Regression models of adsorbing nickel (II) ions by carbon sorbents

Abstract: The use of inexpensive materials such as sorbents increases the competitive advantages of removing heavy metal ions, including nickel (II) ions, from aqueous solutions and wastewater. Such materials include active carbons – carbon sorbents. The oxidized carbon sorbent AD-05-2 and its original analogue have been used as the object of this research. The oxidation of carbon sorbent AD-05-2 was conducted using a solution of nitric acid and urea following a conventional method. Oxidation resulted in improvement of the textural characteristics of the carbon sorbent. The total pore volume increased, including the volume of micropores, which had a positive effect on the sorption properties of the obtained sample. This article studies the adsorption of nickel (II) ions by the oxidized carbon sorbent AD-05-2 and its original analogue. For both models, the total time of establishing adsorptive equilibrium in the system adsorbate–adsorbent was 4 hours, pH = 9,6, and the range of temperatures – 298–338 K. The obtained experimental data on the nickel (II) ion adsorption are processed in the software package Statgraphics Plus. Adsorption isotherms are described using parabolic regression models, which cover 98.86–99.99% of the experimental data. The adsorption of nickel (II) ions increases with temperature, as indicated by a higher value of the first derivative dA/dCp, apparently, due to accelerated external diffusion. A significant steep rise of the isotherms corresponds to the temperature of 338 K, which indicates the diffusion effect on the adsorption process. The estimates of the accuracy of regression models are provided by the mean square σ and absolute Δ errors. Autocorrelation of experimental data is estimated using Durbin – Watson (DW) test. The obtained regression models can be applied for calculating the optimum parameters of nickel (II) ions’ adsorption from aqueous solutions and process stream using the oxidized carbonic sorbent AD-05-2 and its original analog.