Low-Temperature Alkaline Desorption of 2-Nitrophenol from Activated Carbon under Static Conditions

Abstract

The nitro and chloro derivatives of phenols are xenobiotics. Active carbon (AC) is often used for the removal of such substances from natural, drinking, and waste waters. To a large extent, the economic feasibility of using AC depends on the method of their regeneration. Upon treating AC with an alkaline solution, the adsorbed phenols are ionized because of their weak acidic properties. The formed phenolate ions are desorbed from the carbon surface because of their lower adsorption energy and AC is regenerated. The study of low-temperature desorption of phenol derivatives is relevant for the development of technology for the regeneration of AC and biologically active carbon (BAC) directly in adsorbers that are made of modern composite (fiberglass) materials that are not designed for operating at temperatures higher than 40–50°C. The low-temperature alkaline desorption of 2-nitrophenol (NP) from equilibrium exhausted AC (reagent : AC ratio 10 : 1) is studied under laboratory static conditions in the mode of single-batch processing. The optimal alkali concentration (0.1 M) providing the maximum degree of sorbent recovery is determined. It is found that the degree of desorption of NP (5.7–45.6%) depends on the equilibrium concentration of sorbent saturation. The lower the equilibrium concentration at which AC exhausts, the lower the efficiency of alkaline regeneration of AC. The efficiency of NP desorption for operating temperatures of 15–35°C is verified. An increase in the temperature of reagent in the studied range does not lead to a substantial increase in the degree of desorption, but reduces the time required to establish the equilibrium of desorption by a factor of 1.5. More than 85–90% of equilibrium 2-nitrophenol desorbed from AC is removed in the first 4 to 8 h of treatment. Compared to microbial treatment, alkaline desorption allows one to achieve higher levels of AC regeneration (by 10–20%) and shorter processing times (100 times faster), which indicates the promising future for inclusion of this operation into bioadsorption technologies.