| Fluoride is an essential trace element,but excessive intake of fluoride can seriously affect people’s health,so fluoride in drinking water caused widely concern.Activated alumina adsorption method is more commonly used method of fluoride in drinking water. However, Activated Alumina have some problems which is low absorption capacity,andante absorption, the adsorption capacity after repeated regeneration falling faster and producing secondary pollution problem.This article aims to select the best modification methods by activated alumina modified, to improve the adsorption capacity of the activated alumina fluoride.And adsorption, adsorption mechanism and regeneration method of modified Activated alumina were researched and investigated detailedly. The main results were summarized as following:(1)By acid, salt (HCl, HNO3, H2SO4, FeCl3, FeSO4, AlC13) direct immersion method modified activated alumina to investigate the impact of regular patterns of modifier concentration, immersion time and solid-liquid ratio on modified activated alumina adsorption capacity of fluoride. On the basis of that, the orthogonal experiments of three factors and three levels were designed, then the optimal combination of the modified modifier were ultimately selected.In order to further improve the adsorption capacity of activated alumina fluoride removal, reducing the adsorption material costs, so the orthogonal experiments of six factors and five levels of H2SO4-FeCl3,H2SO4-FeSO4 and H2SO4-AlCl3 were designed.The optimal modified combinations were obtained:the optimal modification conditions of H2SO4-FeCl3-MGAA were that concentration of sulfuric acid, immersion time, solid-liquid ratio, concentration of ferric chloride, immersion time, solid-liquid ratio were 0.01 mol·L-1,120 min,1:5,0.1%,180 min,1:10 respectively;the optimal modification conditions of H2SO4-FeSO4-MGAA were that concentration of sulfuric acid, immersion time, solid-liquid ratio, concentration of ferrous sulfate, immersion time, solid-liquid ratio were 0.01 mol·L-1,120 min,1:5,0.5%,90 min,1:15 respectively;the optimal modification conditions of H2SO4-AlCl3-MGAA were that concentration of sulfuric acid, immersion time, solid-liquid ratio, concentration of aluminum chloride, immersion time, solid-liquid ratio were 0.05 mol·L-1,30 min,1:5, 0.5%,60 min,1:5 respectively.(2) Through compared effect of fluoride removal of several modified activated aluminas, we could find the effect of fluoride of H2SO4-AlCl3-MGAA showed a greater advantage than other modification methods. When the original fluoride concentration was 20mg/L, concentration of effluent fluoride ion after H2SO4-AlCl3-MGAA equilibrium adsorption reduced 1.76mg/L, however, the concentration of effluent fluoride ion in the GAA under the same conditions was 13.47mg/L. In addition, the metal ion in the solution was not overweight after H2SO4-AlCl3-MGAA adsorption fluoride.And the other ions introduced did not exceed the national drinking water standards.(3) The adsorption kinetic of H2SO4-AlCl3-MGAA results showed that the adsorption capacity increased quickly in the initial adsorption 4h, several adsorption rate curves were basically reached the adsorption equilibrium after adsorption 12h. And as the temperature increased, the adsorption capacity was increased, the adsorption rate was correspondingly increased.Modified Activated Alumina adsorption kinetics of fluorine in water was accord with pseudo-second order. At the same time,adsorption isotherm research showed that adsorption behavior of modified Activated Alumina conformed to the Langmuir adsorption model, that is adsorption of monolayer adsorption.And the maximum adsorption capacity of H2SO4-AlCl3-MGAA was 7.39 mg/g under 25℃, but the maximum adsorption capacity of GAA was only 1.21 mg/g, the maximum adsorption capacity of modified activated alumina was 6.11 times compared to unchanged activated alumina. Thermodynamic parameter calculation showed that H2SO4-AlCl3-MGAA fluoride ion adsorption was a spontaneous,entropy increasing endothermic process.(4) pH and coexisting anions had a significant impact on the effect of fluoride anions. When pH was 6,H2SO4-AlCl3-MGAA fluoride in the best effect.And when pH was 5-10,modified activated alumina fluoride could maintain good effect of fluoride, the range of optimum pH on activated alumina was broaden,at the same time effluent pH was in line with national standards for drinking water. And influence of coexisting anions from weak to strong was NO3-<Cl-< SO42-<H2PO4-< HCO3-< HPO42-.(5) Fluoride removal mechanism researched showed that H2SO4-AlCl3-MGAA fluoride mainly by Sulphate, chloride and fluoride ion exchange.(6) Research on regeneration of the saturated modified activated alumina showed that the saturated modified activated alumina could maintain a high adsorption capacity after five regeneration recycles,When it used 0.5mol/L NaOH and the solid-liquid ratio of 1:3 to resolving 3h, then used the best conditions for the activation of sulfuric acid and aluminum chloride modified activated alumina adsorption saturation. |
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