Zhu Zhiliang

Effect of metal composition in lanthanum-doped ferric-based layered double hydroxides and their calcined products on adsorption of arsenate

A series of lanthanum-doped ferric-based layered double hydroxides with the carbonate intercalation (Mg–Fe–La–LDHs) of different M2+/M3+ molar ratio and their corresponding calcined products were successfully synthesized and characterized. In order to understand the effect of metal compositions in these materials on their adsorption performances for arsenate, various factors such as solution pH, contact time and initial arsenate concentrations were investigated. The results showed that the maximum adsorption capacity for Mg–Fe–La–LDHs decreased with the increment of the M2+/M3+ molar ratio, but the reversed trend occurred for the calcined products of Mg–Fe–La–CLDHs. This difference is closely related to the different adsorption mechanisms for layered double hydroxides (LDHs) and calcined layered double hydroxide (CLDHs). It was found that the adsorption isotherms can be well described by the Langmuir equation, and the adsorption kinetics followed the pseudo-second-order kinetic model. The results suggested that the obtained Mg–Fe–La–LDHs with lower molar ratio of M2+/M3+ in the materials were more suitable for removal of arsenate, while their calcined products Mg–Fe–La–CLDHs with higher molar ratio of M2+/M3+ were efficient adsorbents for arsenate. When the M2+/M3+ molar ratio in the material was 4.38, the maximum adsorption capacity of CLDH-3 was as high as 47.4 mg g−1.

THE EXTRACTION OF Fe3+ AND La3+ BY SYNERGETIC EFFECTS OF TBP AND p-TERT-BUTYLCALIX[8]ARENE OCTACARBOXYLIC ACID

The extraction of Fe3+ and L3+ with p-tert-butylcalix[8]arene octacarboxylic acid (H8L) and tributyl phosphate (TBP) was studied at 30 ± 1°C and ionic strength of 0.1. Fe3+ and La3+ are highly extractible with H8L; Fe3+ > La3+. The results showed that TBP had a significant synergetic effect on the extraction of Fe3+ by H8L. By the slope method, the extraction mechanism is given as Fe3+ by H8L(o) 2TBP(O) = (TBP)2Fe H5L(O) + 3H+. The equilibrium constant of the extraction reaction was log Kex(s) = 4.68 ± 0.12. However, TBP showed no synergetic effect on the extraction of La3+ with H8L.

Simultaneous Adsorption of Humic Acid and Copper (II) Ions from Aqueous Solution onto Cetylpyridinium Bromide (CPB) Modified Zeolite

Adsorption of humic acid (HA) and Cu(II) ontocetyl pyridinium bromide (CPB) modified zeolite was investigated in single- and binary-adsorbate systems. The equilibrium adsorption data of HA and Cu(II) onto CPB modified zeolite in the single-adsorbate system were analyzed by the Langmuir and Freundlich isotherm models. The equilibrium adsorption data were well described by the Langmuir isotherm model, and the predicted maximum monolayer adsorption capacities for HA and Cu(II) at pH 6.0and temperature 298K were 292 mg/g and 13.3 mg/g, respectively. The pseudo-first-order and pseudo-second-order kinetic models were applied to describe the kinetic adsorption data in the single-adsorbate system. The experimental data fitted well with the pseudo-second-order kinetic model. The presence of HA enhanced Cu(II) adsorption onto CPB modified zeolite. Similarly, the presence of Cu(II) enhanced HA adsorption onto CPB modified zeolite. Results of this work indicate that CPB modified zeolite is a promising adsorbent for simultaneous removal of HA and Cu(II) from aqueous solution.

Comparative study on synchronous adsorption of arsenate and fluoride in aqueous solution onto MgAlFe-LDHs with different intercalating anions

In this study, a series of MgAlFe-LDHs (Cl−, NO3−, intercalation, and calcined products of a CO32− interlayer) was synthesized and used for adsorption of arsenate and fluoride in individual contaminants and coexisting pollutant systems. Effects of various factors such as initial pH of solution, dosage of materials, coexisting ions, contact time, and initial pollutant concentrations were evaluated. Experimental results showed that different intercalating anions had a significant effect on adsorption performance of arsenate and fluoride in water. The adsorption of arsenate and fluoride on MgAlFe-CLDH, MgAlFe–Cl-LDH or MgAlFe–NO3-LDH can be described by different adsorption isotherm equations. During the simultaneous removal process, arsenate and fluoride competed for adsorption sites of the adsorbent materials, and the fluoride ions had advantages in the competitive adsorption on MgAlFe–Cl-LDH and MgAlFe–NO3-LDH. MgAlFe–NO3-LDH was used to adsorb arsenate and fluoride in coexisting pollution systems (the concentration of each pollutant was 2 mg L−1, the adsorbent dosage was 1.5 g L−1). The remaining arsenic concentration was reduced to less than 10 μg L−1 and the remaining fluoride ion concentration to below 20 μg L−1 which meets the World Health Organizations, EPAs and Chinas drinking water standards for arsenic and fluoride limits. A possible mechanism is discussed with support from further XRD, SEM, and XPS analysis of the materials after their adsorption.

Pollution status of organochlorines and heavy metals in surface sediment of southern Lake Taihu

Concentration and distribution of 19 organochlorines and 6 heavy metals in the surface sediment of southern Lake Taihu were studied and the relevant risk assessment was carried out.The results showed the concentrations of organochlorine pesticides(OCPs) and polychlorinated biphenyls(PCBs) detected ranged from 0.51-4.98ng/g(dw) and 1.49-15.15ng/g(dw),respectively,which was at a low contamination level compared to other fresh water sediments in China.The congener of α-hexachlorocyclohexane(α-HCH) was the dominant pollutant among OCPs and CB194,and CB28 were the dominant PCBs.The concentration rangesof Cu,Zn,Cr,Ni,Pb and Cd in the surface sediments of southern Lake Taihu were 14.4-79.7mg/kg,69.3-214mg/kg,65.0-99.5mg/kg,24.8-48.7mg/kg,12.3-39.2mg/kg and 0.015-0.563mg/kg,respectively.Effects range low(ERL) and effects range median(ERM) were used to evaluate the ecological risk of organochlorines.It was found that 90% of the sampling sites had a dichlorodiphenyltrichloroethanes(DDTs) value lower than the ERL,and the γ-HCH and PCBs values of all sites were lower than the ERL.The risk assessment was completed on heavy metals in sediments by using the potential ecological risk index(RI).The results indicated that the overall ecological risk caused by heavy metals was low.The potential ecological risk index of Cd was relatively higher,and the RIs of several heavy metals in XMK-0 were relatively higher than that in other sites.Although the concentration levels of the above organochlroine and heavy metal pollutants in the surface sediments of southern Lake Taihu were low and no serious threat has been observed to the ecological system,the prevention to these contaminations should not be ignored for their accumulative effect and toxicity in the environment.