A two-step leaching method designed based on chemical fraction distribution of the heavy metals for selective leaching of Cd, Zn, Cu, and Pb from metallurgical sludge.

For selective leaching and highly effective recovery of heavy metals from a metallurgical sludge, a two-step leaching method was designed based on the distribution analysis of the chemical fractions of the loaded heavy metal. Hydrochloric acid (HCl) was used as a leaching agent in the first step to leach the relatively labile heavy metals and then ethylenediamine tetraacetic acid (EDTA) was applied to leach the residual metals according to their different fractional distribution. Using the two-step leaching method, 82.89% of Cd, 55.73% of Zn, 10.85% of Cu, and 0.25% of Pb were leached in the first step by 0.7 M HCl at a contact time of 240 min, and the leaching efficiencies for Cd, Zn, Cu, and Pb were elevated up to 99.76, 91.41, 71.85, and 94.06%, by subsequent treatment with 0.2 M EDTA at 480 min, respectively. Furthermore, HCl leaching induced fractional redistribution, which might increase the mobility of the remaining metals and then facilitate the following metal removal by EDTA. The facilitation was further confirmed by the comparison to the one-step leaching method with single HCl or single EDTA, respectively. These results suggested that the designed two-step leaching method by HCl and EDTA could be used for selective leaching and effective recovery of heavy metals from the metallurgical sludge or heavy metal-contaminated solid media.

Selective adsorption and recycle of Cu2+ from aqueous solution by modified sugarcane bagasse under dynamic condition.

Tetraethylenepentamine modified sugarcane bagasse was prepared and applied to test its feasibility in removing and recovering Cu2+ from wastewater under dynamic condition. Results showed that the Cu2+ could be selectively absorbed from wastewater by the modified SCB fixed bed column. To understand the adsorption mechanism, Cd2+ had been selected as the model interfering ion to investigate how co-ions influence the adsorption of Cu2+ on the sorbent. It was observed that the adsorption capacity of the sorbent for Cu2+ (0.26 mmol g-1) was significantly higher than that of Cd2+ (0.03 mmol g-1), even when the Cd2+ initial concentration was 100 times higher than that of Cu2+ in the binary system. This finding indicated that the presence of Cd2+ in the solution exerted negligible influence on the adsorption of Cu2+ on the modified SCB. The selectivity of the modified sorbent was further confirmed in the Cu/Cd/Mg/Pb/K quinary system. Further analysis to dynamic adsorption experiment illustrated that, due to the presence of amine groups, the modified SCB showed strong coordination ability to Cu2+, which allowed the other adsorbed ions (e.g., Cd2+) desorbed. This high adsorption selectivity toward Cu2+ suggested that this prepared sorbent would be a promising candidate for removing and recovering Cu2+ from wastewater.

Chromatographic separation of platinum group metals from simulated high level liquid waste using macroporous silica-based adsorbents.

To separate platinum group metals (PGMs) from high level liquid waste, three novel macroporous silica-based adsorbents, namely, (Crea+Dodec)/SiO2-P, (Crea+TOA)/SiO2-P and (MOTDGA+TOA)/SiO2-P, were synthesized by introducing extractants Crea (N',N'-di-n-hexyl-thiodiglycolamide), TOA (Tri-n-octylamine), MOTDGA (N,N'-dimethyl-N,N'-di-n-octyl-thiodiglycolamide) along with theirs modifier, Dodec (n-dodecyl alcohol), into 50µm diameter SiO2-P particles by impregnation. Chromatographic separation of PGMs from simulated high level liquid waste was investigated by column method. It was found that 100% of Pd(II) and Re(VII) could be eluted out from simulate HLLW in 3.0M HNO3 solution using three adsorbents. For Ru(III) and Rh(III), high temperature has distinct effect on the adsorption rate and a further study for Ru(III) and Rh(III) is necessary to separate them from HLLW completely. In all six column experiments, a relatively satisfactory chromatographic separation operating for PGMs from simulated HLLW was obtained using (Crea+TOA)/SiO2-P adsorbent packed column at 323K.

Adsorption and separation behavior of yttrium and strontium in nitric acid solution by extraction chromatography using a macroporous silica-based adsorbent.

To separate (90)Y from the fission product (90)Sr-(90)Y group, a silica-based TODGA/SiO(2)-P adsorbent was prepared by impregnating N,N,N',N'-tetraoctyl-3-oxapentane-1,5-diamide (TODGA) extractant into the macroporous SiO(2)-P support with a mean diameter of 60 µm. The adsorption behavior of Sr(II) and Y(III) onto TODGA/SiO(2)-P adsorbent from HNO(3) solution and their mutual separation were investigated. Under the experimental conditions, this adsorbent showed high adsorption affinity to Y(III) and weak adsorption to Sr(II). It was found that the adsorption process of Y(III) could be expressed by both of Langmuir monomolecular layer adsorption mode and the pseudo-second order model. From the results of stability experiments, it became clear that TODGA/SiO(2)-P adsorbent is stable in 3M HNO(3) solution for 1 month contact time at 298 K. Using a column packed with TODGA/SiO(2)-P adsorbent, Sr(II) and Y(III) were eluted by distilled water and diethylenetriamine pentaacetic acid (DTPA) solution, respectively. The separation of Y(III) from Sr(II)-Y(III) group was achieved successfully.