羟基磷灰石矿井水除氟试验研究
Experimental study on fluoride removal from mine water by hydroxylapatite
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摘要: 水中过量的氟离子会对人体造成危害,羟基磷灰石( Hydroxylapatite,HAP ) 是一种理想的新 型环境功能除氟材料。 针对矿井水中氟含量超标的问题,采用 HAP 滤料吸附工艺,通过吸附柱动 态实验,考察了空床接触时间(Empty bed contact time,EBCT)、进水滤速、pH 及进水中氟离子质量 浓度等主要因素对含氟矿井水吸附除氟性能的影响;通过 SEM-EDS,FT-IR 等微观表征,探讨分析 了 HAP 滤料对水中氟离子的吸附机理。 结果表明,HAP 的除氟主要是滤料晶体表面的羟基与水 中氟离子的吸附置换反应,同时也存在一定程度的 HAP 的分解反应,反应后 HAP 滤料表面 Ca ∶ P ∶ F(物质的量比)≈5 ∶ 3 ∶ 1,羟基磷灰石主要变成了氟磷灰石。 空床接触时间越长除氟效果越 好,但将 EBCT 增长至 80 min 后,再增加 EBCT 来降低水中的氟化物含量将会很困难;进水滤速越 高出水效果越差,当滤速超过 0.37 m / h 时,会导致水中氟离子与滤料的接触时间相对减少,因氟离 子向滤料晶体结构内部迁移的速度较慢,使得滤料表面处于“ 饱和吸附” 的状态,而内部的晶格羟 基却未得到充分利用;出水中氟离子的质量浓度随进水中氟离子质量浓度的增加而升高,进水氟离 子质量浓度升高则水中氟离子的质量浓度传质推动力增大,但滤料晶体表面的氟离子向晶格内部 的迁移为控制步骤,速率较慢;过高的酸度与碱度均对除氟效果有负面的影响,酸性环境下氟离子 在水溶液中较难电离,碱性条件下 OH- 与氟离子存在竞争吸附,均不利于氟离子的脱除。 最佳的 除氟工艺条件是:EBCT 为 80 min,进水滤速为 0.37 m / h,进水 pH 为 7.5 左右。 在此条件下,进水氟 离子质量浓度为6.0 mg / L 左右时,出水中氟离子质量浓度可在低于 1.0 mg / L 的达标情况下稳定运 行。 进水滤速为 0.21 m / h 时可连续达标处理水量达到滤料床体积的 309 倍,稳定运行阶段的氟离 子脱除率可高达 97.5%以上,该羟基磷灰石滤料可作为矿井水除氟的优良吸附剂。Abstract: Excessive fluorine ions in water can cause harm to human body. Hydroxylapatite(HAP)is an ideal new en⁃ vironmental function for removal fluorine. In view of the problem of excessive fluorine content in the mine water, using HAP filter adsorption process,this paper had investigated the influence of empty bed contact time(EBCT),inlet water filtration speed,pH value and inlet fluorine ion concentration by the adsorption column dynamic experiment. The adsorption mechanism of fluoride on HAP was discussed by means of SEM,EDS and FT⁃IR. The results show that the fluorination removal of HAP is due to the adsorption and replacement reaction between the hydroxyl crystal surface of the filter material and the fluorine ions in water,and there is also a certain degree of HAP decomposition reaction. After the reaction,the HAP filter material surface is Ca ∶ P ∶ F≈5 ∶ 3 ∶ 1,and the hydroxyl apatite has become flu⁃ orapatite. The longer the empty bed contact time,the better fluoride removal,but after increasing EBCT to 80 minutes, it is difficult to reduce the fluoride content in the water. The higher the inlet water filtration rate,the worse the wa⁃ ter treatment effect,when it is more than 0.37 m / h,the contact time between the water fluorine ion and the filter mate⁃ rial is relatively reduced. However,the migration of the fluorine ion to the internal filter material crystal structure is slow,making the filter material surface in a state of “saturated adsorption”,while the internal lattice hydroxyl group is not fully utilized. The concentration of fluoride ions in outgoing water increases with the concentration of fluoride ions in incoming water. When the concentration of fluoride ions become high,the migration of the fluoride ions on the surface of the filter crystal to the lattice is a control step and the rate is slow. Excessive acid and alkali have negative effects on fluoride effect. In the acidic environment, F- is difficult to ionize in aqueous solution, and OH- and F- have competitive adsorption under alkaline conditions.The optimal process conditions for fluoride removal are as fol⁃ lows:EBCT is 80 min,inlet filter rate is 0.37 m / h,and inlet pH is about 7.5. Under this condition,when the incoming water fluoride ion is about 6.0 mg/L,the outgoing water fluoride ion concentration can operate stably at less than 1.0 mg / L. At the inlet water filtration rate of 0.21 m / h,the treatment water can reach 309 Bed volume,and the fluo⁃ rine ion removal rate in the stable operation stage can be above 97.5%. The hydroxyl apatite can be used as an excel⁃ lent adsorbent for the treatment of groundwater containing fluorine in mining areas.