Desorption by ultrasound: Phenol on activated carbon and polymeric resin
An experimental feasibility study of using ultrasound to accomplish the dificult desorption of phenol from activated carbon and polymeric resin adsorbents is discussed. The desorption rates of activated carbon were found to significantly increase by ultrasound at 40 kHz and 1.44 MHz. Attrition of the activated carbon due to cavitation could be prevented by operating at a higher frequency and with an intensity below the threshold of the pulverization of carbon. According to the structural stability study of Amberlite XAD-4 and Dowex Optipore L-493 resins to withstand the abrasive cavitational effects of ultrasound at 40 kHz, the Dowex Optipore resin was stable under experimental conditions and phenol desorption rates were enhanced significantly with sonication. The ultrasonic desorption rates were favored by decreased temperature, aerated liquid medium, and increased ultrasound intensity. The desorption rates obtained without ultrasound appeared to be limited by pore diffusion, whereas those obtained in the presence of ultrasound were limited by surface reaction. The rate enhancement was due to an increase in diffusive transport within the pores caused by acoustic vortex microstreaming. The activation energy for desorption decreased with an increase in ultrasonic power density, thus making the ultrasound weaken the adsorption bond.
Regenerate activated carbon using organic solvents
Adsorption by activated carbon is widely used to remove chemical species from waters and wastewater and volatile organic compounds from vapor streams. In normal applications, the activated carbon gradually accumulates the chemical species removed from the liquid or vapor stream. This causes a progressive reduction in the carbon`s ability to remove additional chemicals from the stream, and eventually the adsorption capacity is consumed and the carbon is spent. At this point, the carbon must either be replaced or be regenerated to restore its adsorptive capacity. Solvent regeneration is one such technology. It uses solvents to dissolve adsorbed material out of the pores of the activated carbon. Then the solvent is removed by steam. This article discusses where solvent regeneration fits into the overall scheme of activated carbon applications and regeneration options. Cost-wise, solvent regeneration of activated carbon is only a few cents per pound more expensive than steam regeneration, and less than one-tenth as expensive as thermal regeneration. Because steam regeneration is appropriate for only certain industrial applications (discussed later), the choice is usually between solvent and thermal regeneration.
Experimental investigation of the geotechnical properties and microstructure of lime-stabilized saline soils under freeze-thaw cycling
Abstract The Song-Nen Plain in northeastern China holds one of the three largest expanses of soda saline-alkali soil in the world. Due to its disadvantageous geotechnical properties, the saline soil in this area is unable to meet the needs of construction projects. This study evaluates the stabilizing effect of adding lime to such soils. Specifically, it investigates how the physicochemical and mechanical properties and microstructure of soda saline-alkali soil are altered by lime and how these changes are affected by both freeze-thaw cycling and the duration of curing. The results reveal that adding lime to saline soil transforms clay particles into sand and silt particles and causes the pore size distribution (PSD) to become bimodal, with small-pore and macropore populations. An increase in lime content leads to an increase in the unconfined compressive strength (UCS) but a gradual decrease in both the cation exchange capacity (CEC) and plastic index. Freeze-thaw cycles break up coarse particles and aggregate finer particles, increasing the diameter of macropores and decreasing the USC; however, the effect on specimens with >9% lime is negligible. It is further shown that the geotechnical properties of the soil change immediately after the addition of lime, indicating that the cation exchange reaction takes place very quickly. Furthermore, the pozzolanic reaction leads to an increase in the percentage of sand-sized particles and a decrease in porosity after 28 days of curing. Overall, these results indicate that it is feasible to use lime to improve the engineering properties of soda saline-alkali soil in this area.