Adsorption Performance And Regeneration Of Porous Clay Heterostructures For Naphthalene

Because Polycyclic Aromatic Hydrocarbons (PAHs) has carcinogenic, teratogenic and mutagenic effects on human health, the purification of PAHs is one of the hotspot in research of environment. In this paper, a representative PAHs, naphthalene, was selected to (1) study the effects of surfactant/co-surfactant type, drying time and calcination methods on the adsorption properties of porous clay heterostructures (PCHs), prepared by using bentonite as a matrix, for naphthalene to get the optimum preparation conditions of PCHs; investigate the adsorption mechanism based on structural characterization and adsorption isotherm of PCHs; discuss the effects of temperature, humidity, initial concentration and other factors on adsorption properties of PCHs. (2) regenerate PCHs by using plasma technology after adsorption saturation of naphthalene, and characterize the structural of regenerated PCHs to further explore the mechanism of regeneration; investigate the effects of discharge atmosphere, oxygen flow, discharge time, discharge gap and initial discharge voltage on PCHs regeneration. In addition, the effect of PCHs’recycling was also studied. Some valuable results were obtained below:(1) The PCHs, using bentonite as a matrix, possess a larger specific surface area, higher total pore volume, more abundant porosity, and better distributed pore size with micro and pore structure than traditional PCHs. It possess a better adsorptive property for naphthalene. With 0% RH and the initial concentration of 560 mg/m3 at temperature of 30℃, the adsorption property of PCHs was close to or a little higher than ordinary granular activated carbon (303 mg/g) and far higher than the original soil (50 mg/g) and CTMAB-Bent (182 mg/g).The adsorption heat of naphthalene on PCHs is-16.6 kJ/mol, less than adsorption heat value of ligand exchange (> 42 kJ/mol) and other strong chemical bond force, indicating the adsorption mechanism was mainly physical surface adsorption and organic matter distribution, without ligand exchange, bond or other strong force in.The effects of temperature, humidity, initial concentration of naphthalene and other factors on the adsorption properties of PCHs were investigated. Adsorption is an exothermic reaction and the adsorption capacity decreased when the temperature increased. The better the hydrophobic properties of the sorbent are, the stronger the adsorption force for non/weak polar substances is. The presence of water vapor in the gas mixture will compete for the limited active sites on the surface of PCHs with naphthalene and cause the decline of adsorption equilibrium of PCHs for naphthalene. The initial concentration of naphthalene was proportional to capacity of PCHs in a certain range of initial concentration.(2) Compared with the regeneration effect of heat regeneration, plasma method showed better regeneration effect (97.8%). The effect of 5 influence factors, the discharge atmosphere, oxygen flow, discharge time, discharge gap and the starting voltage on the regeneration was investigated respectively. Results showed that, effect with oxygen as a regeneration discharge atmosphere (88.3%) was better than that with the standard air (51.8%). The regenerating result was increased firstly and then decreased with the increasing oxygen flow rate. When the oxygen flow rate reached 100 mL/min, the regeneration effect reached the best (89.3%). With the extension of the discharge time, regeneration effect increased and then decreased, showing the best result (88.4%) when the discharge time was 20 min. When the discharge gap was larger, more energy was injected in regeneration, and the regeneration effect was better. The best regeneration effect was 93.8% when the discharge gap is 1.5 cm, Similarly, the starting voltage was positively correlated with the regeneration effect in a certain range, the regeneration effects (85.2%) is the best when the starting voltage is 12.5 kV.Plasma process was found to perform very well on the recycling regeneration of PCHs under the optimum regeneration conditions. The regeneration effect still reached 79.2% after 5 times regeneration.Plasma regenerating PCHs is essentially a process of degradation of naphthalene adsorbed on PCHs. On the one hand, active substances in the plasma field reacted with naphthalene adsorbed on the PCHs’surface; on the other hand, they can enter the interior hole and react with naphthalene that adsorbed on the hole wall, naphthalene was released from the active adsorption sites to achieve regeneration purposes.