[Influence of speciation on the bioavailability of particle-bound cadmium in sediments].

In the present work, the impact of speciation on the bioavailability of cadmium in sediments was investigated. Bioaccumulation of cadmium adsorbed on various (hydr)oxide minerals, i.e. ferric hydroxide, aluminum hydroxide and manganese dioxide, by bivalve Meretrix meretrix Linnaeus, was measured using a suspending system. The results showed that the bioavailability of cadmium was significantly different for different minerals. At Cd concentration of 70 mg/kg, the accumulation of Cd by clams in Cd-Fe(OH)3 and Cd-Al(OH)3 system was not detectable after 22 days of exposure. In comparison, the clams absorbed appreciable amount of Cd from 70 mg/kg of Cd-MnO2 system. An average uptake rate of (0.0094 +/- 0.0010) microg/(g x d) for 70 mg/kg Cd-MnO2 was obtained by linear fitting curve (r2 = 0.853 9, p < 0.000 1). When Cd concentration was increased to 140 mg/kg, bioaccumulation of Cd from Cd-Fe(OH)3 system was still not observed, while for the clams cultivated in Cd-Al(OH)3 and Cd-MnO2 systems, Cd was apparently assimilated in the body of the animals. The uptake rates were determined to be (0.0166 +/- 0.0017) microg/(g x d) for Cd-Al(OH)3 and (0.024 8 +/- 0.0017) microg/(g x d) for Cd-MnO2. Generally, The bioaccumulation sequence of the Cd-(hydr) oxides is Cd-MnO2 > Cd-Al (OH)3 > Cd-Fe (OH)3. The type of minerals determines both assimilation efficiency and ingestion rate, consequently controls the bioaccumulation of adsorbed cadmium.

[Removal of arsenite from drinking water by activated carbon supported nano zero-valent iron].

Nano zero-valent iron was loaded onto activated carbon by deoxidizing Fe2+ in aqueous solution and approximately 8.2% (wt) of iron was loaded it. The size of the needle-shaped iron particles in the pores of carbon was (30-500) x (1 000-3 000) nm. The adsorption capacity for arsenic was approximately 1.997 mg/g activated carbon supported nano zero-valent iron (NZVI/AC) in the 2 mg/L As(III) solution at pH 6.5 and (25 +/- 2) degrees C. The uptake of arsenic by NZVI/AC was rapid in the first 12 h (94.3%) and equilibrium was achieved at 72 h (99.86%). As(III) was partly oxidized by the absorbent in the process of absorption. The presence of phosphate and silicate ions significantly decreased arsenic removal rate while the effect of other common ions such as sulfate, carbonate and oxalate was insignificant. NZVI/AC was effectively regenerated after adsorption of arsenic when elution was applied with 0.1 mol/L NaOH solution. The results suggest that NZVI/AC is an ideal candidate for the treatment of arsenic contaminated drinking water.

[Bioavailability of adsorbed Cd on typical oxides of sediment in Phragmites australis].

Effects of different chemical speciation (e.g. adsorbed on different metal oxides) in environment on Cd bioavailability were studied. Goethite, magnetite, gibbsite, alumina, and manganese oxide were chosen as representatives of oxides commonly present in sediment. In cultivar system, Hoagland solution was used as nutrition supply, and single metal oxide adsorbed Cd as the only source of contamination and Phragmites australis was induced to study Cd bioaccumulation. After 45-day cultivation, Cd was uptake and accumulated in P. australis, with different bioaccumulation from 72.70 mg x kg(-1) to 320.44 mg x kg(-1) which in root followed degressive order: Al(OH)3 > Al203 > Fe3O4 > MnO2 > FeOOH. Acetic acid, malic acid and citric acid were used to demonstrate the variation of desorption of Cd from different oxides which indicated the adsorption ability and stability. Desorption of Cd by acetic acid and malic acid followed the descending order: Al(OH)3 > Fe3O4 > Al2O3 > FeOOH > MnO2; by citric acid was Al(OH)3 > Al2O3 > Fe3O4 > FeOOH > MnO2, which was consistent with the Cd accumulation in root. The chemical speciation was the main factor to affect the bioavailability of Cd.

[Removal of arsenate from drinking water by activated carbon supported nano zero-valent iron].

A new adsorbent, activated carbon impregnated with nano zero-valent iron was prepared, which size of the needle-shaped iron particles in the pores of carbon was (30-500) nm x (1000-3000) nm and approximately 8.2% of iron was loaded onto it. The arsenate removal percentage was 99.5% by 1.5 g/L NZVI/AC in the 2 mg/L arsenic solution at pH 6.5 and (25 +/- 2) degrees C. The adsorption capacity was about 15.4 mg/g when equilibrium concentration was 1.0 mg/L. Kinetics revealed that uptake of arsenate ion by NZVI/AC was 91.4% in the first 12 h and equilibrium time was about 72 h. The intraparticle diffusion model was applied to study the mechanics of arsenate in the activated carbon. The presence of phosphate and silicate could significantly decrease arsenate removal while the effects of the other anions and cations on the arsenic removal were neglectable. NZVI/AC can be effectively regenerated when elution is done with 0.1 mol/L NaOH solution. Our results suggest that NZVI/AC is a suitable candidate for drinking water treatment due to its high reactivity.