Oxidation of As（Ⅲ） by three types of manganese oxides and the effects ofpH, ion strength and tartaric acid on the oxidation were investigated by means of chemical analysis, equilibrium redox, X-ray diffraction （XR...Oxidation of As（Ⅲ） by three types of manganese oxides and the effects ofpH, ion strength and tartaric acid on the oxidation were investigated by means of chemical analysis, equilibrium redox, X-ray diffraction （XRD） and transmission electron microscopy （TEM）. Three synthesized Mn oxide minerals, bimessite, cryptomelane, and hausmannite, which widely occur in soil and sediments, could actively oxidize As（Ⅲ） to As（Ⅴ）. However, their ability in As（Ⅲ）-oxidation varied greatly depending on their structure, composition and surface properties. Tunnel structured cryptomelane exhibited the highest ability of As （Ⅲ） oxidation, followed by the layer structured birnessite and the lower oxide hausmannite. The maximum amount of As （Ⅴ） produced by the oxidation was in the order （mmol/kg） of cryptomelane （824.2） 〉 bimessite （480.4） 〉 hausmannite （117.9）, As pH increased from the very low value（pH 2.5）, the amount of As（Ⅲ） oxidized by the tested Mn oxides was firstly decreased, then negatively peaked in pH 3.0 6.5, and eventually increased remarkably. Oxidation of As（Ⅲ） by the Mn oxides had a buffering effects on the pH variation in the solution. It is proposed that the oxidative reaction processes between As （Ⅲ） and biruessite（or cryptomelane） are as follows： （1） at lower pH condition： （MnO2）x＋ H3AsO3 ＋ 0.5H^＋=0.5H2AsO4^- ＋ 0.5HAsO4^2- ＋Mn〉^2＋ （MnO2）x-1 ＋ H2O; （2） at higher pH condition： （MnO2）x ＋ H3AsO3 = 0.5H2AsO4^- ＋ 0.5HAsO4^2- ＋ 1.5H^＋ ＋ （MnO2）x-1. MnO. With increase of ion strength, the As（Ⅲ） oxidized by bimessite and cryptomelane decreased and was negatively correlated with ion strength. However, ion strength had little influence on As （Ⅲ） oxidation by the hausmarmite. The presence of tartaric acid promoted oxidation of As（Ⅲ） by birnessite. As for cryptomelane and hansmannite, the same effect was observed when the concentration of tartaric acid was below 4 mmol/L, otherwise the oxidized As（Ⅲ） decreased. These findings are of great significance in improving our understanding of As geochemical cycling and controlling As contamination.展开更多
In order to enhance the removal efficiency of As（III）, a pre-oxidation process is generally applied first to convert As（III） to As（V）, which may cause unwanted new contaminants. To overcome this problem, efforts...In order to enhance the removal efficiency of As（III）, a pre-oxidation process is generally applied first to convert As（III） to As（V）, which may cause unwanted new contaminants. To overcome this problem, efforts were made to develop an effective way to remove As（III）directly without an oxidation step. The effect of polyacrylamide polymers（PAMs） such as anionic PAM, cationic PAM and nonionic PAM, on As（III） ion adsorption by spent grain（SG）was investigated. The physico-chemical properties of the three PAM-polymerized SGs（APSG（anionic PAM-polymerized modified spent grain）, CPSG（cationic PAM-polymerized spent grain） and NPSG（nonionic PAM-polymerized spent grain）） were analyzed using Fourier transform infrared（FT-IR）, scanning electron microscope（SEM） and zeta potential.Batch experimental data showed that the sequence of preferential adsorption for As（III） was APSG 〉 CPSG 〉 NPSG. Active functional groups such as amino group（NH2）, carbonyl group（C_O）, C–N bond of the amide group（CONH2）, and hydroxyl group（O–H） were responsible for As（III） adsorption. Many tubular structures occurring on the surface of APSG possibly increase the specific surface areas and favor the adsorption of As（III） ions. A fixed-bed study was carried out by using APSG as an adsorbent for As（III） from water. Three factors such as bed height, initial concentration and flow rate were studied, and breakthrough curves of As（III） were obtained. The Adams–Bohart model was used to analyze the experimental data and the model parameters were evaluated.展开更多
Organic matters（OMs） and their oxidization products often influence the fate and transport of heavy metals in the subsurface aqueous systems through interaction with the mineral surfaces. This study investigates the...Organic matters（OMs） and their oxidization products often influence the fate and transport of heavy metals in the subsurface aqueous systems through interaction with the mineral surfaces. This study investigates the ethanol（EtO H）-mediated As（Ⅲ） adsorption onto Zn-loaded pinecone（PC） biochar through batch experiments conducted under Box–Behnken design. The effect of EtO H on As（Ⅲ） adsorption mechanism was quantitatively elucidated by fitting the experimental data using artificial neural network and quadratic modeling approaches. The quadratic model could describe the limiting nature of EtO H and pH on As（Ⅲ） adsorption,whereas neural network revealed the stronger influence of Et OH（64.5%） followed by pH（20.75%）and As（Ⅲ） concentration（14.75%） on the adsorption phenomena. Besides, the interaction among process variables indicated that Et OH enhances As（Ⅲ） adsorption over a pH range of2 to 7, possibly due to facilitation of ligand–metal（Zn） binding complexation mechanism.Eventually, hybrid response surface model–genetic algorithm（RSM–GA） approach predicted a better optimal solution than RSM, i.e., the adsorptive removal of As（Ⅲ）（10.47 μg/g） is facilitated at 30.22 mg C/L of Et OH with initial As（Ⅲ） concentration of 196.77 μg/L at pH 5.8. The implication of this investigation might help in understanding the application of biochar for removal of various As（Ⅲ） species in the presence of OM.展开更多
