Aminated hydroximoyl camelthorn residues as a novel adsorbent for extracting Hg(II) from contaminated water : studies of isotherm, kinetics, and mechanism

Camelthorn, a desert plant, has been utilized as an adsorbent material for the extraction of Hg(II) ions from aqueous solution after grafting with acrylonitrile followed by amination with hydroxylamine hydrochloride in basic medium to obtain aminated hydroximoyl camelthorn (AHCT). AHCT were found to exhibit excellent adsorption capacity over a wide range of Hg(II) concentration. The surface functional groups and morphology of AHCT were determined. The influences of time (0–60 min), pH (2–6), and dose (0.3–8 g/L) were also evaluated. The adsorption data were analyzed using the Langmuit, Freundlich and Temkin tr models at 30 °C using nonlinear regression analysis. The maximum adsorption capacity (qmax) of Hg(II) onto AHCT was 272.9 mg/g at an initial pH of 6 and a temperature of 30 °C and the Freundlich constants, KF and n, at 30 °C were found to be 25.47 mg/g and 3.2, respectively. The value of n (3.2), which being in the range 0–10 indicate that adsorption of Hg(II) ions onto AHCT is favorable. Various kinetics models including the pseudo-first-order, pseudo-second-order and intraparticle diffusion models have been applied to the experimental data to predict the adsorption kinetics. Kinetic study was carried out by varying initial concentration of Hg(II) at constant temperature and it was found that pseudo-second-order rate equation was better obeyed than pseudo-first-order and intraparticle diffusion supporting that chemisorption process was involved. The examination of R2 values and error analysis method (ARE) showed that the Langmuir model provide the best fit to experimental data than other isotherms and follow the following order: Langmuir > Freundlich > Temkin. The results revealed that the AHCT-Hg(II) ions adsorption system was promoted by the high density of active sites and the adsorption process is independent of the adsorbent surface area. Consequently, AHCT residues can offer an effective method of Hg (II) ion removal from aqueous solutions, demonstrating its potential role in water remediation processes