物理化学学报 >> 2019, Vol. 35 >> Issue (3): 317-326.doi: 10.3866/PKU.WHXB201805021

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活性氧化铝及其再生氧化铝对水中氟离子的吸附

徐向宇,廖艳清,孙建川,王旭辉,陈帅奇,吕志,宋家庆*()   

  • 收稿日期:2018-03-23 发布日期:2018-08-28
  • 通讯作者: 宋家庆 E-mail:songjq@126.com
  • 基金资助:
    上海华东师范大学绿色化学与化学过程重点实验室(H2016107)

Removal of Fluorides from Aqueous Solutions Using Fresh and Regenerated Activated Alumina

Xiangyu XU,Yanqing LIAO,Jianchuan SUN,Xuhui WANG,Shuaiqi CHEN,Zhi LV,Jiaqing SONG*()   

  • Received:2018-03-23 Published:2018-08-28
  • Contact: Jiaqing SONG E-mail:songjq@126.com
  • Supported by:
    Shanghai Key Laboratory of Green Chemistry and Chemical Processes, East China Normal University, China(H2016107)

摘要:

水的氟污染是全世界普遍存在的问题,因此受到了人们的极大关注。我们研究重点是使用活性氧化铝及再生后的活性氧化铝脱除水中的氟离子。为了得到合适的吸附剂,我们将工业薄水铝石在573 K至1473 K范围内进行煅烧,并对其进行表征。从X射线衍射图中可以看出,当煅烧温度在773 K至1473 K之间时,样品转化为γ-氧化铝(活性氧化铝)。且BET数据显示,当煅烧温度在773 K至1473 K之间时,样品的比表面积逐渐降低。在本实验中,我们选用773 K、873 K、973 K煅烧的活性氧化铝作为除氟吸附剂,同时选用动态吸附法移除水中的氟离子。突破曲线表明吸附容量随着煅烧温度的增加而降低。为了研究氟离子的初始浓度对吸附容量的影响,我们选用15 mg·L-1、20 mg·L-1、25 mg·L-1的氟离子溶液作为初始溶液,且吸附剂的吸附容量随着初始浓度的增加而增加。当活性氧化铝吸附氟离子达到饱和后,用pH值为13.0、13.3和13.5的氢氧化钠溶液对其再生,并用0.1 mol·L-1的盐酸溶液对其进行活化以提高吸附剂的吸附能力。通过比较五次再生过程中的解吸率和铝溶解率,可以看出pH值为13.0的氢氧化钠溶液最适合作解吸剂。通过分析吸附剂的氮气吸-脱附等温线,发现再生后的吸附剂的氮气吸脱附等温线的形状并没有发生很大的变化,说明再生过程中吸附剂的孔结构并没有被破坏。五次再生过程中吸附剂的比表面积和等电点的变化是影响吸附容量很重要的两个因素,发现吸附剂再生后其比表面积和等电点均增加。为检测再生吸附剂的吸附效果,每次再生后都需要进行一次吸附实验。突破曲线表明,和初始活性氧化铝相比,再生后达到饱和所用的时间更短,吸附量越大。为了探究吸附机理,我们用红外光谱表征吸附剂中的羟基,发现再生过程中吸附剂中Al―O―H含量的变化是影响活性氧化铝对氟离子吸附量的关键因素。

关键词: 除氟, 再生, 活性氧化铝, 突破曲线, Zeta电位

Abstract:

Fluoride contamination of water is a problem worldwide and has caused great concern. Our study focused on the removal of fluorides from aqueous solutions using newly prepared and regenerated activated alumina. To obtain a suitable adsorbent, industrial boehmite was calcined from 573 K to 1473 K and the sample was characterized. The X-ray diffraction patterns showed that the sample was transformed to γ-alumina (activated alumina) at temperatures from 773 K to 1173 K, and the BET dates showed that the specific surface area of the sample decreased gradually from the temperature of 773 K to 1173 K. In our study, the activated alumina calcined from 773 K to 973 K was selected as the defluoridation adsorbent, and dynamic adsorption was employed for the removal of fluorides from aqueous solutions. The breakthrough curves demonstrated that the adsorption capacity of the adsorbent decreased with increasing calcination temperature. To investigate the effect of initial fluoride concentration on the adsorption capacity, 15 mg·L-1, 20 mg·L-1, and 25 mg·L-1 fluoride solutions were selected as the initial aqueous fluoride solution. As a result, the capacity of the adsorbent increased gradually with the increase in the initial fluoride concentration. In order to improve the capacity, we also studied the regeneration process in our experiment. When the activated alumina was saturated by the fluorides, it was regenerated with a NaOH solution (pH = 13.0, 13.3, 13.5) and activated with a HCl solution (0.1 mol·L-1). By a comparison of the five desorption and Al3+ dissolution rates during the regeneration process, it was determined that the NaOH solution with pH 13.0 was the most suitable desorption agent. An analysis of the nitrogen adsorption-desorption isotherm showed that its sharpness was almost unchanged after regeneration, which indicated that the pore structure of the adsorbent was not destroyed during this process. The change in the specific surface area and isoelectric point for the five-times regenerated adsorbent were important impact factors for fluoride adsorption. The specific surface area of the regenerated adsorbent increased, and the study of the zeta potential demonstrated that the isoelectric point also increased after regeneration. To observe the adsorption effect of regenerated activated alumina, we performed an adsorption experiment after each regeneration. The breakthrough curves demonstrated that the regenerated activated alumina exhibited faster saturation and increased adsorption capacity compared to fresh activated alumina. To elucidate the adsorption mechanism, IR spectroscopy was employed to characterize the O―H band of the adsorbent. The change in the Al―O―H content of the activated alumina during regeneration was the main factor impacting the fluoride adsorption capacity of the activated alumina.

Key words: Defluoridation, Regeneration, Activated alumina, Breakthrough curve, Zeta potential

MSC2000: 

  • O647