This work focuses on adsorption kinetics and isotherm modelling in CO2-activated chitosan. Removal efficiency and adsorption capacity were measured for three anionic dyes: Brilliant Blue FCF (BBF), Congo Red (CR), Orange II (O-II) and one cationic dye: Crystal Violet (CV). While the highest removal efficiencies of BBF, O-II and CR were 97%, 91% and 48%, it was found that very low adsorption capacity occurred in the case of CV due to the repulsion between the cationic groups of CV and that of CO2-activated chitosan. In terms of adsorption kinetics, pseudo-first-order and pseudo-second-order models were applied. The adsorption in the CO2-activated system was found to follow the pseudo-first-order model. The activation of adsorption by CO2 was found to lead to a higher adsorption rate constant and a higher adsorption capacity due to the protonation of chitosan’s amino groups. Interestingly, as the temperature of the CO2-activated system increased, the pseudo-first-order model predicted a decrease in adsorption rate constant, k1. This is thought to be a result of lower CO2 dissolution into the aqueous solution, which leads to a slower protonation process of chitosan’s adsorption sites. The chemical structure of the dye species affects the adsorption kinetics in the CO2-activated system. There are four charged functional groups on the CR molecule and three on the BBF molecule, which allow faster alignment onto adsorption sites compared with O-II molecules with only one charged group. In terms of adsorption isotherm, BBF adsorption was found to follow the Langmuir model in the CO2-activated system.
The structure formation of surface-modified nanoparticles during solvent evaporation is investigated by numerical simulation based on the discrete element method (DEM). The interaction forces induced by surface modifiers are considered, in addition to the contact force, Brownian force, capillary force, van der Waals force and hydrodynamic drag force. The effects of the solvent, the surface modifier and the surface coverage of the modifier on the structure formation process during solvent evaporation and the final structure of the nanoparticles on the substrate are clarified. When the affinity between the solvent and the surface modifier is high, the surface-modified nanoparticles are well-dispersed in the solvent and the structures of nanoparticles tend to be well-ordered after solvent evaporation. On the other hand, when the surface coverage of the modifier is fairly high, the final structures of surface-modified nanoparticles are relatively disordered even though the nanoparticles are dispersed in the solvent. Such a structure formation mechanism is explained based on the force curve between two nanoparticles during solvent evaporation.
Radioactive strontium-90 (90Sr) is one of the heat-generating nuclides generated by nuclear reactions in reactors, and selective separation of strontium is an efficient treatment method. It was demonstrated that some metal-doped antimony silicates showed high strontium-adsorption performance under acidic condition. The effects of ionic radii and acidity of dopants, namely, tungsten, vanadium, tantalum, and zirconium, on the strontium-adsorption performance of antimony silicates under acidic condition and a solution containing sodium ions were investigated. The results of the investigation revealed that the ion-exchange capacity of metal-doped antimony silicate was 2.4 mEq/g for vanadium, 1.8 mEq/g for tungsten and tantalum, and 1.3 mEq/g for zirconium; basically, it decreased as a function of the ionic radius of the dopant. The tungsten-, vanadium-, and tantalum-doped antimony silicates had high distribution coefficients for strontium (KdSr) of over 103 L/kg in deionized water, chloride solution, and nitric acid solution under various pH conditions. KdSr under acidic condition increased with increasing acidity of the dopants. At various sodium concentrations, KdSr of tungsten-, vanadium-, and tantalum-doped antimony silicates was greater than KdCa. The selectivity coefficient of strontium over sodium (KSr–Na) was found to depend on the ionic radius of the dopant. These results indicate that the ionic radii and acidity of the dopants affect the total number of adsorption sites and activation of individual adsorption sites; that is, larger ionic radii of dopants cause collapse of the pyrochlore structure of the antimony silicates, thereby decreasing the ion-exchange capacity, and dopants with high acidity support the formation of cationic-exchange groups that increase KdSr for antimony silicates under acidic conditions.
Accurate, reliable prediction of NOx emission in flue gas is of great significance for operation of power station boilers with low nitrogen emissions. To improve the accuracy of a prediction model, a method for predicting NOx emission from boilers based on integration of the whale optimization algorithm and least squares support vector machine (MWOA-LSSVM) is proposed in this paper. First, the sample space is divided, and a segmentation logistic chaotic map is then used to initialize the population. The nonlinear adaptive parameters are improved, and quadratic interpolation update position is used to improve the whale optimization algorithm (WOA) by broadening the global exploration ability of the algorithm. The MWOA is used to globally optimize the kernel function width and penalty factor of the LSSVM sub-model in each subspace, yielding the sub-model as an output. Finally, the sub-model output is integrated using the least squares regression, yielding the output from the integrated model. The simulation results show that the MWOA-LSSVM integrated model has stable, high-precision simulation performance compared with other selected prediction models and can provide more accurate predictions of NOx emissions from boilers.
Electrolytic manganese residue is a kind of acidic waste containing manganese and ammonia nitrogen produced in the process of hydrometallurgical of manganese metal smelting with manganese ore. It is primarily landfill treatment, occupying land resources and threatening human health. Through research of the leaching toxicity changes of electrolytic manganese residue and the leachate added, the feasibility of leachate recirculation and electrokinetic remediation of electrolytic manganese residue powered by solar-cell has been proved by experiments. The reaction mechanism was presumed by studying the changes of leaching toxicity, crystal formation and morphology of manganese residue during electrokinetic remediation. The results revealed that the removal rates of manganese and ammonia nitrogen in manganese residue were 99.49% and 99.70%, respectively, and ammonia nitrogen can be reduced to 2.26 mg/L and manganese concentration to 6.15 mg/L, when leachate was recirculated as electrolyte and a solar-cell provided the electrical energy for the remediation after 72 h. The focal mechanism of manganese and ammonia nitrogen conversion was electromigration and electrochemical oxidation.