Sponge Carbon Supported Cerium-based Adsorbents For As(â…¢) Removal From Water

The problem of arsenic pollution needs to be solved urgently due to its high toxicity.Arsenic in water generally exists in two inorganic forms—arsenate As（Ⅴ）and arsenite As（Ⅲ）.As（Ⅲ）is more toxic than As（Ⅴ）,As（Ⅲ）exists as non-ionic H₃As O₃in a wide p H range,and it is more difficult to remove due to its lower affinity.Adsorption is a widely employed technique for arsenic removal.In this thesis,cerium oxide-macroporous carbon sponge（Ce-NNs/MCS）and lanthanum-doped ceria-macroporous carbon sponge（La-Ce_x-NNs/MCS）adsorbents were prepared using a simple hydrothermal-calcination method.The effects of different chemical conditions on the adsorption of As（Ⅲ）by the two adsorbents were investigated.Finally,the adsorption mechanism of As（Ⅲ）was studied by XPS and other characterization methods.The main findings are as follows:（1）The cerium-based adsorbent Ce-NNs/MCS was prepared and used for the adsorption of As（Ⅲ）.A large number of Ce O₂ nanoneedles were grown vertically on the network framework of the macroporous carbon sponge（MCS）.The large specific surface area of MCS allowed Ce O₂ nanoneedles can be fully exposed,which makes the Ce-NNs/MCS have efficient adsorption of As（Ⅲ）.At 1 g/L of adsorbent,the initial As（Ⅲ）concentration of 826μg/L could be adsorbed to below 10μg/L within 20minutes.The maximum adsorption capacity of Ce-NNs/MCS for As（Ⅲ）was 35.28mg/g.Using 1 g/L Ce-NNs/MCS,the removal rate of As（Ⅲ）with the initial As（Ⅲ）concentration of 1 mg/L can be maintained over 98.8%in the range of p H 3-11,and in the p H range of 3-10,the residual As（Ⅲ）concentration was less than 10μg/L.At the same time,it has strong anti-interference ability to common interfering ions such as carbonate,silicate,phosphate and humic acid,and their addition does not reduce the adsorption performance of Ce-NNs/MCS for As（Ⅲ）.Even if the amount of adsorbent was reduced to 0.1 g/L,Ce-NNs/MCS could still maintain 96%removal rate in the p H range of 3-10,and was little affected by interfering anions and humic acid,demonstrated super-strong affinity of Ce-NNs/MCS for As（Ⅲ）.Using 1 g/L Ce-NNs/MCS to remove trace amounts of As（Ⅲ）in four simulated waters,it only took 5minutes to remove As（III）to less than 10μg/L.Using 1M Na OH as the desorbent,Ce-NNs/MCS maintained over 95%removal of As（Ⅲ）in 5 cycles with an initial As（Ⅲ）concentration of 1 mg/L.Finally,the Ce-NNs/MCS（900 mg adsorbent,effective bed volume of 7.85 m L,empty bed residence time 3.9 minutes）could be effectively applied to the fixed-bed operation,and the Ce-NNs/MCS column could purify 4035 bed volume（BV）and 1605 BV effluent from the As（Ⅲ）-spiked groundwater containing 100μg/L and 600μg/L of As（Ⅲ）,respectively.It indicated that Ce-NNs/MCS has practical application ability in removing As（Ⅲ）.（2）The Ce-NNs/MCS adsorbent was doped with a small amount of La to obtain lanthanum-doped ceria-macroporous carbon sponge（La-Ce_x-NNs/MCS）and used for the adsorption of As（Ⅲ）.After La doping,the dispersion of Ce O₂ is increased.Using0.5 g/L La-Ce₁₀-NNs/MCS can adsorb As（Ⅲ）to below 10μg/L within 45 minutes when the initial As（Ⅲ）concentration of 822μg/L.And the maximum adsorption capacity of La-Ce₁₀-NNs/MCS for As（Ⅲ）was add to 40.01 mg/g after doping with a small amount of La.When the initial As（Ⅲ）concentration was 1 mg/L,the use of 0.5 g/L La-Ce₁₀-NNs/MCS could maintain 99.9%removal rate to As（Ⅲ）in a wide p H range（3-10）,and the residual As（Ⅲ）concentration was less than 1μg/L.It has good anti-interference ability to interfering anions,and only 50 mg/L phosphate anion has an effect on the adsorption of As（Ⅲ）.Using 0.5 g/L La-Ce₁₀-NNs/MCS can also adsorb trace As（Ⅲ）in groundwater to below 10μg/L.La-Ce₁₀-NNs/MCS maintained a removal rate of more than 90%for As（Ⅲ）in 5 cycles.Finally,the La-Ce₁₀-NNs/MCS（1 g adsorbent,effective bed volume of 7.85 m L,empty bed residence time 3.9 minutes）could be effectively applied to the fixed-bed operation,and the La-Ce₁₀-NNs/MCS column could purify 4586 BV（36.0 L）effluent from the As（Ⅲ）-spiked groundwater containing 100μg/L of As（Ⅲ）.It indicated that La-Ce₁₀-NNs/MCS has practical application ability in removing As（Ⅲ）.