Applicability And Response Mechanism On Defluoridation Effect Under Different Hydrochemical Characters Of Porous Aluminum And Magnesium Oxide

High-fluorine groundwater is widely distributed in china and has regional existence characteristics. Appropriate defluoridation technology should be adopted to solve the drinking water problem in these areas without alternate low fluoride water sources.Based on literature review and investigation of built fluoride removal systems, this research focus on adsorption defluoridation method, combines with the current application difficulties, and aims to improve the relevance between hydrochemical characteristics and adsorbents. Through field survey and lab experiment, this research means to elaborate hydrochemistry of high-fluoride groundwater and applicability and response mechanism of adsorbent defluoridation effect. The main conclusions are shown as follows:(1) Based on hydrogeological investigations in high-fluoride groundwater areas, different district had different hydrochemistry status due to various hydrogeochemical conditions, also had common charactors meanwhile. Groundwater samples with high fluoride accompanied with higher pH value, sodium and less total hardness, calcium content, magnesium content and belonged to Na-HCO3 water type. The parameters such as pH value, total alkalinity, bicarbonate, sodium, residual alkalinity were closely related to fluoride and could affect hydrochemistry status of high-fluoride groundwater. Cation exchange through water-rock interaction and dissolution of fluorite were the dominant hydrochemical processes in the formation of high-fluoride groundwater. Besides, calcium and magnesium decided the fluoride existence form.(2) Based on the hydrochemistry of high-fluoride groundwater, to overcome the current application difficulties and achieve high fluoride removal effect and well economic effect, two new adsorbents were prepared. The amorphous aluminum hydroxide adsorbent was prepared with coprecipitation method by controlling pH value of the reaction process. MgO adsorbent was prepared by hydrothermal method and calcinated the precursor. The obtained new adsorbents present excellent adsorption properties and the maximum adsorption capacity calculated from the Langmuir model were 167.7 mg/g and 125 mg/g respectively. And also could be repeated use at least five cycles. The two adsorbents improved the adaptive ability of pH value and strengthened the relation with natural high-fluoride groundwater.(3) The amorphous aluminum hydroxide and MgO adsorbents’s fluoride removal effect had different extend response of pH, bicarbonate, sulfate, chloride, and phosphate parameters, and decreased along with increasing pH, bicarbonate, sulfate, chloride, and phosphate. The pH value and bicarbonate could generate multiple level competitive adsorptions compared with fluoride. The adsorption of bicarbonate and sulfate were fitted well with the Freundlich model, and the adsorption capacities were larger than 31 mg/g and 14 mg/g at netural pH respectly, and belong to the preferential adsorption. These coexistence competitive anions decrease the absorption rate and affinity of fluoride.(4) Through low-fluoride and high-fluoride groundwater experiment, the amorphous aluminum hydroxide and MgO adsorbents possessed well applicability and could removal fluoride below the drinking water standard’s limit value at the first adsoption cycle. Meanwhile, the adsorbents also adsorbed a lot of coexistence competitive anions, especially bicarbonate. Due to large surface area and excellent adsoption properties, these coexistence competitive anions had no significant effect on the first adsorption process.(5) Compared with deionized water with NaF, the reused performance of adsorbents decreased significantly under natural high-fluoride groundwater (F=1.72 mg/L). The regeneration method under the condition of deionized water with NaF can hardly satisfy the actual demand of high-fluoride groundwater. As to the regeneration method, it is not only need to consider the desorption and regeneration of fluoride, but also more comprehensive consideration should be given to desorption of bicarbonate, sulfate and chloride and thus releasing more adsorption sites.Through this basic research, this work elaborated the hydrochemistry and key characteristics of high-fluoride groundwater, made clear the key restricting factors of fluoride removal effect, explained the competitive mechanism of coexistence competitive anions and indicated the response mechanism and application of adsorbent defluoridation effect on different hydrochemical characters. This work provides a new direction for the development and application of adsorption defluoridation method. And also lays the foundation for solving drinking water problems.