Comparison of the defluoridation efficiency of calcium phosphate and chitin in the exoskeleton of Antarctic krill

Calcium （Ca）, phosphorus （P）, and chitin are the main components of the exoskeleton of krill. Defluoridation of a solution of sodium fluoride （NaF） using calcium phosphate （Ca3（PO4）2） and chitin as defluoridation agents was studied. Orthogonal experiments were designed to find the optimum reaction conditions for defluoridation, to obtain the maximum defluoridation efficiency and fluoride removal capacity of calcium phosphate and chitin. At the same time, a comparison of the capacity of the two defluoridation agents was made. The results suggest that calcium phosphate has a far greater capability than chitin for the removal of fluoride （F） from water under similar reaction conditions. It is also suggested that Antarctic krill is likely to adsorb fluoride via compounds such as calcium phosphate, hydroxyapatite, and other compounds of Ca and P with the general form （Ca, X）x（PO4, HPO4, Y）y（OH, Z）z, in addition to chitin.

Defluoridation of water using biosorbents

Contamination of drinking water due to fluoride is a severe health hazard problem. Excess of fluoride (>1.5 mg/l) in drinking water is harmful to human health. Various treatment technologies for removing fluoride from groundwater have been investigated. The present study showed that Vetiveria zizanioides, a herbal plant of Kerala—commonly known as Vetiver is an effective adsorbent for the removal of fluoride from aqueous solution. Phosphoric acid activated Vetiver root showed good adsorption capacity than the fresh powdered Vetiver root. Batch sorptive defluoridation was conducted under variable experimental conditions such as pH, agitation time, dose of adsorbent and particle size. Maximum defluoridation was achieved at pH 6;there is a greater possibility of columbic interaction between fluoride ion and adsorbent surface at this pH. The percentage of fluoride removal in- creases with adsorbent dose and time at a given initial solute concentration. The surface and sorption characteristics were analyzed using SEM techniques. Freundlich as well as Langmuir isotherm were plotted and kinetic constants were determined.

Defluoridation of Water by a Biomass: <i>Tinospora cordifolia</i>

This research is focused on the search of a biomass for the sequestration of fluoride from drinking water. Defluoridation of water was studied by batch experiments in biosorption process. The biomass was found to reduce fluoride to permissible limit 1.5 mg/L as prescribed by WHO. The efficiency of the sorption process was investigated under different experimental parameters such as pH 7, standing time 120 min and biomass doses 7.0 g with 5 mg/L concentration of fluoride. Neutral pH was identified as the optimum condition of the medium and 120 minutes was the best contact time for maximum fluoride adsorption. The experimental data was found good fitting to Langmuir and Freundlich isotherm models. In interference study tolerable effect was found with 50 mg/L concentration of co-ions, whereas increasing the concentration of co-ions retarded the fluoride removal capacity in some extent. FT-IR spectrum analysis showed fluoride binding in the different frequency ranges of the biomass. Eventually, this plant biomass is recommended as a suitable and low cost adsorbent to reduce fluoride into standard permissible limit.

Sorption Kinetics, Isotherm and Thermodynamic Modeling of Defluoridation of Ground Water Using Natural Adsorbents

The aim of study is to investigate the removal ability of some natural adsorbents for fluoride ion from aqueous solution. The batch dynamic adsorption method was carried out at neutral pH as the functions of contact time, adsorbent dose, adsorbate concentration, temperature and effect of co-anions, which are commonly present in water. The sorption kinetics and equilibrium adsorption isotherms of fluoride on natural adsorbing materials had been investigated at afore-mentioned optimized. Equilibrium adsorption isotherms, viz., Freundlich and Langmuir isotherms were investigated. Lagergren and Morris-Weber kinetic equations were employed to find the rate constants. The negative enthalpy ΔH = -46.54 KJ·mol-1 and Gibbs free energy calculated was ΔG288-333—(2.07785, 3.08966, 4.1064, 4.90716 and 5.38036 KJ·mol-1) respectively, envisage exothermic and spontaneous nature of sorption.

Fish Swim Bladder-Derived Porous Carbon for Defluoridation at Potable Water pH

The levels of fluoride in various ground water sources in East Africa are above the World Health Organization upper limit of 1.5 mg/L. Research on diverse defluoridation technologies has proven that adsorption stands out as an affordable, efficient, and facile technology. Fish swim bladder-derived porous carbon (FBPC) activated by KOH and surface oxidized by nitric acid was successfully investigated as an adsorbent for defluoridation at portable water pH. The FBPC was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). Batch methods were used to study physiochemical parameters viz., initial fluoride concentration, temperature, adsorbate dosage, contact time and pH. Freundlich, Temkin, Langmuir and Dubinin-Radushkevich isotherms were plotted and analyzed to understand the adsorption process. Bangham, Weber Morris, pseudo first and second-order models were used to elucidate the kinetics of adsorption. Optimal conditions for fluoride removal were found to be: pH of 6, FBPC adsorbent dose of 5.0 g/L and contact time of 50 min. Flouride adsorption followed pseudo second-order kinetic model and Langmuir isotherm best describes the adsorption process.

