Selective removal of radiocesium from micaceous clay for post-accident soil decontamination by temperature-controlled Mg-leaching in a column.

The effective and efficient removal of radioactive Cs from contaminated soil is highly urgent for the nuclear post-accident remediation. In present study, we achieved rapid Cs desorption from both a typical micaceous clay (i.e., vermiculitized biotite, VB) and actually contaminated soil by high-speed ion exchange through temperature-controlled continuous leaching with Mg-solutions in a column reactor. Cs-sorbed VB was firstly employed as a soil surrogate to explore the macro-Cs desorption process and micro-mechanism in detail. Results showed that VB sandwiched the adsorbed Cs to its interlayers within collapsed structure (10.7 Å) and prevent Cs release even by abundant extraction with H2O at 250 °C or Mg2+ at 25 °C. However, Mg2+-extracted Cs desorption boosted significantly with elevating temperatures and 100 % of sorbed-Cs was removed from Cs-VB leached above 150 °C. Further structural and composition analysis of the leached specimen ensured that solvated Mg2+ preferentially entered into Cs+-collapsed interlayers at 150 °C than K+-interlayers above 200 °C, leading to prior complete Cs removal over K from VB at lower temperatures. By contrast, the Cs-contaminated soil reduced by ∼39 % but ∼82 % of its initial radioactivity after equally leaching with same volumes of Mg2+-solution at 150 and 200 °C, respectively. These temperature-controlled Cs desorption validated that radioactive Cs in actual soil indeed be tightly trapped by micaceous clays nearly in the Cs-K co-collapsed interlayers, to which its extraction by other cations can conditionally occur above enough high leaching temperatures. These superior features would inspire new insights for the design of novel practical technologies for treatment and decontamination of the nuclear post-accident soils.

Sodium dodecylsulfate-layered double hydroxide and its use in the adsorption of 17ß-estradiol in wastewater.

Modified Mg3Al layered double hydroxide (LDH) intercalated with dodecylsulfate anion composites, which were designated as SDS-LDH composites, were synthesized by coprecipitation. The samples were characterized using SEM, EDX, FT-IR, zeta potential analysis, and XRD. The results showed that the SDS-LDH composites contain a thicker and larger porous interconnected network than inorganic LDH due to the enlarged inter-layer distance. The outstanding adsorption performance of SDS-LDH composites toward 17ß-estradiol (E2) was investigated under different conditions, including solution pH, adsorbent dosage, ion strength, reaction time, and temperature. When the solution pH was 7 and the adsorbent dosage was 2 g L-1, the removal rate of E2 reached the maximum at 94%, whereas inorganic LDH displayed a poor E2 removal rate of 10%. The presence of various ions (Na+, SO4 2-, CI-, and H2PO4 -) in aqueous solution exerted no significant adverse effects on the adsorption process. The adsorption equilibrium was reached within 20 min, and the adsorption fitted well with the pseudo-second-order model and the Freundlich isotherm. The thermodynamic test revealed that the adsorption process was spontaneous and endothermic. Phosphorus was selected as the index for evaluating the adsorption capacity of SDS-LDH composites for inorganic ions. The removal rates of total phosphorus and PO4 3- were 43.71% and 55.93% for SDS-LDH composites at 2 g L-1. The removal rate of PO4 3- reached up to 85% when the contact time was 120 min and the dosage was 3 g L-1 for SDS-LDH composites, which were approximately close to those of inorganic LDH of 30 min and 2 g L-1, respectively. This finding indicates that the removal capacity of SDS-LDH composites for PO4 3- decreased after the dodecylsulfate anions intercalated into the interlayer. The composites retained their high efficiency and stability after desorption and regeneration with alkali treatment. This study demonstrated that SDS-LDH composites are a promising adsorbent for the recovery and abatement of trace-level E2 in secondary effluents of wastewater treatment plants.

Wastewater sludge dewaterability enhancement using hydroxyl aluminum conditioning: Role of aluminum speciation.

Chemical conditioning is one of the most important processes for improve the performance of sludge dewatering device. Aluminum salt coagulant has been widely used in wastewater and sludge treatment. It is generally accepted that pre-formed speciation of aluminum salt coagulants (ASC) has an important influence on coagulation/flocculation performance. In this study, the interaction mechanisms between sludge particles and aluminum salt coagulants with different speciation of hydroxy aluminum were investigated by characterizing the changes in morphological and EPS properties. It was found that middle polymer state aluminum (Alb) and high polymer state aluminum (Alc) performed better than monomer aluminum and oligomeric state aluminum (Ala) in reduction of specific resistance to filtration (SRF) and compressibility of wastewater sludge due to their higher charge neutralization and formed more compact flocs. Sludge was significantly acidified after addition Ala, while pH was much more stable under Alb and Alc conditioning due to their hydrolysis stability. The size of sludge flocs conditioned with Alb and Alc was small but flocs structure was denser and more compact, and floc strength is higher, while that formed from Ala is relatively large, but floc structure was loose, floc strength is relatively lower. Scanning environmental microscope analysis revealed that sludge flocs conditioned by Alb and Alc (especially PAC2.5 and Al13) exhibited obvious botryoidal structure, this is because sludge flocs formed by Alb and Alc were more compact and floc strength is high, it was easy generated plentiful tiny channels for water release. In addition, polymeric aluminum salt coagulant (Alb, Alc) had better performance in compressing extracellular polymeric substances (EPS) structure and removing sticky protein-like substances from soluble EPS fraction, contributing to improvement of sludge filtration performance. Therefore, this study provides a novel solution for improving sludge dewatering property by controlling aluminum speciation.