文摘Oxidation of As（Ⅲ） by three types of manganese oxides and the effects ofpH, ion strength and tartaric acid on the oxidation were investigated by means of chemical analysis, equilibrium redox, X-ray diffraction （XRD） and transmission electron microscopy （TEM）. Three synthesized Mn oxide minerals, bimessite, cryptomelane, and hausmannite, which widely occur in soil and sediments, could actively oxidize As（Ⅲ） to As（Ⅴ）. However, their ability in As（Ⅲ）-oxidation varied greatly depending on their structure, composition and surface properties. Tunnel structured cryptomelane exhibited the highest ability of As （Ⅲ） oxidation, followed by the layer structured birnessite and the lower oxide hausmannite. The maximum amount of As （Ⅴ） produced by the oxidation was in the order （mmol/kg） of cryptomelane （824.2） 〉 bimessite （480.4） 〉 hausmannite （117.9）, As pH increased from the very low value（pH 2.5）, the amount of As（Ⅲ） oxidized by the tested Mn oxides was firstly decreased, then negatively peaked in pH 3.0 6.5, and eventually increased remarkably. Oxidation of As（Ⅲ） by the Mn oxides had a buffering effects on the pH variation in the solution. It is proposed that the oxidative reaction processes between As （Ⅲ） and biruessite（or cryptomelane） are as follows： （1） at lower pH condition： （MnO2）x＋ H3AsO3 ＋ 0.5H^＋=0.5H2AsO4^- ＋ 0.5HAsO4^2- ＋Mn〉^2＋ （MnO2）x-1 ＋ H2O; （2） at higher pH condition： （MnO2）x ＋ H3AsO3 = 0.5H2AsO4^- ＋ 0.5HAsO4^2- ＋ 1.5H^＋ ＋ （MnO2）x-1. MnO. With increase of ion strength, the As（Ⅲ） oxidized by bimessite and cryptomelane decreased and was negatively correlated with ion strength. However, ion strength had little influence on As （Ⅲ） oxidation by the hausmarmite. The presence of tartaric acid promoted oxidation of As（Ⅲ） by birnessite. As for cryptomelane and hansmannite, the same effect was observed when the concentration of tartaric acid was below 4 mmol/L, otherwise the oxidized As（Ⅲ） decreased. These findings are of great significance in improving our understanding of As geochemical cycling and controlling As contamination.
基金supported the National Natural Science Foundation of China (No. 51164014)the Jiangxi Provincial Department of Education of China (No. GJJ14419)
文摘In order to enhance the removal efficiency of As（III）, a pre-oxidation process is generally applied first to convert As（III） to As（V）, which may cause unwanted new contaminants. To overcome this problem, efforts were made to develop an effective way to remove As（III）directly without an oxidation step. The effect of polyacrylamide polymers（PAMs） such as anionic PAM, cationic PAM and nonionic PAM, on As（III） ion adsorption by spent grain（SG）was investigated. The physico-chemical properties of the three PAM-polymerized SGs（APSG（anionic PAM-polymerized modified spent grain）, CPSG（cationic PAM-polymerized spent grain） and NPSG（nonionic PAM-polymerized spent grain）） were analyzed using Fourier transform infrared（FT-IR）, scanning electron microscope（SEM） and zeta potential.Batch experimental data showed that the sequence of preferential adsorption for As（III） was APSG 〉 CPSG 〉 NPSG. Active functional groups such as amino group（NH2）, carbonyl group（C_O）, C–N bond of the amide group（CONH2）, and hydroxyl group（O–H） were responsible for As（III） adsorption. Many tubular structures occurring on the surface of APSG possibly increase the specific surface areas and favor the adsorption of As（III） ions. A fixed-bed study was carried out by using APSG as an adsorbent for As（III） from water. Three factors such as bed height, initial concentration and flow rate were studied, and breakthrough curves of As（III） were obtained. The Adams–Bohart model was used to analyze the experimental data and the model parameters were evaluated.
基金supported by the research funds from the University of Ulsan in South Korea during the financial year 2012–2013
文摘Organic matters（OMs） and their oxidization products often influence the fate and transport of heavy metals in the subsurface aqueous systems through interaction with the mineral surfaces. This study investigates the ethanol（EtO H）-mediated As（Ⅲ） adsorption onto Zn-loaded pinecone（PC） biochar through batch experiments conducted under Box–Behnken design. The effect of EtO H on As（Ⅲ） adsorption mechanism was quantitatively elucidated by fitting the experimental data using artificial neural network and quadratic modeling approaches. The quadratic model could describe the limiting nature of EtO H and pH on As（Ⅲ） adsorption,whereas neural network revealed the stronger influence of Et OH（64.5%） followed by pH（20.75%）and As（Ⅲ） concentration（14.75%） on the adsorption phenomena. Besides, the interaction among process variables indicated that Et OH enhances As（Ⅲ） adsorption over a pH range of2 to 7, possibly due to facilitation of ligand–metal（Zn） binding complexation mechanism.Eventually, hybrid response surface model–genetic algorithm（RSM–GA） approach predicted a better optimal solution than RSM, i.e., the adsorptive removal of As（Ⅲ）（10.47 μg/g） is facilitated at 30.22 mg C/L of Et OH with initial As（Ⅲ） concentration of 196.77 μg/L at pH 5.8. The implication of this investigation might help in understanding the application of biochar for removal of various As（Ⅲ） species in the presence of OM.