磁性Ce-La-MOFs@Fe_(3)O_(4)的除氟性能

通过水热法制备了Ce-La-MOFs@Fe_(3)O_(4)复合材料,研究了Ce-La-MOFs@Fe_(3)O_(4)对水溶液中F^(-)的吸附性能,并通过响应曲面法优化了吸附条件。实验结果表明:在pH=3.6、实验温度为40℃、初始氟离子浓度为17.4 mg/L的条件下,Ce-La-MOFs@Fe_(3)O_(4)的吸附效果最佳,F^(-)去除率可达94.5%。除氟特性实验数据更适合用Langmuir模型进行描述,拟合得到最大吸附容量(q_(max))为147.23 mg/g,热力学参数ΔG^(o)、ΔH^(o)和ΔS^(o)表明该吸附反应是一个自发吸热的熵增过程。动力学研究表明Ce-La-MOFs@Fe_(3)O_(4)对F^(-)的吸附符合准二级反应动力学过程。对复合材料的形貌和结构进行了表征分析,并结合吸附热力学和动力学研究探讨了吸附机理,该吸附过程主要是离子交换和静电吸附共同作用。共存离子实验、循环再生实验结果显示,Ce-La-MOFs@Fe_(3)O_(4)对F^(-)具有较好的选择性,该复合材料的再生性能较好,回收率可达96%,两次循环后对F^(-)的去除率仍达81.74%。

高比表面积羟基磷灰石的制备及其在磷酸铁废水除氟中的应用

为提高羟基磷灰石(Hydroxyapatite,HAP)对氟离子的吸附效率,采用化学沉淀法,通过优化反应温度、Ca/P摩尔比、陈化时间等合成条件制备高比表面积HAP,通过FTIR、XRD、XPS、SEM和BET等对合成的HAP进行表征,并评价HAP对模拟废水中氟离子的吸附性能。结果表明:HAP的最优制备条件为反应温度20℃、Ca/P摩尔比1.6、陈化时间24 h,所制备的HAP比表面积达108.0 m^(2)/g;HAP对氟离子的吸附为自发和吸热过程,符合Langmuir吸附模型,在303 K下氟离子的最大吸附容量为13.53 mg/g,吸附过程符合准二级反应动力学模型;在酸性条件下,HAP的除氟机理为离子交换。磷酸铁废水HAP吸附除氟实验表明,出水氟离子浓度可连续32 h低于1.0 mg/L,体现了较好的除氟效果。研究结果可为高效除氟吸附剂的制备以及磷酸铁废水深度除氟提供一定的指导。

除氟剂在矿井水除氟实验中的应用研究

通过对比4种药剂的除氟性能,挑选出最佳除氟剂并探究了不同因素对其除氟效果的影响。结果显示:4种药剂氟化物去除效果为:ZMCF>CF-B>CF-A>PAC。最佳实验条件ZMCF除氟剂投加量为100 mg/L,PAC投加量为160 mg/L,PAM投加量为1.2 mg/L,pH为6~7,反应沉淀30 min后,出水氟化物浓度为0.52 mg/L。共存阴离子Cl-和SO_(4)_(2-)对除氟效果影响较小。现场实验结果显示,最佳实验条件下处理后出水氟化物含量为0.75~0.93 mg/L,平均值为0.83 mg/L,氟化物浓度可稳定在1.0 mg/L以下,符合煤矿矿井水排放要求。出水浊度为8.9~14.6 NTU,经后续系统过滤后进一步降低出水浊度,从而排放利用。

