Sorption study of radionickel on attapulgite as a function of pH, ionic strength and temperature

Purification of acidic lignocellulose hydrolysate using anion-exchange resin: Multicomponent adsorption, kinetic and thermodynamic study

Acid hydrolysis of lignocellulosic biomass to produce high value-added products presents a breathtaking industrial application foreground. However, the hydrolysate under harsh conditions contains extremely complex degradations, resulting in many restrictions or lethal toxicity on the following utilization and bioconversion. In this study, the anion-exchange resin 335 was exploited to separate and purify main degradations from the acidic corncob-hydrolysate. A comprehensive investigation was explored on equilibrium isotherms, adsorption kinetics, and thermodynamic parameters of the representative substances in the hydrolysate. The results indicated that the removal of acetic acid, furfural, and lignin reached 90.13%, 92.58%, and 94.85% respectively, while the loss rate of xylose was well controlled within 20%. Based on these studies, various models and parameters were evaluated to uncover the mechanisms. In conclusion, this work offered a theoretical basis for the application in the separation and purification of acidic lignocellulose-hydrolysate and further bioconversion.

Influence of colloidal Fe(OH)3 on the adsorption characteristics of strontium in porous media from a candidate high-level radioactive waste geological disposal site

Colloids in groundwater or geological barriers generally play a key role in the migration of special nuclides. Adsorption characteristics of strontium were investigated on porous media in the presence of colloidal Fe(OH)₃ from the Beishan Site, the only high-level radioactive waste disposal site candidate in China. The effects of colloid amounts, solid contents, and pH were determined and studied by batch texts. The results revealed that the presence of colloidal Fe(OH)₃ in porous media contributed to promotion of the sorption effect, and the influencing factors had a significant impact on the adsorption process. The sorption ability increased with increasing colloid amount when the equilibrium time was approximately 10 h under an optimal solid-liquid ratio of 20 g L^-1. The sorption effect in alkaline conditions was better than that under acidic conditions. The sorption kinetics indicated that the strong chemical interaction and/or surface complexation contributed primarily to strontium sorption. The sorption isotherms and model fitting revealed that the sorption of strontium onto porous media in the presence of colloidal Fe(OH)₃ was a monolayer adsorption, and the presence of colloidal Fe(OH)₃ is an important factor that greatly influences the removal of strontium from aqueous solutions. These findings provide useful information for the treatment of strontium in radioactive waste disposal sites.

Utilization of Modified Attapulgite for the Removal of Sr(II), Co(II), and Ni(II) Ions from Multicomponent System, Part I: Kinetic Studies

Radionuclide sorption by natural and modified clays is extensively accepted to be an important process from the radioactive waste point of view. This work focused on modification of natural attapulgite with a layered double hydroxide to produce a novel chemisorbent for Sr²⁺, Ni²⁺, and Co²⁺ removal from multicomponent solution. The structural and surface characteristics of both attapulgite (ATP) and modified attapulgite (LDH-ATP) were investigated using XRD, FTIR, SEM, and thermal analysis. Comparison of sorption features of Sr²⁺, Ni²⁺, and Co²⁺ onto ATP and LDH-ATP was achieved; the results indicated that LDH-ATP was the most efficient sorbent for Sr²⁺, Ni²⁺, and Co²⁺. Kinetic studies established that the sorption is fast and reaching >90% within 30 min. The sorption of Sr²⁺, Ni²⁺, and Co²⁺ are well defined by non-linear pseudo-second-order model and controlled by an intra-particle diffusion mechanism. The diffusivity was determined using homogeneous surface diffusion (HSDM) model and found in the order 10^-13 m²/min; this confirmed that the sorption of the three ions is chemisorption process. LDH-ATP can be employed as a candidate chemisorbent for the removal of some metal ions from waste solution.