow through the device equipped with a fluoride removal adsorbent,then fluoride ion will exchange position with other ions or groups and remain in the adsorbent.We can restore the exchange capacity of sorbents by regenerating its performance.Adsorption method is mainly used to deal with low concentration of fluorine-containing water,but it also be used as the depth of the water treatment methods.This approach use ion-exchange agent in the contact bed or packed bed for fluoride removal,the use of dynamic adsorption method making this method simple and stable.And the key of this method is preparation of an efficient,low-cost,easy regeneration and long-life high quality adsorbent.Sources of this study is small town northeast of low-temperature water drinking water treatment technology research and demonstration(2006BAJ08B09).In this paper, for the actual rural family situation in the north-eastern part of the small towns and rural areas,we product a fluoride removal adsorbent for purifying fluorine-contained drinking water quality,required for the simple operation and getting materials easy in small household appliances.The test used dog bone as a raw material to obtain the bone char defluoridation adsorbents by the high temperature calcined separated from oxygen.We also determined the best preparation conditions of the bone char defluoridation adsorbents and studied their adsorption properties.Analysis of experimental results showed that dog bones need to calcined in Box Resistor-Stove after encapsulating with clay,when the calcined temperatures is 450℃or 500℃and the calcined time is 2 hours,you can achieve the best effect of bone charcoal adsorption.Considering the practical application of economic factors,we determined the optimum preparation conditions:450℃calcined for two hours. grainsize 30 mesh.The static absorption isotherms of defluorination of bone char could well fit the Langmuir equation,performing the characteristics of chemical adsorption.Adsorption capacity increased with time until saturation when we used bone char as the adsorbent.In the first 3h,the adsorption of bone char increased rapidly,between 3-12 hours adsorption capacity increased slowly,adsorption capacity would remain basically unchanged after 12h and reach the saturation state.The study used comparison test to determine dosing quantity of bone char defluorination agent,adding 0.3,0.6,1.0,1.3,1.6,3g bone char respectively to 300ml water samples,which fluoride content are 5.85mg/L.The test results show that when the dosage of bone char is 1.0g,the bone char for fluoride adsorption reached saturation.As the adsorbent dosage increases,its adsorption capacity of fluoride showed a gradual downward trend,indicated that while the dosage of adsorbent increasing,it would not improve the adsorption capacity of bone char.When the dosage of bone char is 0.6g.it reached the maximum adsorption capacity, approximately 1.62mg/g.However.fluoride ion concentrations of solution after adsorption exceed 1mg/L.the national hygiene standards for drinking water.When the dosage of bone char is 1g,fluoride ion concentrations of solution after adsorption is approximately 0.57mg/g,lower than the national hygiene standards for drinking water. Therefore,we determine to use the ratio for the follow-up experiment,adding 1.0g bone char to 300ml fluorine-contained water.The results of conditional experiments about the application of bone char showed that there are no significant impact while the temperature is held between 10℃-35℃and pH value is in range of 6-8.When the pH value keep around 5.the bone char for fluoride adsorption capacity reached a peak,the adsorption capacity of bone char showed an apparent downward trend with the rise in pH value.Because there is the inhibition of exchanging hydroxyapatite of bone char with the fluoride ion when the fluorine-containing water was alkaline,so making adsorption capacity of bone char decreased.The application range of pH value fit drinking water basically,which is able to meet the fluoride removal conditions of drinking water.When studied the effect of ion,we found that all the anions inhibited defluoridation and all the cations promoted defluoridation to a certain degree.There are four ions,CO_3~(2-),HCO_3~-,Ca~(2 ) and Mg~(2 ),that affect defluoridation much.CO_3~(2-) and HCO_3~- which could generate basicity and compare to Fluoride ion with bone char obviously reduce the adsorption capacity of bone char.However,Ca~(2 )and Mg~(2 ) have the familiar ability with Fluoride ion.and they can promote defluoridation to some extent.Cl~-,SO_4~(2-),Fe~(2 ) and Mn~(2 ) have little effect with the adsorption capacity of bone char.The continuous operation ability of bone char as an adsorbent has been studied by dynamic experiment.The influent concentration of Fluoride ion was 5.85mg/L,and Fluorine-containing water went through 30 heads of bone char particles which have 150g weight.The 150g-weight bone char defluorination agent reduce Fluorine-containing water which have 37.2L and 5.85mg/L-concentration to the national standard(the concentration of Fluoride ion＜1mg/L).The saturated bone char could be regenerated when NaOH solution was used as regenerant.The results of experiment show that when NaOH solution concentration is 0.5%.and the solid-liquid ratio between NaOH solution and bone char is 1:40 is the best conditions for the bone char defluorination agent.Immersed the saturated bone char as such a condition for 24 hours,then used HCl solution which concentration is 0.05mol/L to adjust the pH value of solution to neutral.Do as above regeneration step for three times,and obtain three different regeneration efficiencies.96.8%,91.9%and 88.3%.the result shows that the bone char have a high efficiency as a adsorbent.From the above conclusions of the experiment is not difficult to find that the bone char as a defluorination agent which do for the actual situation of small towns and rural areas in the Northeast have many advantages:The first,the method is simple,and the material can be got easily,and the cost of the production is very low;The second,the adsorption capacity of bone char is large and has less effect by other factors;The third,the regeneration has a simple method and a high efficiency,so the bone char can be reused for times.

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