一步固相反应制备铝改性活性炭对矿井水中氟化物的超快去除

矿井水中(F^(−))超标已成为制约我国西部矿区煤炭绿色开发的主要挑战之一。针对该问题,开发了机械化学法一步固相反应制备Al改性活性炭(AC-Al)的方法,解决了常规水热法改性活性炭产生废液废渣、制备周期长的问题,并实现了矿井水中F^(−)的快速、高效去除。研究了Al添加量、pH、共存阴离子和有机物、吸附剂投加量及反应时间等对除氟性能的影响。AC-Al除氟性能与Al添加量成正比,添加量为0.32 g,吸附反应30 s时,水中F^(−)去除率达到80%以上。pH在3~10范围内,F^(−)去除率均大于80%,具有良好的水质适应性。吸附过程更符合Langmuir模型,即为单层吸附,理论饱和吸附量为1.47 mg/g。吸附过程符合准一级动力学模型。硫酸根离子、氯离子和碳酸氢根离子(1000 mg/L时)、腐殖酸对F^(−)去除没有影响,氯离子和碳酸氢根离子质量浓度为3000 mg/L时,除氟率分别降低约21%和11%。AC-Al投加量为10 g/L时,矿井水中F^(−)去除率达84.9%(30 s内),质量浓度从4.85 mg/L降低至0.73 mg/L,满足《地表水环境质量标准》(GB3838—2002)中F^(−)浓度限值(I、II、III类),矿井水中F^(−)吸附过程同样符合准一级动力学模型。元素面分布表明,Al均匀地负载于活性炭表面;F^(−)均匀吸附在AC-Al上,与Al分布特征相似,证明Al是F^(−)吸附潜在活性位点。X射线光电子能谱结果表明,F^(−)吸附前后,AC-Al表面的Al元素结合能从74.20 eV升高至74.28、77.80 eV等2种状态,说明Al与F结合形成了Al-FOH、Al-F化学键,是快速稳定除氟的直接原因。同时,AC-Al吸附剂上的Al溶出量很低(0.34μg/g)。机械化学法制备的Al改性活性炭除氟效果良好,可为除氟吸附剂制备提供新的普适性技术路径,同时为解决矿井水除氟问题提供技术支撑。

PES/PDA-Al_(2)O_(3)复合膜的制备及其除氟性能的探究

通过真空辅助过滤(VAF)制备了PES/PDA-Al_(2)O_(3)复合膜,并系统地评估了复合膜的除氟性能.考察了初始pH值、初始F-浓度、吸附时间以及共存阴离子等因素对吸附效果的影响.结果表明:在pH=4,温度为25℃,氟离子浓度为10 mg/L条件下,该复合膜最大吸附容量为3.041 mg/g.复合膜对氟离子的吸附动力学遵循拟二级动力学反应模型,相对于Langmuir模型,复合膜对氟离子的吸附更加符合Freundlich模型.

基于电絮凝法深度去除矿区地下水中氟的研究

采用电絮凝法处理矿区含氟地下水,考察了电絮凝除氟效果及其影响因素,探讨了其除氟动力学过程。结果表明:电絮凝对矿区地下水中氟有较好的去除率,在电流密度为30 A/m^(2)、极板间距为6 mm、进水pH为6.5的最佳操作条件下,当进水F-为8.20 mg/L、反应60 min时,出水F-为0.85 mg/L,去除率为89.63%,且整个除氟过程遵循一级反应动力学模型。电絮凝反应器内絮体X射线衍射和铝、氟元素分析发现,在进水pH为中性偏酸性条件下絮体多为无定型羟基铝化合物,F-去除率最好;较高的进水F-浓度使絮体中铝和氟元素摩尔比下降。

矿井水深度除氟的实验研究及经济技术分析

为将矿井水的氟化物从6.2 mg/L降低到1 mg/L以下,对化学沉淀、羟基磷灰石吸附、离子交换等工艺进行了实验研究及工程经济技术分析。实验结果表明:复配除氟剂沉淀、羟基磷灰石吸附、树脂离子交换工艺能够将氟离子从6.2 mg/L降低到1 mg/L以下。但钙铝药剂难以稳定将氟离子降低到1 mg/L以下。复配除氟剂沉淀、羟基磷灰石吸附及树脂离子交换除氟工艺的处理成本分别为1.14、0.91、1.59元/t。3种工艺中,投资费用最高的是树脂离子交换工艺,最低的是化学沉淀工艺。

高氟地下水中氟的来源及去除措施分析

本文从人为、自然两方面分析高氟地下水中氟的来源,探索其形成条件及影响因素,并提出抑制其形成的措施以及解决方案。结果表明:高氟地下水的形成主要由于含氟矿物岩石的风化瓦解,同时,半干旱的气候条件、适度的水温、独特的水文地质构造以及碱性的水化学环境亦是其形成的有利条件;根据高氟地下水形成机制及水化学特性,提出几种人为控制高氟地下水形成措施,但存在操作周期长、效果不显著、耗费资金多等缺点,为切实解决当前以高氟地下水为饮用水源地区的饮水安全问题,建议采取更换饮用水水源措施,如无适宜可更换水源,可考虑采取适宜、管理操作简便、经济可行的除氟技术。

六氟磷酸锂副产含氟盐酸连续脱氟技术的开发与实践

含氟盐酸是六氟磷酸锂的副产物,氟的脱除是其回收利用的关键。在分析间歇脱氟工艺的问题与不足的基础上,提出了连续脱氟技术。连续脱氟技术明显地改善了脱氟过程的自动化程度、品质、产能及环境等,从而实现了盐酸中氟质量浓度由55 g/L降低至11 g/L,产能提升118%,人均劳动效率提升337%,氟化钙粒度增长约30%,固体废弃物排放量减少52%,尾气达到超低排放标准(氟化物体积质量≤3 mg/m^(3),颗粒物体积质量≤10 mg/m^(3))。

