摘要
观察了三种吸附剂吸附亚砷酸根离子过程中溶液pH值随时间的变化。氢氧化铁在吸附过程中的pH值变化大致可分为三个阶段,0～6分钟为第一阶段,体系的pH值快速上升,指示亚砷酸根置换了固相中的氢氧根;7～40分钟为第二阶段,pH值变化不大,指示Fe(OH)3凝胶对亚砷酸根离子的吸附达到动态平衡;40分钟后为第三阶段,溶液的pH值呈单边下降趋势,这一阶段吸附剂与被吸附的阴离子之间发生了缩合反应,并释放出H+。MgAlLDO在吸附亚砷酸根的反应过程中pH值持续上升,它具有从水溶液中获取阴离子以恢复其前驱体结构的能力,这一反应中有氢氧根生成;MgFeLDO兼有前两者的吸附机理,吸附反应过程pH值的变化趋势介于二者之间。氢氧化铁在加热前后吸附容量变化不大,25℃和90℃时分别为69.7mg/g和73.7mg/g,而MgAlLDO和MgFeLDO的吸附容量在25℃时分别为62.4mg/g和82.5mg/g,在90℃时分别增加到114.9mg/g和199.0mg/g。MgAlLDO和MgFeLDO在90℃条件下吸附容量的大幅增加,可能和溶解CO的干扰被抑制有关。
Three types of absorbents, ferric hydroxide, Mg-A1 layered double oxide （ Mg-A1-LDO ） and Mg-Fe layered double oxide （Mg-Fe-LDO） were studied for their absorption behavior on arsenite. Initial pH value of NaAsO2 solution was 9.71. After ferric hydroxide being added, the pH variation with time can be divided into 3 stages： in the first 6 minutes, pH increased from 9.71 to 10.36, which indicates a OHrelease from the solid phase into the solution; during 7^th - 40^th minutes, pH changed only a little＇between 10.36-10.34, which indicates absorption of ferric hydroxide on AsO2 and a dynamic equilibrium is reached; after 40^th minute, pH value decreased continuously to 9.72 at the 360^th minute, which is caused by condensation reaction between the arsenite and absorbent, and H^＋ is released as a result. During the absorption of Mg-A1-LDO on arsenite, pH values increased with time continuously, because Mg-A1-LDO takes anions from the solution to recover the crystal structure of its precursor, and in this reaction hydroxyl is formed. In the case of Mg-Fe-LDO, the absorption effects on arsenite for former two absorbents were observed, and pH-time curve is between these two absorbents. The absorption capacity of ferric hydroxide on arsenite changed a little with temperature, from 69.7 mg/g at 25℃ to 73.7 mg/g at 90℃. Absorption capacity of Mg-A1-LDO and Mg-Fe-LDO increased apparently when the medium was heated, from 62.4 mg/g and 82.5 mg/g at 25℃, to 114.9 mg/g and 199.0 mg/g at 90℃, respectively. Ascending absorption capacity of Mg-A1-LDO and Mg-Fe-LDO on arsenite at 90℃ is quite possibly because the disturbance of dissolved carbonic anion on arsenite is suppressed by heating, which expelled dissolved CO2 from the solution.
出处
《高校地质学报》
CAS
CSCD
北大核心
2006年第2期228-233,共6页
Geological Journal of China Universities
基金
国际科学基金组织(No.W/37871)