新型饮水除氟剂蛇纹石降氟效果研究

目的 研究确定蛇纹石降氟效果和最佳降氟条件 ,为广大地氟病病区提供新的防病措施。方法 通过实验室检测和现场观察 ,利用单因素分析和正交实验方法确定水温、p H、粒度、接触时间、再生剂浓度对蛇纹石降氟容量的影响。结果 对蛇纹石降氟效果影响较大的因素依次为 :接触时间、粒度、再生剂浓度。降氟最佳操作条件为 :粒度 6 0～ 80目 ,明矾液浓度 0 .0 739mol/L ,接触时间 30 min。水温对降氟效果无显著影响 ;p H在 7.16～ 8.18之间 ,蛇纹石降氟容量没有差异 (P >0 .0 5 )。结论 利用蛇纹石降氟 ,效果明显 ,简便易行 。

活化蛇纹石降砖茶水氟含量可行性研究

目的 观察蛇纹石活化后降砖茶水氟效果及降氟前、后砖茶水化学成分的改变。方法 按少数民族饮砖茶习惯熬制的砖茶水 (含茶 5 g/ L,砖茶水含氟量约 3.5 2 m g/ L)经活化蛇纹石处理后 ,观察其氟含量及砖茶水水质变化。用电极法测砖茶水氟含量。用原子吸收分光光度法测砖茶水中 Mg、Ca、Zn、Fe、Cu等元素含量。结果 活化蛇纹石对砖茶水有降氟作用 ,在最佳条件下蛇纹石降氟容量可达 0 .31m g/ g;降氟后砖茶水中镁、钙、锌、铁、铜含量均有不同程度升高。结论 蛇纹石作为一种降氟剂是安全、价廉、有效 ,并能释放有益人体健康的元素。

除氟剂筛选及其与茶汤相互影响的研究

目的筛选一种砖茶除氟剂,研究除氟剂与茶汤的相互影响。方法感官品评与理化成分分析相结合。结果DFR能将茶汤中的氟含量降至卫生标准以下,且茶汤环境对DFR性能影响均较理想,茶汤氟浓度越高,DFR除氟量越大。茶汤的pH值与DFR的最佳使用pH值范围相符。接触时间超过15min,除氟量趋于稳定。DFR对茶汤感官、有害成分、有益成分影响均较小。结论DFR能用于砖茶除氟。

碳纳米管负载氧化铝材料的制备及其吸附水中氟离子的研究

采用碳纳米管和硝酸铝制备了碳纳米管负载氧化铝新型除氟材料 .X射线衍射检测发现 ,当焙烧温度低于 85 0℃时 ,氧化铝为无定形态 ,当焙烧温度为 1 0 5 0℃时 ,氧化铝为α形态 ,扫描电子显微镜观察到碳纳米管与氧化铝均匀掺杂 .同时用碳纳米管负载氧化铝复合材料进行水中氟离子的吸附研究 ,结果表明 ,该复合材料具有优良的除氟效能 .氧化铝负载量为 30 %、焙烧温度为 4 5 0℃条件下制备的碳纳米管负载氧化铝复合材料的吸附除氟能力是 γ-氧化铝的 2 .0～ 3.5倍 ,与 IRA-4 1 0聚合树脂的吸附除氟能力相当 ,适宜p H范围为 5 .0～ 9.0 ,吸附等温线符合 Freundlich方程 .

负载金属镧的壳聚糖对含氟水的处理

采用负载镧的壳聚糖作为含氟水的吸附剂,最佳制备工艺条件为:壳聚糖用量为1g·L-1,La3+浓度为0.15mol·L-1,反应时间为6h,吸附剂粒径为0.1mm;除氟剂的最优工作条件为:pH为7,温度50℃,搅拌速度400r·min-1,吸附时间60min。当吸附剂用量为1.6g·L-1时,对水中浓度为20mg·L-1的F-去除率达到98.4%。用0.1mol·L-1的NaOH对吸附饱和后的吸附剂进行解吸处理24h,可以有效地恢复其吸附性能。吸附剂对F-的吸附过程符合Langmuir吸附等温线方程;对F-的饱和吸附容量为476.190mg·g-1。

羟基磷灰石降氟剂合成方法降氟机理研究进展

合成羟基磷灰石用作饮水降氟剂具有降氟容量大、操作简便 ,处理后水质基本不变化 ,滤料容易再生 ,且不产生二次污染的特点。羟基磷灰石的降氟方法优于目前较普及的活性氧化铝、骨碳和电渗析除氟法。